Contents
- Configuring Secure Shell
- Finding Feature Information
- Prerequisites for Configuring SSH
- Restrictions for Configuring SSH
- Information About Secure Shell (SSH)
- SSH Server
- SSH Integrated Client
- RSA Authentication Support
- How to Configure SSH
- Configuring an SSH Server
- Invoking an SSH Client
- Troubleshooting Tips
- Configuration Examples for SSH
- Example: Configuring an SSH Server
- Example: Invoking an SSH Client
- Example: Verifying SSH
- Additional References
- Feature Information for Configuring Secure Shell
Configuring Secure Shell
The Secure Shell (SSH) feature is an application and a protocol that provides a secure replacement to the Berkeley r-tools. The protocol secures sessions using standard cryptographic mechanisms, and the application can be used similarly to the Berkeley rexec and rsh tools. Two versions of SSH are available: SSH Version 1 and SSH Version 2. Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. For information about SSH Version 2, see the “ Secure Shell Version 2 Support” feature module.
- Finding Feature Information
- Prerequisites for Configuring SSH
- Restrictions for Configuring SSH
- Information About Secure Shell (SSH)
- How to Configure SSH
- Configuration Examples for SSH
- Additional References
- Feature Information for Configuring Secure Shell
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and 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 table at the end of this module.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Prerequisites for Configuring SSH
 Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
Download the required image on the device. The Secure Shell (SSH) server requires an IPsec (Data Encryption Standard [DES] or 3DES) encryption software image; the SSH client requires an IPsec (DES or 3DES) encryption software image.) For information about downloading a software image, see the Loading and Managing System Images Configuration Guide.
Configure a hostname and host domain for your device by using the hostname and ip domain-name commands in global configuration mode.
Generate a Rivest, Shamir, and Adleman (RSA) key pair for your device. This key pair automatically enables SSH and remote authentication when the crypto key generate rsa command is entered in global configuration mode.
Note | To delete the RSA key pair, use the crypto key zeroize rsa global configuration command. Once you delete the RSA key pair, you automatically disable the SSH server. |
Restrictions for Configuring SSH
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
The Secure Shell (SSH) server and SSH client are supported on Data Encryption Standard (DES) (56-bit) and 3DES (168-bit) data encryption software images only. In DES software images, DES is the only encryption algorithm available. In 3DES software images, both DES and 3DES encryption algorithms are available.
Execution shell is the only application supported.
The login banner is not supported in Secure Shell Version 1. It is supported in Secure Shell Version 2.
Information About Secure Shell (SSH)
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
SSH Server
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
The Secure Shell (SSH) Server feature enables an SSH client to make a secure, encrypted connection to a Cisco device. This connection provides functionality that is similar to that of an inbound Telnet connection. Before SSH, security was limited to Telnet security. SSH allows a strong encryption to be used with the Cisco software authentication. The SSH server in Cisco software works with publicly and commercially available SSH clients.
SSH Integrated Client
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
The Secure Shell (SSH) Integrated Client feature is an application that runs over the SSH protocol to provide device authentication and encryption. The SSH client enables a Cisco device to make a secure, encrypted connection to another Cisco device or to any other device running the SSH server. This connection provides functionality similar to that of an outbound Telnet connection except that the connection is encrypted. With authentication and encryption, the SSH client allows for secure communication over an unsecured network.
The SSH client in Cisco software works with publicly and commercially available SSH servers. The SSH client supports the ciphers of Data Encryption Standard (DES), 3DES, and password authentication. User authentication is performed like that in the Telnet session to the device. The user authentication mechanisms supported for SSH are RADIUS, TACACS+, and the use of locally stored usernames and passwords.
Note | The SSH client functionality is available only when the SSH server is enabled. |
RSA Authentication Support
Rivest, Shamir, and Adleman (RSA) authentication available in Secure Shell (SSH) clients is not supported on the SSH server for Cisco software by default. For more information about RSA authentication support, see the “Configuring a Router for SSH Version 2 Using RSA Pairs” section of the “Secure Shell Version 2 Support” module.
How to Configure SSH
Configuring an SSH Server
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
1.
enable
2.
configure
terminal
3.
ip
ssh
{timeout
seconds |
authentication-retries
integer}
4.
ip
ssh
rekey
{time
time |
volume
volume}
5.
exit
6.
show
ip
ssh
DETAILED STEPS
Invoking an SSH Client
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
Perform this task to invoke the Secure Shell (SSH) client. The SSH client runs in user EXEC mode and has no specific configuration tasks.
