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Overview
Reverse Telnet is a mean of connecting to a TTY line via a regular telnet connection. That way, you may seem as you are connected to an RS-232 serial terminal line through the telnet daemon. In other words, it is the initiation of a telnet session from a DTE to one of its remote users.
It is typically used to connect to modems or other external asynchronous devices. However, today, reverse telnet is used mostly for terminal service purposes. That is having a server dedicated for connecting directly to a console port of a router, switch or other device.
Example
A typical client connection would look like this: #telnet 172.16.1.254 2002, where 172.16.1.254 is the IP address of the interface of the local device, and 2002 is the TTY line, not the TCP port.
A typical server connfiguration (on a Cisco Router) would look like this:
version 12.3
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname Terminal_Server
!
ip host Router1 2101 8.8.8.8
ip host Router2 2102 8.8.8.8
ip host Router3 2113 8.8.8.8
!
interface Loopback0
description Used for Terminal Service
ip address 8.8.8.8 255.255.255.255
!
line con 0
exec-timeout 0 0
password MyPassword
login
line 97 128
transport input telnet
line vty 0 4
exec-timeout 0 0
password MyPassword
login
transport input none
!
end
Reverse telnet should not be confused with the telnet application.
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