Secure Shell Version 2 Support

Last Updated: July 20, 2011

The Secure Shell Version 2 Support feature allows you to configure Secure Shell (SSH) Version 2 (SSH Version 1 support was implemented in an earlier Cisco IOS software release). SSH runs on top of a reliable transport layer and provides strong authentication and encryption capabilities. The only reliable transport that is defined for SSH is TCP. SSH provides a means to securely access and securely execute commands on another computer over a network. The Secure Copy Protocol (SCP) feature that is provided with SSH allows for the secure transfer of files.

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 Table at the end of this document.

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 Secure Shell Version 2 Support

Prior to configuring SSH, ensure that the required image is loaded on your router. The SSH server requires you to have a k9 (Triple Data Encryption Standard [3DES]) software image from Cisco IOS Release 12.3(4)T, 12.2(25)S, or 12.3(7)JA downloaded on to your router.


Note
The SSH Version 2 server is supported in Cisco IOS Release 12.3(4)T, 12.3(2)XE, 12.2(25)S, and 12.3(7)JA; the SSH Version 2 client is supported beginning with Cisco IOS Release 12.3(7)T and is supported in Cisco IOS Release12.3(7)JA. (The SSH client runs both the SSH Version 1 protocol and the Version 2 protocol and is supported in both k8 and k9 images in Cisco IOS Release 12.3(4)T.)

For more information about downloading a software image, refer to Cisco IOS Configuration Fundamentals Configuration Guide, Release 12.4T and Cisco IOS Network Management Configuration Guide, Release 15.0.

Restrictions for Secure Shell Version 2 Support

  • SSH servers and SSH clients are supported in 3DES software images.
  • Execution Shell, remote command execution, and SCP are the only applications supported.
  • Rivest, Shamir, and Adleman (RSA) key generation is an SSH server-side requirement. Routers that act as SSH clients need not generate RSA keys.
  • The RSA key pair size must be greater than or equal to 768.
  • The following functionality is not supported:
    • Port forwarding
    • Compression

Information About Secure Shell Version 2 Support

Secure Shell Version 2

The Secure Shell Version 2 Support feature allows you to configure SSH Version 2.

The configuration for the SSH Version 2 server is similar to the configuration for SSH Version 1. The ip ssh version command was introduced so that you may define which version of SSH to configure. If you do not configure this command, SSH by default runs in compatibility mode; that is, both SSH Version 1 and SSH Version 2 connections are honored.


Note
SSH Version 1 is a protocol that has never been defined in a standard. If you do not want your router to fall back to the undefined protocol (Version 1), you should use the ip ssh version command and specify Version 2.

The ip ssh rsa keypair-name command was also introduced in Cisco IOS Release 12.3(4)T so that you can enable an SSH connection using the RSA keys that you have configured. Previously, SSH was linked to the first RSA keys that were generated (that is, SSH was enabled when the first RSA key pair was generated). The behavior still exists, but by using the ip ssh rsa keypair-name command, you can overcome that behavior. If you configure the ip ssh rsa keypair-name command with a key pair name, SSH is enabled if the key pair exists, or SSH will be enabled if the key pair is generated later. If you use this command to enable SSH, you are not forced to configure a hostname and a domain name, which was required in SSH Version 1 of the Cisco IOS software.


Note
The login banner is supported in SSH Version 2, but it is not supported in Secure Shell Version 1.

Secure Shell Version 2 Enhancements

The SSH Version 2 Enhancements feature includes a number of additional capabilities such as supporting VRF-aware SSH, SSH debug enhancements, and Diffie-Hellman (DH) group exchange support.


Note
Only the VRF-aware SSH feature is supported in Cisco IOS Release 12.2(50)SY.

The Cisco IOS SSH implementation has traditionally used 768-bit modulus, but with an increasing need for higher key sizes to accommodate DH Group 14 (2048 bits) and Group 16 (4096 bits) cryptographic applications a message exchange between the client and the server to establish the favored DH group becomes necessary. The ip ssh dh min size command was introduced in Cisco IOS Release 12.4(20)T so that you can configure the modulus size on the SSH server. In addition to this the sshcommand was extended to add VRF awareness to the SSH client-side functionality through which the VRF instance name in the client is provided with the IP address to look up the correct routing table and establish a connection.

Debugging was enhanced by modifying SSH debug commands. The debug ip ssh command was extended to allow you to simplify the debugging process. Previously, this command printed all debug messages related to SSH regardless of what was specifically required. The behavior still exists, but if you configure the debug ip ssh command with a keyword, messages are limited to information specified by the keyword.

Secure Shell Version 2 Enhancements for RSA Keys

Cisco IOS SSH Version 2 (SSHv2) supports keyboard-interactive and password-based authentication methods. The SSHv2 Enhancements for RSA Keys feature also supports RSA-based public key authentication for the client and the server.

User authentication--RSA-based user authentication uses a private/public key pair associated with each user for authentication. The user must generate a private/public key pair on the client and configure a public key on the Cisco IOS SSH server to complete the authentication.

An SSH user trying to establish the credentials provides an encrypted signature using the private key. The signature and the user’s public key are sent to the SSH server for authentication. The SSH server computes a hash over the public key provided by the user. The hash is used to determine if the server has a matching entry. If a match is found, an RSA-based message verification is performed using the public key. Hence, the user is authenticated or denied access based on the encrypted signature.

Server authentication--While establishing an SSH session, the Cisco IOS SSH client authenticates the SSH server by using the server host keys available during the key exchange phase. SSH server keys are used to identify the SSH server. These keys are created at the time of enabling SSH and must be configured on the client.

