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2026-02-01T03:12:00.000-08:00

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ICMP (Internet Control Message Protocol) - Study Notes for PSC, SSC, and IT Exams

2026-01-30T11:37:00.000-08:00

Published By Alex George

Welcome to the Computer Science and Technology Study Materials section from CoreNetworkZ EdTech Solutions, a leading mock test and competitive exam preparation platform, for students preparing for SSC, DSSSB, and Kerala PSC examinations. Today, I will explain ICMP.

I will explain ICMP and related questions asked in the Government competitive examinations.

What is ICMP?

John Samuel, a CCNA student at CoreNetworkZ EdTech Solutions, asked this question in one of our induction classes.

ICMP = Internet Control Message Protocol

ICMP (Internet Control Message Protocol) is a network layer protocol that generates error reports when facing problems with receiving or delivering packets.

It is a connectionless protocol with the primary duty of error reporting.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding ICMP is essential for candidates appearing for the DSSSB PGT/TGT Computer Science, Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), VSSC Technical Assistant, and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions that require them to explain the reasons behind ICMP error codes. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

So, why is ICMP important?

Ashiq Muhammed, a B.Tech 3^rd year student from Delhi, asked, "What is the importance of ICMP in a network?" He is preparing for SSC Scientific Assistant (CS) examination.

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Let me answer Ashiq in this section. The primary reason for the importance of ICMP is its error reporting and the support for ping and tracert.

ICMP helps troubleshoot the connection between two hops.

Why Do We Need ICMP?

Sonya Merchant, a client of CoreNetworkZ EdTech Solutions, asked, "Why do you network engineers need this protocol?"

Let us check why we need ICMP.

Let me explain one critical duty of a network engineer: network troubleshooting. Checking the connectivity between two devices is the primary focus of network troubleshooting.

We have many utilities to check the connectivity and availability of the destination device.

But all these utilities are based on ICMP, as defined in RFC 792.

The Internet Control Message Protocol (ICMP) is used to transmit error and control messages between devices that support the TCP/IP protocol suite.

ICMP operates behind utilities such as ping and tracert. Now, I will answer a question asked by a reader in the comment section.

Ping Error - Request Timed Out

Akhil Raj, a regular reader of CoreNetworkZ EdTech Solutions, asked, "Can you explain the functions of ICMP and provide a list of the error messages it generates?"

Let us now explore the key functions of the Internet Control Message Protocol.

Important Functions of ICMP

Let me answer the first part of Akhil's question here.

Send echo requests from a TCP/IP device to another.
Responds to Echo request.
It helps to find routing path issues.
ICMP echo message verifies the availability of the destination.

List of Messages Generated by ICMP

In this section, I will answer the second part of Akhil Raj's question. He asked about the list of messages generated by ICMP.

Address Request
Address reply
Destination unreachable
To learn more about the Destination Unreachable message generated by the Internet Control Message Protocol, visit the links below.
- Destination Net Unreachable
- Destination Host Unreachable
Subnet Mask Request
Time Exceeded

ICMP Type	Meaning / Message	Exam Scenario
Type 0	Echo Reply	The "Success" response to a Ping.
Type 3	Destination Unreachable	Router cannot find a path to the host.
Type 8	Echo Request	The initial "Hello" sent by the Ping tool.
Type 11	Time Exceeded	TTL reached zero (used by Tracert).

How to Use ICMP in Troubleshooting a Network?

You have already learned about the Internet Control Message Protocol (ICMP). Now, let us explore its practical applications in real-world scenarios.

I have a home network with several devices connected to the Internet via an ISP-provided modem.

Additionally, I manage a small office network with ten computers. Let us consider a hypothetical connectivity issue between my home computer and the office network.

So, how should I begin troubleshooting if I am unable to access the office network from home?

The first step is to ping one of the devices on the office network from my personal computer at home.

As explained earlier, the ping utility operates based on ICMP.

It sends ICMP echo request packets from my home computer to the office computer. Here, we can observe two key functions of ICMP at work:

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It tests the connectivity between my home computer and office computer.
It also generates error messages (if a connectivity issue occurs).

I believe my students enjoyed today's tutorial. To pass the CCNA and JNCIA examinations, I recommend you read the following additional resources.

Reference

https://community.cisco.com/t5/networking-knowledge-base/icmp-internet-control-message-protocol/ta-p/3116636
https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/security_guide/sec-managing_icmp_requests
https://www.juniper.net/documentation/us/en/software/junos/transport-ip/topics/topic-map/icmp.html
https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-adts/b78f5642-0cb3-4d37-9a71-e08731a5d000
https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Fiber Distributed Data Interface (FDDI) - Study Notes for PSC, SSC, and IT Exams

2026-01-30T11:36:00.000-08:00

Published By Alex George

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding FDDI is essential for candidates appearing for the DSSSB PGT/TGT Computer Science, Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), VSSC Technical Assistant, and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions from FDDI. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

FDDI is an Obsolete Standard now.

FDDI stands for Fiber Distributed Data Interface (FDDI), a Local Area Network standard. Today, we check the data transfer speed, maximum distance it supports, different versions, working principle, and the specifications of this network standard.

American National Standards Institute (ANSI) developed FDDI.

Krishna Ravi, a B.Tech student, asked, "I heard ISPs are using FDDI standards. Can you tell me why?"

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He asked this question in our support forum. Some technicians also asked me why the FDDI was popular with ISPs.

The truth is that ISPs are no longer using the FDDI standard. But, it was popular once because it supported high bandwidth and security.

FDDI Communication and Data Transfer Speed

Aditi Gupta, a System Admin trainee at CoreNetworkZ EdTech Solutions, said, "I read communication through FDDI offers high security. Why is that?"

I will answer Aditi's question here.

Communication through this standard is very secure due to its dual-ring structure. As you understand, the FDDI standard uses the primary ring for communication. It supports up to 100 Mbps in standard case.

The second token ring is for possible backup ( in case of the failure of the primary ring). If the second ring is also used to carry data, the total speed will increase up to 200 Mbps.

Now, let us check the different versions of this data communication standard.

Different versions of FDDI

Muneesh Ali Muhammad, a regular reader of CoreNetworkZ EdTech Solutions, asked, "Hello Alex, I am preparing for CCNA. According to the exam syllabus, I should learn about various types of FDDI. Can you explain them?"

He asked this question in our support forum. Let me share two popular versions here.

FDDI-II
This version is suitable for transmitting video, with voice, over a network. FDDI-2 supports the transmission of voice and video information as well as data. This version adds the capability to add circuit-switched service to the network.
FDDI Full Duplex Technology (FFDT)
It uses the same network infrastructure but can potentially support data rates up to 200 Mbps. So, this standard can offer the data transfer rate of an ordinary FDDI network where both Token Rings transfer data.

Feature	FDDI Specification
Topology	Dual Counter-Rotating Ring
Access Method	Token Passing
Standard Speed	100 Mbps (up to 200 Mbps with both rings)
Max Distance	200 Kilometers
OSI Layer	Physical & Data Link Layers

A Complete Explanation of The Working of FDDI

Rony Mathew, a Software Engineer from Bengaluru, said, "One of my projects needs apps based on FDDI standard. However, after reading the FDDI documentation, I have more doubts. Can you explain the working of the Fiber Distributed Data Interface standard? Please note that I am not from a Network Engineer background."

Many beginners find the workings of FDDI confusing. So, read this part carefully.

FDDI uses a dual-ring architecture with traffic on each ring flowing in opposite directions. If the data transfer in ring 1 is in the clockwise direction, the second ring sends data in an anticlockwise direction.

Fiber Distributed Data Interface is treated as highly secure because of its dual-ring character. FDDI uses optical fiber as the primary transmission medium, but it also can run over copper cabling.

What are the FDDI Specifications?

A few readers of CoreNetworkZ EdTech Solutions asked me about different FDDI specifications.

FDDI is a collection of four specifications, each with a specific function. The function of the multi-specification is to provide high-speed connectivity between upper-layer protocols.

Physical Layer Protocol (PHY)
Physical-Medium Dependent (PMD)
Media Access Control (MAC)
Station Management (SMT)

To read more about the FDDI specification, visit this link.

https://ipsit.bu.edu/sc546/sc441Spring2003/fddi/specs.htm

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Why FDDI is No Longer Popular?

Hemanth Reddy, a Computer Science and Engineering student from Vijayawada, said, "I read the documentation, and the FDDI technology is awesome. I wonder why no one is using this technology anymore."

The answer to his question is simple. We have better technologies now. FDDI is costly and obsolete. I believe you found this article helpful. Feel free to share your comments about FDDI below.

Reference

https://www.ibm.com/docs/en/aix/7.2.0?topic=control-data-link-fddi-dlc-fddi-overview
https://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1905.pdf
https://answers.microsoft.com/en-us/windows/forum/all/fddi-network-card-where-to-download-the-driver/9c578ffd-7995-44e5-84a8-b7f2848e1e6c
https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://www.juniper.net/documentation/en_US/junos/topics/concept/fddi-overview.html

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Differences Between Bridge Mode and PPPoE Mode

2026-01-30T11:34:00.000-08:00

Published By Alex George

I received multiple questions (from my readers) asking about the differences and benefits of configuring an ISP modem in PPPoE mode vs Bridge mode. So, I am writing this detailed article to answer all those questions.

What Are PPPoE and Bridge Configurations?

In this section, I will answer a repeated question from my readers about what PPPoE and Bridge configurations are.

Regular readers of CoreNetworkZ EdTech Solutions know I worked as an apprentice for an ISP during my B.Tech days.

The first lesson I learned was to set up a home LAN with their ISP devices. During this period, they trained me to configure a DSL modem in bridge and PPPoE modes.

PPPoE = Point to Point Protocol over Ethernet

So, now you understand how I learned to set up a broadband modem in PPPoE and bridge modes. Now, let me answer one question from Julia.

She is a regular reader and DSSSB TGT Computer Science aspirant.

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She wanted to know the practical difference between PPPoE and Bridge modems. She also wanted to learn how to recognize a PPPoE modem.

Julia asked this question in the comment section, and I will answer it in this section.

The practical difference is the use of a dialer to access the Internet.

If you configure the modem in bridge mode, you need a dialer to connect to the Internet. The dialer will ask you to enter the ISP-provided username and password.

They are the credentials to access the Internet.

If your modem is in PPPoE mode, the connection is always on. What does it mean? It means you do not need a dialer to access the Internet.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding the differences between Bridge Mode and PPPoE Mode is essential for candidates appearing for the DSSSB PGT/TGT Computer Science, Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), VSSC Technical Assistant, and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions that require them to explain the differences between Bridge and PPPoE Modes. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

Feature	PPPoE Mode (Router Mode)	Bridge Mode
Device Role	Modem acts as a Router/Gateway.	Modem acts as a "Dumb" Converter.
IP Assignment	Modem receives the Public IP.	Public IP passes through to the PC/External Router.
NAT & DHCP	Enabled (Modem manages devices).	Disabled (Modem is transparent).
OSI Layer	Layer 3 (Network Layer)	Layer 2 (Data Link Layer)

PPPoE vs Bridge Modes

I explained one practical difference, but that is not all. Let me compare the key differences between a modem in bridge mode and a modem in PPPoE Passthrough mode. In this section, I will teach you six key differences.

Number of Supporting Devices

Let me explain the first difference. The primary difference is the number of supported devices. Bridge Mode Supports only one computer, but PPPoE supports multiple computers.
ON or OFF State

I explained this point before. In bridge mode, you need to dial every time to go online. PPPoE mode is always connected.
Cyber security

PPPoE is more secure than bridge mode. So, why is that? The reason is simple. The modem firewall will not work in bridge mode.
Port Forwarding

In Bridge mode, there is no need for port forwarding. In PPPoE mode, you may need port forwarding. This point is helpful for online gamers. Arun Gopi, one online gamer, complained about port blocking.

He asked my advice.

