Cisco Networking: Using Telnet

If you need to remotely manage your Cisco switch, you will be able to choose between Telnet and Secure Shell (SSH). There are dangers to using Telnet, it sends data over the network in plain text, which makes Telnet less secure when compared to SSH. Some people will make a justification for Telnet, and if they are running it only within a secured management network, then some of the risks are indeed mitigated.

In spite of risks, you should know how Telnet works and how to administer it, and how to do the setup. Telnet accesses the switch through the Virtual Terminal ports or vty ports. To see whether you are set up with vty ports on your switch, use the following command:

Switch1>enable
Password:
Switch1#show running-config | include line vty
line vty 0 4

The fourth line in the preceding code indicates that there are five vty ports on the switch, numbered from 0 to 4. This means that up to five concurrent Telnet connections can be hosted simultaneously on the switch. The chance of having five network administrators making connections to this switch at the same time is somewhat low.

If you want to know how many connections your switch will support, use the following command to find out.

Switch1>enable
Password:
Switch1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch1(config)#line vty 0 ?
  <1-181>  Last Line number
  <cr>

The preceding output tells you that the switch will support up to 182 total vty ports, but I can configure it to as low as 1 port by inserting a carriage return (pressing Enter).

To set the password for Telnet or vty port, use the following commands.

Switch1>enable
Password:
Switch1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Switch1(config)#line vty 0 4
Switch1(config-line)#password vtypass
Switch1(config-line)#exit
Switch1(config)#exit

Note the appearance of the Line Configuration mode prompt (config-line). This is the first time you have seen this in this book. Line Configuration mode configures different command line interfaces, such as the console and virtual terminal ports (vty).

To have access to the switch for Telnet, you need to specify both an enable password and the Telnet password in your configuration.

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