CCNA certification - Guide for success

Using Brain Dumps to Pass Your Cisco Certification - Is This Cheating?

2012-02-21T08:35:00.001-08:00

By Joseph L Wilson

Most network engineers either have a vendor certification from Cisco (or some other network equipment manufacturer) or at some point think about getting a certification some time in their career.

Cisco certifications are notorious for being extremely difficult and include many hands on simulations to prove the skill level of the candidate. Being certified helps prove the engineers skill set and knowledge in a particular area of computer networking.

To prepare for one of these Cisco certification exams, candidates will read books, watch videos, take live instructor lead classes, virtual online classes and take practice simulation exams to help them learn the material.

But when it comes to practice simulation exams, not all are the same. There are some companies that create practice exams known as "brain dumps" or exact word for word duplicates of the exact official test questions.

Many arguments can be found on various forums and website discussion boards from engineers who believe that tests like these are cheating. And to some extent this is a very valid argument. They believe that any one who uses tests like these not only discredit engineers who study using other methods but should not be given credit for passing the official exams.

The counter argument to this is that it is not cheating because of the live simulated practical portions of the official exams which prove the candidates know the material. Other counter arguments are that the official tests are written specifically to "trick" candidates with unreal situations and scenarios. Brain dump exams simple provide candidates a way to be fully prepared by understand the exact types of questions that will be found on the official exam.

Both sides of this argument are very valid. But what is not debated is the same type of arguments from live instructor lead classes.

Is it cheating to Take an Instructor Lead Class?

Human beings love to network. We get together, create relationships and help each other out. In live instructor lead classes students work with each other to learn the material and pass the exam. This includes students often asking the instructor questions like "Is this on the REAL test?" or "What type of questions can I expect?".

There have even been instances where a "brain dump" tests were used in instructor lead classes to provide examples of tough questions students may expect to see. Pressure to live up to 100% pass guarantee no doubt have an influence on this.

Are brain dumps cheating? Have you seen cheating going on in instructor lead classes?

Some engineers would say it's all hype and certifications are not necessary at all. Being certified doesn't make you a good engineer, being a good engineer makes you a good engineer. Companies like Cisco simply use certifications to drive sales of their own products.

Summary

All in all - using a "brain dump" test to pass an exam doesn't help you be a better engineer, it only helps you to be a better test taker. Where it counts is in the real world.

Joseph L Wilson is a Senior Network Engineer in Austin TX and has worked with Cisco devices and IP networks for over 13 years.

Article Source: http://EzineArticles.com/6879308

How To Get Started With A Career In Computer Networking

2012-02-21T08:33:00.001-08:00

By Chester Flake

Computer networking is becoming extremely useful in today's society. There are many courses that you can take to start with learning about the networking of computers, many of which can be learned from the comfort of your own home. It is worth looking into the different Microsoft certifications available if you are interested in this.

By having certification for your skills, you will be able to prove that you know what you are doing. This is something that many people will want to see, whether they are employers or people looking to hire you as an independent contractor. You have the choice over whether you want to do distance learning (so teach yourself) or whether you want to learn from the classroom.

You will need to have some basic knowledge before you even start with a computer networking course. The first is knowledge about hardware and software on a computer. You will need to know what everything is and how to operate the basic software that you find. You should also become aware of the different operating systems that are available, such as Windows and Linux.

You will learn about the different types of connections on computers. This is how the computers network. You should practice setting up the connections on your own computer. A LAN connection is one of the most basics and all you need is your computer and a router. This is probably something that you have already done at least once in your life. The best part is that there are instructions with any device that you buy to help you with the connection.

You need to know about the principles of networking with computers. There are a number of textbooks available, whether you buy online or in a book store. Look out for those that specifically cover computer networking. You should also look into the textbooks that your course requires you to have. This will help you to gain Microsoft MCITP Certifications.

Whenever you are in class, take notes. This is the best way to remember everything that the instructor is telling you. Even if you are learning online, you should take notes to help you with your study. You are not going to remember everything off the top of your head. There are high chances that you will actually forget the most important part of the lesson without the notes.

Make sure that any course you do find covers MCITP Certification Training curriculum. If you are in doubt, send an email to the people who run the course and then double-check with the Microsoft certification center. The last thing you want to do is waste money on a course that will not help you get certified.

When it comes to computer networking, you need to gain experience. This is the only way that you will become better at your job. Take your time to volunteer if you need to and be prepared to start from the bottom of the pile. As you gain more experience, you can gain better jobs with your new knowledge.

Chester Flake is the CEO of Certification Camps which is the industry leader in training for Microsoft Certifications. He offers Microsoft courses on MCTS, MCPD or Microsoft MCITP Certifications. Plus Microsoft Training in SQL, Windows Server, Lync Server and more.

