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The Reverse SSH Enhancements feature provides an alternative method of configuring reverse Secure Shell (SSH). Using this feature, you can configure reverse SSH without having to list separate lines for every terminal or auxiliary line on which SSH has to be enabled. This feature also eliminates the rotary-group limitation. This feature is supported for SSH Version 1 and SSH Version 2.
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Reverse SSH Enhancements" section.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
•Prerequisites for Reverse SSH Enhancements
•Restrictions for Reverse SSH Enhancements
•Information About Reverse SSH Enhancements
•How to Configure Reverse SSH Enhancements
•Configuration Examples for Reverse SSH Enhancements
•Feature Information for Reverse SSH Enhancements
•SSH must be enabled.
•The SSH client and server must be running the same version of SSH.
•The -l keyword and userid :{number} {ip-address} delimiter and arguments are mandatory when configuring the alternative method of Reverse SSH for console access.
Cisco IOS XE 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 telnetting has often been used to connect a router that has many terminal lines to the consoles of other routers or to other devices. Telnetting makes it easy to reach the router console from anywhere simply by telnetting to the terminal server on a specific line. This telnetting approach can be used to configure a router even if all network connectivity to that router is disconnected. Reverse telnetting also allows modems that are attached to routers to be used for dial-out (usually with a rotary device).
Reverse telnetting can be accomplished using SSH. Unlike reverse telnetting, 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 the section "How to Configure Reverse SSH Enhancements."
•Configuring Reverse SSH for Console Access
•Configuring Reverse SSH for Modem Access
•Troubleshooting Reverse SSH on the Client
•Troubleshooting Reverse SSH on the Server
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}
Reverse SSH is configured on a modem used for dial-out lines. To get any of the dial-out modems, you can use any SSH client and start a SSH session as shown (in Step 10) to get to the next available modem from the rotary device.
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}
To troubleshoot the reverse SSH configuration on the client (remote device), perform the following steps.
1. enable
2. debug ip ssh client
To troubleshoot the reverse SSH configuration on the terminal server, perform the following steps. The steps may be configured in any order or independent of one another.
1. enable
2. debug ip ssh
3. show ssh
4. show line
•Example: Reverse SSH Console Access
•Example: Reverse SSH Modem Access
The following configuration example shows that reverse SSH has been configured for console access for terminal lines 1 through 3:
Terminal Server Configuration
line 1 3
no exec
login authentication default
transport input ssh
Client Configuration
The following commands configured on the SSH client will form the reverse SSH session with lines 1, 2, and 3, respectively:
ssh -l lab:1 router.example.com
ssh -l lab:2 router.example.com
ssh -l lab:3 router.example.com
The following configuration example shows that dial-out lines 1 through 200 have been grouped under rotary group 1 for modem access:
line 1 200
no exec
login authentication default
rotary 1
transport input ssh
exit
The following command shows that reverse SSH will connect to the first free line in the rotary group:
ssh -l lab:rotary1 router.example.com
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Cisco IOS commands |
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Security commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples |
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Configuring Secure Shell |
Configuring Secure Shell and Secure Shell Version 2 Support feature modules. |
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To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL: |
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Table 1 lists the release history for this feature.
Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.
Note Table 1 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.