Reverse SSH Enhancements

Cisco IOS software has for quite some time included a feature called Reverse telnet, whereby you can telnet to a certain port range and connect to terminal or auxiliary lines. Reverse telnet has often been used to connect a Cisco IOS router that has many terminal lines to the consoles of other Cisco IOS routers or to other devices. Telnet makes it easy to reach the router console from anywhere simply by telnet to the terminal server on a specific line. This telnet approach can be used to configure a router even if all network connectivity to that router is disconnected. Reverse telnet also allows modems that are attached to Cisco IOS routers to be used for dial-out (usually with a rotary device).

Reverse telnet can be accomplished using SSH. Unlike reverse telnet, SSH provides for secure connections. The Reverse SSH Enhancements feature provides you with a simplified method of configuring SSH. Using this feature, you no longer have to configure a separate line for every terminal or auxiliary line on which you want to enable SSH. The previous method of configuring reverse SSH limited the number of ports that can be accessed to 100. The Reverse SSH Enhancements feature removes the port number limitation. For information on the alternative method of configuring reverse SSH, see How to Configure Reverse SSH Enhancements.”

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    line line-number ending-line-number

4.    no exec

5.    login authentication listname

6.    transport input ssh

7.    exit

8.    exit

9.    ssh -l userid : {number} {ip-address}

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	line line-number ending-line-number Example: Router# line 1 3	Identifies a line for configuration and enters line configuration mode.
Step 4	no exec Example: Router (config-line)# no exec	Disables EXEC processing on a line.
Step 5	login authentication listname Example: Router (config-line)# login authentication default	Defines a login authentication mechanism for the lines. Note    The authentication method must use a username and password.
Step 6	transport input ssh Example: Router (config-line)# transport input ssh	Defines which protocols to use to connect to a specific line of the router. The ssh keyword must be used for the Reverse SSH Enhancements feature.
Step 7	exit Example: Router (config-line)# exit	Exits line configuration mode.
Step 8	exit Example: Router (config)# exit	Exits global configuration mode.
Step 9	ssh -l userid : {number} {ip-address} Example: Router# ssh -l lab:1 router.example.com	Specifies the user ID to use when logging in on the remote networking device that is running the SSH server. userid --User ID. : --Signifies that a port number and terminal IP address will follow the userid argument. number --Terminal or auxiliary line number. ip-address --Terminal server IP address. Note    The userid argument and :rotary{number}{ip-address} delimiter and arguments are mandatory when configuring the alternative method of Reverse SSH for modem access.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    line line-number ending-line-number

4.    no exec

5.    login authentication listname

6.    rotary group

7.    transport input ssh

8.    exit

9.    exit

10.    ssh -l userid :rotary {number} {ip-address}

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	line line-number ending-line-number Example: Router# line 1 200	Identifies a line for configuration and enters line configuration mode.
Step 4	no exec Example: Router (config-line)# no exec	Disables EXEC processing on a line.
Step 5	login authentication listname Example: Router (config-line)# login authentication default	Defines a login authentication mechanism for the lines. Note    The authentication method must use a username and password.
Step 6	rotary group Example: Router (config-line)# rotary 1	Defines a group of lines consisting of one or more virtual terminal lines or one auxiliary port line.
Step 7	transport input ssh Example: Router (config-line)# transport input ssh	Defines which protocols to use to connect to a specific line of the router. The ssh keyword must be used for the Reverse SSH Enhancements feature.
Step 8	exit Example: Router (config-line)# exit	Exits line configuration mode.
Step 9	exit Example: Router (config)# exit	Exits global configuration mode.
Step 10	ssh -l userid :rotary {number} {ip-address} Example: Router# ssh -l lab:rotary1 router.example.com	Specifies the user ID to use when logging in on the remote networking device that is running the SSH server. userid --User ID. : --Signifies that a port number and terminal IP address will follow the userid argument. number --Terminal or auxiliary line number. ip-address --Terminal server IP address. Note    The userid argument and :rotary{number}{ip-address} delimiter and arguments are mandatory when configuring the alternative method of Reverse SSH for modem access.

SUMMARY STEPS

1.    enable

2.    debug ip ssh client

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	debug ip ssh client Example: Router# debug ip ssh client	Displays debugging messages for the SSH client.

SUMMARY STEPS

1.    enable

2.    debug ip ssh

3.    show ssh

4.    show line

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	debug ip ssh Example: Router# debug ip ssh	Displays debugging messages for the SSH server.
Step 3	show ssh Example: Router# show ssh	Displays the status of the SSH server connections.
Step 4	show line Example: Router# show line	Displays parameters of a terminal line.