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Using Telnet

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Using Telnet

elnet is a virtual terminal protocol that is part of the TCP/IP protocol

suite. Telnet allows you to make connections to remote devices, gather infor-
mation, and run programs.

After your routers and switches are configured, you can use the Telnet

program to configure and check your routers and switches so that you don't
need to use a console cable. You run the Telnet program by typing telnet
from any command prompt (DOS or Cisco). VTY passwords must be set on
the routers for this to work.

You cannot use CDP to gather information about routers and switches that

are not directly connected to your device. However, you can use the Telnet
application to connect to your neighbor devices and then run CDP on those
remote devices to gather CDP information about remote devices.

You can issue the telnet command from any router prompt, as in the fol-

lowing example:

Todd2509#telnet 172.16.10.2

Trying 172.16.10.2 ... Open

Password required, but none set

[Connection to 172.16.10.2 closed by foreign host]

Todd2509#

If you have all Cisco routers and switches, then CDP can be really helpful.

Telnet or console into a router or switch and type show cdp neighbor. You

will see directly connected neighbors. Write these down. Then type show

cdp

neighbors detail and write down the IP addresses for each of these

devices.

Now go to each of these devices and do that same thing. Just keep writing

down what you find until you have drawn out the entire network.

If you don't know the passwords of these devices, this will be a show-

stopper unless you can find out the access passwords or perform pass-

word recovery.

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