CCNA Networking Interview Questions

GNS3

2011-07-30T09:31:00.000+02:00

http://network-ing.blogspot.com/p/links.html

1.GNS3 Quick Start Guide for Linux Users

2.GNS3 Quick Start Guide for Windows Users

2011-07-26T11:29:00.001+02:00

Educational and Referal Links

2011-07-26T07:35:00.000+02:00

http://www.cisco.com/

What is CDP?

2011-07-26T06:41:00.000+02:00

CDP - Cisco Discovery Protocol is a Cisco proprietary Layer 2 protocol.

CDP uses a multicast packet to the common destination address 01-00-0c-cc-cc.

CDP packets are sent out with a non zero TTL after an interface is enabled and with a zero TTL value

immediately before and interface is made idle. This enables the neighboring devices to quickly discover the

state of neighbors.

CDP packets will never be forwarded beyond the directly connected devices. To find CDP information

on indirectly connected routers, administrators can 'telnet' to the intended destination device and run CDP

command.

Telnet, FTP, and TFTP

2011-07-26T06:36:00.000+02:00

Telnet is used for terminal emulation that runs programs remotely.

Telnet uses TCP/IP protocol.

Telnet requires a username and password to access.

FTP (File Transfer Protocol) is a connection oriented protocol. It

uses TCP/IP for file transfer.

Compare this with TFTP (Trivial File Transfer Protocol) that uses

UDP (Connectionless protocol). SNMP uses UDP over IP.

Tracert, Ping uses ICMP as their base protocol. FTP is used to

transfer files.

Both FTP and Telnet are client-server protocols. Note that TCP/IP is a client server oriented protocol.

What is static route?

2011-07-20T08:09:00.000+02:00

Config# ip route Net_Add SN_Mask Next_Hop_Add -

Example: ip route 192.168.15.0 255.255.255.0 205.5.5.2

Config# ip route 0.0.0.0 0.0.0.0 Next_Hop_Add - Default route

Config# ip default-network Net_Add - Gateway LAN network

How to clear the counters?

2011-07-20T08:06:00.000+02:00

clear interface Ethernet 0 - Clears counters on the specified interface

clear counters- Clears all interface counters

clear cdp counters - Clears CDP counters

Differance between TCP and UDP

2011-07-20T07:41:00.000+02:00

TCP	UDP
Transmission Control Protocol	User Datagram Protocol
Connection oriented	Connectionless
Its works as delivery of courier	Its works as delivery of letter
communication among sender or user	No communication among sender or user.
Its make a reliable delivery of data	Its provide unreliable communication
There is acknowledgement of sending data	There is no acknowledgement
Its provide connection oriented services	Its provides the connectionless services.
TCP is slower data communication process	It is fast data communication process
TCP support the flow controls	It does not support flow controls
Support sequencing	Does not support sequencing
Support windowing	Does not supports windowing

Difference between Distance Vector & Link State

2011-07-18T13:50:00.000+02:00

Distance Vector RIP(Routing Information Protocol) ver 1 IGRP(Interior Gateway Routing Protocol)	Link State OSPF(Open Shortest Path First)IS-IS(Intermediate System to Intermediate System)
1) Neighbor to Neighbor (Slow)	1) Information in Flooded (Fast)
2) Complete Routing table exchange No Hallow Packet Sent Slow Convergence Small Network	2) Only Incremental & Decremental Updates Hallow Packets Sent Band Width Fast Convergence Big Network
3) Calssfull(Sent only Net ID’s) No Support of Subnatting	3) Classless(Sent Net ID’s & Subnet Mask) Support of Subnatting
4) Routing Loops is exist	4) Routing Loops is not exist

Verifying or Troubleshooting a Serial Link/PPP Encapsulation

2011-07-12T08:03:00.000+02:00

Router#show interfaces serial x

Router#show controllers serial x

Router#debug serial interface

Router#debug ppp

Router#debug ppp packet

Router#debug ppp negotiation

Router#debug ppp error

Router#debug ppp authentication

Router#debug ppp compression

Conﬁguring PPP on a Serial Line

2011-07-12T07:57:00.000+02:00

Router#configure terminal

Moves to global conﬁguration mode

Router(config)#interface serial

0/0/0

Moves to interface conﬁguration mode

Router(config-if)#encapsulation

ppp

Changes encapsulation from default

HDLC to PPP

Conﬁguring HDLC Encapsulation on a Serial Line

2011-07-12T07:49:00.000+02:00

Router#configure terminal

Router(config)#interface serial

0/0/0

Moves to interface conﬁguration mode

Router(config-if)#encapsulation

hdlc

Sets the encapsulation mode for this

interface to HDLC

NOTE: HDLC is the default encapsulation for synchronous serial links on

Cisco routers. You would only use the encapsulation hdlc command to return

the link to its default state.