So, my advice to online gamers is to choose a bridged modem.
Support for NAT

Let me explain the 5^th difference between PPPoE and Bridge mode. It is about the NAT feature on an ISP modem. So, do you know which mode of modem configuration supports the NAT feature?

PPPoE mode supports NAT.

There is no NAT in bridge mode. Samantha Turner asked why bridge mode does not support the NAT feature.

Samantha is a Computer Science student.

The answer is simple. By bridging, the modem passes the connection directly from the ISP to the computer/router. So, it cannot support the NAT feature.

NAT = Network Address Translation

I believe I have answered her question.
The Supported IP Addresses

Let us recall the question from Julia. She asked how to recognize if the modem is in PPPoE mode.

We can find it easily. All we need to do is check the IP address modem assigned to the connected PC.

The computer connected to the modem in bridge mode gets the public IP address. Your computers get private IP addresses in PPPoE mode. So, you have learned the 6th difference between a bridge and a PPPoE modem.

I have explained the six key differences between PPPoE and Bridge mode. Now, let me answer a few questions asked by readers.

Max Cassidy asked me if a bridged modem supports the DHCP. The answer is no. Only a modem configured in PPPoE supports the DHCP.

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I feel I must mention the comment by Laxmi Rao. She shared her experience with a faster Internet connection on a bridged modem. I support her view because a bridged modem does not waste time on features like NAT and DHCP.

Now, I am concluding this article. Today, you learned the differences between PPPoE and Bridge mode. If you wish to further studies, I suggest you visit the following links under the reference headline.

Reference

https://www.cisco.com/c/en/us/td/docs/optical/15000r4_5/ethernet/454/guide/ios4145/45bridg.pdf
https://www.juniper.net/documentation/us/en/software/junos/multicast-l2/topics/topic-map/bridging-and-vlans.html
https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://www.systosys.com/viewtopic.php?t=14
https://community.cisco.com/t5/routing/configure-two-routers-in-bridge-mode/td-p/1189709

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

OSI Reference Model - Study Notes for PSC, SSC, and IT Exams

2026-01-30T11:33:00.000-08:00

Aspirants of DSSSB and SSC Scientific Assistant often get confused between these two. While OSI is a Theoretical Model (7 layers), TCP/IP is the Implementation Model (4 or 5 layers). For the exam, remember that OSI was developed by ISO in 1984.

Today, you will learn about the OSI Reference Model and its seven-layer structure.

The International Organization for Standardization (ISO) developed a seven-layer model called the Open Systems Interconnection (OSI) Reference Model to help vendors and network experts learn how data transmits between two devices in a network.

ISO developed the OSI Reference model.

So, you might ask why we need such a reference model. The answer is simple. We need a standard to follow while developing Network devices.

OSI Reference Model helps networking device manufacturers to implement new network standards and policies. It also helps network administrators reduce the complexity of networks and makes it easier to troubleshoot networking issues.

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How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts like.

Understanding the OSI model is essential for candidates appearing for the DSSSB PGT/TGT Computer Science, Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), VSSC Technical Assistant, and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions from the OSI Reference Model. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

Layer #	Layer Name	PDU (Data Unit)	Key Features & Functions	Common Protocols
7	Application	Data	Interface for end-users, resource sharing, and network services.	HTTP, FTP, SMTP, DNS, DHCP
6	Presentation	Data	Data translation, Encryption, Decryption, and Compression.	SSL, TLS, JPEG, MPEG, GIF
5	Session	Data	Session establishment, management, and termination; Dialog control.	NetBIOS, RPC, PPTP, SQL
4	Transport	Segments	End-to-end delivery, Segmentation, Reassembly, Flow control, Error recovery.	TCP, UDP
3	Network	Packets	Logical addressing (IP), Routing, Best path determination.	IP, ICMP, IGMP, OSPF, RIP
2	Data Link	Frames	Physical addressing (MAC), Error detection (CRC), Framing, Media Access Control.	Ethernet, PPP, Switch, Bridge
1	Physical	Bits	Raw bit streaming, Physical cables, Connectors, Pin layouts, Hub behavior.	Bluetooth, WiFi, DSL, Cables

What is The Importance of the OSI Reference Model?

The introduction of the OSI reference model was a revolution. Before it, device manufacturers did not have a common standard. So, there was no hope of interoperability between devices from different companies.

OSI Model Brings a common standard.

Now you can see how critical was the introduction of the OSI reference model.

Seven Layers of OSI Reference Model

There are seven layers in the OSI Reference Model. Each layer has a specific role in data communication. A network engineer must learn the importance and functions of each layer in detail.

Seven layers of the OSI reference model are listed below.

What is The Need For the OSI Reference Model?

I explained the need for a common standard before. Let me explain it in detail. There was no common standard before the Open System Interconnection (OSI) Reference Model.

It forced the user to stick with a single vendor for all his networking needs because devices from different vendors were incompatible. The International Organization for Standardization (ISO) introduced the seven-layer OSI architecture to overcome it.

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OSI Reference Model tells how to connect and configure a network. It helps vendors to make products with universal standards.

Benefits of the OSI Reference Model

I believe you enjoyed this tutorial. So, let me conclude with the actual benefits of the OSI Reference Model in the real world.

The benefits of the OSI Reference Model in a computer network are listed below.

OSI Reference Model promotes interoperability by defining the process of connecting two layers.
By dividing a network into layers, we split complex network activities into simple components.
Helps vendors to follow a modular design.

Reference

https://learningnetwork.cisco.com/s/article/osi-model-reference-chart
https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://aws.amazon.com/what-is/osi-model/

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

NAT (Network Address Translation) - Study Notes for PSC, SSC, and IT Exams

2026-01-30T11:32:00.000-08:00

Published By Alex George

Network Address Translation (NAT) is a technique used to convert one IP address into another.

NAT = Network Address Translation

This article explains the functions and advantages of NAT in detail. We will also examine the importance of Network Address Translation and how it helps in our daily lives.

What is NAT?

Arun Kumar, a 3^rd year Computer Science student from Delhi, asked, "I am preparing for CCNA and wish to become a Network Engineer. Can you explain NAT in simple terms? Please share some repeated CCNA questions from the topic NAT." Arun is preparing for the SSC Scientific Assistant (CS) recruitment test.

Let me answer Arun's question here. Network Address Translation (NAT) is a method used in networking to allow multiple devices on a private network to access the internet using a single public IP address.

I will explain it in simple terms. Network Address Translation (NAT) allows the conversion of one IP address into another.

Critical Functions of NAT

Ben Johnson, a client of CoreNetworkZ EdTech Solutions, inquired about the functions of Network Address Translation (NAT) during one of our project discussions.

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To provide clarity for a wider audience, I will share the key points I explained to Ben:

The primary function of NAT is IP Address Translation. It converts a public IP address into a private IP Address and vice versa.
The second function of NAT is to enhance security and privacy. NAT translates public IP addresses into private IP addresses. So, an external agent cannot easily identify or access the internal network.

I believe now you understand the functions of Network Address Translation.

How NAT Helps a Regular Person?

Julia James, one regular reader of CoreNetworkZ EdTech Solutions, asked this question in our support section.

Let us now explore how NAT benefits us in our daily lives.

Assume you have two laptops, two smartphones, and a desktop computer at home. You use a Cox Internet connection and a Belkin wireless router. The home network setup is simple: the Belkin router connects to the Cox modem, and all your devices connect to the Belkin router.

The Belkin router has an inbuilt NAT feature. So, it allows it to share a single Internet connection among all connected devices.

I guess a visual diagram will help you understand this concept better. Have a look at the diagram below.

A single public IP address converts into multiple private IP addresses.

Different Types of Network Address Translation (NAT)

Atul Krishna, a VSSC Technical Assistant aspirant, asked, "Hello Alex, I am studying for CCNA. Can you explain the different kinds of NAT in real life?"

He asked this question on the support section of CoreNetworkZ EdTech Solutions. I will answer his question here.

Network Address Translation comes in various types, depending on the method and the number of IP addresses it translates.

Static NAT

In Static Network Address Translation, one IP address in a packet is translated to a different IP address manually. It is a one-to-one mapping.
Dynamic NAT

In Dynamic Network Address Translation, the address translation device picks an IP address dynamically to convert from a list of allowed IP addresses.

Dynamic NAT has two sets of IP addresses.

One is a list of IP addresses that get converted, and the second is the list of IP addresses as the final IP addresses.

Let us check the advantages and disadvantages of Dynamic Network Address Translation.

The major problem with static and dynamic NAT is they convert just one IP address to another IP address.

It cannot convert multiple IP addresses to a public IP address or vice versa.
Port Address Translation

Port Address Translation (PAT) helps all the private IP addresses in the network to use a single public IP address with different port numbers.
So by using PAT, we overcome the limitation of NAT that uses one-to-one mapping.

PAT works with only TCP and UDP protocols.

PAT is not free from disadvantages. Not all applications work with PAT.
Port Address Redirection

Port Address Redirection (PAR) is the reverse of PAT. In PAR, multiple public IP addresses convert to a single private IP address.

PAR works with only TCP and UDP protocols.

However, Port Address Redirection also does not work with all applications.

The Major Benefits of Network Address Translation

One System Admin trainee from CoreNetworkZ EdTech Solutions asked me for the real-life benefits of using a NAT in a computer network. I believe some of my readers also have the same question.

So, I will list the most critical advantages of NAT in a network.

Address Translation fixed the scarcity of IP addresses.
NAT successfully hides the internal network design from external parties.
NAT helps network admins to have tighter control over network traffic.

NAT Type	Mapping Ratio	Best Use Case
Static NAT	1-to-1 (Fixed)	Hosting internal Web/Email servers.
Dynamic NAT	1-to-1 (From Pool)	Large orgs with many users but few public IPs.
PAT (Overload)	Many-to-1	Home/SOHO routers (Most Common).

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding the NAT is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), VSSC Technical Assistant, and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions that require them to explain the rworking of NAT. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

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Disadvantages of Address Translation

Though NAT is helpful, it has some drawbacks. Some of them are:

PAT and PAR work with only TCP and UDP protocols.
Not all applications support Address Translation.
Address Translation causes an extra delay in each connection.
NAT makes network troubleshooting more complex.

Reference

https://www.cisco.com/c/en/us/support/docs/ip/network-address-translation-nat/13772-12.html
https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/user-guide/setup-nat-network
https://www.keralapsc.gov.in/question-paper-descriptive-exam
https://www.juniper.net/documentation/us/en/software/junos/nat/topics/topic-map/security-nat-overview.html
https://www.juniper.net/documentation/us/en/software/junos/nat/topics/topic-map/security-nat-configuration-overview.html

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Ethernet Hub - Study Notes for PSC, SSC, and IT Exams

2026-01-30T11:31:00.000-08:00

Published By Alex George

I published a series of tutorials for beginners to understand network engineering concepts on CoreNetworkZ EdTech Solutions.

This post is part of my ongoing series on legacy networking devices. Today, I will explore one such piece of hardware—the network hub. Though largely obsolete in modern enterprise environments, some students asked me for a tutorial on the Hub.

It is a dumb device.

On the support section of CoreNetworkZ EdTech Solutions, many students asked questions (for CCNA and JNCIA-Junos). Many PSC and SSC aspirants asked me for potential exam questions from this topic.

So, I will explain a few Juniper JNCIA-Junos and CCNA questions from the Hub section. Let us first check the Hub and its role in a LAN.

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What is a Hub?

Aishwarya Narayan, an SSC Scientific Assistant (CS) aspirant from Chennai, asked, "What is a Hub, and in what OSI layer does this device operate?"

She asked this question on the support community of CoreNetworkZ EdTech Solutions. I will answer her question in this section.

A Hub is a network device that connects multiple devices in a single network segment. It is a basic layer one connector without any intelligence.

That means we can connect multiple devices to a Hub. However, it has many limitations.

Now, I will answer Aishwarya's second question. The Hub operates at the Physical layer of the OSI Reference Model.

Hub is a Physical Layer Device.

Let me add a few more points that will help her prepare for the coming CCNA examination.