Article Source: http://EzineArticles.com/6884145

CCNA Self study guide

2011-11-27T10:07:00.000-08:00

CCNA Free Self study guide - Download E book

Welcome to the exciting world of internetworking. This first chapter will really help you understand the basics of internetworking by fucusing on how to connect networks together using Cisco routers and switches. First, you need to know exactly what an internetwork is, right? You create an internetwork when you take two or more LANs or WANs and connect them via a router, and configure a logical network addressing scheme with a protocol such as IP.I'll be covering these four topics in this chapter

1. Internetworking basics
2. Network segmentation
3. How bridges, switches, and routers are used to physically segment a network
4. How routers are employed to create an internetwork

I’m also going to dissect the Open Systems Interconnection (OSI) model and describe each part to you in detail because you really need a good grasp of it for the solid foundation you'll build your networking knowledge upon. The OsI model has seven hierarchical layers that were developed to enable different networks to communicate reliably between disparate systems

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Download CCNA Portable Command Guide PDF

2011-11-08T07:09:00.000-08:00

CCNA portable command guide for your self studies

About the Author

Scott Empson is the associate chair of the Bachelor of Applied Information Systems Technology degree program at the Northern Alberta Institute of Technology in Edmonton, Alberta, Canada, where he teaches Cisco routing, switching, and network design courses in a variety of different programs (certificate, diploma, and applied degree) at the postsecondary level. Scott is also the program coordinator of the Cisco Networking Academy Program at NAIT, a Regional Academy covering Central and Northern Alberta. He has earned three undergraduate degrees: a Bachelor of Arts, with a major in English; a Bachelor of Education, again with a major in English/Language Arts; and a Bachelor of Applied Information Systems Technology, with a major in Network Management. He currently holds several industry certifications, including CCNP, CCDA, CCAI, and Network+. Before instructing at NAIT, he was a junior/senior high school English/Language Arts/Computer Science teacher at different schools throughout Northern Alberta. Scott lives in Edmonton, Alberta, with his wife, Trina, and two children, Zachariah and Shaelyn, where he enjoys reading, performing music on the weekend with his classic/80s rock band “Miss Understood,” and studying the martial art of Taekwon-Do.

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ip subnetting workbook

2011-10-01T06:55:00.000-07:00

IP subnetting workbook is one of the best ways to get expertise in the subject of subnetting, calculating IPs. It is all about how much you are practicing. As a networking professional, you will have to face real situations of planning network structures, decide and design subnets, calculate IP address's, almost everything. You will never have confidence to face such situations unless you haven't practiced. You can find lots of free IP subnetting workbooks on the internet. So.. start downloading and practicing.

Ccna PrepCenter - IP Subnetting from Networkers

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IP addressing and Subnetting workbook

2011-07-06T01:24:00.000-07:00

Every networking student should have a solid understanding of TCP/IP subnetting (Loshin, 1997). Subnetting’s importance in modern networking is reflected by its many and varied uses. It can enhance network performance by splitting up collision and broadcast domains in a routed network (Odom, 2000). Large networks can be organized into separate subnets representing departmental, geographical, functional, or other divisions (Feit, 1997). Since hosts on different subnets can only access each other through routers, which can be configured to apply security restrictions, subnetting can also serve as a tool for implementing security policies (Bulette, 1998). Dividing a large network into subnets and delegating administrative responsibility for each subnet can make administration of a large network easier. Routers can require that a WAN link connecting two networks must itself form a separate subnet (Bulette, 1998). Troubleshooting, diagnosing, and fixing problems in a TCP/IP internetwork typically require thorough familiarity with subnetting. Network design requires both the ability to understand and carry out subnetting.

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Subnetting Principles

2011-07-06T01:18:00.000-07:00

Subnetting lets you borrow bits from the host and use them to allow for more networks. When subnetting, separating the network and host requires a special mechanism called a subnet mask. A subnet mask, which contains a binary bit pattern of ones and zeros, is applied to an address to extract the network ID for purposes of determining whether an address is on the local network. If not, the address is switched or routed on.

The function of a subnet mask is to extract the network ID portion of an IP destination address and determine whether an IP address exists on the local network or whether it must be routed outside the local network. If the extracted network ID matches the local network ID, the destination is located on the local network. However, if they don't match, the message must be routed outside the local network. The process used to apply the subnet mask involves Boolean algebra to filter out nonmatching bits.

IP Subnetting

2011-03-24T23:07:00.000-07:00

Visual ip subnettingA subnet allows the flow of network traffic between hosts to be segregated based on a network configuration. By organizing hosts into logical groups, subnetting can improve network security and performance.Subnet MaskPerhaps the most recognizable aspect of subnetting is the subnet mask. Like IP addresses, a subnet mask contains four bytes (32 bits) and is often written using the same "dotted-decimal" notation. For example, a very common subnet mask in its binary representation.

Lab guide - Lab 1-1: Cisco Remote Lab Connection

2011-01-09T06:00:00.000-08:00

Following content has extracted from ICND (Interconnecting Cisco Networking Devices) Lab guide and added further clarifications where required for your convenience. **Important before start practicing, keep in mind that you would need a correctly wired and configured system as diagram unless some commands may not work correctly.

Complete this lab activity to practice what you learned in the related module.
Activity Objective
In this activity, you will Telnet to the terminal server to access the devices in your pod. After
completing this activity, you will be able to meet these objectives:
􀂄 Run Telnet to connect to the ICND remote lab
􀂄 Verify connectivity to the ICND remote lab terminal server
􀂄 Clear the connections to your workgroup switch and workgroup server

Visual Objective
The figure illustrates what you will accomplish in this activity.