For server authentication, the Cisco IOS SSH client must assign a host key for each server. When the client tries to establish an SSH session with a server, it receives the signature of the server as part of the key exchange message. If the strict host key checking flag is enabled on the client, the client checks if it has the host key entry corresponding to the server. If a match is found, the client tries to validate the signature using the server host key. If the server is successfully authenticated, the session establishment continues; otherwise, it is terminated and displays a “Server Authentication Failed” message.


Note
Storing public keys on a server uses memory; therefore, the number of public keys configurable on an SSH server is restricted to ten users, with a maximum of two public keys per user.

Note
RSA-based user authentication is supported by the Cisco IOS server, but Cisco IOS clients cannot propose public key as an authentication method. If the Cisco IOS server receives a request from an open SSH client for RSA-based authentication, the server accepts the authentication request.

Note
For server authentication, configure the RSA public key of the server manually and configure the ip ssh stricthostkeycheck command on the Cisco IOS SSH client.

SNMP Trap Generation

Effective with Cisco IOS Release 12.4(17), Simple Network Management Protocol (SNMP) traps are generated automatically when an SSH session terminates if the traps have been enabled and SNMP debugging has been turned on. For information about enabling SNMP traps, see the Configuring SNMP Support module in the Cisco IOS Network Management Configuration Guide, Release 15.0 .


Note
When you configure the snmp-server host command, the IP address must be the address of the PC that has the SSH (telnet) client and that has IP connectivity to the SSH server. For an example of an SNMP trap generation configuration, see the Example Setting an SNMP Trap.”

You must also turn on SNMP debugging using the debug snmp packet command to display the traps. The trap information includes information such as the number of bytes sent and the protocol that was used for the SSH session. For an example of SNMP debugging, see the Example SNMP Debugging.

SSH Keyboard Interactive Authentication

The SSH Keyboard Interactive Authentication feature, also known as Generic Message Authentication for SSH, is a method that can be used to implement different types of authentication mechanisms. Basically, any currently supported authentication method that requires only user input can be performed with this feature. The feature is automatically enabled.

The following methods are supported:

  • Password
  • SecurID and hardware tokens printing a number or a string in response to a challenge sent by the server
  • Pluggable Authentication Module (PAM)
  • S/KEY (and other One-Time-Pads)

For examples of various scenarios in which the SSH Keyboard Interactive Authentication feature has been automatically enabled, see the Examples SSH Keyboard Interactive Authentication.

How to Configure Secure Shell Version 2 Support

Configuring a Router for SSH Version 2 Using a Hostname and Domain Name

Perform this task to configure a router for SSH Version 2 using a hostname and domain name. You may also configure SSH Version 2 by using the RSA key pair configuration (see the Configuring a Router for SSH Version 2 Using RSA Key Pairs).

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    hostname hostname

4.    ip domain-name name

5.    crypto key generate rsa

6.    ip ssh [time-out seconds | authentication-retries integer]

7.    ip ssh version [1 | 2]


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
hostname hostname


Example:

Router(config)# hostname cisco 7200

 

Configures a hostname for your router.

 
Step 4
ip domain-name name


Example:

Router(config)# ip domain-name example.com

 

Configures a domain name for your router.

 
Step 5
crypto key generate rsa


Example:

Router(config)# crypto key generate rsa

 

Enables the SSH server for local and remote authentication.

 
Step 6
ip ssh [time-out seconds | authentication-retries integer]


Example:

Router(config)# ip ssh time-out 120

 

(Optional) Configures SSH control variables on your router.

 
Step 7
ip ssh version [1 | 2]


Example:

Router(config)# ip ssh version 1

 

(Optional) Specifies the version of SSH to be run on your router.

 

Configuring a Router for SSH Version 2 Using RSA Key Pairs

Perform this task to enable SSH Version 2 without configuring a hostname or a domain name. SSH Version 2 will be enabled if the key pair that you configure already exists or if it is generated later. You may also configure SSH Version 2 by using the hostname and domain name configuration (see the Configuring a Router for SSH Version 2 Using a Hostname and Domain Name).

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    ip ssh rsa keypair-name keypair-name

4.    crypto key generate rsa usage-keys label key-label modulus modulus-size

5.    ip ssh [time-out seconds | authentication-retries integer]

6.    ip ssh version 2


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
ip ssh rsa keypair-name keypair-name


Example:

Router(config)# ip ssh rsa keypair-name sshkeys

 

Specifies which RSA key pair to use for SSH usage.

Note    A Cisco IOS router can have many RSA key pairs.
 
Step 4
crypto key generate rsa usage-keys label key-label modulus modulus-size


Example:

Router(config)# crypto key generate rsa usage-keys label sshkeys modulus 768

 

Enables the SSH server for local and remote authentication on the router.

  • For SSH Version 2, the modulus size must be at least 768 bits.
Note    To delete the RSA key pair, use the crypto key zeroize rsa command. After you have deleted the RSA key pair, you automatically disable the SSH server.
 
Step 5
ip ssh [time-out seconds | authentication-retries integer]


Example:

Router(config)# ip ssh time-out 12

 

Configures SSH control variables on your router.

 
Step 6
ip ssh version 2


Example:

Router(config)# ip ssh version 2

 

Specifies the version of SSH to be run on a router.

 

Configuring the Cisco IOS SSH Server to Perform RSA-Based User Authentication

Perform this task to configure the Cisco IOS SSH server to perform RSA-based user authentication. The user authentication is successful if the RSA public key stored on the server is verified with the public or the private key pair stored on the client.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    hostname name

4.    ip domain-name name

5.    crypto key generate rsa

6.    ip ssh pubkey-chain

7.    username username

8.    key-string

9.    exit

10.    key-hash key-type key-name

11.    end


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
hostname name


Example:

Router(config)# hostname host1

 

Specifies the hostname.