Since it is a Layer 1 device, it cannot read the signals it transmits. In networking terms, all devices connected to a Hub feel as if they are on the same cable.

How To Power Cycle a Hub?

So, we can say that the Hub has a single collision domain. In other words, a Hub repeats the signal it receives.

The Working of a Hub

Let us now check the working of a Hub. Vijay Nair, a regular reader of CoreNetworkZ EdTech Solutions, asked, "Hello Alex, I am preparing for my CCNA examination. Can you explain the working of a network Hub in simple words?"

I will answer Vijay here.

I will explain the operation of a Hub.

Consider a network including five devices and a Hub. Now, the first computer wants to send a packet to the fourth computer.

Let us see how the Hub handles this situation.

When a computer connected to a Hub sends packets, the Hub broadcasts the packets to all ports except the one from which it received the packets.

I believe I explained everything about the working of a Network Hub.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding Computer Network Devices is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect ten questions. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

Limitations of a Network Hub

Aparna Rajeev, a B.Tech Student from Cochin, asked, "Why is no one using a Network Hub anymore? What are the limitations of a Hub?"

I ask you to recall my previous tutorial published on CoreNetworkZ EdTech Solutions ( about the Switch).

Switch is an intelligent device.

Here, we can see the difference between a Switch and a Hub. A Hub does not read the packets; it simply broadcasts them to all ports.

A Switch, on the other hand, reads the packet and unicasts it. So, a Switch is more efficient than a Hub.

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Another problem with the Hub is the higher chance of packet collisions. We know a Hub has a single collision domain, so the chances of collisions are very high.

Feature	Network Hub	Network Switch
OSI Layer	Layer 1 (Physical)	Layer 2 (Data Link)
Intelligence	Dumb (Broadcasts to all)	Smart (Sends to specific MAC)
Duplex Mode	Half-Duplex	Full-Duplex
Collision Domain	Single (High Collisions)	Multiple (Each port is separate)

Does Anyone Use Hubs Now?

I saw a comment on CoreNetworkZ EdTech Solutions asking if anyone is using Network Hub.

The Hub is an obsolete device.

I rarely see Hubs in a LAN to connect network devices. Most networks use Switches to connect multiple network devices in a single network.

However, it is an excellent device for a beginner in network engineering to create a dummy network in a lab. So, they can learn the basics of computer networking.

Reference

https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://standards.ieee.org/ieee/802.3/10422/

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

What is a Router & Its Functions?

2026-01-30T11:30:00.000-08:00

Published By Alex George

After completing this tutorial, you will learn the definition, functions, and different types of routers.

What is a Router?

Let me start the tutorial by explaining the definition of a router. CoreNetworkZ EdTech Solutions defines a router as an intelligent network device that connects multiple network devices and communicates between them.

Now, I will explain each term of this standard definition. First, I will explain why I used the term 'intelligent device' in the definition.

A router is an intelligent layer three networking device. It can read and analyze the IP packets sent by other network devices. So it does not blindly forward packets. I hope you understand the reason why it is called an intelligent device.

A router receives and forwards IP packets by reading the destination addresses.

Do you wonder how a router forwards IP packets? It does it with the help of a routing table and routing protocols.

Let us check how routing tables and protocols assist a router in packet forwarding.

I will explain it in the next section of this tutorial.

Now, I will explain the second part of the router definition. A router is a layer three device used to connect different networks. It also connects networks with different network addresses.

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The router works in the Network Layer (OSI Reference Model) and connects similar and different types of networks.

Ethernet and FDDI are two different LAN technologies.

We need a router to communicate between one FDDI and another Ethernet network.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding a Network Router is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions from the Network Devices. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

Router and Routing Table

Ashish Mudgal insisted on including the routing table in this tutorial. My regular readers know him. Ashish is a senior network engineer at CoreNetworkZ EdTech Solutions.

So, let me start this section by explaining the relation between a router and the routing table. A router makes routing decisions based on its routing table.

The routing table consists of path information to send packets to neighboring routers.

Sarah Brodrecht asked how the routing table helps a router. She asked this question in the comment section. So, I will answer her question here.

A router finds the shortest path to send packets to the destination by calculating the entries in the routing table with the routing protocol.

Feature	Key Specification / Fact
OSI Layer	Layer 3 (Network Layer)
Data Unit	Packets
Primary Task	Path Determination & Switching
Address Type	Logical Addresses (IP Addresses)
Standard Device	Gateway of Last Resort

Examples of Routing Protocols

Carol Allison asked in the comments about the role of Routing protocols in today's router models. Her question requires a detailed article that I will write soon. So, I suggest she read my previous articles on popular routing protocols. The links are below.

You have learned about routers and routing tables. Now, let us check the router functions.

Functions of a Router

Aleena Xavio, an Information Technology student, asked, "I am preparing for the CCNA examination. Can you list the critical functions of a layer three router?"

She asked this question on the support section of CoreNetworkZ EdTech Solutions.

Aleena is right in asking this question. Those preparing for the CCNA and the Juniper Networks Certification Program (JNCP) know the importance of router functions.

We cannot finish an article about routers without mentioning their functions. The primary functions of a router are:

Router Connects Different Network Types.
It joins networks with different network addresses.
It finds the shortest path to send packets to the destination.
It defines logical address schemes.
The router supports VLANs.
The router has features like Quality of Service and Filtering.
It builds routing tables to make layer three decisions fast.

I covered seven functions of a router and hope it will help you in your preparation for CCNA and JNCIA-Junos.

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Different Types of Routers

Nirupama Rao asked me about different kinds of routers. According to Cisco's guidelines, we can classify routers into five categories. They are:

Core router
Edge router
Distribution router
Wireless router
Virtual router

Links to Router Configuration Guides

Here we provide links to some of our popular configuration and troubleshooting guides.

Since I have explained the router definition and functions already, let me conclude this article. If anyone is looking for more details, I suggest the following references.

Reference

https://www.cisco.com/c/en/us/solutions/small-business/resource-center/networking/what-is-a-router.html
https://www.systosys.com/viewtopic.php?t=107
https://www.juniper.net/us/en/research-topics/what-is-a-router.html
https://www.hp.com/us-en/shop/tech-takes/modem-vs-router

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Dynamic Host Configuration Protocol (DHCP) - Competitive Exam Questions

2026-01-30T11:26:00.000-08:00

Published By Alex George

So, what is DHCP?

Dynamic Host Configuration Protocol (DHCP) is an application layer protocol that automatically assigns IP addresses to devices on a network.

Role of DHCP in a Computer Network

Anagha Sivakumar, a Network Engineer trainee at CoreNetworkZ EdTech Solutions, asked, "What is the role of DHCP in networking?"

I know many of my students might have the same question. Let me explain it. DHCP simplifies the process of assigning IP addresses to connected devices.

DHCP Assigns IP Addresses automatically.

Imagine managing a network with thousands of devices. Do you think it is practical to assign static IP addresses to each one manually, without errors? That is where DHCP comes in.

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It allows devices to obtain IP addresses automatically, reducing human error and administrative burden.

What is The Working of Dynamic Host Configuration Protocol?

Nimin Marcos, an SSC Scientific Assistant (CS) aspirant , mentioned a question in our support forum. He asked, "Hello Alex, can you explain the complete working of Dynamic Host Configuration Protocol?"

I will answer Nimin's question in this section.

DHCP operates on a client-server model, where the server assigns IP addresses and other network configuration details to client devices. Let us explore how DHCP functions within a network.

We can use the term DORA to explain the working of DHCP. It is a four-stage process.

Step	Message	Description	Traffic Type
D	DISCOVER	Client looks for Server	Broadcast
O	OFFER	Server offers an IP	Unicast (or Broadcast)
R	REQUEST	Client accepts the IP	Broadcast
A	ACK	Server confirms	Unicast (or Broadcast)

Let us check each stage.

D-- Discovery

When a client connects to a network, it sends a broadcast to discover the DHCP server. This broadcast is termed DHCPDISCOVER.
O--- Offer
At this stage, the server responds to the client DISCOVERY message and sends a DHCPOFFER unicast message. DHCPOFFER includes IP address, subnet mask, default gateway address, DNS address, etc.
R---- Request
Here the client sends a DHCPREQUEST message to the server.
A--- Acknowledgment

Here server sends an acknowledgment (DHCPACK) to the client indicating it received the DHCPREQUEST from the client, and the client accepted the IP address information.

Advantages of Using DHCP

Ashi Vohra, a student from CoreNetworkZ EdTech Solutions preparing for ISRO System Analyst post, asked, "What are the advantages of using the dynamic host configuration protocol (dhcp)?"

I developed three network apps for his company. One of them used the DHCP feature. So, he asked this question.

The advantages of using Dynamic Host Configuration Protocol are:

There is no chance of getting IP addressing errors if you use DHCP to assign IP addresses to devices in a network.
The second advantage of using Dynamic Host Configuration Protocol in a network is the efficient control of IP addressing. The reason is simple. It is centralized.
The third advantage is scalability and cost-effectiveness.

Allen Donald asked in a comment why I said cost-effectiveness as an advantage. It is simple. We can avoid the heavy work of manual IP addressing once DHCP assigns IP addresses automatically.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding the DHCP is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions that require them to explain the DHCP. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

Cisco Certification Exam Tips

If you prepare for Cisco certification exams( like CCNA), you must learn more about DHCP. If you follow the CCNA DUMP for your next exam, let me help you in this section.

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A few students asked for my support in learning CCNA questions from the DHCP section. Some important points about Dynamic Host Configuration Protocol for your Cisco Certification exams are listed below.

Command to Enable or Disable DHCP on Cisco IOS Router --service dhcp
Cisco Command to create address pool -- ip dhcp pool
Command to assign a domain name to client --domain-name
Command to specify DHCP IP range -- network
The command to check if the server can use an IP address in the pool -ip dhcp ping timeout
The command to exclude an IP address from the DHCP address pool --ip dhcp excluded-address
Show addresses assigned to clients --show ip dhcp binding
DHCPNACK - This acknowledgment from the server tells the client the offer is no longer valid.
DHCPDECLINE - The client tells the server, it cannot use the offer from the server.

Let me share a few more expected CCNA questions from DHCP.

Sanal Mohan, a student preparing for CCNA, asked, "Does DHCP use ports to communicate? If yes, which ports it uses?"

Resolve APIPA

DHCP servers use UDP port 67 to receive requests, while clients use UDP port 68 to send them.

Ashams asked in our support forum, "What is the default lease time of an IP address assigned by DHCP?" DHCP assigns IP addresses by default with a lease time of 24 hours. However, network administrators can change it.

Ashish Mudgal, a senior Network Engineer at CoreNetworkZ EdTech Solutions, mentioned, "One critical point many students do not know is DHCP communicates using the UDP protocol. "

Reference

https://www.juniper.net/documentation/us/en/software/junos/dhcp/index.html
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dhcp/configuration/15-sy/dhcp-15-sy-book/config-dhcp-server.html
https://docs.redhat.com/en/documentation/red_hat_enterprise_linux/7/html/networking_guide/sec-dhcp-configuring-server
https://learn.microsoft.com/en-us/windows-server/networking/technologies/dhcp/dhcp-top

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Routing Information Protocol (RIP)

2026-01-30T11:24:00.000-08:00

Welcome to the Networking Fundamentals series by CoreNetworkZ EdTech Solutions, a trusted Mock Test and Competitive exam coaching platform. This module is for candidates preparing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (Computer Science), and ISRO Technical Assistant posts.

The Routing Information Protocol (RIP) is a dynamic routing protocol that helps to find the shortest path between two hops. This tutorial checks the working of the RIP protocol, its importance, and its different versions.

RIP is an interior gateway protocol (IGP) using the distance-vector routing algorithm.

The Importance of Routing Information Protocol

It creates a routing table that helps routers to find the network layout. Dynamic Routing table helps to understand the changes in network connections.

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Working of Routing Information Protocol

John Bailey asked me in the comment section to explain the workings of this protocol.

RIP is a distance-vector routing protocol. It uses hop count as the routing metric.