Required Resources
These are the resources and equipment required to complete this activity:
􀂄 PC connected to an onsite laboratory or PC with an Internet connection to access the remote laboratory
􀂄 Terminal server connected to a console port of each laboratory device if using a remote laboratory
􀂄 ICND pod assigned by your instructor

Command List
The table describes the commands used in this activity.

Command
telnet ip-address
Description
Starts a terminal emulation program from a PC, router, or switch that permits you to access network devices remotely over the network.

Task 1: Run Telnet to Connect to the ICND Remote Lab
To begin the lab activities, you will use the Telnet utility to establish a connection to the remote lab equipment for this course.

Activity Procedure
Complete these steps from your PC:
Step 1 From the Microsoft Windows Start menu, choose Run. The Run window appears.
Step 2 In the Open field, type the telnet command followed by the IP address for your
terminal server, provided by your instructor. For example, if the terminal server
address that your instructor provided is 10.1.1.254, you would type:
telnet 10.1.1.254
If your Telnet session successfully connects to the terminal server, you should see an
opening menu similar to the following:
**************************************************************
*******
CISCO ICND STUDENT MENU
CONNECT TO YOUR POD LETTER
**************************************************************
*******
ITEM# DEVICE NAME
--------------------------------------------------------------
-------
1 Connect to pod A
2 Connect to pod B
3 Connect to pod C
4 Connect to pod D
5 Connect to pod E
6 Connect to pod F
7 Connect to pod G
8 Connect to pod H
9 Connect to pod I
10 Connect to pod J
11 Connect to pod K
12 Connect to pod L
13 EXIT
Please enter selection:

Step 3 At the "Please enter selection:" prompt, enter your workgroup number and
press Return. Your output should look similar to the following:
***********************************************************
POD L
To exit back out to the menu press "CTRL+SHIFT+6" then "X".
You must clear the line before re-connecting to a device.
***********************************************************
1 Connect to workgroup switch L
2 Connect to workgroup router L
3 Clear connection to w/g switch L
4 Clear connection to w/g router L
5 Return to main menu
Please enter selection:

The menu, called the Pod menu, lists your pod letter at the top. In the example, the current pod is Pod L.
From the menu, you can connect to either your workgroup switch or your workgroup router.

Once you connect to a network device from the terminal server, you will need to use a special keystroke sequence, Ctrl-Shift-6, then x, to return to the menu. (To do this, hold down the Shift key, press the Ctrl key and the 6, then press the x key.)

Step 4 Enter 1 to connect to your workgroup switch. You should see the following (or something similar) in your Telnet session:

Please enter selection: 1
Trying h26 (10.10.10.10, 2058)... Open

Step 5 Press Return to access the device prompt.
Note Your output will vary depending on the switch type that you are connected to. On an
unconfigured Catalyst 2950 series switch, setup mode appears if no previous configuration
changes have been made.

Step 6 To return to the menu, enter Ctrl-Shift-6, then x. The Pod menu appears again. When you return to the Pod menu, your session to your workgroup switch is still open. You should clear all open connections on a terminal server before exiting. If you do not close your open sessions, the Cisco IOS software will prompt you to close your open connections. To close a session, you must select the appropriate
option from the menu.

Step 7 Enter option 3 to clear the connection to your workgroup switch. When the "[confirm]" prompt appears, press Return.

What does the prompt say now?

Step 8 Enter option 2 to connect to your workgroup router.
What does the prompt say now? As with the switch, you may need to press Return one time to see the prompt on your terminal screen.

Step 9 Enter Ctrl-Shift-6, then x, to return to the Pod menu.

Step 10 Enter option 4 to clear the connection to your workgroup router. When the "[confirm]" prompt appears, press Return.

Step 11 Enter option 5 to return to the Main menu from the Pod menu.

Step 12 Exit the terminal server by entering the option from the Pod menu to exit. If there is no option to exit on the menu, contact your instructor for instructions.

Step 13 If you see the "You have open connections [confirm]" prompt, enter yes and press Return. Depending on which operating system is running on your PC, you may need to press Return after terminating your Telnet session.

Step 14 Notify your instructor that you have completed the activity.

Activity Verification
You have completed this task when you attain these results:
􀂄 You can successfully log on to the terminal server and navigate the menus to access your workgroup switch and workgroup router
􀂄 You can clear the connections to your workgroup switch and workgroup router

Address Resolution Protocol (ARP)

2010-12-01T05:02:00.000-08:00

What is ARP broadcast ?

A well known and common term ARP Broadcast in the network industry, is simply stands for Address Resolution Protocol. knowing the following terms are also will be helpful to understand the functions of this protocol.

Broadcast - Send to many
Multicast - Send to many, but not to all
Unicast - Send to specific destination

Address Resolution Protocol is a something to gather data about destination MAC address before starting to send data packets. The method to find out the destination's MAC address is send broadcast messages to all the connected devices with requesting their MAC addresses. As seems as the name, In the ARP broadcast, A data packet will be sent to the all connected devices within the network. The word "within the network" is important, because the ARP broadcast message will never go beyond the router. that usually means only in local network.

There's a reason to not to allow ARP broadcasts beyond the router. because such messages are making remarkable traffic on network. Since the every drop of bandwidth is very precious on internet, such traffic making packets are restricted to go beyond router.

