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Ch.4 – Learning About Other Devices (CDP and Telnet)
CCNA 1 version 3.0
Rick Graziani
Cabrillo College
Rick Graziani [email protected] 2
Note to instructors
• If you have downloaded this presentation from the Cisco Networking Academy Community FTP Center, this may not be my latest version of this PowerPoint.
• For the latest PowerPoints for all my CCNA, CCNP, and Wireless classes, please go to my web site:
http://www.cabrillo.cc.ca.us/~rgraziani/• The username is cisco and the password is perlman for all of
my materials.
• If you have any questions on any of my materials or the curriculum, please feel free to email me at [email protected] (I really don’t mind helping.) Also, if you run across any typos or errors in my presentations, please let me know.
• I will add “(Updated – date)” next to each presentation on my web site that has been updated since these have been uploaded to the FTP center.
Thanks! Rick
Rick Graziani [email protected] 3
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
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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).
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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 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.
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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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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
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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.
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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.
Rick Graziani [email protected] 16
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
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• You must have the vty password set on the remote routers.
• We will always use cisco 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>
RouterA>telnet 10.1.1.1
Trying 10.1.1.1 ... Open
User Access Verification
Password:cisco
RouterB>
RouterB>exit
[Connection to 10.1.1.1 closed by foreign host]
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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RouterA>telnet 10.1.1.1
Trying 10.1.1.1 ... Open
User Access Verification
Password:cisco
RouterB>ena
% No password set
RouterB>exit
RouterA>telnet 10.1.1.1
Trying 10.1.1.1 ... Open
User Access Verification
Password:cisco
RouterB>ena
Password:class
RouterB#exit
[Connection to 10.1.1.1 closed by foreign host]
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 classConfigure vty password
on RouterB
Telnet and the privilege password
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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.
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RouterA>connect
Host: 10.1.1.1
Trying 10.1.1.1 ... Open
User Access Verification
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
[Connection to 10.1.1.1 closed by foreign host]
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
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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.
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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.
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Alternative connectivity tests
• More on ping (ICMP Echo) in a special presentation.
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Alternative connectivity tests
• 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.
Rick Graziani [email protected] 25
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.