 
Step 4
ip domain-name name


Example:

Router(config)# ip domain-name name1

 

Defines a default domain name that the Cisco IOS software uses to complete unqualified hostnames.

 
Step 5
crypto key generate rsa


Example:

Router(config)# crypto key generate rsa

 

Generates RSA key pairs.

 
Step 6
ip ssh pubkey-chain


Example:

Router(config)# ip ssh pubkey-chain

 

Configures SSH-RSA keys for user and server authentication on the SSH server and enters public-key configuration mode.

 
Step 7
username username


Example:

Router(conf-ssh-pubkey)# username user1

 

Configures the SSH username and enters public-key user configuration mode.

 
Step 8
key-string


Example:

Router(conf-ssh-pubkey-user)# key-string

 

Specifies the RSA public key of the remote peer and enters public-key data configuration mode.

Note    You can obtain the public key value from an open SSH client; that is, from the .ssh/id_rsa.pub file.
 
Step 9
exit


Example:

Router(conf-ssh-pubkey-data)# exit

 

Exits public-key user configuration mode.

 
Step 10
key-hash key-type key-name


Example:

Router(conf-ssh-pubkey-data)# key-hash ssh-rsa key1

 

(Optional) Specifies the SSH key type and version.

  • The key type must be ssh-rsa for configuration of private public key pairs.
  • This step is optional only if the key-string command is configured.
  • You must configure either the key-string command or the key-hash command.
Note    You can use a hashing software to compute the hash of the pubkey string or you can also copy the hash value from another Cisco IOS router. Entering the public key data using the key-string command is the preferred way to enter the public key data for the first time.
 
Step 11
end


Example:

Router(conf-ssh-pubkey-data)# end

 

Exits the current mode and returns to privileged EXEC mode.

 

Configuring the Cisco IOS SSH Client to Perform RSA-Based Server Authentication

Perform this task to configure the Cisco IOS SSH client to perform RSA-based server authentication.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    hostname name

4.    ip domain-name name

5.    crypto key generate rsa

6.    ip ssh pubkey-chain

7.    server server-name

8.    key-string

9.    exit

10.    key-hash key-type key-name

11.    end

12.    configure terminal

13.    ip ssh stricthostkeycheck


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
hostname name


Example:

Router(config)# hostname host1

 

Specifies the hostname.

 
Step 4
ip domain-name name


Example:

Router(config)# ip domain-name name1

 

Defines a default domain name that the Cisco IOS software uses to complete unqualified hostnames.

 
Step 5
crypto key generate rsa


Example:

Router(config)# crypto key generate rsa

 

Generates RSA key pairs.

 
Step 6
ip ssh pubkey-chain


Example:

Router(config)# ip ssh pubkey-chain

 

Configures SSH-RSA keys for user and server authentication on the SSH server and enters public-key configuration mode.

 
Step 7
server server-name


Example:

Router(conf-ssh-pubkey)# server server1

 

Enables the SSH server for public-key authentication on the router and enters public-key server configuration mode.

 
Step 8
key-string


Example:

Router(conf-ssh-pubkey-server)# key-string

 

Specifies the RSA public-key of the remote peer and enters public key data configuration mode.

Note    You can obtain the public key value from an open SSH client; that is, from the .ssh/id_rsa.pub file.
 
Step 9
exit


Example:

Router(conf-ssh-pubkey-data)# exit

 

Exits public-key data configuration mode and enters public-key server configuration mode.

 
Step 10
key-hash key-type key-name


Example:

Router(conf-ssh-pubkey-server)# key-hash ssh-rsa key1

 

(Optional) Specifies the SSH key type and version.

  • The key type must be ssh-rsa for configuration of private/public key pairs.
  • This step is optional only if the key-string command is configured.
  • You must configure either the key-string command or the key-hash command.
Note    You can use a hashing software to compute the hash of the public key string or you can copy the hash value from another Cisco IOS router. Entering the public key data using the key-string command is the preferred way to enter the public key data for the first time.
 
Step 11
end


Example:

Router(conf-ssh-pubkey-server)# end

 

Exits public-key server mode and returns to privileged EXEC mode.

 
Step 12
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 13
ip ssh stricthostkeycheck


Example:

Router(config)# ip ssh stricthostkeycheck

 

Ensures that the server authentication takes place.

  • The connection is terminated on a failure.
 

Starting an Encrypted Session with a Remote Device

Perform this task to start an encrypted session with a remote networking device, (You need not enable your router. SSH can be run in disabled mode.)


Note
The device you want to connect with must support an SSH server that has an encryption algorithm that is supported in Cisco IOS software.
SUMMARY STEPS

1.    ssh [-v {1 | 2}][-c {3des | aes128-cbc | aes192-cbc | aes256-cbc}] [-m {hmac-md5 | hmac-md5-96 | hmac-sha1 | hmac-sha1-96}] [l userid] [-o numberofpasswordprompts n] [-p port-num]{ip-addr | hostname} [command]


DETAILED STEPS
  Command or Action Purpose
Step 1
ssh [-v {1 | 2}][-c {3des | aes128-cbc | aes192-cbc | aes256-cbc}] [-m {hmac-md5 | hmac-md5-96 | hmac-sha1 | hmac-sha1-96}] [l userid] [-o numberofpasswordprompts n] [-p port-num]{ip-addr | hostname} [command]


Example:

Router# ssh -v 2 -c aes256-cbc -m hmac-sha1-96 -l user2 10.76.82.24

 

Starts an encrypted session with a remote networking device.

 

Troubleshooting Tips

The ip ssh version command can be used for troubleshooting your SSH configuration. By changing versions, you can determine which SSH version has a problem.

Enabling Secure Copy Protocol on the SSH Server

Perform this task to enable secure copy protocol on the SSH server. This task configures the server-side functionality for SCP. This task shows a typical configuration that allows the router to securely copy files from a remote workstation.