15 is the maximum number of hops allowed in RIP.

RIP sends routing-update messages at regular intervals and and updates the routing table when the network topology changes. The average RIP update time is 30 seconds, while the hold-down time is 180 seconds.

In Which OSI Layer RIP Works?

Sharanya Mohan, a reader of our blog, CoreNetworkZ, asked this question. It is an important question.

One of the interviewer's favorite questions for a network engineer recruitment is which OSI layer RIP works. RIP is based on UDP and working in the Transport layer.

Routing by RIP is also called routing by rumor.

We have covered the importance and the working of the RIP. Let us check how the Routing Information Protocol maintains stability.

RIP Stability Features

I read one question from Arun Kumar in the blog comment section. He wanted to know how RIP keeps its stability. RIP implements the following mechanisms to maintain stability. They are:

Split horizon
Route poisoning
Hold down mechanisms

What Are the Different Versions of Routing Information Protocol?

One of the repeated CCNA questions is about the different types of RIP. I do not wonder why I keep getting this question. Robin Matthews asked this question in the comments. There are three versions of Routing Information Protocol. They are:

RIP version
RIP version 2
RIPng

RIP version 1 is the basic RIP which doesn't support VLSM. This drawback is fixed on the RIP version 2 where it supports Variable Length Subnet Mask (VLSM).

RIPv1 is a Classful Routing Protocol.

RIP version 2 uses multicast where RIP version 1 uses broadcast to send routing updates.

RIPv2 is a Classless Routing Protocol.

RIP version 2 multicasts routing updates to the address 224.0.0.9. RIPng is specially defined for IP version 6.

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How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts. Understanding Routing Information Protocol is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and VSSC System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions that require them to explain the Routing Information Protocol. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

Reference

Today, I have covered the basics of Routing Information Protocol. If anyone is looking for a detailed tutorial, I suggest these references.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960xr/software/15_2_7_e/configuration_guide/b_1527e_consolidated_2960xr_cg/routing_information_protocol.pdf
https://www.ibm.com/docs/en/zos/3.1.0?topic=omproute-routing-information-protocol

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

The Functions of A Wide Area Network (WAN)

2026-01-30T11:23:00.000-08:00

A Wide Area Network (WAN) is a network that covers a large area. Its coverage extends from country to continent.

We can say a WAN is a connection of multiple LANs.

The primary function of a WAN is to connect two Local Area Networks located in different locations. When we need to connect two LANs at different locations separated by a long distance, we need WAN to connect them.

Different WAN services are available to connect two remote LANs. Once we connect two LANs with a WAN connection, we can communicate between them.

The best example of a WAN is the Internet.

Cable and DSL are the two most popular WAN connections. Other than these two, there is a list of WAN services available.

Application of WAN Services in Today's World

Without the concept of a Wide Area Network (WAN), there is no Internet. Without the Internet, none of the Information Technology developments were possible.

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So, we can say WAN technology is the backbone of today's Information exchange. An example is this website. You are reading www.CoreNetworkZ.com on your mobile phone.

How is it possible? A WAN technology transfers this web page from the server to your mobile phone. Without a WAN, you cannot access this web page.

Another example is a corporate company that has offices in various countries. Communication between their offices works due to a WAN.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding the functions of A Wide Area Network (WAN) is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

List of Popular WAN Services

Digital Subscriber Line (DSL)
Cable
Dedicated circuits
ATM
Analog Dialup
Frame Relay
ISDN
X.25
SMDS (Switched Multi-megabit Data Services)

Popular Connection Types in WAN Services

There are four different connection types used in Wide Area Networks service. They are:

Circuit-switched:

Circuit-switched services provide a temporary connection using a phone circuit. Analog dialup and ISDN are examples of circuit-switched WAN connection types.
Cell Switched:

Cell Switched service uses dedicated connections, but it can connect multiple devices by a single device using the same interface. It is advanced compared to dedicated switched services.
Packet Switched:

Packet Switched services use variable-length packets to connect multiple devices from a single device over a dedicated connection.
Dedicated connections:

As the name suggests, it uses a dedicated connection to connect two devices.

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Important WAN Network Devices:

Networking devices in Wide Area Networks are:

DSL and Cable Modems
Firewall
Carrier Switches
NT1s
Routers

Reference

https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://www.cisco.com/site/us/en/learn/topics/networking/what-is-a-wan-wide-area-network.html

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Flow Control in Computer Networks: Study Notes for PSC, SSC, and IT Exams

2026-01-30T11:22:00.000-08:00

Published By Alex George

Welcome to the Computer Science & Technology study section by CoreNetworkZ EdTech Solutions, a leading mock test and competitive exam preparation platform, for students appearing PSC and SSC exams. This guide is specifically designed for candidates preparing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant, and other IT support jobs exams.

What is Network Flow Control?

Many students (who are new to Network Engineering) asked me this question. They are not alone. A few of our readers also asked the same question. So, let me explain what network flow control is in this section.

Network Flow Control Prevents data loss in a communication.

Network flow control is a technique that regulates the number of frames transmitted between two network interfaces to avoid data conjunction. This technique is helpful when one Network Interface is faster than the other. Since you have learned the concept, let us go to the next section.

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Importance of Enabling Flow Control Feature On a Network Interface Card

I write this section based on my personal experience as a Network Engineer. You can also consider it a supporting article for my other network troubleshooting guides published by CoreNetworkZ EdTech Solutions.

We need to turn on or off the flow control property of the adapter to troubleshoot some network connectivity issues.

Consider a scenario where your computer is a part of a high-speed network. What will happen if your Network Adapter receives input frames more than it can handle ( without a flow control enabled option)?

The answer is simple. It will result in frame loss.

Network Flow Control Feature Prevents Frame Loss.

Do you know why? The sender is not getting information about the possible frame loss. So, it will not stop sending more frames.

With the flow control enabled option, your Network Adapter will send a pause frame that tells the sender (sender of frames to your NIC) to pause the transmission until its buffer is free.

So, if your NIC is slower (while connecting to a high-speed network), you may need to enable the Flow Control property to avoid packet loss. I believe you have understood the importance of this feature.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

Understanding Flow Control in Computer Networks is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and ISRO System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions that require them to explain the Flow Control in Computer Networks. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

How To Enable or Disable Flow Control?

In this section, I will explain how to activate the Adapter flow control on a Windows computer.

Go to Network Connections Window

We can access the Network Connections Window via two methods. The first method is via the Run command. The second method is the Windows GUI. I will explain both methods in this section.
1. By Run Command
2. By GUI
Now, you are in the Network Adapter window, where you can see all the NICs installed on your computer.
Right-click on the Local Area Connection, and click on the Properties option. You can see the screenshot of the right-click menu below.
Click the Configure button

Now, you may receive one warning message, "You have made changes to the properties of this connection. If you proceed, your changes will be lost. Do you wish to proceed?".

Click on the yes button to proceed.
Click the Advanced Tab
Select Flow Control from the list and choose Enable.

After selecting the option, you should click OK. Now, the flow control property of the Ethernet adapter is enabled.

If you want to change the link speed and duplex settings, select Speed and Duplex.

With these five steps, you can turn on or deactivate the Network Adapter flow control on a Windows device.

Steps to Enable NIC Flow Control On an Ubuntu Linux Laptop

I saw comments from Stephen Curry and Chris Paul asking me to explain how to enable Network Interface flow control on a Linux device. I will answer their questions in this section.

You can perform it on an Ubuntu PC by following the steps below.

Open Terminal and type the following commands.

sudo apt-get update

sudo apt-get install ethtool
Type the following command to enable NIC flow control.

sudo ethtool -A eth0 rx on tx on
Type the following command to disable NIC flow control on an Ubuntu PC.

sudo ethtool -A eth0 rx off tx off

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Uses of Network Adapter Flow Control?

Richard Durrant asked me about the uses of this feature. He is a CCNA student and a regular reader of tutorials prepared by CoreNetworkZ EdTech Solutions. So, let me answer his question in this section.

The primary use is to avoid frame conjunction at the slower NIC. It will prevent data loss and improve the communication between sender and receiver Network Interfaces.

Reference

https://www.juniper.net/documentation/us/en/software/junos/interfaces-ethernet/topics/topic-map/flow-control-ethernet-interfaces.html
https://community.cisco.com/t5/switching/flow-control/td-p/2463281

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Virtual Router Redundancy Protocol (VRRP)

2026-01-30T11:21:00.000-08:00

Virtual Router Redundancy Protocol (VRRP) is an open protocol (not a proprietary protocol). It introduces the concept of the virtual router to improve the redundancy of the default gateway of hosts.

This article checks the uses and importance of VRRP.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding Virtual Router Redundancy Protocol (VRRP) is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions from Network Protocols. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

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How Does VRRP Assure Network Redundancy?

One commenter, Frank, asked about how VRRP ensures the Network Redundancy. Another reader, Kevin Thomas, asked about using a virtual router in this protocol. Let me answer both here.

According to VRRP, a virtual router (VR) is not just a physical router but includes the master and backup routers.

So, the default gateway of a host is the VR instead of a single physical router.

This VR concept ensures that if one router fails, another will take the charge immediately. However, at a time, only one master acts as the default gateway, and the master informs the backup routers of its current status.

The backup router will take place in the position of the master if the master becomes unavailable.

Can I Use VRRP with HSRP?

Ronald asked me if he could configure a Cisco router with VRRP. Cisco uses a different protocol, HSRP.

Virtual Router Redundancy Protocol is an open-source protocol similar to Cisco's proprietary protocol, the Hot Standby Router Protocol (HSRP). However, both protocols are not compatible despite their similarities.

We cannot use VRRP with HSRP.

You have learned the basics of VRRP. Let us check how to configure the Virtual Router Redundancy Protocol.

VRRP Configurations Tips

Kanaka Raj, a young network engineer, wanted a tutorial on configuring VRRP. I guess the steps below will help him learn it.

The Virtual Router (VR) works as the default gateway of hosts.
A group of physical routers comes under VR, but only one master at a time.
The master router informs backup routers of its current status (all the time).
When the master fails, one backup router assumes the role of master.
The concept of VirtualRuter by Virtual Router Redundancy Protocol improves network redundancy.
The MAC address of the VR must be in this format: 00-00-5E-00-01-XX.
The IP address used for multicast is 224.0.0.18.

You have learned the basics of the Virtual Router Redundancy Protocol and its application in a network.

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Study Notes: High Availability & Gateway Redundancy (VRRP)- This topic is a key part of the Computer Networks syllabus for the Kerala PSC Degree Level Exams, SSC Scientific Assistant (Computer Science), and DSSSB PGT/TGT Computer Science. Expect questions on protocol standards, Master/Backup roles, and Virtual IP logic.

Reference

You have learned the basics of VRRP. For further studies, I recommend the following tutorials from Cisco and Juniper.

https://www.juniper.net/documentation/us/en/software/junos/high-availability/topics/topic-map/vrrp-understanding.html
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp_fhrp/configuration/15-mt/fhp-15-mt-book/fhp-vrrp.html
https://www.cisco.com/c/en/us/td/docs/routers/crs/software/crs_r4-0/addr_serv/configuration/guide/ic40crs1book_chapter10.html

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Demilitarized Zone (DMZ) - Competitive Exam IT Study Notes

2026-01-30T11:20:00.000-08:00

Welcome to the Computer Science and Technology Study Materials section from CoreNetworkZ EdTech Solutions, a leading mock test and exam preparation platform, for students preparing for SSC, DSSSB, and Kerala PSC examinations. Today, I will explain Demilitarized Zone (DMZ).

Understanding the Demilitarized Zone (DMZ) is necessary for candidates appearing for the Kerala PSC Degree Level exam and SSC Scientific Assistant (CS). You can expect questions from this section in the Computer Science and Technology part. In network security, a DMZ acts as a buffer zone between a trusted internal network and an untrusted external network (the Internet).

Have you ever noticed a feature DMZ while configuring an ISP modem or router? DMZ is one of the network features available in every SOHO router.