Moves to global conﬁguration mode

Troubleshooting Frame Relay

2011-07-11T12:56:00.000+02:00

Router#debug frame-relay lmi

Used to help determine whether a router

and Frame Relay switch are exchanging

LMI packets properly

Frame Relay show command

2011-07-11T12:54:00.000+02:00

Router#show frame-relay map

Router#show frame-relay pvc

Displays the status of all PVCs conﬁgured

Router#show frame-relay lmi

Displays LMI statistics

Router#clear frame-relay counters

Clears and resets all Frame Relay counters

Router#clear frame-relay inarp

Clears all Inverse ARP entries from the

map table

Displays IP/DLCI map entries

Conﬁguring Frame Relay Using Subinterfaces

2011-07-11T08:53:00.000+02:00

Router(config)#interface serial

0/0/0

Router(config-if)#encapsulation

frame-relay ietf

Router(config-if)#frame-relay

lmi-type ansi

Router(config-if)#no ip address

Router(config-if)#no shutdown

Router(config-if)#interface

serial 0/0/0.102 point-to-point

Router(config-subif)#ip address

192.168.10.1 255.255.255.0

Router(config-subif)#frame-relay

interface-dlci 102

Router(config-subif)#interface

serial 0/0/0.103 point-to-point

Router(config-subif)#ip address

192.168.20.1 255.255.255.0

Router(config-subif)#frame-relay

interface-dlci 103

Router(config-subif)#exit

Router(config-if)#exit

Router(config)#

Conﬁguring a Description of the Interface (Optional)

2011-07-11T08:50:00.000+02:00

Router(config-if)#description

Connection to the office

Optional command to allow you to enter

in additional information such as contact

name, PVC description, and so on

Conﬁguring a Frame Relay map Statement

2011-07-11T08:44:00.000+02:00

Router(config-if)#frame-relay map

ip 192.168.100.1 111 broadcast

Maps the remote IP address

(192.168.100.1) to the local DLCI

number (111).

The optional broadcast keyword speciﬁes

that broadcasts across IP should be

forwarded to this address. This is

necessary when using dynamic routing

protocols.

Router(config-if)#no frame-relay

inverse arp

Turns off Inverse ARP.

Setting the Frame Relay DLCI Number

2011-07-11T08:34:00.000+02:00

Router(config-if)#frame-relay

interface-dlci 110

Sets the DLCI number of 110 on the local

interface-dlci 110

Router(config-fr-dlci)#exit

Returns to interface conﬁguration mode

Router(config-if)#exit

Returns to global conﬁguration mode

Router(config)#

interface and enters Frame Relay DLCI

conﬁguration mode

Setting the Frame Relay Encapsulation LMI Type

2011-07-11T08:26:00.000+02:00

Router(config-if)#frame-relay lmi-

type {ansi | cisco | q933a}

Depending on the option you select, this

command sets the LMI type to the ANSI

standard, the Cisco standard, or the ITU-T

Q.933 Annex A standard.

Setting the Frame Relay Encapsulation Type

2011-07-11T08:24:00.000+02:00

Router(config)#interface serial 0/0/0

Router(config-if)#encapsulation

frame-relay

Turns on Frame Relay

encapsulation with the default

encapsulation type of cisco.

WAN protocols

2011-07-11T08:00:00.000+02:00

Frame Relay

A packet-switched technology that emerged in the early 1990s, Frame Relay is a Data Link and Physical layer specification that provides high performance. Frame Relay is a successor to X.25, except that much of the technology in X.25 used to compensate for physical errors (noisy lines) has been eliminated. Frame Relay can be more cost-effective than point-to-point links, and can typically run at speeds of 64Kbps up to 45Mbps (T3). Frame Relay provides features for dynamic bandwidth allocation and congestion control.

ISDN

Integrated Services Digital Network (ISDN) is a set of digital services that transmit voice and data over existing phone lines. ISDN can offer a cost-effective solution for remote users who need a higher-speed connection than analog dial-up links offer. ISDN is also a good choice as a backup link for other types of links such as Frame Relay or a T-1 connection.

