Transcript Learning About Other Devices (CDP and Telnet)

Ch.4 – Learning About Other
Devices (CDP and Telnet)
CCNA 1 version 3.0
Rick Graziani
Cabrillo College
Note to instructors
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classes, please go to my web site:
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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
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Thanks! Rick
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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
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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.
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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
This router’s interface
Remote 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
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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
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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
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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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Establishing and verifying a Telnet
connection
RouterA#conf t
Enter configuration commands, one per line. End with CNTL/Z.
RouterA(config)#ip host RouterA 10.1.1.1
Does not have to be
RouterA(config)#exit
the router-name
but it is generally a good idea.
RouterA#telnet routera
Trying RouterA (10.1.1.1)... Open
Not case sensitive.
User Access Verification
Password:
RouterB>
• This is where the ip host commands can be helpful.
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Telnet password – line vty
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>
RouterB(config)#line vty 0 4
Configure vty password
RouterB(config-line)#login
RouterB(config-line)#password cisco
on RouterB
RouterA>telnet 10.1.1.1
Trying 10.1.1.1 ... Open
User Access Verification
Password:cisco
RouterB>
RouterB>exit
Telnet works! Enter vty password
Exit closes (ends) telnet session
[Connection to 10.1.1.1 closed by foreign host]
RouterA>
• You must have the vty password set on the remote routers.
• We will always use cisco as our vty passwords!
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Telnet and the privilege password
RouterA>telnet 10.1.1.1
Trying 10.1.1.1 ... Open
User Access Verification
Password:cisco
RouterB>ena
% No password set
RouterB>exit
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.
Configure vty password
on RouterB
RouterB(config)#enable secret class
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>
• 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
RouterA>connect
Or the
Host: 10.1.1.1
Trying 10.1.1.1 ... Open
“telnet” command
User Access Verification
Password:cisco
RouterB>
RouterB> <control-shift-6, x>
RouterA>show sessions
Conn Host
* 1 10.1.1.1
Address
10.1.1.1
Byte
0
Idle Conn Name
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!
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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
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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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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
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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
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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
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