Cisco Discovery Protocol CDP
This chapter provides information and commands concerning the following topic: • Cisco Discovery Protocol (CDP)
Cisco Discovery Protocol
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Router#show cdp |
Displays global CDP information (such as timers) |
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Router#show cdp neighbors |
Displays information about neighbors |
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Router#show cdp neighbors detail |
Displays more detail about the neighbor device |
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Router#show cdp entry word |
Displays information about the device named word |
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Router#show cdp entry * |
Displays information about all devices |
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Router#show cdp interface |
Displays information about interfaces that have CDP running |
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Router#show cdp interface x |
Displays information about specific interface x running CDP |
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Router#show cdp traffic |
Displays traffic information—packets in/out/version |
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Router(config)#cdp holdtime x |
Changes the length of time to keep CDP packets |
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Router(config)#cdp timer x |
Changes how often CDP updates are sent |
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Router(config)#cdp run |
Enables CDP globally (on by default) |
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Router(config)#no cdp run |
Turns off CDP globally |
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Router(config-if)#cdp enable |
Enables CDP on a specific interface |
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Router(config-if)#no cdp enable |
Turns off CDP on a specific interface |
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Router#clear cdp counters |
Resets traffic counters to 0 |
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Router#clear cdp table |
Deletes the CDP table |
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Router#debug cdp adjacency |
Monitors CDP neighbor information |
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Router#debug cdp events |
Monitors all CDP events |
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Router#debug cdp ip |
Monitors CDP events specifically for IP |
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Router#debug cdp packets |
Monitors CDP packet-related information |
CAUTION: Although CDP is necessary for some management applications, CDP should still be disabled in some instances.
Disable CDP globally if
• The device is located in an insecure environment. Use the command no cdp run to disable CDP globally:
RouterOrSwitch(config)#no cdp run Disable CDP on any interface if
• Management is not being performed.
• The switch interface is a nontrunk interface.
• The interface is connected to a nontrusted network.
Use the interface configuration command no cdp enable to disable CDP on a specific interface:
RouterOrSwitch(config)#interface fastethernet 0/1
RouterOrSwitch(config-if)#no cdp enable
This chapter provides information and commands concerning the following topics:
• Using Telnet to remotely connect to other devices
• Configuring the Secure Shell Protocol (SSH)
Using Telnet to Remotely Connect to Other Devices
The following five commands all achieve the same result: the attempt to connect remotely to the router named Paris at IP address 172.16.20.1.
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Denver>telnet paris |
Enter if ip host command was used previously to create a mapping of an IP address to the word paris. |
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Denver>telnet 172.16.20.1 |
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Denver>paris |
Enter if ip host command is using default port #. |
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Denver>connect paris |
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Denver>172.16.20.1 |
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Any of the preceding commands lead to the following configuration sequence: |
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Paris> |
As long as vty password is set. See the Caution following this table. |
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Paris>exit |
Terminates the Telnet session and returns you to the Denver prompt. |
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Denver> |
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Paris>logout |
Terminates the Telnet session and returns you to the Denver prompt. |
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Denver> |
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Paris> M-kShift)-6. release, then press ® |
Suspends the Telnet session but does not terminate it, and returns you to the Denver prompt. |
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Denver> |
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Denver>(^Enter) |
Resumes the connection to Paris. |
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Paris> |
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Denver>resume |
Resumes the connection to Paris. |
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Paris> |
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Denver>disconnect paris |
Terminates the session to Paris. |
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Denver> |
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Denver#show sessions |
Displays connections you opened to other sites. |
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Denver#show users |
Displays who is connected remotely to you. |
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Denver#clear line x |
Disconnects the remote user connected to you on line x. The line number is listed in the output gained from the show users command. |
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Denver(config)#line vty 0 4 |
Moves to line configuration mode for vty lines 0-4. |
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Denver(config-line) session-limit x |
Limits the number of simultaneous sessions per vty line to x number. |
CAUTION: The following configuration creates a big security hole. Never use it in a live production environment. Use it in the lab only!
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Denver(config)#line vty 0 4 |
Moves you to line configuration mode for vty lines 0-4. |
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Denver(config-line)#no password |
The remote user is not challenged when Telnetting to this device. |
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Denver(config-line)#no login |
The remote user moves straight to user mode. |
NOTE: A device must have two passwords for a remote user to be able to make changes to your configuration:
• Line vty password (or have it explicitly turned off; see the preceding Caution)
• Enable or enable secret password
Without the enable or enable secret password, a remote user will only be able to get to user mode, not to privileged mode. This is extra security.
Configuring the Secure Shell Protocol (SSH)
CAUTION: SSH Version 1 implementations have known security issues. It is recommended to use SSH Version 2 whenever possible.
NOTE: To work, SSH requires a local username database, a local IP domain, and an RSA key to be generated.
The Cisco implementation of SSH requires Cisco IOS Software to support Rivest-Shamir-Adleman (RSA) authentication and minimum Data Encryption Standard (DES) encryption—a cryptographic software image.
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Router(config)#username Roland password tower |
Creates a locally significant username/ password combination. These are the credentials needed to be entered when connecting to the router with SSH client software. |
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Router(config)#ip domain-name test.lab |
Creates a host domain for the router. |
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Router(config)#crypto key generate rsa |
Enables the SSH server for local and remote authentication on the router and generates an RSA key pair. |
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Continue reading here: The ping and traceroute Commands
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