Now let's see how is the Address Resolution Protocol is functioning.
we'll just consider the following scenario

Think that the HOST A wants to send some data to HOST B. But HOST A still don't know the MAC address of the HOST B. Then before starting to send data packets, The HOST A sends a ARP broadcast message to request the HOST B's MAC address. All devices in the local network receive the ARP and as same as HOST B is also receive the ARP Broadcast from HOST A because it's also in the same network. Then HOST B sends a uncast ARP reply message to HOST A including his MAC address. The word "unicast" is important because HOST B know where to send the reply and he directly send it to HOST A. After that the HOST A starting to send data to HOST B.

Let's look at a little bit different situation like this.

Think, in the above network, HOST A wanted to send some data to HOST B. But keep in mind the HOST A and HOST B are on different networks current situation because a router is in between them. You already know that the ARP broadcast messages are not passes through the router.

Now what happen is, Router knows the HOST B's MAC address. when the ARP broadcast gets to the router, the router sends a message to the HOST A like this. "The ARP broadcast can't be allow through me, but the destination you are looking for may be outside the network. so, this is the MAC address of the default gateway (ethernet 0). please send data to here and I'll send them to the correct destination on behalf you."

Then the data transferring is taking place.

Important.
ARP messages are broadcasts
Successfully forwards through Switches and hubs
Not allow beyond or through router

TCP - Transmission Control Protocol

2010-08-17T07:25:00.000-07:00

Windowing - Automatic Flow Control

Click on image if not clear

As we discussed about how a connection being established between two devices in TCP ( please refer the topic 3 way handshake concept ), The next immediate step is to start transferring data packets. It just happen like this.

Step 1. Establishing Connection

A -->>-->>-->>-->>-- Synchronization -->>-->>-->>-->>-- B

A --<<--<<--Acknowledgement + Synchronization--<<--<<--B

A-->>-->>-->>-->>--Acknowledgement-->>-->>-->>-->>--B

A ---<<--<<--<<---Connection Established---<<--<<--<<---B

Step 2. Data Transferring

A -->>-->>-->>-->>-->>--Packet 1-->>-->>-->>-->>-->>--B

A--<<--<<--<<--<<--Acknowledgement 2--<<--<<--<<--<<--B

Remember that when B receives the packet number 1, B send Acknowledgement number 2

A--->>-->>-->>-->>---Packet 2, 3, 4, 5--->>-->>-->>-->>---B

A--<<--<<--<<--<<--Acknowledgement 6--<<--<<--<<--<<--B

A->>-->>-->>---Packet 6, 7, 8, 9, 10, 11, 12, 13-->>-->>-->>-B

A--<<--<<--<<--<<--Acknowledgement 11--<<--<<--<<--<<--B

See the above incident, A sends packet number 6 to 13 but B sends the acknowledgement number 11. That means B has only received packets up to number 10. Then A have to send lost packets again.

A->>-->>-->>-->>---Packet 11, 12, 13, 14->>-->>-->>--->>--B

A--<<--<<--<<--<<--Acknowledgement 15--<<--<<--<<--<<--B

Likewise A always wants to finish sending packets as possible as early. So A gradually increase the number of packets sending in one time. But at a certain level B gets busy and fails to handle all the packets, Then B send a message to A to say that the number of packets sending in one time is too much, so please decrease the number of packets. Then A decrease the number of packets and in such case the data flowing rate is increasing and decreasing automatically. If you observe the data flowing rate via a graphical chart you can see the rate is going up and down like this.

This process calling windowing (automatic flow control) in TCP

Three way handshake Concept (3 Way handshake)

2010-08-11T03:15:00.000-07:00

How a Connection establish in TCP/IP according to the Three way Handshake (3Way handshake) concept

Three way handshake is regarding establishing a TCP socket connection between two pc's in three steps. It just happens like this. Assume that you have two pc's called host A and host B. They are connected physically with appropriate cables via Ethernet ports. TCP/IP protocol is running.

Step 1. Host A sends a synchronization packet to the Host B

just asking "Hello friend, I would like to establish a connection with you. Would you like ?

Step 2. Host B replies to Host A with a Acknowledgement packet + synchronization packet

Acknowledgement packet says that "Yes I like to establish a connection with you" and Synchronization packet says "Please confirm it"

Step 3. Host A sends an Acknowledgement packet to Host B

To say that " OK, then we'll establish a connection"

This is how a connection establish with 3way handshake (Threeway handshake) concept

Then three way handshake CONNECTION ESTABLISHED and starts to flow data between two hosts. In next post we'll see how the data flowing taking place between two hosts and controlling flow by them self. think all are very clean and clear here and you enjoyed it.

Rapid Spanning Tree Protocol - 802.1d

2010-04-09T23:36:00.001-07:00

RSTP bridge port roles:

Root - A forwarding port that is the best port from Nonroot-bridge to Rootbridge

Designated - A forwarding port for every LAN segment
Alternate - An alternate path to the root bridge. This path is different than using the root port.
Backup - A backup/redundant path to a segment where another bridge port already connects.
Disabled - Not strictly part of STP, a network administrator can manually disable a port

RSTP is a refinement of STP and therefore shares most of its basic operation characteristics. However there are some notable differences as summarized below:

Detection of root switch failure is done in 3 hello times, which is 6 seconds if default hello times have not been changed.