Before You Begin

SCP relies on authentication, authorization, and accounting (AAA) to function correctly. Therefore, AAA must be configured on the router.


SUMMARY STEPS

1.    enable

2.    configure terminal

3.    aaa new-model

4.    aaa authentication login default local

5.    aaa authorization exec default local

6.    username name privilege privilege-level password password

7.    ip ssh time-out seconds

8.    ip ssh authentication-retries integer

9.    ip scp server enable


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
aaa new-model


Example:

Router(config)# aaa new-model

 

Enables the AAA access control model.

 
Step 4
aaa authentication login default local


Example:

Router(config)# aaa authentication login default local

 

Sets AAA authentication at login to use the local username database for authentication.

 
Step 5
aaa authorization exec default local


Example:

Router(config)# aaa authorization exec default local

 

Sets the parameters that restrict user access to a network, runs the authorization to determine if the user ID is allowed to run an EXEC shell, and specifies that the system uses the local database for authorization.

 
Step 6
username name privilege privilege-level password password


Example:

Router(config)# username samplename privilege 15 password password1

 

Establishes a username-based authentication system, and specifies the username, privilege level, and an unencrypted password.

Note    The minimum value for the privilege-level argument is 15. A privilege level of less than 15 results in the connection closing.
 
Step 7
ip ssh time-out seconds


Example:

Router(config)# ip ssh time-out 120

 

Sets the time interval (in seconds) that the router waits for the SSH client to respond.

 
Step 8
ip ssh authentication-retries integer


Example:

Router(config)# ip ssh authentication-retries 3

 

Sets the number of authentication attempts after which the interface is reset.

 
Step 9
ip scp server enable


Example:

Router(config)# ip scp server enable

 

Enables the router to securely copy files from a remote workstation.

 

Troubleshooting Tips

To troubleshoot SCP authentication problems, use the debug ip scpcommand.

Verifying the Status of the Secure Shell Connection Using the show ssh Command

To display the status of the SSH connection on your router, use the show ssh command.

SUMMARY STEPS

1.    enable

2.    show ssh


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
show ssh


Example:

Router# show ssh

 

Displays the status of SSH server connections.

 

Examples

The following sample output from the show ssh command display status about various SSH Version 1 and Version 2 connections. 

-----------------------------------------------------------------------
Router# show ssh
Connection      Version Encryption      State                   Username
 0              1.5     3DES            Session started         lab
Connection Version Mode Encryption  Hmac                State          
Username
1          2.0     IN   aes128-cbc  hmac-md5     Session started       lab
1          2.0     OUT  aes128-cbc  hmac-md5     Session started       lab
-------------------------------------------------------------------------
-------------------------------------------------------------------------
Router# show ssh
Connection Version Mode Encryption  Hmac                State          
Username
1          2.0     IN   aes128-cbc  hmac-md5     Session started       lab
1          2.0     OUT  aes128-cbc  hmac-md5     Session started       lab
%No SSHv1 server connections running.
-------------------------------------------------------------------------
-------------------------------------------------------------------------
Router# show ssh
Connection      Version Encryption      State                   Username
 0              1.5     3DES            Session started         lab
%No SSHv2 server connections running.
-------------------------------------------------------------------------

Verifying the Secure Shell Status

Perform this task to verify your SSH configuration.

SUMMARY STEPS

1.    enable

2.    show ip ssh


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
show ip ssh


Example:

Router# show ip ssh

 

Displays the version and configuration data for SSH.

 

Examples

The following sample output from the show ip ssh command displays the version of SSH that is enabled, the authentication timeout values, and the number of authentication retries: 

-----------------------------------------------------------------------
Router# show ip ssh
SSH Enabled - version 1.99
Authentication timeout: 120 secs; Authentication retries: 3
-----------------------------------------------------------------------
------------------------------------------------------------------------
Router# show ip ssh
SSH Enabled - version 2.0
Authentication timeout: 120 secs; Authentication retries: 3
------------------------------------------------------------------------
------------------------------------------------------------------------
Router# show ip ssh
3d06h: %SYS-5-CONFIG_I: Configured from console by console
SSH Enabled - version 1.5
Authentication timeout: 120 secs; Authentication retries: 3
------------------------------------------------------------------------

Monitoring and Maintaining Secure Shell Version 2

To display debug messages about the SSH connections, use the debug ip ssh command and the debug snmp packet command.

SUMMARY STEPS

1.    enable

2.    debug ip ssh

3.    debug snmp packet


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 SSH.

 
Step 3
debug snmp packet


Example:

Router# debug snmp packet

 

Displays information about every SNMP packet sent or received by the router.

 

Example

The following sample output from the debug ip ssh command shows that the digit 2 keyword has been assigned, signifying that it is an SSH Version 2 connection: 

