Tài liệu học CCNA kỳ 2 mod4 CDP

• CDP is used to obtain information about neighboring devices, such as: – the types of devices connected – the router interfaces they are connected to – the interfaces used to make the c

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Module 4 – Learning About Other

Devices

Overview

Students completing this module should be able to:

which local interfaces

devices using CDP

• Disconnect from a Telnet session

• Suspend a Telnet session

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NIIT-ICT Hanoi info@niithanoi.vn 3

Introduction to CDP

• Cisco Discovery Protocol (CDP) is a Layer 2 protocolthat connects

lower physical media and upper network layer protocols

• CDP is used to obtain information about neighboring devices, such as:

– the types of devices connected

– the router interfaces they are connected to

– the interfaces used to make the connections

– the model numbers of the devices

• CDP is media and protocol independent, and runs on all Cisco

equipment over the Subnetwork Access Protocol (SNAP)

Information obtained with CDP

• CDP Version 2 (CDPv2) is the most recent release of the protocol

Cisco IOS (Release 12.0(3)T or later) supports CDPv2

• CDP Version 1 (CDPv1) is enabled by default with Cisco IOS (Release

10.3 to 12.0(3)T)

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Implementation, monitoring, and maintenance of CDP

Remote router’s interface This router’s interface

• The cdp runcommand is used to enable CDPgloballyon the router

• By default, CDP is globally enabled

• The cdp enablecommand is used to enable CDP on a particular

interface

• On Cisco IOS Release 10.3 or higher, CDP is enabled by default on all

supported interfaces to send and receive CDP information

• CDP could be enabled on each of the devices interfaces by using the

cdp enablecommand

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Disabling CDP

To disable CDP on a specific interface after it has been

enabled, use the no

CDP enable

command in interface configuration mode.

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Troubleshooting CDP

Getting Information about Remote Devices

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Telnet

TCP/IP protocol suite

Establishing and verifying a Telnet connection

• To initiate a Telnet session any of the following alternatives can be

used:

Denver>connect paris

Denver>paris

Denver>131.108.100.152

Denver>telnet paris

• A hostname table or access to DNS for Telnet must be present for a

name to work

• Otherwise, the IP address of the remote router must be entered

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RouterA#conf t

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

RouterA(config)#ip host RouterA 10.1.1.1

RouterA(config)#exit

RouterA#telnet routera

Trying RouterA (10.1.1.1) Open

User Access Verification

Password:

RouterB>

• This is where the ip host commands can be helpful.

Does not have to be the router-name but it is generally a good idea.

Not case sensitive.

Establishing and verifying a Telnet connection

RouterA>telnet 10.1.1.1

Trying 10.1.1.1 Open

Password required, but none set

[Connection to 10.1.1.1 closed by foreign host]

RouterA>

Password:cisco

RouterB>

RouterB>exit

RouterA>

RouterB(config)#line vty 0 4 RouterB(config-line)#login RouterB(config-line)#password cisco

Configure vty password

on RouterB

Telnet works! Enter vty password

Exit closes (ends) telnet session

Telnet password – line vty

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Password:cisco

RouterB>ena

% No password set

RouterB>exit

Password:cisco

RouterB>ena

Password:class

RouterB#exit

RouterA>

Cannot enter privilege mode because there is no privilege password (enable secret) Can only enter this mode from the console until the password is created.

• If there is no privilege password on the remote router, you cannot enter

privilege mode!

RouterB(config)#enable secret class

Configure priviledge

password on RouterB

Telnet and the privilege password

Disconnecting and suspending Telnet sessions

• A session is suspended for a limited time, to resume a Telnet session

that has been suspended, just press Enter

• The command show sessions will show what Telnet sessions are

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RouterA>connect

Host: 10.1.1.1

Password:cisco

RouterB>

RouterB> <control-shift-6, x>

RouterA>show sessions

Conn Host Address Byte Idle Conn Name

* 1 10.1.1.1 10.1.1.1 0 0 10.1.1.1

RouterA> <enter>

[Resuming connection 1 to 10.1.1.1 ]

RouterB>exit

RouterA>show sessions

% No connections open

RouterA>

• If there is no privilege password on the remote router, you cannot enter

privilege mode!

Or the “telnet” command

Disconnecting and suspending Telnet sessions

Advanced Telnet operation

• If the resume command is used it requires a connection ID

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Alternative connectivity tests

network protocols support an echo protocol.

successfully to all five datagrams sent

exclamations on the display, the application on the router

(or source device) timed out waiting for a given packet

echo from the ping target

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• The traceroute command is the ideal tool for finding where data is

being sent in a network

• If one of these routers is unreachable, three asterisks (*) will be

returned instead of the name of the router

• The traceroute command will continue attempting to reach the next

step until the Ctrl-Shift-6 escape sequence is used

Troubleshooting IP addressing issues

• pinguses the ICMP protocol to verify the hardware connection and

the IP address of the network layer This is a basic testing mechanism

• telnetverifies the application layer software between source and

destination This is the most complete test mechanism available

• tracerouteallows the location of failures in the path from the source

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Summary

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