LAPB

Link Access Procedure, Balanced (LAPB) was created to be a connection-oriented protocol at the Data Link layer for use with X.25. It can also be used as a simple data link transport. LAPB causes a tremendous amount of overhead because of its strict timeout and windowing techniques.

HDLC

High-Level Data-Link Control (HDLC) was derived from Synchronous Data Link Control (SDLC), which was created by IBM as a Data Link connection protocol. HDLC is a protocol at the Data Link layer, and it has very little overhead compared to LAPB. HDLC wasn’t intended to encapsulate multiple Network layer protocols across the same link. The HDLC header carries no identification of the type of protocol being carried inside the HDLC encapsulation. Because of

this, each vendor that uses HDLC has their own way of identifying the Network layer protocol, which means that each vendor’s HDLC is proprietary for their equipment.

PPP

Point-to-Point Protocol (PPP) is an industry-standard protocol. Because all multi-protocol versions of HDLC are proprietary, PPP can be used to create point-to-point links between different vendors’ equipment. It uses a Network Control Protocol field in the Data Link header to identify the Network layer protocol. It allows authentication and multilink connections and can be run over asynchronous and synchronous links.

ATM

Asynchronous Transfer Mode (ATM) was created for time-sensitive traffic, providing simultaneous transmission of voice, video, and data. ATM uses cells instead of packets that are a fixed 53 bytes long. It also can use isochronous clocking (external clocking) to help the data move faster.

comapre OSPF and RIPv1 comparison

2011-07-11T07:16:00.000+02:00

Open Shortest Path First (OSPF) Basics

OSPF and RIPv1 comparison

Characteristic

OSPF V/s RIPv1

Type of protocol Link-state Distance-vector

Classless support Yes No

VLSM support Yes No

Auto summarization No Yes

Manual summarization Yes No

Route propagation Multicast on change Periodic broadcast

Path metric Bandwidth Hops

Hop count limit None 15

Convergence Fast Slow

Peer authentication Yes No

Hierarchical network Yes (using areas) No (flat only)

Route computation Dijkstra Bellman-Ford

Spanning Tree Protocol (STP)

2011-07-11T07:14:00.000+02:00

Spanning Tree Protocol (STP)

Spanning-Tree Port States

The ports on a bridge or switch running STP can transition through five different states:

Blocking A blocked port won’t forward frames; it just listens to BPDUs. The purpose of the

blocking state is to prevent the use of looped paths. All ports are in blocking state by default

when the switch is powered up.

Listening The port listens to BPDUs to make sure no loops occur on the network before passing

data frames. A port in listening state prepares to forward data frames without populating

the MAC address table.

Learning The switch port listens to BPDUs and learns all the paths in the switched network.

A port in learning state populates the MAC address table but doesn’t forward data frames.

Forwarding The port sends and receives all data frames on the bridged port. If the port is still

a designated or root port at the end of the Learning state, it enters this state.

Disabled A port in the disabled state (administratively) does not participate in the frame forwarding

Baisc router configuration

2011-07-05T12:58:00.000+02:00

Router>enable

Router#clock set 18:30:00 15 May 2011

Router#configure terminal

Router(config)#hostname New York

Newyork(config)#no ip domain-lookup

Newyork(config)#banner motd #

This is the New York Router.

Authorized Access Only

Newyork(config)#clock timezone EST –5

Newyork(config)#enable secret cisco

Newyork(config)#service password-encryption

Newyork(config)#line console 0

Newyork(config-line)#logging synchronous

Newyork(config-line)#password class

Newyork(config-line)#login

Newyork(config-line)#line vty 0 4

Newyork(config-line)#password class

Newyork(config-line)#login

Newyork(config-line)#line aux 0

Newyork(config-line)#password class

Newyork(config-line)#login

Newyork(config-line)#exit

Newyork(config)#no service password-

encryption

Newyork(config)#interface fastethernet 0/

Newyork(config-if)#description Engineering

LAN

Newyork(config-if)#ip address 172.16.10.1

255.255.255.0

Newyork(config-if)#no shutdown

Newyork(config-if)#interface serial 0/0/0

Newyork(config-if)#description Link to

Buffalo Router

Newyork(config-if)#ip address 172.16.20.1

255.255.255.252

Newyork(config-if)#clock rate 56000

Newyork(config-if)#no shutdown

Newyork(config-if)#exit

Newyork(config)#ip host buffalo 172.16.20.2

Newyork(config)#exit

Newyork#copy running-config startup-config

Assigning a Local Host Name to an IP Address

2011-07-05T12:43:00.000+02:00

Router(config)#ip host USA 172.17.2.5