Router# debug ip ssh
00:33:55: SSH1: starting SSH control process
00:33:55: SSH1: sent protocol version id SSH-1.99-Cisco-1.25
00:33:55: SSH1: protocol version id is - SSH-2.0-OpenSSH_2.5.2p2
00:33:55: SSH2 1: send: len 280 (includes padlen 4)
00:33:55: SSH2 1: SSH2_MSG_KEXINIT sent
00:33:55: SSH2 1: ssh_receive: 536 bytes received
00:33:55: SSH2 1: input: packet len 632
00:33:55: SSH2 1: partial packet 8, need 624, maclen 0
00:33:55: SSH2 1: ssh_receive: 96 bytes received
00:33:55: SSH2 1: partial packet 8, need 624, maclen 0
00:33:55: SSH2 1: input: padlen 11
00:33:55: SSH2 1: received packet type 20
00:33:55: SSH2 1: SSH2_MSG_KEXINIT received
00:33:55: SSH2: kex: client->server aes128-cbc hmac-md5 none
00:33:55: SSH2: kex: server->client aes128-cbc hmac-md5 none
00:33:55: SSH2 1: expecting SSH2_MSG_KEXDH_INIT
00:33:55: SSH2 1: ssh_receive: 144 bytes received
00:33:55: SSH2 1: input: packet len 144
00:33:55: SSH2 1: partial packet 8, need 136, maclen 0
00:33:55: SSH2 1: input: padlen 5
00:33:55: SSH2 1: received packet type 30
00:33:55: SSH2 1: SSH2_MSG_KEXDH_INIT received
00:33:55: SSH2 1: signature length 111
00:33:55: SSH2 1: send: len 384 (includes padlen 7)
00:33:55: SSH2: kex_derive_keys complete
00:33:55: SSH2 1: send: len 16 (includes padlen 10)
00:33:55: SSH2 1: newkeys: mode 1
00:33:55: SSH2 1: SSH2_MSG_NEWKEYS sent
00:33:55: SSH2 1: waiting for SSH2_MSG_NEWKEYS
00:33:55: SSH2 1: ssh_receive: 16 bytes received
00:33:55: SSH2 1: input: packet len 16
00:33:55: SSH2 1: partial packet 8, need 8, maclen 0
00:33:55: SSH2 1: input: padlen 10
00:33:55: SSH2 1: newkeys: mode 0
00:33:55: SSH2 1: received packet type 2100:33:55: SSH2 1: SSH2_MSG_NEWKEYS received
00:33:56: SSH2 1: ssh_receive: 48 bytes received
00:33:56: SSH2 1: input: packet len 32
00:33:56: SSH2 1: partial packet 16, need 16, maclen 16
00:33:56: SSH2 1: MAC #3 ok
00:33:56: SSH2 1: input: padlen 10
00:33:56: SSH2 1: received packet type 5
00:33:56: SSH2 1: send: len 32 (includes padlen 10)
00:33:56: SSH2 1: done calc MAC out #3
00:33:56: SSH2 1: ssh_receive: 64 bytes received
00:33:56: SSH2 1: input: packet len 48
00:33:56: SSH2 1: partial packet 16, need 32, maclen 16
00:33:56: SSH2 1: MAC #4 ok
00:33:56: SSH2 1: input: padlen 9
00:33:56: SSH2 1: received packet type 50
00:33:56: SSH2 1: send: len 32 (includes padlen 13)
00:33:56: SSH2 1: done calc MAC out #4
00:34:04: SSH2 1: ssh_receive: 160 bytes received
00:34:04: SSH2 1: input: packet len 64
00:34:04: SSH2 1: partial packet 16, need 48, maclen 16
00:34:04: SSH2 1: MAC #5 ok
00:34:04: SSH2 1: input: padlen 13
00:34:04: SSH2 1: received packet type 50
00:34:04: SSH2 1: send: len 16 (includes padlen 10)
00:34:04: SSH2 1: done calc MAC out #5
00:34:04: SSH2 1: authentication successful for lab
00:34:04: SSH2 1: input: packet len 64
00:34:04: SSH2 1: partial packet 16, need 48, maclen 16
00:34:04: SSH2 1: MAC #6 ok
00:34:04: SSH2 1: input: padlen 6
00:34:04: SSH2 1: received packet type 2
00:34:04: SSH2 1: ssh_receive: 64 bytes received
00:34:04: SSH2 1: input: packet len 48
00:34:04: SSH2 1: partial packet 16, need 32, maclen 16
00:34:04: SSH2 1: MAC #7 ok
00:34:04: SSH2 1: input: padlen 19
00:34:04: SSH2 1: received packet type 90
00:34:04: SSH2 1: channel open request
00:34:04: SSH2 1: send: len 32 (includes padlen 10)
00:34:04: SSH2 1: done calc MAC out #6
00:34:04: SSH2 1: ssh_receive: 192 bytes received
00:34:04: SSH2 1: input: packet len 64
00:34:04: SSH2 1: partial packet 16, need 48, maclen 16
00:34:04: SSH2 1: MAC #8 ok
00:34:04: SSH2 1: input: padlen 13
00:34:04: SSH2 1: received packet type 98
00:34:04: SSH2 1: pty-req request
00:34:04: SSH2 1: setting TTY - requested: height 24, width 80; set: height 24, 
width 80
00:34:04: SSH2 1: input: packet len 96
00:34:04: SSH2 1: partial packet 16, need 80, maclen 16
00:34:04: SSH2 1: MAC #9 ok
00:34:04: SSH2 1: input: padlen 11
00:34:04: SSH2 1: received packet type 98
00:34:04: SSH2 1: x11-req request
00:34:04: SSH2 1: ssh_receive: 48 bytes received
00:34:04: SSH2 1: input: packet len 32
00:34:04: SSH2 1: partial packet 16, need 16, maclen 16
00:34:04: SSH2 1: MAC #10 ok
00:34:04: SSH2 1: input: padlen 12
00:34:04: SSH2 1: received packet type 98
00:34:04: SSH2 1: shell request
00:34:04: SSH2 1: shell message received
00:34:04: SSH2 1: starting shell for vty
00:34:04: SSH2 1: send: len 48 (includes padlen 18)
00:34:04: SSH2 1: done calc MAC out #7
00:34:07: SSH2 1: ssh_receive: 48 bytes received
00:34:07: SSH2 1: input: packet len 32
00:34:07: SSH2 1: partial packet 16, need 16, maclen 16
00:34:07: SSH2 1: MAC #11 ok
00:34:07: SSH2 1: input: padlen 17
00:34:07: SSH2 1: received packet type 94
00:34:07: SSH2 1: send: len 32 (includes padlen 17)
00:34:07: SSH2 1: done calc MAC out #8
00:34:07: SSH2 1: ssh_receive: 48 bytes received
00:34:07: SSH2 1: input: packet len 32
00:34:07: SSH2 1: partial packet 16, need 16, maclen 16
00:34:07: SSH2 1: MAC #12 ok
00:34:07: SSH2 1: input: padlen 17
00:34:07: SSH2 1: received packet type 94
00:34:07: SSH2 1: send: len 32 (includes padlen 17)
00:34:07: SSH2 1: done calc MAC out #9
00:34:07: SSH2 1: ssh_receive: 48 bytes received
00:34:07: SSH2 1: input: packet len 32
00:34:07: SSH2 1: partial packet 16, need 16, maclen 16
00:34:07: SSH2 1: MAC #13 ok
00:34:07: SSH2 1: input: padlen 17
00:34:07: SSH2 1: received packet type 94
00:34:07: SSH2 1: send: len 32 (includes padlen 17)
00:34:07: SSH2 1: done calc MAC out #10
00:34:08: SSH2 1: ssh_receive: 48 bytes received
00:34:08: SSH2 1: input: packet len 32
00:34:08: SSH2 1: partial packet 16, need 16, maclen 16
00:34:08: SSH2 1: MAC #14 ok
00:34:08: SSH2 1: input: padlen 17
00:34:08: SSH2 1: received packet type 94
00:34:08: SSH2 1: send: len 32 (includes padlen 17)
00:34:08: SSH2 1: done calc MAC out #11
00:34:08: SSH2 1: ssh_receive: 48 bytes received
00:34:08: SSH2 1: input: packet len 32
00:34:08: SSH2 1: partial packet 16, need 16, maclen 16
00:34:08: SSH2 1: MAC #15 ok
00:34:08: SSH2 1: input: padlen 17
00:34:08: SSH2 1: received packet type 94
00:34:08: SSH2 1: send: len 32 (includes padlen 16)
00:34:08: SSH2 1: done calc MAC out #12
00:34:08: SSH2 1: send: len 48 (includes padlen 18)
00:34:08: SSH2 1: done calc MAC out #13
00:34:08: SSH2 1: send: len 16 (includes padlen 6)
00:34:08: SSH2 1: done calc MAC out #14
00:34:08: SSH2 1: send: len 16 (includes padlen 6)
00:34:08: SSH2 1: done calc MAC out #15
00:34:08: SSH1: Session terminated normally