In my experience, many people without a network engineering background have zero ideas about this feature.

DMZ stands for Demilitarized Zone.

If you place a device in your network in DMZ, that device won't have much access to other devices connected to the network.

A device placed in DMZ is more exposed to external threats. Logically the device in DMZ is outside of the network with limited security.

All ports of the DMZ host are open and exposed to the external elements.

So, why do we use DMZ?

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DMZ host has its own merits and demerits.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding Demilitarized Zone (DMZ) is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions from Demilitarized Zone (DMZ) in Computer Networks. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

What is The Use of DMZ in a Network?

If you are a hardcore online gamer, you know the hurdles of the router firewall and NAT.

In most cases, simple port forwarding allows you to continue online gaming, but rarely it does not work.

The ultimate solution for firewall issues in online gaming is to place your gaming computer in DMZ.

Placing your gaming PC in DMZ means the PC is outside the router firewall protection.

Also, your computer has a limited connection to other computers in your home network.

Technically DMZ host is outside the network. So other hosts in your network are safe even if the DMZ host is compromised.

Though a hacker compromised the DMZ computer, the attacker will not get access to other devices in the network.

So you can run a web server on your computer that can be in DMZ without risking the security of other devices in your network.

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Practical Use of DMZ in a Home Network

Consider a home network having three laptops and two desktop computers connected to a wireless router. One desktop computer is a gaming PC.

Now you are playing a new online game, but the router firewall blocks a few crucial network ports. Port forwarding does not work.

So, what do we do if the port forwarding does not work for your online game?

The last solution is to place the gaming PC in DMZ to bypass the router firewall restriction.

Once you place your gaming PC in the DMZ, it can access all ports without restriction.

It is an example of the practical use of DMZ in a home network.

Reference

https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://www.cisco.com/c/dam/assets/sol/sb/isa500_emulator/help/guide/ad1681599.html

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Metropolitan Area Network (MAN)

2026-01-30T11:18:00.000-08:00

The Metropolitan Area Network (MAN) is a core topic in the Networking Fundamentals syllabus for Kerala PSC Degree Level Exams, SSC Scientific Assistant, and ISRO Technical Assistant posts. Understanding the distance, speed, and IEEE standards (802.6) is crucial for securing marks in the Data Communication section.

Metropolitan Area Network( MAN ) is a network that covers an area equivalent to a metropolitan city.

It is easier to understand this network by comparing other two popular networks. MAN covers a larger area than a LAN but smaller than a WAN. This type of network covers a few kilometers.

Let us check the examples of a Metropolitan Area Network. The cable TV network is an example of the Metropolitan Area Network. But there is a difference.

The classic example of a MAN is Metro Cable Network.

MAN is a computer network, but cable TV connection provides TV broadcasts. In a Metropolitan Area Network, two buildings in a city are connected and start data transfer. That means this connects two devices located far away but limited to a metropolitan location.

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One of the differences between WAN and MAN is the connection speed. WAN offers low to medium connection speed, but Metropolitan Area Network offers high-speed connection.

Technologies Used in MAN

ATM (Asynchronous Transfer Mode)
FDDI
SMDS
Ethernet-based MAN

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding Metropolitan Area Network (MAN) is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

MAN Standards for Data Communication

Distributed Queue Dual Bus (DQDB) is the Metropolitan Area Network standard for data communication. It is in the IEEE 802.6 standard. Using DQDB, networks can be as long as 30 miles and operate at speeds of 34 to 155 Mbit/s.

Devices Provide MAN Connections

Devices used to provide connections here are:

ATM
High-end routers
Switches
Optical switches

Can a Corporate Company Campus Be Classified as MAN?

One comment I received was about the status of a corporate office campus.

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I consider a corporate office campus as a Metropolitan Area Network. I understand that this network does not cover the area of a metropolitan city. However, per the definition, a MAN is a network of multiple Local Area Networks.

A corporate office campus is a MAN.

A corporate office campus must have multiple LANs. They are interconnected and come under the category of a MAN.

Reference

https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://standards.ieee.org/featured/ieee-802/

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Computer Troubleshooting Study Notes: Reasons for Automatic Restarting (Kerala PSC & SSC IT Prep)

2026-01-30T11:17:00.000-08:00

Published By Alex George

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Learning computer Hardware is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. Computer fundamentals are core parts of the PSC Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions from Computer Hardware topic. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

You read many hardware-related issues and solutions on CoreNetworkZ. Today we are discussing the reasons for an unexpected automatic restarting of a computer.

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Once I faced this problem, where my computer rebooted automatically without providing any warning, and I lost every unsaved work.

I took one week to troubleshoot and fix the problem. This guide is the result of my one-week troubleshooting experience.

Automatic restarting is one of the most frustrating computer-related problems you can experience.

I believe having a guide for those who face the same problem can be very helpful in identifying the reasons for the automatic restarting of their systems.

If you can identify why your PC is rebooting suddenly without warning, you will be able to solve it. At first, we check common reasons for the issue.

Some of them are software conflicts, hardware issues, and virus infections.

Let us check carefully why a Laptop restarts without giving a warning.

Reasons for Unexpected Automatic Reboot of Your Computer

Software Conflicts
- Outdated Driver
- Recently Installed Incompatible Software
- Failed Windows Update
Malware Infection
Hardware Issues
- Overheat
- Corrupted System Memory
- Dust Particles in Your System Cabinet
- Problems with the Power Supply
- Possible Loose Connections

Let us check how to troubleshoot an automatic rebooting laptop or PC. I have created this guide based on my troubleshooting experience with my device.

How to Fix Automatic Restarting Problem on a Laptop & Desktop PC?

Now we will check how to fix the automatic computer rebooting without warning due to software conflicts, malware infections, and hardware issues.

We divide this part into three. The first part explains how to resolve frequent rebooting problems due to incompatible Apps installed. The second part deals with removing malware infections to prevent your computer from an unexpected restart.

The third part explains how faulty hardware invites automatic restart problems.

Fix Frequent Computer Restarting Due to Software Conflicts

Let us check how to fix software conflicts that cause computer reboots frequently without warning.
1. System Restore
  
  If your computer restarts automatically due to software conflicts, the first solution is to choose Last Known Good Configuration using the Windows System Restore.
  - Open Windows Search
    
    You can open Windows Search by pressing Windows and S keys together.
  - Type Recovery in the Search box.
    
    Click the Open.
  - Click Open System Restore.
  - Restore System Files and Settings.
    
    Click the Next button.
  - Select a Restore Point
    
    Choose a Restore point before your computer starts showing problems.
    
    Click Next to Continue the process.
  If the System Restore fixed the issue, the reason for the unexpected restarting of your PC was due to a corrupted driver or App recently installed.
  
  Avoid the recently installed software and update the driver as soon as possible.
  
  If the issue persists, I suggest you go for the next solution.
2. Check for Possible Windows Update Error
  
  This issue is limited to Windows machines(not applicable to Linux computers). Windows 11 and Windows 10 laptops need to reboot after downloading updates.
  
  A failed Windows 11 update (or Windows 10 update) will cause a computer reboots automatically in an attempt to fix the problem.
  
  An interrupted Windows update can invoke a loop of computer rebooting. Make sure your device has the latest Windows update.
  - Open Windows Search.
  - Type Windows Update in the Search box. Open Windows Update Settings.
  - Tap on the Download to complete the Windows Update.
Computer Reboots Frequently Due to Malware Infections

If your device restarts automatically without warning, even after uninstalling the recently installed software, you must check for possible Virus Infections.

Install a reputed AntiVirus application on your laptop and update the virus definition.

Perform a full system scan to detect and remove all malware infections. It will resolve unexpected computer restarting due to Virus infections. If the issue persists, you must check for hardware problems.
Resolve Faulty Hardware Issues Prompting Automatic System Reboot

If there are no software compatibility and malware issues, check for possible hardware issues.

To check Hardware issues, I assume you have a decent knowledge of computer hardware troubleshooting. You may require to open the system cabinet and inspect each component.

If you do not have enough knowledge, I recommend you seek a qualified computer professional.

Here is a list of potential hardware problems that can make your PC restart automatically.
1. Heat-related Issues
  
  Brand-new Laptops and PCs will shut down or restart automatically if the processor heat exceeds a certain level. Make sure your laptop does not have heat-related issues to avoid this situation.
2. Corrupted System Memory
  
  Corrupted RAM modules will trigger an automatic system reboot. To verify it, remove the current RAM and start your PC with another piece of RAM module.
3. Dust Particles in The System Cabinet
  
  The presence of dust particles in the CPU may trigger an automatic system restart. It is a good practice to clean the system cabinet to make your PC free from dust particles.
4. Test Power Supply
  
  A faulty power supply to your PC will force it to shut down or reboot automatically without warning.
  
  Test the power supply. If you find any issues, replace the Power Supply Unit immediately.
5. Possible Loose Connections
  
  Disconnect the hard disk and DVD drive from the motherboard and reconnect to avoid any loose connection.

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Quick Fix to Automatic System Reboot Issue

If you are desperately looking for a quick fix to the automatic rebooting issue, you can tell your computer to don't restart automatically for any system error.

By default, Windows trigger an automatic system reboot on every system failure.

This option prevents further damage to your device. But it will trigger automatic rebooting for petty issues.

If you want to disable automatic system reboot on system failure set on your computer, you can disable it under Startup and Recovery. You will see a checkbox to stop Automatic Reboot on the Startup and Recovery settings window.

Click Windows Start.
Right Click the Computer in the Start menu and click Properties.
Click Advanced System Settings.
Click the Settings button under Startup and Recovery.
Uncheck the Checkbox near Automatically restart.

For Windows XP

Right-click on the My Computer icon.
Click the Properties.
Click on the Advanced tab.
Click on the Settings button under Startup and Recovery.
In the Startup and Recovery window, uncheck the Automatically restart check box.

Click OK.

PS: It is not a good practice to keep the checkbox Automatically restart unchecked without fixing the exact reasons for the system failure.

Reference

https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://www.dell.com/support/contents/en-us/article/product-support/self-support-knowledgebase/fix-common-issues/computer-automatic-restart-or-reboot

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Router Cascading - A Complete Guide

2026-01-30T11:15:00.000-08:00

Are you trying to add a new router to your existing home network?

Or are you simply trying to extend your existing LAN?

Then you must learn the concept of router cascading. It is the art of adding new routers to the existing primary router.

Without knowing how to perform router cascading, you will fail to add an extra router successfully to the network.

In this tutorial, you will learn how to connect additional routers to the current network by cascading routers without having any network issues.

This tutorial covers the theoretical concept of router cascading. To read the practical guide, I recommend you read the following article.

There are two ways to cascade a router to another router. Before configuring the second router for router cascade, ensure that it has no connection to the main router (where the broadband modem is connected).

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How is this post helpful for New York City’s municipal IT examinations?

For a NYC DCAS Computer Associate aspirant, this post on router cascading is invaluable because it directly addresses the Network Operations and Connectivity domain of the exam. The DCAS 1113/1131 syllabus requires candidates to demonstrate proficiency in extending local networks and managing device communication across multiple segments. Understanding the nuances between LAN-to-LAN (Layer 2 bridging) and LAN-to-WAN (Layer 3 routing) is a classic exam favorite.

Different Methods to Cascade Two Routers

LAN to LAN Router Cascade

In this method, we connect an Ethernet cable to one of the LAN ports of the primary router to one of the LAN ports of the secondary router.

In this method, we extend the same network.

In this method, the devices connected to the second router and the first router are in the same network and can communicate with each other directly.
LAN to WAN Router Cascade

Let me explain the LAN to WAN Router Cascading.

Here we create a new network using the second router.

Each new routers added to the network using this method create new networks.

Let us check each method in detail. Each method has different effects in extending a network.

Before configuring the settings on the second router, you must have the IP address of the first router.

LAN to LAN Router Cascading Method

We use LAN to LAN Cascading when you want the same network address for devices connected to the second router.

In this method, the second router acts as a switch to extend the current network.

