Abstract of CCNA study guide-19 -Documenting a Network Topology Using CDP

Documenting a Network Topology Using CDP

You can determine the router types, interface types, and IP addresses of various interfaces using only CDP commands and the show running-config command.

Using Telnet

Telnet, part of the TCP/IP protocol suite, is a virtual terminal protocol that allows you to make connections to remote devices, gather information, and run programs.

You run the Telnet program by typing telnet from any command prompt (DOS or Cisco). You need

to have VTY passwords set on the routers for this to work. Remember, you can’t use CDP to gather information about routers and switches that aren’t directly connected to your device. But you can use the Telnet application to connect to your neighbor devices and then run CDP on those remote devices to get information on them.

You can issue the telnet command from any router prompt like this:

Corp#telnet 10.2.2.2

Trying 10.2.2.2 ... Open

Password required, but none set

[Connection to 10.2.2.2 closed by foreign host]

Corp#

On a Cisco router, you don’t need to use the telnet command; you can just type in an IP address from a command prompt Here’s how that looks using just the IP address:

Corp#10.2.2.2

Trying 10.2.2.2 ... Open

Password required, but none set

[Connection to 10.2.2.2 closed by foreign host]

Corp#

Now set  VTY passwords on the router I want to telnet into (chapter4).

Now let’s try this again:

 Corp#10.2.2.2

Trying 10.2.2.2 ... Open

User Access Verification

Password:

R1>

Remember that the VTY password is the user-mode password, not the enable-mode password. Watch what happens when I try to go into privileged mode after telnetting into router R1:

R1>en

% No password set

R1>

It is basically saying, “No way!” This is a really good security feature because you don’t want anyone telnetting into your device and being able to just type the enable command to get into privileged mode. You’ve got to set your enable-mode password or enable secret password to use Telnet to configure remote devices!

Telnetting into Multiple Devices Simultaneously

If you telnet to a router or switch, you can end the connection by typing exit at any time. But what if you want to keep your connection to a remote device but still come back to your original router console? To do that, you can press the Ctrl+Shift+6 key combination, release it, and then press X.

Here’s an example of connecting to multiple devices from my Corp router console:

Corp#10.2.2.2

Trying 10.2.2.2 ... Open

User Access Verification

Password:

R1>Ctrl+Shift+6

Corp#

In this example, I telnetted to the R1 router and then typed the password to enter user mode.I next pressed Ctrl+Shift+6, then X (but you can’t see that because it doesn’t show on the screen output). Notice that my command prompt is now back at the Corp router.

Checking Telnet Connections

To see the connections made from your router to a remote device, use the show sessions command:

Corp#sh sessions

Conn    Host                 Address           Byte                 Idle      Conn Name

   1       10.2.2.2           10.2.2.2           0                      0          10.2.2.2

* 2       10.1.1.2           10.1.1.2           0                      0          10.1.1.2

Corp#

See that asterisk (*) next to connection 2? It means that session 2 was your last session. You can return to your last session by pressing Enter twice. You can also return to any session by typing the number of the connection and pressing Enter.

Checking Telnet Users

You can list all active consoles and VTY ports in use on your router with the show users command:

Corp#sh users

Line                 User                 Host(s)                         Idle                  Location

*          0 con 0                                                10.1.1.2           00:00:01

10.2.2.2           00:01:06

In the command’s output, con represents the local console. In this example, the console is connected

to two remote IP addresses, or in other words, two devices.

Closing Telnet Sessions

You can end Telnet sessions by typing exit or disconnect.

To end a session from a remote device, use the exit command:

ap>exit

[Connection to 10.1.1.2 closed by foreign host]

Corp#

To end a session from a local device, use the disconnect command:

Corp#sh session

Conn    Host                 Address           Byte                 Idle      Conn Name

  2        10.2.2.2           10.2.2.2           0                      0          10.2.2.2

Corp#disconnect 2

Closing connection to 10.2.2.2 [confirm][enter]

Corp#

In this example, I used the session number 2 because that was the connection to the R1 router that I wanted to end. As I showed, you can use the show sessions command to see the connection number.

Notice the show users command :

R1#sh users

Line                 User                 Host(s)                         Idle                  Location

*          0 con 0                                                idle                 00:00:00

vty 194                                                idle                 00:00:21          10.2.2.1

This output shows that VTY has IP address 10.2.2.1 connected. That’s the Corp router. Also notice that the Corp router connected to line 194—remember, you cannot choose which line you connect to! This is why we set the same password on all lines. To clear the connection, use the clear line # command:

R1#clear line 194

[confirm][enter]

[OK]

R1#sh users

Line                 User                 Host(s)                         Idle                  Location

*          0 con 0                                                idle                 00:00:00

This output confirms that the line has been cleared.