Configuration Examples for Secure Shell Version 2 Support

Example Configuring Secure Shell Version 1

The following example shows how to configure SSH Version 1:

Router# configure terminal
Router(config)# ip ssh version 1
Router(config)# end

Example ConfiguringSecureShellVersion2

The following example shows how to configure SSH Version 2:

Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# ip ssh version 2
Router(config)# end

Example Configuring Secure Shell Versions 1 and 2

The following example shows how to configure both SSH Version 1 and SSH Version 2:

Router# configure terminal
Router(config)# no ip ssh version
Router(config)# end

Example Starting an Encrypted Session with a Remote Device

The following example shows how to start an encrypted session with a remote device:

Router# ssh -v 2 -c aes256-cbc -m hmac-sha1-160 -l shaship 10.76.82.24

Example Configuring Server-Side SCP

The following example shows how to configure the server-side functionality for SCP. This example also configures AAA authentication and authorization on the router. This example uses a locally defined username and password. 
Router# configure terminal
Router(config)# aaa new-model
Router(config)# aaa authentication login default local
Router(config)# aaa authorization exec default local
Router(config)# username samplename privilege 15 password password1
Router(config)# ip ssh time-out 120
Router(config)# ip ssh authentication-retries 3
Router(config)# ip scp server enable
Router(config)# end

Example Setting an SNMP Trap

The following example shows that an SNMP trap has been set. The trap notification is generated automatically when the SSH session terminates. In the example, a.b.c.d is the IP address of the SSH client. For an example of SNMP trap debug output, see the section Example SNMP Debugging.”

snmp-server
snmp-server host a.b.c.d public tty

Examples SSH Keyboard Interactive Authentication

Client-Side Debugs

In the following example, client-side debugs are turned on and the maximum number of prompts = six, (three for the SSH Keyboard Interactive Authentication method and for the password method of authentication).

Password:
Password:
Password:
Password:
Password:
Password: cisco123
Last login: Tue Dec 6 13:15:21 2005 from 10.76.248.213
user1@courier:~> exit
logout
[Connection to 10.76.248.200 closed by foreign host]
Router1# debug ip ssh client
SSH Client debugging is on
Router1# ssh -l lab 10.1.1.3
Password:
*Nov 17 12:50:53.199: SSH0: sent protocol version id SSH-1.99-Cisco-1.25
*Nov 17 12:50:53.199: SSH CLIENT0: protocol version id is - SSH-1.99-Cisco-1.25
*Nov 17 12:50:53.199: SSH CLIENT0: sent protocol version id SSH-1.99-Cisco-1.25
*Nov 17 12:50:53.199: SSH CLIENT0: protocol version exchange successful
*Nov 17 12:50:53.203: SSH0: protocol version id is - SSH-1.99-Cisco-1.25
*Nov 17 12:50:53.335: SSH CLIENT0: key exchange successful and encryption on
*Nov 17 12:50:53.335: SSH2 CLIENT 0: using method keyboard-interactive
Password:
Password:
Password:
*Nov 17 12:51:01.887: SSH2 CLIENT 0: using method password authentication
Password:
Password: lab
Router2>
*Nov 17 12:51:11.407: SSH2 CLIENT 0: SSH2_MSG_USERAUTH_SUCCESS message received
*Nov 17 12:51:11.407: SSH CLIENT0: user authenticated
*Nov 17 12:51:11.407: SSH2 CLIENT 0: pty-req request sent
*Nov 17 12:51:11.411: SSH2 CLIENT 0: shell request sent
*Nov 17 12:51:11.411: SSH CLIENT0: session open