Let us check how to do LAN to LAN Router Cascading.

Connect your computer to the LAN Port of the Second Router using an Ethernet cable.
Log in to Second Router
Change the IP Address of Router 2

When the router’s web-based setup page appears, look for the Local IP Address and change it to “192.168.X.Y { Most commonly router IP address is 192.168.X.1 where X and Y start from 0 to 255 }. We must ensure that Y is a number between 0 to 255 and is out of the DHCP range of router 1.

Example

IP Address of the Primary Router - 192.168.1.1

Subnet Mask - 255.255.255.0

Then Assign the IP Address 192.168.1.200 to the second router.

Explanation: Assign IP address 192.168.X.200 (Where X is the same value as in router 1. Eg the X value of router 1 with address 192.168.1.5 is 1) to the second router where the IP address of the first router(main router connected to the modem) is 192.168.X.1.
Disable DHCP On Router 2

When the web-based setup page opens, look for DHCP Server and click Disable. Do not forget to save the changes.

Click Advanced Routing and change Operating Mode to Router. (It may be different depending on the router models and vendor.}.
Connect Router 2 to Router 1

Connect a LAN Port of Router 1 to a LAN Port of Router 2 using an Ethernet cable.
1. Connect a standard Ethernet network cable to one of the numbered Ethernet ports on the first router, where the broadband modem is connected.
2. Then, connect the other end of the Ethernet cable to one of the LAN ports of the router that you have just configured.

If the primary router has an IP address of 192.168.0.1 with a DHCP range of 100, then the second router should have an IP address of 192.168.0.101. Then only this kind of router cascade works.

Many users use this method to cascade a new wireless router with an existing wired router to extend the primary router to connect other wireless devices and still have the same network addresses assigned by the first router.

This method is helpful when a user needs to cascade a wireless router with another existing router in the network. Do not confuse this method with the step to cascade two wireless routers.

LAN to WAN Router Cascade (Method 2)

Before connecting a router to another router in the LAN to WAN cascade Method, ensure that both routers have different IP addresses.

LAN to WAN Router Cascading creates one more network.

If both routers have the same IP address, you need to change the IP address of the second router to prevent any conflict.

Steps to configure the second router in the LAN to WAN cascading method are:

Make sure Both Routers have Different Network Addresses

If both routers have the same network addresses, change them.

Check the third octet and ensure both have different third octet numbers.

Example: 192.168.1.5 for the primary router and 192.168.2.1 for the second router.

If both routers have the same third octet number, proceed to step 2.
Change Third Octet of Router 2 IP Address

Access the second router’s web-based setup page and look for the Local IP Address. Change the local IP to 192.168.X.1.

X is any number between 0 to 255 except the number in the first router.

If the IP address of the first router is 192.168.5.1, then X of the second router is any number between 0 to 255 other than 5.

Do not forget to save the settings.
Make sure the DHCP server on the second router is on.
Connect the Second router to the WAN port of the First router

Connect a standard Ethernet network cable to one of the numbered Ethernet ports on the first router, where the broadband modem is connected.

Then connect the other end of the Ethernet cable to the Internet port of the second router (that you have just configured).

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4	Assign Static IP Address
5	WiFi Standards
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Cascading Routers From Different Vendors

One of the most asked questions from my readers is about possible issues with cascading routers from different vendors. There are no issues with cascading them.

You can cascade a Linksys router with a Belkin router or D-Link router without any problems. It is because router cascading is vendor-free.

Can I Cascade Three Routers?

Yes, you can cascade three or more routers.

Assign Static IP Address From Command Prompt: NYC DCAS Computer Associate Study Note

2026-01-30T11:14:00.000-08:00

This tutorial covers key competencies required for DCAS exams, specifically focusing on Network Administration and Command-Line Configuration. Candidates are expected to know how to manage network interfaces when the Graphical User Interface (GUI) is unavailable or when managing remote servers.

No device can communicate over a network without a valid IP address. Usually, the DHCP server provides IP ( Internet Protocol ) addresses to devices connected to the network.

Sometimes we must assign a static IP address to a PC while troubleshooting the network.

We use Static IP Address to fix APIPA (Windows IP Configuration).

There are different ways to assign it to a PC, but the easiest method is the DOS method.

There is a DOS prompt command to set a static IP address on a Windows computer.

This tutorial explains how to configure a static IP address from Command Prompt and explains the procedure with a practical example.

At the end of this tutorial, you can see how to perform the same procedure on Mac.

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Steps to Assign Static IP To Any Interface From Command Prompt

Start MS-DOS as Administrator

You must start the command prompt as administrator to set a static Internet Protocol number (IP) on your computer from the command prompt.

Press the Windows key and S together to open the Search box.

Type cmd on the Windows Search and right-click the Command Prompt icon.

Tap on the Run as Administrator to open Command Prompt with administrative privileges.
Set Static IP Address Command Line

DCAS questions often ask you to identify the correct syntax among four very similar-looking options. Type the following command on the DOS window.

netsh interface ip set address name="[Interface Name]" static [IP Address] [Subnet Mask] [Default Gateway]
Press the Enter key.

It is the theoretical explanation of configuring a logical address on a laptop without the help of a DHCP server.

Now let us check a practical example to learn it.

A Practical Guide to Set Static IP From Command Line

Here I assign a Static IP Address 192.168.42.1 to my computer with default gateway 192.168.42.129 and subnet mask 255.255.255.0.

We need to find the Ethernet Adapter name ( Interface name) to execute the DOS command to set a static IP address.

So, follow the steps carefully.

Check the Current IP Address and The Interface Name

Type ipconfig on the Command Line and Press the Enter key.

You can see the IP address and the respective Ethernet adapter name (Interface name).

The Interface name is Local Area Connection 2.
Execute the Static IP Command

Type the following command on the DOS window.

netsh interface ip set address name="Local Area Connection 2" static 192.168.42.1 255.255.255.0 192.168.42.129

Press the Enter key to execute the command.
Check the Static IP Address From the Command Prompt

Type ipconfig on the Command Line and press the enter key.

We have successfully assigned the static IP address 192.168.42.1 to this Windows 11 laptop from the Command Line.

How to Release Static IP From Command Prompt

You cannot release and renew a static IP address by using ipconfig/release.

There is another DOS Prompt command to remove the static IP address set on a computer.

netsh interface ip set address connected adapter name dhcp

Have a look at the screenshot below and find the Ethernet adapter name.

In our case, the adapter name is Local Area Connection 2.

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So, to release the static IP address we assigned, use the following command on the DOS prompt.

netsh interface ip set address Local Area Connection 2 dhcp

For modern NYC agency environments (using Windows 10/11), DCAS may also refer to the PowerShell equivalent: New-NetIPAddress. However, netsh remains the 'legacy' standard that is frequently tested.

Reference

https://www.nyc.gov/assets/dcas/downloads/pdf/noes/20255050000.pdf
https://www.nyc.gov/assets/dcas/downloads/pdf/noes/20255052000.pdf
https://www.nyc.gov/assets/dcas/downloads/pdf/noes/20255051000.pdf

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

IEEE 802.11 WiFi Standards Backward Compatibility: Study Notes for Kerala PSC, SSC, and IT Exams

2026-01-30T11:13:00.000-08:00

The IEEE 802.11 standards are a core part of the Networking & Data Communication syllabus for the Kerala PSC Degree Level Exam, SSC Scientific Assistant, and ISRO VSSC Technical Assistant posts. Understanding frequency bands and backward compatibility is essential for the Technical Assistant and Computer Assistant exams.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding IEEE 802.11 standards is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

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Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions from this topic. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

WiFi is the term used to denote Wireless Local Area Networks using IEEE802.11 wireless standards. Now, the term WiFi represents all Wireless Local Area Networks.

Wireless technologies use the IEEE 802.11 a, b, g, n, and ac standards.

The first part of this tutorial checks the term WiFi and the major 802.11 standards. You can also see a list of WiFi devices that support them.

You will get a backward compatibility checker chart in the last part of this tutorial.

Using this chart, you can make decisions on extending your WLAN networks.

With the help of the chart, you can avoid buying a device with compatibility issues with existing devices (standards that are not backward compatible).

IEEE 802.11 Wireless Standards Available In Industry

IEEE 802.11 A
IEEE 802.11 B
IEEE 802.11 G
IEEE 802.11 N
IEEE 802.11 AC

Compatibility Between Different 802.11 Wireless Standards

Not all 802.11 technologies are backward compatible because of the different frequencies supported. So, if you plan to extend your current WLAN with new devices, ensure the new devices are compatible with existing devices.

It is critical to know the technologies supported by the existing equipment.

Once you have noted down the technologies (that are in your network), you may check which 802.11 standards are compatible with them. You can see a list of different WiFi standards that support each other.

If you see 'Yes' in that chart, the technologies in the row and column are backward compatible. On the other hand, if you see 'No' in the chart, it tells you the standards listed in rows and columns are not backward compatible.

WiFi Standard	IEEE802.11a	IEEE802.11b	IEEE802.11g	IEEE802.11n	IEEE802.11ac
11a	Yes	No	No	Yes	Yes
11b	No	Yes	Yes	Yes	No
11g	No	Yes	Yes	Yes	No
11n	Yes	Yes	Yes	Yes	Yes
11ac	Yes	No	No	Yes	Yes

Frequencies Supported By Different WiFi Standards

You must be wondering why different wireless standards cannot connect. The frequency mode supported is the primary reason for the incompatibility between different IEEE 802.11 technologies.

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Let us check the frequencies supported by IEEE 802.11 WiFi connections.

1. IEEE 802.11 a ---5 GHz

2. IEEE 802.11 b ---2.4 GHz

3. IEEE 802.11 g ---2.4 GHz

4. IEEE 802.11 n -- Supports both 2.4GHz and 5GHz

5. IEEE 802.11 ac -- Supports 5GHz

Reference

https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://standards.ieee.org/beyond-standards/the-evolution-of-wi-fi-technology-and-standards/

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

S.M.A.R.T. Technology in Hard Disks: Study Notes for Kerala PSC & SSC IT Exams

2026-01-30T11:11:00.000-08:00

Expansion of S.M.A.R.T. is a frequently asked question in the Computer Assistant and Data Entry Operator exams. This technology is vital for the 'Maintenance & Troubleshooting' section of the Kerala PSC Degree Level syllabus and ISRO VSSC Technical Assistant test. Candidates must understand how BIOS interacts with hardware to predict failures.

My First Experience

Last night I encountered a strange error on my computer. I couldn't boot my PC and failed my efforts to load the Operating System. Instead of the Windows login screen, I reached an error message: Hard Disk SMART Command Failed. Whatever the error, it affected the keyboard. Other than the Tab key, no other keys were working. This article explains the meaning of the Hard Disk SMART Command Failed error message.

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Why Am I Getting S.M.A.R.T. Command Failed Boot Error?

SMART is a BIOS feature that stands for Self-Monitoring, Analysis, and Reporting Technology, which monitors the health of the Hard Disk Drive.

If the S.M.A.R.T. feature in BIOS detects HDD malfunctioning, you will get this error message while booting your computer. It is a confusing situation because whenever you reboot your PC, it returns to the same error page in a loop. Whatever you do, this error will prevent you from booting your computer.

Reasons

Physical Wear and Tear (Mechanical Failure)
Excessive Bad Sectors (Reallocated Sectors)
Excessive Heat (Thermal Stress)
Electronic Component Failure
Loose SATA/IDE Cables

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

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Understanding S.M.A.R.T. Technology is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These hardware fundamentals are core parts of the Computer Science syllabus.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions that require them to explain the reasons behind S.M.A.R.T. Technology error codes. You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

Reference

https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://www.dell.com/community/en/conversations/storage-drives-media/smart-error/647e4018f4ccf8a8de9d073d

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Reply from X.X.X.X: Destination Host Unreachable - : Study Notes for Kerala PSC & SSC Exams

2026-01-30T11:09:00.000-08:00

Published By Alex George

During my network engineer career, one of the common ICMP errors I received while troubleshooting connectivity issues was Destination Host Unreachable.

