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

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

• CCNA 1 version 3.0
• Rick Graziani
• Cabrillo College

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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 routers interface
This routers 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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Implementation, monitoring, and maintenance of CDP
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Implementation, monitoring, and maintenance of CDP
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Implementation, monitoring, and maintenance of CDP
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Implementation, monitoring, and maintenance of CDP
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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
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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
• Denvergtconnect paris
• Denvergtparis
• Denvergt131.108.100.152
• Denvergttelnet 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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Establishing and verifying a Telnet connection
RouterAconf t Enter configuration commands, one
per line. End with CNTL/Z. RouterA(config)ip
host RouterA 10.1.1.1 RouterA(config)exit Router
Atelnet routera Trying RouterA (10.1.1.1)...
Open User Access Verification Password RouterB
gt
Does not have to be the router-name but it is
generally a good idea.
Not case sensitive.

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

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Telnet password line vty
RouterAgttelnet 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 RouterAgt RouterAgttelnet 10.1.1.1 Trying
10.1.1.1 ... Open User Access Verification Passw
ordcisco RouterBgt RouterBgtexit Connection to
10.1.1.1 closed by foreign host RouterAgt
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

• You must have the vty password set on the remote
  routers.
• We will always use vtypass as our vty passwords!

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Telnet and the privilege password
RouterAgttelnet 10.1.1.1 Trying 10.1.1.1 ...
Open User Access Verification Passwordcisco Rou
terBgtena No password set RouterBgtexit Router
Agttelnet 10.1.1.1 Trying 10.1.1.1 ... Open User
Access Verification Passwordvtypass RouterBgtena
Passwordcisco RouterBexit Connection to
10.1.1.1 closed by foreign host RouterAgt
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.
RouterB(config)enable secret cisco
Configure vty password on RouterB

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

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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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Disconnecting and suspending Telnet sessions
RouterAgtconnect Host 10.1.1.1 Trying 10.1.1.1
... Open User Access Verification Passwordvtypa
ss RouterBgt RouterBgt ltcontrol-shift-6,
xgt RouterAgtshow sessions Conn Host
Address Byte Idle Conn Name 1
10.1.1.1 10.1.1.1 0
0 10.1.1.1 RouterAgt ltentergt Resuming connection
1 to 10.1.1.1 ... RouterBgtexit Connection to
10.1.1.1 closed by foreign host RouterAgtshow
sessions No connections open RouterAgt
Or the telnet command

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

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Advanced Telnet operation
Multiple Telnet sessions
Connection ID

• 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
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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.

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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.

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Summary