Ports may be configured as edge ports if they are attached to a LAN that has no other bridges attached. These edge ports transition directly to the forwarding state. RSTP still continues to monitor the port for BPDUs in case a bridge is connected. RSTP can also be configured to automatically detect edge ports. As soon as the bridge detects a BPDU coming to an edge port, the port becomes a non-edge port.

Unlike in STP, RSTP will respond to BPDUs sent from the direction of the root bridge. An RSTP bridge will "propose" its spanning tree information to its designated ports. If another RSTP bridge receives this information and determines this is the superior root information, it sets all its other ports to discarding. The bridge may send an "agreement" to the first bridge confirming its superior spanning tree information. The first bridge, upon receiving this agreement, knows it can rapidly transition that port to the forwarding state bypassing the traditional listening/learning state transition. This essentially creates a cascading effect away from the root bridge where each designated bridge proposes to its neighbors to determine if it can make a rapid transition. This is one of the major elements that allows RSTP to achieve faster convergence times than STP.

As discussed in the port role details above, RSTP maintains backup details regarding the discarding status of ports. This avoids timeouts if the current forwarding ports were to fail or BPDUs were not received on the root port in a certain interval.

802.1d - How the STP functioning ?

2010-03-23T11:02:00.000-07:00

Function of Spanning Tree Protocol - 802.1d

At the first I think it's better to have a brief description on STP.

STP is directly responsible for avoid following errors occur in a switched network, where the switches are connected in a loop.

1. Avoid receiving multiple frames of same data to hosts

2. Avoid packets going on an endless loop

3. Make MAC address table steady

all of above errors are possible to occur in an environment where the STP in not available. STP blocks a selected port on a loop to avoid those errors. The blocking port selected as follows.

STP blocks the designated port of highest cost path bearing switch to the root bridge. Then what are the designated ports and root bridge ?

Bridge ID, BPDU and Root bridge

Every switch has a bridge ID. Bridge ID is a combination of Priority value and lowest MAC address value. Priority value is 32768 by default in catalyst switches and it could be configure manually. The first factor is to consider for bridge ID is priority value. If the value is low, Bridge ID is high. value 1 is the maximum and value 0 is not be consider. If some switches have same priority, then the MAC address will be considered. Lower the MAC address is higher the Bridge ID.

Scene 1

In every 2 seconds, every switch send a packet named BPDU ( Bridge Protocol Datagram Unit ) which includes details about bridge ID and etc. By BPDU's every switch came to know about all other switch's Bridge IDs and they automatically appointed a leader switch which have the highest Bridge ID ( Highest priority and lowest MAC ). The leader is named as Root bridge.

Scene 2

After appointing a root bridge the switches mark their ports as following

1. Root port - Outgoing port towards the root bridge

2. Designated port - Other ports in the loop except Root port

Scene 3

Calculate the costs of paths as follows

old new

10Gbps 2

01Gbps 1 4

100Mbps 10 19

10Mbps 100 100

After that the STP blocks the designated port at the port where the highest cost path to the root bridge. Then the loop will no available any more. Remember that the BPDU's can go through blocked port while other packets can't.

Scene 3

let's see what will happen when a link to the root port is went down. Remember that the STP can keep a port on 4 modes as follows

1. blocking

2. listening

3. learning

4. forwarding

When a link to the root bridge is down the blocked port have to come up for the proper functioning of the network. Bringing a port to the forwarding mode happen as follows

step 1. when a link is down the switch will not receive anymore BPDU's from that side. In certain cases a switch may miss some BPDUs. because of that switch stay for 20 seconds ( 10 BPDU ) to exactly know whether the link is down. If no any BPDU received from that side for 20 seconds, then the switch know exactly there's a problem.

step 2. After 20 seconds the port will be changed the status in to listening mode. in listening mode, the switch send BPDU's through the blocked port and listen do they come back from the other side. That's to make sure that there will not occur any loops if the blocked port is opened. The port keep on listening mode for 15 seconds and then go to the next step if there's no BPDU receiving from the other side.

step 3. Then the port will change the status to learning mode where the switch learns MAC addresses of network. Stay another 15 seconds on learning mode

step 4. The port will be opened for packets and start forwarding.

like that in STP it takes minimum of 50 seconds to network bring back to functioning. It is a big disadvantage taking so much time to bring the network up and working. All of the above described mode changing activities can be observe in a real switched network or by using Packet tracer with some techniques. For packet tracer users, I can send a simulation file on your request. please leave a comment or send a message via facebook if you need those simulation files.

Spanning Tree Protocol - 802.1d

2010-03-16T10:33:00.000-07:00

Overview and introduction to Spanning tree protocol

STP is a standard protocol which is works on any brand of switches. ISL ( Inter Switch Link ) is the Cisco proprietary protocol instead of STP. STP cannot be explained alone since it's related with several number of operations on switches such as Bridge ID, BPDU and etc.

Spanning-Tree Protocol (STP) as defined in the IEEE 802.1D is a link management protocol that provides path redundancy while preventing undesirable loops in the network. For an Ethernet network to function properly, only one active path can exist between two stations. Loops occur in networks for a variety of reasons. The most common reason you find loops in networks is the result of a deliberate attempt to provide redundancy - in case one link or switch fails, another link or switch can take over.

