CCNA 29

Good management of telnet sessions are vital in labs. You can actually use Cisco devices to telnet to another device. Before telnetting, it's good practice to ping the target first because telnet will stall for a long time if the target device is not responding.
In Cisco devices, you can suspend telnet sessions using: CTRL+Shift+6 then X. To kill a session, type "exit". To see a list of suspended sessions, use:
show sessions

You should see an output like:

Conn Host        Address     Byte Idle Conn Name
*  1 192.168.1.1 192.168.2.2 0    0    192.168.1.1

From here, you can resume a connection simply by typing:
resume 1

You can also resume a connection simply by typing the connection number:
1

Hitting enter without typing anything will resume the most recently accessed session (denoted by a * in "show sessions"). You can open multiple sessions.

To see the users connected to your router, use:
show users

The "show users" command is also affected by reverse domain-lookup. To disable it, type:
no ip domain-lo

To kills one of your open sessions:
disconnect SESSION

To boot a user connected to your router, use:
clear line LINENUMBER

CDP stands for the Cisco Discovery Protocol. CDP allows to see directly connected Cisco Devices. CDP is proprietary and is useful for building accurate network diagrams. CDP is usable by 3Com and HP devices, but treat it as a Cisco-only protocol in the examination.

CDP is allowed in User Mode. To see your neighbors, use:
show cdp nei

To see the IP address of your neighbors, use:
show cdp entry *
show cdp nei detail

These commands lets you detail your ports as well as the ports of the neighbors you're connected to. To continue with the diagram, you'll have to telnet to your neighbors.

CDP tosses out a lot of sensitive information. You would typically want to disable CDP on public interfaces like the internet. To disable CDP on an interface, use:
no cdp enable

To disable CDP on the entire device, use:
no cdp run