Cdp & Telnet

Ch.4 – Learning About Other Devices (CDP and Telnet)

CCNA 1 version 3.0

Rick Graziani

Cabrillo College

Overview

Students completing this module should be able to: • Enable and disable CDP • Use the show cdp neighbors command • Determine which neighboring devices are connected to

which local interfaces • Gather network address information about neighboring

devices using CDP • Establish a Telnet connection • Verify a Telnet connection • Disconnect from a Telnet session • Suspend a Telnet session • Perform alternative connectivity tests • Troubleshoot remote terminal connections

Introduction to CDP

• Cisco Discovery Protocol (CDP) is a Layer 2 protocol that 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).

Implementation, monitoring, and maintenance of CDP

Remote router’s interfaceThis router’s interface

• The cdp run command is used to enable CDP globally on the router. • By default, CDP is globally enabled. • The cdp enable command 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 enable command.





Disabling CDP

To disable CDP on a specific interface after it has been enabled, use the no CDP enable command in interface configuration mode.

Troubleshooting CDP

Getting Information about Remote Devices

• Establish a Telnet connection

• Verify a Telnet connection

• Disconnect from a Telnet session

• Suspend a Telnet session

• Perform alternative connectivity tests

• Troubleshoot remote terminal connections

Telnet

• Telnet is a virtual terminal protocol that is part of the TCP/IP protocol suite.

• It allows connections to be made to remote hosts.

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.

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

• You must have the vty password set on the remote routers.

• We will always use vtypass as our vty passwords!

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




Password:cisco

RouterB>ena

% No password set

RouterB>exit




Password:vtypass

RouterB>ena

Password:cisco

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 ciscoConfigure vty 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 taking place.

RouterA>connect

Host: 10.1.1.1



Password:vtypass

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.

• The connection ID is shown by using the show sessions command.

Multiple Telnet sessions

Connection ID

Alternative connectivity tests

• As an aid to diagnosing basic network connectivity, many network protocols support an echo protocol.

• The ping target 172.16.1.5 in Figure responded successfully to all five datagrams sent.

• The exclamation points (!) indicate each successful echo. • If one or more periods (.) are received instead of

exclamations on the display, the application on the router (or source device) timed out waiting for a given packet echo from the ping target.



• 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

• ping uses the ICMP protocol to verify the hardware connection and the IP address of the network layer. This is a basic testing mechanism.

• telnet verifies the application layer software between source and destination. This is the most complete test mechanism available.

• traceroute allows the location of failures in the path from the source to the destination. Trace uses Time to Live values to generate messages from each router along the path.

Summary

Documents

Cdp & Telnet