STP is a technology that allows bridges to communicate with each other to discover physical loops in the network. The protocol then specifies an algorithm that bridges can use to create a loop-free logical topology. In other words, STP creates a tree structure of loop-free leaves and branches that spans the entire Layer 2 network.

Spanning-Tree Protocol operation is transparent to end stations, which are unaware whether they are connected to a single LAN segment or a switched LAN of multiple segments. Where two bridges are used to interconnect the same two computer network segments, spanning tree is a protocol that allows the bridges to exchange information so that only one of them will handle a given message that is being sent between two computers within the network.

Bridge Protocol Data Units (BPDUs) is used by bridges in a network to exchange information regarding their status. The Spanning-Tree Protocol uses the BPDU information to elect the root switch and root port for the switched network, as well as the root port and designated port for each switched segment.

The program in each bridge that allows it to determine how to use the protocol is known as the spanning tree algorithm, which is specifically constructed to avoid bridge loops. The algorithm is responsible for a bridge using only the most efficient path when faced with multiple paths. If the best path fails, the algorithm recalculates the network and finds the next best route.

The spanning tree algorithm determines the network (which computer hosts are in which segment) and this data is exchanged using Bridge Protocol Data Units (BPDUs). It is broken down into two steps:

Step 1: The algorithm determines the best message a bridge can send by evaluating the configuration messages it has received and choosing the best option.

Step 2: Once it selects the top message for a particular bridge to send, it compares its choice with possible configuration messages from the non-root-connections it has. If the best option from step 1 isn't better than what it receives from the non-root-connections, it will prune that port.

Lab commands - VTP configurations

2010-03-15T06:05:00.000-07:00

How to Configure VTP and how to view configurations ?

Since you have practiced certain commands and been in touch with cisco devices i assume that i don't need to explain basic commands from here.

As you know by default all the Catalyst switches are on server mode. To view the current mode,

in CLI ( Command Line Interface )

go to privilege mode enter following command.

Switch#show vtp status

VTP Version : 2

Configuration Revision : 0

Maximum VLANs supported locally : 255

Number of existing VLANs : 5

VTP Operating Mode : Server

VTP Domain Name :

VTP Pruning Mode : Disabled

VTP V2 Mode : Disabled

VTP Traps Generation : Disabled

MD5 digest : 0x7D 0x5A 0xA6 0x0E 0x9A 0x72 0xA0 0x3A

Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00

Local updater ID is 0.0.0.0 (no valid interface found)

You can see the VTP operating mode is Server and many details which we have to discuss in advance.

Now enter to Global configuration mode and type following commands

Switch(config)#vtp mode client " To change the VTP mode from server to client "

Setting device to VTP CLIENT mode.

Switch(config)#vtp domain cisco " To assign the domain name as cisco "

Changing VTP domain name from NULL to cisco

As i explained in earlier articles, the domain name must be same in all switches which you want to make receive updates from a server switch. That meant when you assign domain name as cisco for one switch in server mode and assign all other client mode switched the sane domain name, All client switches which have domain name as cisco will receive updates from server switch.

Lab commands - VLAN configurations

2010-03-13T19:44:00.000-08:00

Lab commands - VLAN configurations

Switch#enable "enter to privilage mode"

Switch#configure terminal "Enter to Global configuration mode"

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)#interface vlan 1 "Go to interface mode of VLAN 1"

Switch(config-if)#ip address 10.1.1.1 255.255.255.0 "Assign IP address for interface VLAN 1 with the subnet mask"

Switch(config-if)#no shutdown "make the interface up"

%LINK-5-CHANGED: Interface Vlan1, changed state to up
Switch(config-if)#
%SYS-5-CONFIG_I: Configured from console by console
Switch#

VIEW CONFIGURATIONS

Switch#show interfaces VLAN 1 "Show details of interface VLAN 1"
Vlan1 is up, line protocol is down "Both vlan1 and line protocol must be up for working condition"

Hardware is CPU Interface, address is 0010.1116.ce76 (bia 0010.1116.ce76)
  Internet address is 10.1.1.1/24
  MTU 1500 bytes, BW 100000 Kbit, DLY 1000000 usec,
  reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 21:40:21, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
   1682 packets input, 530955 bytes, 0 no buffer
   Received 0 broadcasts (0 IP multicast)
   0 runts, 0 giants, 0 throttles
   0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
   563859 packets output, 0 bytes, 0 underruns
   0 output errors, 23 interface resets
   0 output buffer failures, 0 output buffers swapped out

Switch#SHOW running-config "view running configurations of interface VLAN 1"

!
interface Vlan1
ip address 10.1.1.1 255.255.255.0
!

Test Inside 640-802 (CCNA Exam Simulator)

2010-03-12T11:56:00.000-08:00

Test Inside 640-802 (CCNA Exam Simulator)

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VTP ( VLAN Trunking Protocol) - 802.1Q

2010-03-11T23:34:00.000-08:00

VTP ( VLAN Trunking Protocol) - 802.1Q

VLAN Trunking Protocol (VTP) is a Cisco Layer 2 messaging protocol that manages the addition, deletion, and renaming of VLANs on a network-wide basis. Virtual Local Area Network (VLAN) Trunk Protocol (VTP) reduces administration in a switched network. When you configure a new VLAN on one VTP server, the VLAN is distributed through all switches in the domain. This reduces the need to configure the same VLAN everywhere. VTP is a Cisco-proprietary protocol that is available on most of the Cisco Catalyst Family products.

