Cisco IOS Security Configuration Guide: Securing User Services, Release 12.4T - Secure Shell Version 2 Support [Cisco IOS Software Releases 12.4 T]

Table Of Contents

Secure Shell Version 2 Support

Finding Feature Information

Contents

Prerequisites for Secure Shell Version 2 Support

Restrictions for Secure Shell Version 2 Support

Information About Secure Shell Version 2 Support

Secure Shell Version 2

Secure Shell Version 2 Enhancements

Secure Shell Version 2 Enhancements for RSA Keys

SNMP Trap Generation

SSH Keyboard Interactive Authentication

How to Configure Secure Shell Version 2 Support

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

Configuring a Router for SSH Version 2 Using RSA Key Pairs

Configuring a Router for SSH Version 2 Using Private Public Key Pairs

Starting an Encrypted Session with a Remote Device

Troubleshooting Tips

Enabling Secure Copy Protocol on the SSH Server

Prerequisites

Troubleshooting Tips

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

Examples

Verifying the Secure Shell Status Using the show ip ssh Command

Examples

Monitoring and Maintaining Secure Shell Version 2

Example

Configuration Examples for Secure Shell Version 2 Support

Configuring Secure Shell Version 1: Example

Configuring Secure Shell Version 2: Example

Configuring Secure Shell Versions 1 and 2: Example

Starting an Encrypted Session with a Remote Device: Example

Configuring Server-Side SCP: Example

Setting an SNMP Trap: Example

SSH Keyboard Interactive Authentication: Examples

SNMP Debugging: Example

SSH Debugging Enhancements: Examples

Where to Go Next

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for Secure Shell Version 2 Support

Secure Shell Version 2 Support

First Published: November 3, 2003

Last Updated: October 8, 2009

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. 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 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 for Secure Shell Version 2 Support" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for Secure Shell Version 2 Support

•Restrictions for Secure Shell Version 2 Support

•Information About Secure Shell Version 2 Support

•How to Configure Secure Shell Version 2 Support

•Configuration Examples for Secure Shell Version 2 Support

•Where to Go Next

•Additional References

•Feature Information for Secure Shell Version 2 Support

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 Cisco IOS Release 12.3(4)T, 12.2(25)S, or 12.3(7)JA downloaded on 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 and Version 2 protocol and is supported in both k8 and k9 images in Cisco IOS Release 12.3(4)T.)

For more information on downloading a software image, refer to Cisco IOS Configuration Fundamentals 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 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:

–Port forwarding

–Compression

Information About Secure Shell Version 2 Support

To configure SSH Version 2, you should understand the following concepts:

•Secure Shell Version 2

•Secure Shell Version 2 Enhancements

•Secure Shell Version 2 Enhancements for RSA Keys

•SNMP Trap Generation

•SSH Keyboard Interactive Authentication

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 in Cisco IOS Release 12.3(4)T 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 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 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 size command was introduced in Cisco IOS Release 12.4(20)T so you can configure modulus size on the SSH server. In addition to this the ssh command 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.

Secure Shell Version 2 Enhancements for RSA Keys

Cisco IOS SSH supports keyboard-interactive and password-based authentication methods. In addition to these authentication methods SSHv2 Enhancements for RSA Keys supports public key-based user authentication in Cisco IOS SSH. The RSA-based user authentication method uses private-public key pair association. SSH users present a private key encrypted authentication signature. This authentication signature along with their public keys are sent to the SSH server for authentication. If a match is found, the RSA-based verification is completed using the public key.

To complete authentication you must generate a private-public key pair. The public key must be configured and saved on the SSH server.

Note Storing public keys on a server uses memory; therefore, the number of public keys configurable on an SSH server is restricted to 10 users, with a maximum of two public keys per user.

SNMP Trap Generation

Effective with Cisco IOS Release 12.4(17), 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" module in the Cisco IOS Network Management Configuration Guide, Release 15.0.

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. For an example of an SNMP trap generation configuration, see the section "Setting an SNMP Trap: Example" section."

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 section "SNMP Debugging: Example" 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 deployed.

The following methods are currently 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 deployed, see the chapter "SSH Keyboard Interactive Authentication: Examples" section."

How to Configure Secure Shell Version 2 Support

This section contains the following procedures:

•Configuring a Router for SSH Version 2 Using a Host Name and Domain Name (required)

•Configuring a Router for SSH Version 2 Using RSA Key Pairs (optional)

•Configuring a Router for SSH Version 2 Using Private Public Key Pairs (optional)

•Starting an Encrypted Session with a Remote Device (optional)

•Enabling Secure Copy Protocol on the SSH Server (optional)

•Verifying the Status of the Secure Shell Connection Using the show ssh Command (optional)

•Verifying the Secure Shell Status Using the show ip ssh Command (optional)

•Monitoring and Maintaining Secure Shell Version 2 (optional)

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

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

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 the section ""Configuring a Router for SSH Version 2 Using a Host Name and Domain Name" section").