TACACS ACS Is the Back-end AAA Server ChPass Is Enabled and a Blank Password Change Is Made

In the following example, a TACACS+ access control server (ACS) is the back-end AAA server, the ChPass feature is enabled, and a blank password change is accomplished using the SSH Keyboard Interactive Authentication method: 

Router1# ssh -l cisco 10.1.1.3
Password:
Old Password: cisco
New Password: cisco123
Re-enter New password: cisco123
Router2> exit
[Connection to 10.1.1.3 closed by foreign host]

TACACS ACS Is the Back-end AAA Server ChPass Is Enabled and the Password Is Changed on First Login

In the following example, a TACACS+ ACS is the back-end server and the ChPass feature is enabled. The password is changed on the first login using the SSH Keyboard Interactive Authentication method. 

Router1# ssh -l cisco 10.1.1.3
Password: cisco
Your password has expired.
Enter a new one now.
New Password: cisco123
Re-enter New password: cisco123
Router2> exit
[Connection to 10.1.1.3 closed by foreign host]
Router1# ssh -l cisco 10.1.1.3
 
Password:cisco1
Your password has expired.
Enter a new one now.
New Password: cisco
Re-enter New password: cisco12
The New and Re-entered passwords have to be the same.
Try again.
New Password: cisco
Re-enter New password: cisco
Router2>

TACACS ACS Is the Back-end AAA Server ChPass Is Enabled and the Password Expires After Three Logins

In the following example, a TACACS+ ACS is the back-end AAA server and the ChPass feature is enabled. The password expires after three logins using the SSH Keyboard Interactive Authentication method. 

Router# ssh -l cisco. 10.1.1.3
Password: cisco
Router2> exit
[Connection to 10.1.1.3 closed by foreign host]
Router1# ssh -l cisco 10.1.1.3
Password: cisco
Router2> exit
Router1# ssh -l cisco 10.1.1.3
Password: cisco
Router2> exit
[Connection to 10.1.1.3 closed by foreign host]
Router1# ssh -l cisco 10.1.1.3
Password: cisco
Your password has expired.
Enter a new one now.
New Password: cisco123
Re-enter New password: cisco123
Router2>

Example SNMP Debugging

The following is sample output from the debug snmp packet command. The output provides SNMP trap information for an SSH session.

Router1# debug snmp packet
SNMP packet debugging is on
Router1# ssh -l lab 10.0.0.2
Password:
Router2# exit
[Connection to 10.0.0.2 closed by foreign host]
Router1#
*Jul 18 10:18:42.619: SNMP: Queuing packet to 10.0.0.2
*Jul 18 10:18:42.619: SNMP: V1 Trap, ent cisco, addr 10.0.0.1, gentrap 6, spectrap 1
local.9.3.1.1.2.1 = 6
tcpConnEntry.1.10.0.0.1.22.10.0.0.2.55246 = 4
ltcpConnEntry.5.10.0.0.1.22.10.0.0.2.55246 = 1015
ltcpConnEntry.1.10.0.0.1.22.10.0.0.2.55246 = 1056
ltcpConnEntry.2.10.0.0.1.22.10.0.0.2.55246 = 1392
local.9.2.1.18.2 = lab
*Jul 18 10:18:42.879: SNMP: Packet sent via UDP to 10.0.0.2
Router1#

Examples SSH Debugging Enhancements

The following is sample output from the debug ip ssh detailcommand. The output provides debugging information about the SSH protocol and channel requests.

Router# debug ip ssh detail
00:04:22: SSH0: starting SSH control process
00:04:22: SSH0: sent protocol version id SSH-1.99-Cisco-1.25
00:04:22: SSH0: protocol version id is - SSH-1.99-Cisco-1.25
00:04:22: SSH2 0: SSH2_MSG_KEXINIT sent
00:04:22: SSH2 0: SSH2_MSG_KEXINIT received
00:04:22: SSH2:kex: client->server enc:aes128-cbc mac:hmac-sha1 
00:04:22: SSH2:kex: server->client enc:aes128-cbc mac:hmac-sha1 
00:04:22: SSH2 0: expecting SSH2_MSG_KEXDH_INIT
00:04:22: SSH2 0: SSH2_MSG_KEXDH_INIT received
00:04:22: SSH2: kex_derive_keys complete
00:04:22: SSH2 0: SSH2_MSG_NEWKEYS sent
00:04:22: SSH2 0: waiting for SSH2_MSG_NEWKEYS
00:04:22: SSH2 0: SSH2_MSG_NEWKEYS received
00:04:24: SSH2 0: authentication successful for lab
00:04:24: SSH2 0: channel open request
00:04:24: SSH2 0: pty-req request
00:04:24: SSH2 0: setting TTY - requested: height 24, width 80; set: height 24, width 80
00:04:24: SSH2 0: shell request
00:04:24: SSH2 0: shell message received
00:04:24: SSH2 0: starting shell for vty
00:04:38: SSH0: Session terminated normally

The following is sample output from the debug ip ssh packetcommand. The output provides debugging information about the SSH packet.