VTP has 3 operational modes as follows

1. Server ( default )

2. Client

3. Transparent

How it's operating ?

As usual all the Cisco switches are on VTP server mode by default. that means such switched works as a server to manage VLANs. When we configure VLANs on switch in server mode and connects it to the network, it sends advertisement to the other switches on the network in every 5 minute which contain details about VLANs where configured on him self.

The network can be contain other switched in client mode and transparent mode. When a Vlan advertisement received by a client switch, it automatically make configurations of vlan on him self according to the advertisement and pass it to the next switch.

When a advertisement received by a transparent switch, it only pass it to the next and no make any configurations on him self.

Configurations can be done as follows.

Server mode - can configure VLANs on switch, Send advertisements, Don't receive updates

Client mode - can't configure VLANs on switch, don't send advertisements, receive updates

Transparent mode - can configure VLANs on switch, Pass through advertisements

What is a VLAN?

2010-03-10T07:09:00.000-08:00

What is a VLAN?

A VLAN is a virtual LAN. In technical terms, a VLAN is a broadcast domain created by switches. Normally, it is a router creating that broadcast domain. With VLAN’s, a switch can create the broadcast domain.

This works by, you, the administrator, putting some switch ports in a VLAN other than 1, the default VLAN. All ports in a single VLAN are in a single broadcast domain.

Because switches can talk to each other, some ports on switch A can be in VLAN 10 and other ports on switch B can be in VLAN 10. Broadcasts between these devices will not be seen on any other port in any other VLAN, other than 10. However, these devices can all communicate because they are on the same VLAN. Without additional configuration, they would not be able to communicate with any other devices, not in their VLAN.

Are VLANs required?
It is important to point out that you don’t have to configure a VLAN until your network gets so large and has so much traffic that you need one. Many times, people are simply using VLAN’s because the network they are working on was already using them.
Another important fact is that, on a Cisco switch, VLAN’s are enabled by default and ALL devices are already in a VLAN. The VLAN that all devices are already in is VLAN 1. So, by default, you can just use all the ports on a switch and all devices will be able to talk to one another.

When do I need a VLAN?
You need to consider using VLAN’s in any of the following situations:
You have more than 200 devices on your LAN
You have a lot of broadcast traffic on your LAN
Groups of users need more security or are being slowed down by too many broadcasts?
Groups of users need to be on the same broadcast domain because they are running the same applications. An example would be a company that has VoIP phones. The users using the phone could be on a different VLAN, not with the regular users.
Or, just to make a single switch into multiple virtual switches.

How to Create a VLAN ?

2010-03-10T07:02:00.000-08:00

Three methods to create a VLAN

Switch>enable "Enter to privilege mode"
Switch#configure terminal "Enter to Global Configuration mode"
Enter configuration commands, one per line. End with CNTL/Z.

Method 1
Switch(config)#vlan 10 "Create VLAN 10"
Switch(config-vlan)#name admin "Name VLAN as admin"
Switch(config-vlan)#exit

Method 2
Switch(config)#interface vlan 20

Method 3
Switch#vlan data "Enter to VLAN database"
% Warning: It is recommended to configure VLAN from config mode,
as VLAN database mode is being deprecated. Please consult user
documentation for configuring VTP/VLAN in config mode.

Switch(vlan)#?
VLAN database editing buffer manipulation commands:
exit Apply changes, bump revision number, and exit mode
no Negate a command or set its defaults
vlan Add, delete, or modify values associated with a single VLAN
vtp Perform VTP administrative functions.

Switch(vlan)#vlan 30 name accounts "Create VLAN 30 and name it as Accounts in VLAN database"
VLAN 30 added:
Name: accounts

Secure port on cisco switch

2010-03-09T07:11:00.000-08:00

Understand the basics

In its most basic form, the Port Security feature remembers the Ethernet MAC address connected to the switch port and allows only that MAC address to communicate on that port. If any other MAC address tries to communicate through the port, port security will disable the port. Most of the time, network administrators configure the switch to send a SNMP trap to their network monitoring solution that the port's disabled for security reasons.

Of course, implementing any security solution always involves a trade-off—most often, you trade increased security for less convenience. When using port security, you can prevent devices from accessing the network, which increases security.

However, as you know, there's usually a downside. In this case, it's that the network administrator is the only one who can "unlock" the port, which can cause problems when there are legitimate reasons to change out devices.

