Telnet

Telnet (Teletype Network) is a protocol used to remotely access the CLI of a remote host.

Telnet was developed in 1969.

Telnet has been largely replaced by SSH, which is more secure.

Telnet sends data in plain text. No encryption!

The Telnet server (the device being connected to) listens for Telnet traffic on TCP port 23.

Configuration

1. enable secret ccna -> If an enable password/secret isn't configured, you won't be able to access privileged exec mode when connecting via Telnet.

2. username jeremy secret ccna

3. access-list 1 permit host 192.168.2.1 -> Configure an ACL to limit which devices can connect to the VTY lines.

4. line vty 0 15 -> Telnet/SSH access is configured on the VTY lines. There are 16 lines available, so up to 16 users can be connected at once. (VTY stands for Virtual TeleType).

5. login local

6. exec-timeout 5 0

7. transport input ...

   1. ... telnet -> allows only Telnet connections.

   2. ... ssh -> allows only SSH connections.

   3. ... telnet ssh -> allows both.

   4. ... all -> allows all connections.

   5. ... none -> allows no connections.

8. access-class 1 in -> Apply the ACL to the VTY lines.

   1. *access-class applies an ACL to the VTY lines.

   2. ip access-group -> applies an ACL to an interface.