Reverse Telnet

Reverse telnet allows you to configure a device to listen on a specific port for telnet and SSH services. When you connect to that port, the device provides an interface to the auxiliary port on the device. You use a rollover cable to connect the auxiliary port from the device on which reverse Telnet is enabled to the console port of the device you want to manage.

Note: Reverse telnet is supported only on J Series devices.

• Reverse Telnet Overview
• Configuring Reverse Telnet and Reverse SSH

Reverse Telnet Overview

In order to use reverse telnet, you must have the following devices:

• A device with an auxiliary port running the appropriate version of Junos OS
• A device with a console port for remote management if network connectivity fails and you want to use console access

Reverse Telnet Options

When you enable reverse telnet, you can control the port that is used, and you can optionally turn on reverse SSH to encrypt the reverse telnet communication between the device and the client. By default, reverse telnet uses port 2900 and reverse SSH uses port 2901.

Note: Enable reverse SSH, requires an additional command. By default, when you enable reverse telnet, the connection is not encrypted.

Reverse Telnet Restrictions

Keep the following restrictions in mind when you attempt to use reverse telnet or reverse SSH:

• Multiple connections to the serial port are not allowed. If there is an existing connection to the serial port, any other connections are denied.
• If the auxiliary port is enabled (through the system services port auxiliary configuration statement), you cannot use reverse telnet or reverse SSH because another service is already using the auxiliary port.

Configuring Reverse Telnet and Reverse SSH

This topic contains the following section:

• CLI Configuration

CLI Configuration

1. To enable reverse telnet:
   user@host# set system services reverse telnet
2. You can specify the port to be used for reverse telnet. If you do not specify a port, 2900 (the default) is used.
   user@host# set system services reverse telnet port 5000
3. You can enable reverse SSH to encrypt the connection between the device and the client.
   user@host# set system services reverse ssh
4. You can specify the port for reverse SSH. If you do not specify a port, 2901 is the default port that is used.
   user@host# set system services reverse ssh port 6000