This error was the cause of my Internet connectivity problems most of the time.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts.

Understanding ICMP error messages is essential for candidates appearing for the Kerala PSC Degree Level Exam, SSC Scientific Assistant (CS), and System Analyst posts. These networking fundamentals are core parts of the Computer Science syllabus.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

Destination Host Unreachable is a Common ICMP Error Message.

In this tutorial, I will explain everything about this error. I developed this tutorial in three parts.

This tutorial has three parts.

The first part of this tutorial explains the meaning of the ICMP reply Destination Host Unreachable.
The second part explains the reasons for the ping reply Destination Host Unreachable.
The third part explains the steps to fix this error message.

So, let me start the tutorial developed for the fresh Network Engineers at CoreNetworkZ EdTech Solutions.

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What Does Destination Host Unreachable Ping Reply Mean?

Before proceeding to the core of this tutorial, let me explain the meaning of this ping reply.

The Destination Host Unreachable reply says that the ping packets from your computer couldn't find the destination device or something prevents them from reaching it.

Now that you understand the meaning of this ICMP error message. Let me answer two questions posed by two Network Engineer trainees at CoreNetworkZ EdTech Solutions.

Christo Fernandes asked, "Hello Alex, I see the Destination Host Unreachable Error message, but I do not know which device is responsible for showing this ICMP reply?"

Christo is a Computer Science Graduate.

Anita Thomas, an SSC System Analysts aspirant at CoreNetworkZ EdTech Solutions, asked, "What does my PC mean by showing this Ping reply?"

I will answer Christo and Anita. But before I answer them, you must learn how the ping test works. Then only I can explain it.

Let us check how the Ping Test works.

I will explain the workings of a ping test by showing a practical example. For that, I am pinging my blog by typing ping www.corenetworkz.com into the Command Prompt.

So, what will happen? Well, you can see the complete process below.

My computer sends ICMP Echo Requests to the remote host www.CoreNetworkZ.com.

ICMP Echo Requests travel out of my computer through the network adapter.
Ping packets reach the default gateway. The default gateway is the router in most cases.
The default gateway needs to find a route to the destination address. So, the next step is checking the ARP table and Routing table.
Default Gateway finds a route to the Remote Gateway of the destination IP address.
Remote Gateway receives the packets.
Remote Gateway forwards the ping packets to the remote host (the final destination - server of CoreNetworkZ.com).
The Remote Host (web server of CoreNetworkZ.com) acknowledges by sending ICMP Echo Replies.

Now, let us come back to Christo's question. Can you tell me the potential sources for a Destination Host Unreachable reply from this ping workflow algorithm?

You can get this reply from two possible sources.

Your Default Gateway
Remote Gateway

How do we know whether the reply comes from the Default Gateway or Remote Gateway?

Well, it is simple.

All you have to do is to analyze the ping reply carefully. Check the format of the message. It comes in two different forms.

Reply from x.x.x.x Destination Host Unreachable

Before explaining it, let me quote a comment from one of my readers.

Kenney Jacob, preparing for the ISRO VSSC Technical Assistant examination, asked, "Hello Alex, I see a strange response on the DOS window. It says Reply from 192.168.1.101: Destination Host Unreachable. What is it?"

If you see the following format, check the IP address.

Most of the time, x.x.x.x must be a Remote Gateway address.

It shows that the error message you received was from the remote gateway.
Destination Host Unreachable

If you don't see an IP address in the error replies, they came from the Default Gateway.

In a home network, your home router is the Default Gateway.

Both error formats have different reasons. I will explain the reasons in the next part.

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Reasons to Get the ICMP Error Destination Host Unreachable

Let us check why your computer displays the message Reply From x.x.x.x Destination Host Unreachable.

Have a look at the list below.

One of the reasons listed below can get you to the ICMP Echo message Destination Host Unreachable.

Your Default Gateway doesn't know the route to the destination IP address.
Packet Routing issues on Remote Gateway.
The destination host might be down.
Loose Connection.
Strict Firewall Settings.

One of the frequent questions I receive from our readers is whether this error is related to Operating Systems ( like Windows and Linux ).

Lakshmi Dixit, an Engineering student, asked, "Hello Alex, I plan to install Ubuntu Linux on my Windows 11 laptop. Windows 11 frequently shows connection issues. When I ping Google, I get this reply: Reply from 192.168.100.65: Destination Host Unreachable. Is it a Windows 11 problem? Is Ubuntu free from it?"

The answer is no.

Analyzing the ICMP Echo Destination Host Unreachable

Let me explain why I received this ICMP Echo Reply by analyzing a live example.

I send ping packets to the global DNS address 4.2.2.2 to troubleshoot the connectivity problem. The screenshot below shows the reply I received.

Microsoft Windows [Version 6.1.7600]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:\corenetworkz;ping 4.2.2.2

Pinging 4.2.2.2 with 32 bytes of data:

Destination host unreachable.
Destination host unreachable.
Destination host unreachable.
Destination host unreachable.

Ping statistics for 4.2.2.2:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

C:\corenetworkz>

Since you have learned the two types of this ICMP reply, let me ask you a simple question. Which format is this? It is the second format of the Destination Host Unreachable error.

How To Fix Ping Error Destination Host Unreachable?

It is the final part of this tutorial. Let us check how to resolve Destination Host Unreachable error on a PC.

Turn Off The Firewall

According to Ashish Mudgal, a senior Network Engineer at CoreNetworkZ EdTech Solutions, aggressive firewall settings can interrupt the ICMP Echo Requests and cause the Destination Host Unreachable error.

Turn Off the Firewall to check whether the firewall is the reason for this issue on your computer.

Try to access the Internet after the firewall is Off.

Now, I suggest you ping a website and check whether the issue persists. If so, go to the second solution.
Power Cycle The Network

A loose connection in your home network can invite the Destination Host Unreachable ICMP Echo Reply.

Outdated Routing and ARP tables also result in Ping errors.

A proper home network Power Cycle can fix this. Let us check the steps.
- Switch off every device in the network.
- Disconnect power cables from Modem, PC, and Router.
- Disconnect the Ethernet cables from Modem, Computer, and Router.
- Reconnect the power and ethernet cables.
- Power On the Modem and wait for one minute.
- Power On the Router and wait for one minute.
- Power On the PC and ping Google to check whether the Destination Host Unreachable error persists.
Shalini Menon, a B.Tech Computer Science and Engineering student, mentioned she could fix this issue by power cycling the home network. She asked why it fixed the problem.

The answer is simple.

A proper Power Cycle will fix issues like corrupted ARP and Routing tables and loose connections.

In my experience, this solution usually resolves the issue. However, if it persists, proceed to the final solution.
Disable IPv6 and Test the Connectivity

Sometimes devices fall into IP version conflicts. Different operating systems have separate IP version priorities.

Windows 10 prefers IPv6 to IPv4. Linux variants like Ubuntu, Fedora, and Debian prefer IPv6 to IPv4.

However, sometimes devices fail to work with IPv6.

It results in ICMP error messages. We can check for this by turning off IPv6 on your device.
Let's see how to disable IPv6 on a Windows 11 computer and test whether it resolves the 'Destination Host Unreachable' issue.
- Right-click on the Network Adapter at the system tray.
- Click on Open Network & Internet settings.
- Click on Change Adapter options.
- Right Click on the current connection and click properties.
- Uncheck the Internet Protocol Version 6 (TCP/IPv6).
- Click OK
- Reboot your Computer.
Once you reboot your computer, check for the connection.

Let me conclude this article now. I understand it was a long read, but you learned about a critical ICMP error: 'Destination Host Unreachable.' What do you think of my article? I welcome your questions and suggestions in the comment section.

Reference

https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://learningnetwork.cisco.com/s/question/0D56e0000Dp18MDCQY/solveddestination-host-unreachable

Author: Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Understanding Power Cycle in Networking: Study Notes for Kerala PSC & SSC Exams

2026-01-30T11:07:00.000-08:00

Welcome to the Computer Science and Technology Study Materials section from CoreNetworkZ EdTech Solutions for students preparing for SSC, DSSSB, and Kerala PSC examinations. Today, I will explain the concept of Power cycling.

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

SSC, DSSSB, and Kerala PSC conduct examinations for various IT posts. The concept of a 'Power Cycle' is a fundamental troubleshooting step frequently asked in Computer Assistant, System Analyst, and Scientific Assistant exams.

Kerala PSC Degree Level examinations have a Computer Science section where students can expect questions about Power Cycling.

You can check the Kerala PSC Degree Level Common Prelims Syllabus under the Computer Science section. I recommend you download the syllabus using this official link.

Reference: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

How to Power Cycle a Modem or Router?

Let us check how to power cycle a modem/router. Power cycling is the process of turning off and on devices in a systematic order. To do it, follow the instructions provided below.

Disconnect Power from your Modem /Router (unplug the Power Cable)
Wait 30 seconds
Reconnect the Power supply
Wait for one minute and ensure the active LED lights on the device are not blinking (Power light, Internet light, etc. ).

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Power Cycle A Computer Network

If you are appearing for the System Analyst post from SSC or PSC, they might ask you this question. The process is simple.

Unplug the Power Cable from the Modem.
Unplug the Power Cable from the Router.
Wait for one minute, then connect the power cable.
Power on the Router and wait till the lights are steady on the Router (the WAN light will not light as the Modem is not on).
Power on the Modem and wait till all modem lights are on and steady.

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Reference

https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://community.cisco.com/t5/switching/switch-manual-power-cycle/td-p/4927390

Alex George

Alex George is the Chief Editor and founder of CoreNetworkZ EdTech Solutions. He is a software engineer and has 20 years of experience in the EdTech niche.

He graduated with a B.Tech in Computer Science & Engineering from CUSAT and worked with three leading IT companies before starting CoreNetworkZ EdTech Solutions.

He possesses sound knowledge of SOHO Network Engineering and has completed various IT certifications, including CCNA, RHCE, and CEH.

He developed and published more than twenty professional custom themes for Blogger and is an expert in software app development.

You can contact him at alex.george@corenetworkz.com.

Reset a Router or Modem - Kerala PSC Computer Science Section Study Materials

2026-01-30T11:05:00.000-08:00

Welcome to the Computer Science and Technology Study Materials for Kerala PSC Degree Level Common Prelims and Mains.

How Does This Study Material Help PSC, SSC, and DSSSB Aspirants?

Kerala PSC, SSC, and DSSSB occasionally announce notifications for IT roles in various Government Departments.

Understanding the difference between a Soft Reset and a Hard Reset is a fundamental skill for IT professionals and candidates appearing for Kerala PSC Computer Assistant, SSC System Analyst, and DSSSB Scientific Assistant exams. Practical troubleshooting questions are common in the technical interview and practical modules of these examinations.

Is This Part Of Kerala PSC Degree Level Exams?

Yes, Computer Network Devices are a part of the Kerala PSC Degree Level syllabus (Computer Science Section). You can expect questions about the device's technical details, its uses, and troubleshooting.

Ref: https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf

When should I reset my router?

You might expect questions like this in the System Analyst SSC question paper. The answers are when the router or modem stops responding, or it has an incorrect configuration. Sometimes, after upgrading to the latest router /modem firmware, you may need to reset your router/modem as instructed by the manufacturer.

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In rare cases, if you forgot the router login password, you may need to reset the router to set a new password.

Different methods to reset a router

There are three different types of router resetting.

Soft Reset
Hard Reset
Power Reset

Soft Reset

It is possible to reset the router by selecting the reset option through the router administration page (web interface). Depending on the firmware and manufacturer, these options may appear in different forms, such as Reset to Factory Default or Reboot with Factory Settings.

Select the desired option and click OK. The router will then begin rebooting, and within about one minute, it will return to its default factory settings.

Hard Reset

Hold down the reset button using a pen tip or pin for 30 seconds.
Ensure the power light is blinking while you continue pressing the reset button.
After 30 seconds, release the button and wait for about one minute.
Confirm that the power light is steady.