1.
enable
2.
ssh
-l
username
-vrf
vrf-name
ip-address
DETAILED STEPS
| Command or Action | Purpose |
|---|
Troubleshooting Tips
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
If your Secure Shell (SSH) configuration commands are rejected as illegal commands, you have not successfully generated an Rivest, Shamir, and Adleman (RSA) key pair for your device. Make sure that you have specified a hostname and domain. Then use the crypto key generate rsa command to generate an RSA key pair and enable the SSH server.
When configuring the RSA key pair, you might encounter the following error messages: - No hostname specified.
You must configure a hostname for the device using the hostname global configuration command. See the “IPsec and Quality of Service” module for more information.
- No domain specified.
You must configure a host domain for the device using the ip domain-name global configuration command. See the “IPsec and Quality of Service” module for more information
- No hostname specified.
The number of allowable SSH connections is limited to the maximum number of vtys configured for the device. Each SSH connection uses a vty resource.
SSH uses either local security or the security protocol that is configured through AAA on your device for user authentication. When configuring Authentication, Authorization, and Accounting ( AAA), you must ensure that AAA is disabled on the console for user authentication. AAA authorization is disabled on the console by default. If AAA authorization is enabled on the console, disable it by configuring the no aaa authorization console command during the AAA configuration stage.
Configuration Examples for SSH
Example: Configuring an SSH Server
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
The following is an example of the Secure Shell (SSH) control parameters configured for the server. In this example, the timeout interval of 30 seconds has been specified. This timeout interval is used during the SSH negotiation phase.
Device> enable Device# configure terminal Device(config)# ip ssh timeout 30 Device(config)# end
Example: Invoking an SSH Client
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
In the following example, the Secure Shell (SSH) client has been invoked to connect to IP address 192.0.2.1 in the specified virtual routing and forwarding (VRF) instance:
Device> enable Device# configure terminal Device(config)# ssh -1 user1 -vrf vrf1 192.0.2.1 Device(config)# end
Example: Verifying SSH
Note | Unless otherwise noted, the term “SSH” denotes “SSH Version 1” only. |
To verify that the Secure Shell (SSH) server is enabled and to display the version and configuration data for your SSH connection, use the show ip ssh command. The following example shows that SSH is enabled:
Device# show ip ssh SSH Enabled - version 1.5 Authentication timeout: 120 secs; Authentication retries: 3
The following example shows that SSH is disabled:
Device# show ip ssh %SSH has not been enabled
To verify the status of your SSH server connections, use the show ssh command. The following example shows the SSH server connections on the device when SSH is enabled:
Device# show ssh Connection Version Encryption State Username 0 1.5 3DES Session Started guest
The following example shows that SSH is disabled:
Device# show ssh %No SSH server connections running.
Additional References
Related Documents
|
Related Topic |
Document Title |
|---|---|
|
Cisco IOS commands |
|
|
Authentication, authorization, and accounting (AAA) |
Authentication, Authorization, and Accounting Configuration Guide |
|
IPsec |
“IPsec and Quality of Service” module |
|
SSH Version 2 |
“Secure Shell Version 2 Support” module |
|
Downloading a software image |
Loading and Managing System Images Configuration Guide |
Technical Assistance
|
Description |
Link |
|---|---|
|
The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password. |
Feature Information for Configuring Secure Shell
The following table provides release information about the feature or features described in this module. This table 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.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
|
Feature Name |
Releases |
Feature Information |
|---|---|---|
|
Secure Shell |
12.0(5)S 15.0(2)SE 15.1(1)SY |
The Secure Shell (SSH) feature is an application and a protocol that provides a secure replacement to the Berkeley r-tools. The protocol secures sessions using standard cryptographic mechanisms, and the application can be used similarly to the Berkeley rexec and rsh tools. Two versions of SSH are available: SSH Version 1 and SSH Version 2. This document describes SSH Version 1. This document also includes information about the Secure Shell SSH Version 1 Integrated Client feature and the Secure Shell SSH Version 1 Server Support feature. Both features are part of the Secure Shell functionality. |