Secure Shell Configuration Guide, Cisco IOS XE Release 3S (Cisco ASR 903)
Secure Shell Version 2 Support
Downloads: This chapterpdf (PDF - 211.0KB) The complete bookPDF (PDF - 357.0KB) | Feedback

Secure Shell Version 2 Support

Secure Shell Version 2 Support

Last Updated: November 5, 2012

The Secure Shell Version 2 Support feature allows you to configure Secure Shell (SSH) Version 2. SSH runs on top of a reliable transport layer and provides strong authentication and encryption capabilities. Currently, 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 also 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 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 Secure Shell Version 2 Support

Prior to configuring SSH, perform the following task:

  • Download the required image on your router. The SSH server requires you to have a k9 (Triple Data Encryption Standard [3DES]) software image from downloaded on your router.

Restrictions for Secure Shell Version 2 Support

  • SSH servers and SSH clients are supported in k9 software images.
  • Execution Shell, remote command execution, and Secure Copy Protocol (SCP) are the only applications supported.
  • Rivest, Shamir, and Adelman (RSA) key generation is an SSH server side requirement. Routers that act as SSH clients do not need to generate RSA keys.
  • The RSA key-pair size must be greater than or equal to 768.
  • The following functionality is not supported:
    • RSA user authentication (in the SSH server or SSH client for Cisco IOS XE software)
    • Public key authentication
    • SSH server strict host key check
    • 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 command ip ssh version has been introduced so that you may define which version of SSH that you want 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 so that you can enable a SSH connection using 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 host name and a domain name, which was required in SSH Version 1 of the Cisco IOS XE software.


Note


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

Secure Shell Version 2 Enhancements

The Secure Shell Version 2 Enhancements include a number of additional capabilities such as supporting VRF aware SSH, SSH debug enhancements, and Diffie-Hellman group exchange support.

The Cisco IOS XE SSH implementation has traditionally used 768 bit modulus but with an increasing need for higher key sizes to accommodate Diffie-Hellman (DH) Group 14 (2048 bits) and Group 16 (4096 bits) cryptographic applications a message exchange between the client and server to establish the favored DH group becomes necessary. The ip ssh dh min sizecommand was introduced so you can configure modulus size on the SSH server. In addition to this the sshcommand was extended to add VRF awareness to 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 has been enhanced by modifying SSH debug commands. The debug ip ssh command has been 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.

SNMP Trap Generation

Simple Network Management Protocol (SNMP) traps will be 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 feature module.


Note


When configuring 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. See Example Setting an SNMP Trap for more information.

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. See Example SNMP Debugging for more information.

How to Configure Secure Shell Version 2 Support

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

To configure your router for SSH Version 2 using a host name and domain name, perform the following steps. You may also configure SSH Version 2 by using the RSA key pair configuration. See Configuring a Router for SSH Version 2 Using RSA Key Pairs for more information.

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 host name 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

To enable SSH Version 2 without configuring a host name or domain name, perform the following steps. 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 host name and domain name configuration. See Configuring a Router for SSH Version 2 Using a Host Name and Domain Name for more information.

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 keypair to use for SSH usage.

Note    A 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 120

 

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.

 

Starting an Encrypted Session with a Remote Device

To start an encrypted session with a remote networking device, perform the following step. (You do not have to enable your router. SSH can be run in disabled mode.)


Note


The device you wish to connect with must support a SSH server that has an encryption algorithm that is supported in Cisco IOS XE 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



Example:



Example:

Or



Example:

The above example adheres to the SSH Version 2 conventions. A more natural and common way to start a session is by linking the username with the hostname. For example, the following configuration example provides an end result that is identical to that of the above example:



Example:

Router# ssh -v 2 -c aes256-cbc -m hmac-sha1-96 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 the SSH version that has a problem.

Enabling Secure Copy Protocol on the SSH Server

To configure server-side functionality for SCP, perform the following steps. This example shows a typical configuration that allows the router to securely copy files from a remote workstation.

Before You Begin

SCP relies on AAA authentication and authorization 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 authentication, authorization, and accounting (AAA) access control model.

 
Step 4
aaa authentication login default local


Example:

Router(config)# aaa authentication login default local

 

Sets authentication, authorization, and accounting (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 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, specifies the username, the privilege level, and an unencrypted password.

 
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

SUMMARY STEPS

1.    enable

2.    show ssh

3.    exit


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
show ssh


Example:

Device# show ssh

 

Displays the status of SSH server connections.

 
Step 3
exit


Example:

Device# exit

 

Exits privileged EXEC mode and returns to user EXEC mode.

 

Examples

The following sample output from the show ssh command displays status of various SSH Version 1 and Version 2 connections for Version 1 and Version 2 connections:

-----------------------------------------------------------------------
Device# 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
-------------------------------------------------------------------------

The following sample output from the show ssh command displays status of various SSH Version 1 and Version 2 connections for a Version 2 connection with no Version 1 connection:

-------------------------------------------------------------------------
Device# 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.
-------------------------------------------------------------------------

The following sample output from the show ssh command displays status of various SSH Version 1 and Version 2 connections for a Version 1 connection with no Version 2 connection:

-------------------------------------------------------------------------
Device# show ssh

Connection      Version Encryption      State                   Username
 0              1.5     3DES            Session started         lab
%No SSHv2 server connections running.
-------------------------------------------------------------------------

Verifying the Secure Shell Status Using the show ip ssh Command

To verify your SSH configuration, perform the following steps.

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 examples from the show ip ssh command display the version of SSH that is enabled, the authentication timeout values, and the number of authentication retries.

-----------------------------------------------------------------------
router# show ip ssh
3d06h: %SYS-5-CONFIG_I: Configured from console by consoleh
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.

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 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

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

Example ConfiguringSecureShellVersion2

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

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

Example Starting 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 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 shows that an SNMP trap has been set. The trap notification is generated automatically when the SSH session terminates. 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

Where a.b.c.d is the IP address of the SSH client.

Example SNMP Debugging

The following is sample output using 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#

Example SSH Debugging Enhancements

The following is sample output from the debug ip ssh detailcommand. The output provides debugging information regarding 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 regarding 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 router.

Additional References

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Commands List, All Releases

Security commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples

Cisco IOS Security Command Reference

Authentication, Authorization, and Accounting

Configuring Authentication , Configuring Authorization , and Configuring Accounting feature modules.

Configuring Secure Shell, a host name and host domain

Configuring Secure Shell feature module.

Debugging commands

Cisco IOS Debug Command Reference

IPsec

Configuring Security for VPNs with IPsec feature module.

SNMP, configuring traps

Configuring SNMP Support feature module.

Standards

Standards

Title

Internet Engineering Task Force (IETF) Secure Shell Version 2 Draft Standards

http://www.ietf.org/ Internet Engineering Task Force website.

MIBs

MIBs

MIBs Link

None

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

None

--

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

Cisco IOS XE Release 2.1

The Secure Shell Version 2 Support feature allows you to configure Secure Shell (SSH) Version 2. SSH runs on top of a reliable transport layer and provides strong authentication and encryption capabilities.

In Cisco IOS Release 2.4, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

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

Secure Shell Version 2 Enhancements

Cisco IOS XE Release 2.1

The Secure Shell Version 2 Enhancements include a number of additional capabilities such as support for VRF aware SSH, SSH debug enhancements, and Diffie-Hellman group 14 and group 16 exchange support.

In Cisco IOS Release 2.4, this feature was introduced on the Cisco ASR 1000 Series Aggregation Services Routers.

Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: 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. (1110R)

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.

© 2012 Cisco Systems, Inc. All rights reserved.