Table Of Contents

Reverse SSH Enhancements

Finding Feature Information

Contents

Prerequisites for Reverse SSH Enhancements

Restrictions for Reverse SSH Enhancements

Information About Reverse SSH Enhancements

Reverse Telnet

Reverse SSH

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

Configuration Examples for Reverse SSH Enhancements

Reverse SSH Console Access: Example

Reverse SSH Modem Access: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Reverse SSH Enhancements

Reverse SSH Enhancements

---

First Published: September 18, 2004

Last Updated: October 7, 2009

The Reverse SSH Enhancements feature, which is supported for SSH Version 1 and 2, provides an alternative way to configure reverse Secure Shell (SSH) so that separate lines do not need to be configured for every terminal or auxiliary line on which SSH must be enabled. This feature also eliminates the rotary-group limitation.

Finding Feature Information

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 IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp. An account on Cisco.com is not required.

Contents

•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

•Additional References

•Feature Information for Reverse SSH Enhancements

Prerequisites for Reverse SSH Enhancements

•SSH must be enabled.

•The SSH client and server must be running the same version of SSH.

Restrictions for Reverse SSH Enhancements

•The -l keyword and userid :{number} {ip-address} delimiter and arguments are mandatory when configuring the alternative method of Reverse SSH for console access.

Information About Reverse SSH Enhancements

To configure Reverse SSH Enhancements, you should understand the following concepts:

•Reverse Telnet

•Reverse SSH

Reverse Telnet

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 SSH

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" section."

How to Configure Reverse SSH Enhancements

This section contains the following procedures:

•Configuring Reverse SSH for Console Access

•Configuring Reverse SSH for Modem Access

•Troubleshooting Reverse SSH on the Client

•Troubleshooting Reverse SSH on the Server

Configuring Reverse SSH for Console Access

To configure reverse SSH console access on the SSH server, perform the following steps.

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.

Configuring Reverse SSH for Modem Access

To configure Reverse SSH for modem access, perform the steps shown in the "SUMMARY STEPS" section below.

In this configuration, reverse SSH is being 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.

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.

Troubleshooting Reverse SSH on the Client

To troubleshoot the reverse SSH configuration on the client (remote device), perform the following steps.

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.

Troubleshooting Reverse SSH on the Server

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.

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.

Configuration Examples for Reverse SSH Enhancements

This section includes the following configuration examples:

•Reverse SSH Console Access: Example

•Reverse SSH Modem Access: Example

Reverse SSH Console Access: Example

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

Reverse SSH Modem Access: Example

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

Additional References

The following sections provide references related to Reverse SSH Enhancements.

Related Documents

Related Topic	Document Title
Configuring Secure Shell	See the following modules: •"Configuring Secure Shell" •"Secure Shell Version 2 Support" •"SSH Terminal-Line Access"
Security commands	Cisco IOS Security Command Reference

Standards

Standards	Title
No new or modified standards are supported by this feature.	—

MIBs

MIBs	MIBs Link
None.	To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs

RFCs

RFCs	Title
None.	—

Technical Assistance

Description

Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport

Feature Information for Reverse SSH Enhancements

Table 1 lists the release history for this feature.

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp. An account on Cisco.com is not required.

---

Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

---

Table 1 Feature Information for Reverse SSH Enhancements

Feature Name	Releases	Feature Information
Reverse SSH Enhancements	12.3(11)T Cisco IOS XE Release 2.1	The Reverse SSH Enhancements feature, which is supported for SSH Version 1 and 2, provides an alternative way to configure reverse Secure Shell (SSH) so that separate lines do not need to be configured for every terminal or auxiliary line on which SSH must be enabled. This feature also eliminates the rotary-group limitation. This feature was introduced in Cisco IOS Release 12.3(11)T. This feature was introduced on Cisco ASR 1000 Series Routers. The following command was introduced: ssh.

CCDE, CCENT, CCSI, Cisco Eos, Cisco HealthPresence, Cisco IronPort, the Cisco logo, Cisco Lumin, Cisco Nexus, Cisco Nurse Connect, Cisco Pulse, Cisco StackPower, Cisco StadiumVision, Cisco TelePresence, Cisco Unified Computing System, Cisco WebEx, DCE, Flip Channels, Flip for Good, Flip Mino, Flipshare (Design), Flip Ultra, Flip Video, Flip Video (Design), Instant Broadband, and Welcome to the Human Network are trademarks; Changing the Way We Work, Live, Play, and Learn, Cisco Capital, Cisco Capital (Design), Cisco:Financed (Stylized), Cisco Store, and Flip Gift Card are service marks; and Access Registrar, Aironet, AllTouch, AsyncOS, Bringing the Meeting To You, Catalyst, CCDA, CCDP, CCIE, CCIP, CCNA, CCNP, CCSP, CCVP, Cisco, the Cisco Certified Internetwork Expert logo, Cisco  IOS, Cisco Press, Cisco Systems, Cisco Systems Capital, the Cisco Systems logo, Cisco Unity, Collaboration Without Limitation, Continuum, EtherFast, EtherSwitch, Event Center, Explorer, Fast Step, Follow Me Browsing, FormShare, GainMaker, GigaDrive, HomeLink, iLYNX, Internet Quotient, IOS, iPhone, iQuick Study, IronPort, the IronPort logo, Laser Link, LightStream, Linksys, MediaTone, MeetingPlace, MeetingPlace Chime Sound, MGX, Networkers, Networking Academy, Network Registrar, PCNow, PIX, PowerKEY, PowerPanels, PowerTV, PowerTV (Design), PowerVu, Prisma, ProConnect, ROSA, ScriptShare, SenderBase, SMARTnet, Spectrum Expert, StackWise, The Fastest Way to Increase Your Internet Quotient, TransPath, WebEx, and the WebEx logo are registered trademarks of Cisco Systems, Inc. and/or its affiliates in the United States and certain other countries.

All other trademarks mentioned in this document or website are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (0908R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2004-2009 Cisco Systems, Inc. All rights reserved.