Configure port security

Configuring the Port Security feature is relatively easy. In its simplest form, port security requires going to an already enabled switch port and entering the port-securityInterface Mode command. Here's an example:

"First go to the interface of port that you want to configure"
Switch)# config t
Switch(config)# int fa0/18


"Then change the mode of port to Access, Port-security can't be enabled on a port which is on trunk mode"
Switch(config-if)# switchport mode access


"Enable port-security on port"
Switch(config-if)# switchport port-security


"Assign specific MAC address to the port"
Switch(config-if)# switchport port-security mac address XXXX.XXXX.XXXX


"Limit the number of MAC addresses allowed through the port"
Switch(config-if)# switchport port-security maximum 1


"Set the action to take in case of violating the rule"
Switch(config-if)# switchport port-security violation shutdown
Switch(config-if)#^Z

By entering the most basic command to configure port security, we accepted the default settings of only allowing one MAC address, determining that MAC address from the first device that communicates on this switch port, and shutting down that switch port if another MAC address attempts to communicate via the port. But you don't have to accept the defaults.

Know your options

As you can see in the example, there are a number of other port security commands that you can configure. Here are some of your options:

switchport port-security maximum {max # of MAC addresses allowed}: You can use this option to allow more than the default number of MAC addresses, which is one. For example, if you had a 12-port hub connected to this switch port, you would want to allow 12 MAC addresses—one for each device. The maximum number of secure MAC addresses per port is 132.

switchport port-security violation {shutdown | restrict | protect}: This command tells the switch what to do when the number of MAC addresses on the port has exceeded the maximum. The default is to shut down the port. However, you can also choose to alert the network administrator (i.e., restrict) or only allow traffic from the secure port and drop packets from other MAC addresses (i.e., protect).

switchport port-security mac-address {MAC address}: You can use this option to manually define the MAC address allowed for this port rather than letting the port dynamically determine the MAC address.

Of course, you can also configure port security on a range of ports. Here's an example:

Switch)# config t
Switch(config)# int range fastEthernet 0/1 - 24  
Switch(config-if)# switchport port-security

However, you need to be very careful with this option if you enter this command on an uplink port that goes to more than one device. As soon as the second device sends a packet, the entire port will shut down.

View the status of port security

Once you've configured port security and the Ethernet device on that port has sent traffic, the switch will record the MAC address and secure the port using that address. To find out the status of port security on the switch, you can use the show port-security address and show port-security interface commands. Below are examples for each command's output:

Switch# show port-security address         
          Secure Mac Address Table
-------------------------------------------------------------------
Vlan    Mac Address       Type                Ports   Remaining Age


----    -----------       ----                -----   -------------
                                                         (mins)    
   1    0004.00d5.285d    SecureDynamic       Fa0/18       -


0
Max Addresses limit in System (excluding one mac per port) : 1024
-------------------------------------------------------------------
Total Addresses in System (excluding one mac per port)     :
 



tch# show port-security interface fa0/18
port Security                        : Enabled
PPort Status                        : Secure-up
Violation Mode                     : Shutdown
Aging Time                          : 0 mins
SecureStatic Address Aging  : Disabled
Maximum MAC Addresses    : 1

MAC Addresses                         : 0
Total MAC Addresses                 : 1
Configured MAC Addresses         : 0
Source MAC Address                 : 0004.00d5.285d
Security Violation Count              : 0

Switch#

Basic Switching - Switch Functions

2010-03-08T22:08:00.000-08:00

Basic Switch Functions

In order to forward a packet that has arrived at a router interface, the router must perform a switching function. This switching function has four steps:

• A packet transiting the router will be accepted into the router if the frame header contains the MAC address of one of the router's NIC cards. If properly addressed, the frame and its content will be buffered occurs in memory pending further processing.

• The switching process checks the destination logical network portion of the packet header against the network/subnetwork entries in the routing table. If the search is successful, the switching process associates the destination network with a next-hop logical device and an outbound interface.

• For the next device in the relay chain. The lookup is performed in an Address Resolution Protocol (ARP) table for LAN interfaces or a map table for WAN interfaces.

• Once the physical address of the next-hop device is known, the frame header is overwritten, and the frame is then moved to the outbound interface for transmission onto the media. As the frame is placed on the media, the outbound interface adds the CRC character and ending delimiters to the frame. These characters will need to be validated at the arriving interface on the next-hop relay device.

OSI MODEL

2010-03-08T05:37:00.000-08:00

OSI MODEL (Open System Interconnection Model)

OSI divides telecommunication into seven layers. The layers are in two groups. The upper four layers are used whenever a message passes from or to a user. The lower three layers are used when any message passes through the host computer. Messages intended for this computer pass to the upper layers. Messages destined for some other host are not passed up to the upper layers but are forwarded to another host. The seven layers are:

Layer 7: The application layer ...This is the layer at which communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. (This layer is not the application itself, although some applications may perform application layer functions.)

Layer 6: The presentation layer ...This is a layer, usually part of an operating system, that converts incoming and outgoing data from one presentation format to another (for example, from a text stream into a popup window with the newly arrived text). Sometimes called the syntax layer.

Layer 5: The session layer ...This layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. It deals with session and connection coordination.

Layer 4: The transport layer ...This layer manages the end-to-end control (for example, determining whether all packets have arrived) and error-checking. It ensures complete data transfer.

Layer 3: The network layer ...This layer handles the routing of the data (sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level). The network layer does routing and forwarding.

Layer 2: The data-link layer ...This layer provides synchronization for the physical level and does bit-stuffing for strings of 1's in excess of 5. It furnishes transmission protocol knowledge and management.

Layer 1: The physical layer ...This layer conveys the bit stream through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier.