Secure Shell Configuration Guide, Cisco IOS Release 15SY
Secure Shell Version 2 Support
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Secure Shell Version 2 Support

Contents

Secure Shell Version 2 Support

Last Updated: October 16, 2012

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 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 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

  • Before configuring SSH, ensure that the required image is loaded on your device. The SSH server requires you to have a k9 (Triple Data Encryption Standard [3DES]) software image depending on your release.
  • You have to use a SSH remote device that supports SSH Version 2 and connect to a Cisco device.
  • SCP relies on authentication, authorization, and accounting (AAA) to function correctly. Therefore, AAA must be configured on the device to enable the secure copy protocol on the SSH Server.

Note


The SSH Version 2 server and the SSH Version 2 client are supported on your Cisco software, depending on your release. (The SSH client runs both the SSH Version 1 protocol and the SSH Version 2 protocol. The SSH client is supported in both k8 and k9 images depending on your release.)

For more information about downloading a software image, refer to the Configuration Fundamentals Configuration Guide.

Restrictions for Secure Shell Version 2 Support

  • Secure Shell (SSH) servers and SSH clients are supported in Triple Data Encryption Standard (3DES) software images.
  • Execution Shell, remote command execution, and Secure Copy Protocol (SCP) are the only applications supported.
  • Rivest, Shamir, and Adleman (RSA) key generation is an SSH server-side requirement. Devices that act as SSH clients need not generate RSA keys.
  • The RSA key pair size must be greater than or equal to 768 bits.
  • The following features are 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 defines the SSH version to be configured. 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 device 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 enables an SSH connection using the Rivest, Shamir, and Adleman (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). This behavior still exists, but by using the ip ssh rsa keypair-name command, you can overcome this 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 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 Virtual Routing and Forwarding (VRF)-Aware SSH, SSH debug enhancements, and Diffie-Hellman (DH) group exchange support.


Note


The VRF-Aware SSH feature is supported depending on your release.

The Cisco 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 configures the modulus size on the SSH server. In addition to this, the ssh command 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 simplify the debugging process. Before the simplification of the debugging process, 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 SSH Version 2 supports keyboard-interactive and password-based authentication methods. The SSH Version 2 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 SSH server to complete the authentication.

An SSH user trying to establish 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 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 SSH client must assign a host key for each server. When the client tries to establish an SSH session with a server, the client 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 by 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 server, but Cisco clients cannot propose public key as an authentication method. If the Cisco 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 SSH client.

SNMP Trap Generation

Depending on your release, 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 enabled. For information about enabling SNMP traps, see the "Configuring SNMP Support" module in the SNMP Configuration Guide.


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 "" section.

You must also enable 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 " " section.

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" section.

How to Configure Secure Shell Version 2 Support

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

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    hostname name

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]

8.    exit


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
hostname name


Example:

Device(config)# hostname cisco7200

 

Configures a hostname for your device.

 
Step 4
ip domain-name name


Example:

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

 

Configures a domain name for your device.

 
Step 5
crypto key generate rsa


Example:

Device(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:

Device(config)# ip ssh time-out 120

 

(Optional) Configures SSH control variables on your device.

 
Step 7
ip ssh version [1 | 2]


Example:

Device(config)# ip ssh version 1

 

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

 
Step 8
exit


Example:

Device(config)# exit

 

Exits global configuration mode and enters privileged EXEC mode.

 

Configuring a Device for SSH Version 2 Using RSA Key Pairs

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

7.    exit


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
ip ssh rsa keypair-name keypair-name


Example:

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

 

Specifies the RSA key pair to be used for SSH.

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


Example:

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

 

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

  • 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. When you delete the RSA key pair, you automatically disable the SSH server.
 
Step 5
ip ssh [time-out seconds | authentication-retries integer]


Example:

Device(config)# ip ssh time-out 12

 

Configures SSH control variables on your device.

 
Step 6
ip ssh version 2


Example:

Device(config)# ip ssh version 2

 

Specifies the version of SSH to be run on the device.

 
Step 7
exit


Example:

Device(config)# exit

 

Exits global configuration mode and enters privileged EXEC mode.

 

Configuring the Cisco SSH Server to Perform RSA-Based User 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.    username username

8.    key-string

9.    key-hash key-type key-name

10.    end


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
hostname name


Example:

Device(config)# hostname host1

 

Specifies the hostname.

 
Step 4
ip domain-name name


Example:

Device(config)# ip domain-name name1

 

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

 
Step 5
crypto key generate rsa


Example:

Device(config)# crypto key generate rsa

 

Generates RSA key pairs.

 
Step 6
ip ssh pubkey-chain


Example:

Device(config)# ip ssh pubkey-chain

 

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

  • 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.
 
Step 7
username username


Example:

Device(conf-ssh-pubkey)# username user1

 

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

 
Step 8
key-string


Example:

Device(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
key-hash key-type key-name


Example:

Device(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 the 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 also copy the hash value from another Cisco device. 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 10
end


Example:

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

 

Exits public-key data configuration mode and returns to privileged EXEC mode.

 

Configuring 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:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
hostname name


Example:

Device(config)# hostname host1

 

Specifies the hostname.

 
Step 4
ip domain-name name


Example:

Device(config)# ip domain-name name1

 

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

 
Step 5
crypto key generate rsa


Example:

Device(config)# crypto key generate rsa

 

Generates RSA key pairs.

 
Step 6
ip ssh pubkey-chain


Example:

Device(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:

Device(conf-ssh-pubkey)# server server1

 

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

 
Step 8
key-string


Example:

Device(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:

Device(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:

Device(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 the 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 device. 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:

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

 

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

 
Step 12
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 13
ip ssh stricthostkeycheck


Example:

Device(config)# ip ssh stricthostkeycheck

 

Ensures that server authentication takes place.

  • The connection is terminated in case of a failure.
 

Starting an Encrypted Session with a Remote Device


Note


The device you want to connect with must support a Secure Shell (SSH) server that has an encryption algorithm that is supported in Cisco software. Also, you need not enable your device. SSH can be run in disabled mode.
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:

Device# 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 the SSH version that has a problem.

Enabling Secure Copy Protocol on the SSH Server


Note


The following task configures the server-side functionality for SCP. This task shows a typical configuration that allows the device to securely copy files from a remote workstation.
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

10.    exit

11.    debug ip scp


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Device# configure terminal

 

Enters global configuration mode.

 
Step 3
aaa new-model


Example:

Device(config)# aaa new-model

 

Enables the AAA access control model.

 
Step 4
aaa authentication login default local


Example:

Device(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:

Device(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 must use the local database for authorization.

 
Step 6
username name privilege privilege-level password password


Example:

Device(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:

Device(config)# ip ssh time-out 120

 

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

 
Step 8
ip ssh authentication-retries integer


Example:

Device(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:

Device(config)# ip scp server enable

 

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

 
Step 10
exit


Example:

Device(config)# exit

 

Exits global configuration mode and returns to privileged EXEC mode.

 
Step 11
debug ip scp


Example:

Device# debug ip scp

 

(Optional) Troubleshoots SCP authentication problems.

 

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

SUMMARY STEPS

1.    enable

2.    show ip 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 ip ssh


Example:

Device# show ip ssh

 

Displays the version and configuration data for SSH.

 
Step 3
exit


Example:

Device# exit

 

Exits privileged EXEC mode and returns to user EXEC mode.

 

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 for Version 1 and Version 2 connections:

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

SSH Enabled - version 1.99
Authentication timeout: 120 secs; Authentication retries: 3
-----------------------------------------------------------------------

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 for a Version 2 connection with no Version 1 connection:

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

SSH Enabled - version 2.0
Authentication timeout: 120 secs; Authentication retries: 3
------------------------------------------------------------------------

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 for a Version 1 connection with no Version 2 connection:

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

SUMMARY STEPS

1.    enable

2.    debug ip ssh

3.    debug snmp packet


DETAILED STEPS
  Command or Action Purpose
Step 1
enable


Example:

Device> enable

 

Enables privileged EXEC mode.

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


Example:

Device# debug ip ssh

 

Enables debugging of SSH.

 
Step 3
debug snmp packet


Example:

Device# debug snmp packet

 

Enables debugging of every SNMP packet sent or received by the device.

 

Example

The following sample output from the debug ip ssh command shows the connection is an SSH Version 2 connection:

Device# 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:

Device# configure terminal
Device(config)# ip ssh version 1

Example: Configuring Secure Shell Version 2

The following example shows how to configure SSH Version 2:

Device# configure terminal
Device(config)# ip ssh version 2

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

Example: Starting an Encrypted Session with a Remote Device

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

Device# 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 device. This example uses a locally defined username and password.
Device# configure terminal
Device(config)# aaa new-model
Device(config)# aaa authentication login default local
Device(config)# aaa authorization exec default local
Device(config)# username samplename privilege 15 password password1
Device(config)# ip ssh time-out 120
Device(config)# ip ssh authentication-retries 3
Device(config)# ip scp server enable

Example: Setting an SNMP Trap

The following example shows that an SNMP trap is 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 " Example: SNMP Debugging" section.

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

Examples: SSH Keyboard Interactive Authentication

Example: Enabling Client-Side Debugs

The following example shows that the client-side debugs are turned on, and the maximum number of prompts is six (three for the SSH keyboard interactive authentication method and three for the password authentication method).

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]
Device1# debug ip ssh client

SSH Client debugging is on

Device1# 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
Device2>

*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

Example: Enabling ChPass with a Blank Password Change

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

Device1# ssh -l cisco 10.1.1.3

Password:
Old Password: cisco
New Password: cisco123
Re-enter New password: cisco123

Device2> exit

[Connection to 10.1.1.3 closed by foreign host]

Example: Enabling ChPass and Changing the Password on First Login

In the following example, the ChPass feature is enabled and TACACS+ ACS is used as the back-end server. The password is changed on the first login using the SSH keyboard interactive authentication method.

Device1# 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

Device2> exit

[Connection to 10.1.1.3 closed by foreign host]

Device1# 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

Device2>

Example: Enabling ChPass and Expiring the Password After Three Logins

In the following example, the ChPass feature is enabled and TACACS+ ACS is used as the back-end AAA server. The password expires after three logins using the SSH keyboard interactive authentication method.

Device# ssh -l cisco. 10.1.1.3

Password: cisco

Device2> exit

[Connection to 10.1.1.3 closed by foreign host]

Device1# ssh -l cisco 10.1.1.3

Password: cisco

Device2> exit

Device1# ssh -l cisco 10.1.1.3

Password: cisco

Device2> exit

[Connection to 10.1.1.3 closed by foreign host]

Device1# 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

Device2>

Example: SNMP Debugging

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

Device1# debug snmp packet

SNMP packet debugging is on
Device1# ssh -l lab 10.0.0.2
Password:

Device2# exit

[Connection to 10.0.0.2 closed by foreign host]
Device1#
*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

Device1#

Examples: SSH Debugging Enhancements

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

Device# 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 packet command. The output provides debugging information about the SSH packet.

Device# 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 device.

Additional References

Related Documents

Related Topic

Document Title

Cisco IOS commands

Cisco IOS Master Command List, All Releases

AAA

Hostname and host domain configuration tasks

Secure shell configuration tasks

Security Configuration Guide: Securing User Services

Downloading a software image

Configuration fundamentals

Configuration Fundamentals Configuration Guide

IPsec configuration tasks

Security Configuration Guide: Secure Connectivity

SNMP traps configuration tasks

SNMP Configuration Guide

Standards

Standards

Title

IETF Secure Shell Version 2 Draft Standards

Internet Engineering Task Force website

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 Client and Server Support

12.4(17)

12.3(7)JA

12.0(32)SY

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

Secure Shell Version 2 Enhancements

12.2(50)SY

15.1(2)S

15.1(1)SY

12.4(20)T

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.

Support was added for the Cisco 7600 series router depending on your release.

Note    The VRF-Aware SSH feature is supported depending on your release.

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

Secure Shell Version 2 Enhancements for RSA Keys

15.0(1)M

15.1(1)S

15.1(1)SY

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, and ip ssh stricthostkeycheck.

Secure Shell Version 2 Support

12.2(25)S

12.2(11)T

12.3(4)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 software release). SSH runs on top of a reliable transport layer and provides strong authentication and encryption capabilities.

Support was added for the Cisco 10000 series router depending on your release.

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

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.

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.