Router# debug ip ssh packet 
00:05:43: SSH2 0: send:packet of  length 280 (length also includes padlen of 4)
00:05:43: SSH2 0: ssh_receive: 64 bytes received 
00:05:43: SSH2 0: input: total packet length of 280 bytes
00:05:43: SSH2 0: partial packet length(block size)8 bytes,needed 272 bytes, maclen 0
00:05:43: SSH2 0: ssh_receive: 64 bytes received 
00:05:43: SSH2 0: partial packet length(block size)8 bytes,needed 272 bytes, maclen 0
00:05:43: SSH2 0: ssh_receive: 64 bytes received 
00:05:43: SSH2 0: partial packet length(block size)8 bytes,needed 272 bytes, maclen 0
00:05:43: SSH2 0: ssh_receive: 64 bytes received 
00:05:43: SSH2 0: partial packet length(block size)8 bytes,needed 272 bytes, maclen 0
00:05:43: SSH2 0: ssh_receive: 24 bytes received 
00:05:43: SSH2 0: partial packet length(block size)8 bytes,needed 272 bytes, maclen 0
00:05:43: SSH2 0: input: padlength 4 bytes
00:05:43: SSH2 0: ssh_receive: 64 bytes received 
00:05:43: SSH2 0: input: total packet length of 144 bytes
00:05:43: SSH2 0: partial packet length(block size)8 bytes,needed 136 bytes, maclen 0
00:05:43: SSH2 0: ssh_receive: 64 bytes received 
00:05:43: SSH2 0: partial packet length(block size)8 bytes,needed 136 bytes, maclen 0
00:05:43: SSH2 0: ssh_receive: 16 bytes received 
00:05:43: SSH2 0: partial packet length(block size)8 bytes,needed 136 bytes, maclen 0
00:05:43: SSH2 0: input: padlength 6 bytes
00:05:43: SSH2 0: signature length 143
00:05:43: SSH2 0: send:packet of  length 448 (length also includes padlen of 7)
00:05:43: SSH2 0: send:packet of  length 16 (length also includes padlen of 10)
00:05:43: SSH2 0: newkeys: mode 1
00:05:43: SSH2 0: ssh_receive: 16 bytes received 
00:05:43: SSH2 0: input: total packet length of 16 bytes
00:05:43: SSH2 0: partial packet length(block size)8 bytes,needed 8 bytes, maclen 0
00:05:43: SSH2 0: input: padlength 10 bytes
00:05:43: SSH2 0: newkeys: mode 0
00:05:43: SSH2 0: ssh_receive: 52 bytes received 
00:05:43: SSH2 0: input: total packet length of 32 bytes
00:05:43: SSH2 0: partial packet length(block size)16 bytes,needed 16 bytes, maclen 20

00:05:43: SSH2 0: MAC compared for #3 :ok

Where to Go Next

You have to use a SSH remote device that supports SSH Version 2, and you have to connect to a Cisco IOS router.

Additional References

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

AAA

Cisco IOS Security Configuration Guide: Securing User Services

  • Configuring a hostname and host domain
  • Configuring Secure Shell

“Configuring Secure Shell” module in the Cisco IOS Security Configuration Guide: Securing User Services .

Debugging commands

Cisco IOS Debug Command Reference

Downloading a Cisco software image

Cisco IOS Configuration Fundamentals Configuration Guide Cisco IOS Network Management Configuration Guide

Cisco IOS configuration fundamentals

IPSec

Cisco IOS Security Configuration Guide: Secure Connectivity

Security commands

Cisco IOS Security Command Reference

SNMP, configuring traps

Configuring SNMP Support module in the Cisco IOS Network Management Configuration Guide

Standards

Standards

Title

IETF Secure Shell Version 2 Draft Standards

Internet Engineering Task Force website

MIBs

MIBs

MIBs Link

No new or modified MIBs are supported and support for existing MIBs has not been modified.

To locate and download MIBs for selected platforms, Cisco software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

RFCs

RFCs

Title

No new or modified RFCs are supported and support for existing RFCs has not been modified.

--

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.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for Secure Shell Version 2 Support

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.

Table 1 Feature Information for Secure Shell Version 2 Support

Feature Name

Releases

Feature Information

Secure Shell Version 2 Support

12.2(25)S 12.3(4)T 12.2(11)T

The Secure Shell Version 2 Support feature allows you to configure Secure Shell (SSH) Version 2 (SSH Version 1 support was implemented in an earlier Cisco IOS software release). SSH runs on top of a reliable transport layer and provides strong authentication and encryption capabilities.

In 12.3(11)T, support was added for the Cisco 10000 series router.

The following commands were introduced or modified: debug ip ssh, ip ssh min dh size, ip ssh rsa keypair-name, ip ssh version, ssh.

Secure Shell Version 2 Client and Server Support

12.0(32)SY 12.3(7)JA 12.4(17)

The Cisco IOS image was updated to provide for the automatic generation of SNMP traps when an SSH session terminates.

SSH Keyboard Interactive Authentication

12.4(18) 12.2(33)SXH3

The SSH Keyboard Interactive Authentication feature, also known as Generic Message Authentication for SSH, is a method that can be used to implement different types of authentication mechanisms. Basically, any currently supported authentication method that requires only user input can be performed with this feature.

Secure Shell Version 2 Enhancements

12.4(20)T

15.1(2)S

12.2(50)SY

The Secure Shell Version 2 Enhancements feature includes a number of additional capabilities such as support for VRF-aware SSH, SSH debug enhancements, and DH Group 14 and Group 16 exchange support.

In Cisco IOS 15.1(2)S, support was added for the Cisco 7600 series router.

Note    Only the VRF-aware SSH feature is supported in Cisco IOS Release 12.2(50)SY.

The following commands were introduced or modified: debug ip ssh, ip ssh dh min size.

Secure Shell Version 2 Enhancements for RSA Keys.

15.0(1)M 15.1(1)S

The Secure Shell Version 2 Enhancements for RSA Keys feature includes a number of additional capabilities to support RSA key-based user authentication for SSH and SSH server host key storage and verification.

The following commands were introduced or modified: ip ssh pubkey-chain, ip ssh stricthostkeycheck.

Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned 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. (1005R)

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.