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Power Reset

Vipin Kumar, an SSC Scientific Assistant exam aspirant, asked for the Power Reset guidelines.

Hold down the reset button for 30 seconds (ensure the power light is blinking).
While still holding the reset button, unplug the power cable and keep holding for another 30 seconds.
Reconnect the power cable and continue holding the reset button for an additional 30 seconds.
Release the reset button (you will have held it continuously for 90 seconds).
Wait about one minute and confirm that the power light is steady.

Local Area Network (LAN): Study Notes for Kerala PSC, DSSSB & SSC

2026-01-30T11:03:00.000-08:00

Welcome to the Computer Science & Information Technology study series by CoreNetworkZ EdTech Solutions. This guide on Local Area Networks (LAN) and Network Topologies is for students preparing for Competitive Examinations by Kerala PSC, DSSSB, and SSC.

Questions about LAN technologies are in the Degree Level Kerala PSC exams and DSSSB PGT Computer Science and TGT Computer Science test syllabus.

Let me start this tutorial by explaining the LAN.

A Local Area Network (LAN) is a collection of connected devices within a small area. A home network (with one router connected to computers and smartphones) is an example of a LAN.

Ethernet is the most popular LAN technology today.

A LAN facilitates communication between devices in a small area and improves work efficiency in an office environment.

Which Network Is a LAN?

Sharon Joe, a Kerala PSC student, asked, "What type of network belongs to the category of a LAN?"

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Questions about LAN technologies are in the Degree Level Kerala PSC exams and DSSSB PGT Computer Science and TGT Computer Science tests.

Let me now answer Sharon's question here.

So, how do we determine if a network is a LAN? In a LAN, all devices are connected and can share data. It typically covers a small area, such as an office building or home.

The media types used to connect devices in a Local Area Network (LAN) include Ethernet, FDDI, and Token Ring.

PSC Questions From LAN Topologies

Let us now consider the common topologies used in Local Area Networks, as this topic is part of the PSC exam syllabus.

Laxmi Vinod, a B.Tech (Computer Science) student and a PSC aspirant, from Chennai, asked, "Can you explain the concept of LAN topologies?"

CoreNetworkZ EdTech Solutions classifies topology into two types: physical and logical.

Physical topology refers to the actual layout of devices in a LAN, while logical topology describes how these devices communicate over the network.

LAN Physical Topologies

Point to Point

If we connect two devices without interference from other devices, that is a Point-To-Point physical topology. In this LAN topology, these two devices can communicate without extra support.

Wireless Bridge is an example of Wireless Point-to-Point Topology.
Bus Topology
You can say it is an extension of Point-to-Point topology. In Bus topology, we connect all devices in LAN in a single connection.
Ring

If a Local Area Network has Ring Topology, all devices are in a ring form. It means PC 1 connects to PC 2. PC 2 connects to PC 3, and the last device connects to PC 1. So, it forms a ring structure.

FDDI uses a ring topology.
Star Topology

In start topology, all devices in a LAN have a connection to the central device. An example is all the computers connected to a Switch.

LAN Logical Topologies

Bus Topology

Ethernet is an example of a LAN technology using a logical bus structure to communicate. To learn more about Ethernet, visit the link below.

Fundamentals of Ethernet
Ring Topology
Token Ring is a good example that uses ring logical topology to communicate computers connected to the network.

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The medium of Transmission in LAN

I will complete today's article by explaining the last question asked by a reader on CoreNetworkZ EdTech Solutions.

Sanal Mohan, a working professional from Bengaluru, asked, "I am planning for a career change. I am planning to appear for the System Analyst exam by DSSSB. My question is about the medium of transmission in local networks."

Here is the list of media of transmission as an answer to his question.

Twisted-pair wire
Coaxial cables
Fiber optic cables

Reference

https://www.cisco.com/c/en/us/products/switches/what-is-a-lan-local-area-network.html
https://www.juniper.net/documentation/us/en/software/nce/feature-guide-virtual-private-lan-service/feature-guide-virtual-private-lan-service.pdf
https://www.keralapsc.gov.in/sites/default/files/2021-02/syllubus.pdf
https://answers.microsoft.com/en-us/windows/forum/all/lan-connectioncommunication-defined/9a4d4605-a0f4-4a07-bbba-beaadca676c1

Cox Modem Port Forwarding - Study Notes for NYC DCAS Computer Associate Exam

2026-01-05T06:05:00.000-08:00

Cox Communications is USA's one of the leading cable Internet service providers. Cox cable broadband provides fast Internet and streaming TV services for its customers.

Though they provide reliable connectivity, some users complain of issues with opening ports to activate online services.

Some customers feel Cox disabled some ports intentionally on their modems to control the upstream bandwidth usage.

We can overcome it by manually opening Cox modem ports.

This tutorial teaches you how to perform Port forwarding on a Cox modem.

Why Does Cox Block Internet Ports?

According to Cox's technical support, they block some Internet ports to protect their customers against common worms and dangerous online services.

Another reason for Blocking Internet Ports is to limit upstream bandwidth usage by Cox.

To see the list of Internet ports disabled, visit the link below.

https://www.cox.com/residential/support/internet-ports-blocked-or-restricted-by-cox.html

Why Do I Need to Open Ports In Cox Modem?

By default, Cox blocked some ports, which may allow intruders to attack the customers. For example, users with Cox Panoramic WiFi routers experience issues with forwarding a port.

However, users may need to open some specific ports to run applications like Online Games and torrents on their computers.

For example, torrent applications use Internet port range 6881-6889 to download and upload torrent files.

If Cox blocks this Port Range for your connection, you cannot run torrents on your computer. Your computer will not upload or download files by torrent applications using Cox cable broadband.

If the Internet Port number used by your favorite Online Game belongs to the list of blocked port numbers, you won't be able to play it using the Cox cable Internet connection.

In such situations, your only option is to perform a Port Forwarding.

How to Open a Port in Cox Modem?

Cox provides different models of modems and routers to customers.

They support various modem/ router vendors like ARRIS / Surfboard, Cisco, Asus, DLink, etc.

Though the User Interfaces of different models of Cox modems may vary, the procedure to open a port range on them is the same. Let us check how to open the port number range for torrents on your Cox router.

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How to Port Forward in Cox Panoramic WiFi Routers?

Cox allows Panoramic WiFi customers to open ports using their MyWiFi account.

To activate Panoramic WiFi port forwarding, follow the steps below.

Visit the link https://www.cox.com/mywifi and log in using the Cox credentials.
Select the Network from the top menu.
Click Gateway
Go to the bottom and click more.
Click Advanced Settings.
Click Port Forwarding.

You have learned the procedure to open ports on Cox Panoramic WiFi.

Let us check how to open ports on other Cox routers and gateways.

How to Open an Internet Port On Cisco Modem?

If the modem supplied by Cox is Cisco DPQ3925, follow the steps below.

Assign a Static IP Address to your computer on which you want to exclude the Port Issues.
Type 192.168.0.1 on the browser Address bar and press the Enter button.
Type the Cox modem login username and password. By default, it is admin and admin.
Click on the link Applications & Gaming.
Click on Port Range Forwarding.

If you want to open port numbers for torrents on a Cox modem, fill the start window with 6881 and the end window with 6889. You should mention the static IP address of the computer in the next window.

Port Forwarding on Cox Arris Router

Many Cox users have an Arris modem. If you want to forward a port number on an Arris modem for Cox cable broadband, follow the steps below.

Assign a Static IP Address to your computer.
Type the IP address 192.168.0.1 on the browser address bar and press the enter key. If it is not working, type 192.168.100.1 on the browser address bar.
Type admin as the username and password as the password. Click the Login button to continue.
Click on the Advanced link from the top.
Click on the Port Forwarding button.
Click the Create IPv4 button to create a new port forwarding rule for the Cox Internet connection.

You can enter the port numbers you want to exclude from the default Cox ban here.

How to Open Ports On Cox Dlink Modem?

Let me explain how to open ports on the Dlink DCM-604 modem supplied by Cox Cable Internet Service Provider.

Assign a Static IP Address to your computer.
Type the IP address 192.168.0.1 on the browser address bar and press the enter key.
Type admin in the username field and password in the password field of the login window.
Click on the Advanced link.
Click on Forwarding
On the Port Forwarding window, type the static IP address of the device, both starting and end port numbers.
Click on the Apply button.

Sometimes Cox will detect if you have bypassed their Port blocking.

In such cases, contact their technical support or use a high-quality VPN to override their Port blocks.

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How to Do Port Forwarding On Cox Business Modem?

If you have a Cox business connection and want to open a port number on the Cox Business modem, follow the instructions below. For business users, Cox provides Business Internet Gateway.

Assign a static IP address to the device you want to enjoy the port forwarding.
The default login IP address of Cox Business Internet Gateway is 192.168.0.1.
By default, the username and password fields are both empty. If you have a password and username, you should enter them.
Click on Application Layer Gateway.
Click on the Port Range Forwarding tab.
You should enter the start port, end port, and the static IP address of the device.
Click on the Save Settings button.

Reference

https://www.nyc.gov/assets/dcas/downloads/pdf/noes/20255050000.pdf
https://www.nyc.gov/assets/dcas/downloads/pdf/noes/20255052000.pdf
https://www.nyc.gov/assets/dcas/downloads/pdf/noes/20255051000.pdf

Author: George Renard

George Renard is a senior New York City Civil Service Exam educator at CoreNetworkZ EdTech Solutions.

He has been training students to prepare for the multiple NYC DCAS Civil Service Examinations for the past eight years. He is from Brooklyn and stays with his wife and son.

You can contact him at george.renard@corenetworkz.com.

CoreNetworkZ EdTech Solutions

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ICMP (Internet Control Message Protocol) - Study Notes for PSC, SSC, and IT Exams

What is ICMP?

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

So, why is ICMP important?

Why Do We Need ICMP?

Important Functions of ICMP

List of Messages Generated by ICMP

How to Use ICMP in Troubleshooting a Network?

Reference

Author: Alex George

Fiber Distributed Data Interface (FDDI) - Study Notes for PSC, SSC, and IT Exams

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

FDDI Communication and Data Transfer Speed

Different versions of FDDI

A Complete Explanation of The Working of FDDI

What are the FDDI Specifications?

Why FDDI is No Longer Popular?

Reference

Author: Alex George

Differences Between Bridge Mode and PPPoE Mode

What Are PPPoE and Bridge Configurations?

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

PPPoE vs Bridge Modes

Number of Supporting Devices

ON or OFF State

Cyber security

Port Forwarding

Support for NAT

The Supported IP Addresses

Reference

Author: Alex George

OSI Reference Model - Study Notes for PSC, SSC, and IT Exams

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

What is The Importance of the OSI Reference Model?

Seven Layers of OSI Reference Model

What is The Need For the OSI Reference Model?

Benefits of the OSI Reference Model

Reference

Author: Alex George

NAT (Network Address Translation) - Study Notes for PSC, SSC, and IT Exams

What is NAT?

Critical Functions of NAT

How NAT Helps a Regular Person?

Different Types of Network Address Translation (NAT)

Static NAT

Dynamic NAT

Port Address Translation

Port Address Redirection

The Major Benefits of Network Address Translation

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

Disadvantages of Address Translation

Reference

Author: Alex George

Ethernet Hub - Study Notes for PSC, SSC, and IT Exams

What is a Hub?

The Working of a Hub

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

Limitations of a Network Hub

Does Anyone Use Hubs Now?

Reference

Author: Alex George

What is a Router & Its Functions?

What is a Router?

How does This Study Material help PSC, SSC, and DSSSB Aspirants?

Router and Routing Table

Examples of Routing Protocols

Functions of a Router

Different Types of Routers

Links to Router Configuration Guides

Reference

Author: Alex George

Dynamic Host Configuration Protocol (DHCP) - Competitive Exam Questions

Role of DHCP in a Computer Network

What is The Working of Dynamic Host Configuration Protocol?

D-- Discovery

O--- Offer

R---- Request

A--- Acknowledgment