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
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 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 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.
Configuring a Router for SSH Version 2 Using Private Public Key Pairs

Perform this task to enable SSH Version 2 public key-based user authentication. SSH Version 2 will be approve authentication if the public-key and private-key encryption messages match the keys stored on the SSH server.

SUMMARY STEPS

1. enable

2. configure terminal

3. ip ssh pubkey-chain

4. server server-name

5. username user-name

6. key-hash key-type key-name

7. exit

DETAILED STEPS
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 pubkey-chain 
Example:

Router (config)# ip ssh pubkey-chain
Enters pubkey-chain configuration mode.
Step 4
server server-name
Example:
Router (conf-ssh-pubkey)# server cisco
Enables the SSH server for public key authentication on the router.
Step 5
username user-name
Example:
Router (conf-ssh-pubkey)# username stabilo
Configures the SSH username and enters public key user mode.
Step 6
key-hash key-type key-name
Example:
Router (conf-ssh-pubkey-user)# key-hash ssh-rsa 
lemon
Specifies the SSH key type and version.

Note Key-type must be ssh-rsa for configuration of private public key pairs.
Step 7
exit
Example:
Router (conf-ssh-pubkey-user)# exit
Exits public key user mode.
Starting an Encrypted Session with a Remote Device

Perform this task to start an encrypted session with a remote networking device, (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 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
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
or

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 which SSH version has a problem.

Enabling Secure Copy Protocol on the SSH Server

Perform this task to configure server-side functionality for SCP. This example shows a typical configuration that allows the router to securely copy files from a remote workstation.

Prerequisites

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
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.

Note The minimum privelege-level is 15. A privelege 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 scp command.

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

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

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
-------------------------------------------------------------------------
Version 2 Connection with No Version 1
-------------------------------------------------------------------------
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.
-------------------------------------------------------------------------
Version 1 Connection with No Version 2
-------------------------------------------------------------------------
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 Using the show ip ssh Command

Perform this task to verify your SSH configuration.

SUMMARY STEPS

1. enable

2. show ip ssh

DETAILED STEPS

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.

Version 1 and Version 2 Connections
-----------------------------------------------------------------------
router# show ip ssh
SSH Enabled - version 1.99
Authentication timeout: 120 secs; Authentication retries: 3
-----------------------------------------------------------------------
Version 2 Connection with No Version 1
------------------------------------------------------------------------
Router# show ip ssh
SSH Enabled - version 2.0
Authentication timeout: 120 secs; Authentication retries: 3
------------------------------------------------------------------------
Version 1 Connection with No Version 2
------------------------------------------------------------------------
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

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

This section provides the following configuration examples:

•Configuring Secure Shell Version 1: Example

•Configuring Secure Shell Version 2: Example

•Configuring Secure Shell Versions 1 and 2: Example

•Starting an Encrypted Session with a Remote Device: Example

•Configuring Server-Side SCP: Example

•Setting an SNMP Trap: Example

•SSH Keyboard Interactive Authentication: Examples

•SNMP Debugging: Example

•SSH Debugging Enhancements: Examples

Configuring Secure Shell Version 1: Example
Router# configure terminal
Router (config)# ip ssh version 1
Router (config)# end
Configuring Secure Shell Version 2: Example
Router# configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)# ip ssh version 2
Router(config)# end
Configuring Secure Shell Versions 1 and 2: Example
Router# configure terminal
Router (config)# no ip ssh version
Router (config)# end
Starting an Encrypted Session with a Remote Device: Example
Router# ssh -v 2 -c aes256-cbc -m hmac-sha1-160 -l shaship 10.76.82.24
Configuring Server-Side SCP: Example

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
Setting an SNMP Trap: Example

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 "SNMP Debugging: Example" section."
snmp-server
snmp-server host a.b.c.d public tty
Where a.b.c.d is the IP address of the SSH client.

SSH Keyboard Interactive Authentication: Examples

The following are examples of various scenarios in which the SSH Keyboard Interactive Authentication feature has been automatically deployed:

Client-Side Debugs

In the following example, client-side debugs are turned on and the maximum number of prompts = six, (three each 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 Backend AAA Server, ChPass Is Enabled, and a Blank Password Change Is Made

In the following example, a TACACS+ access control server (ACS) is the backend Accounting, Authentication, and Authorization (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 Backend AAA Server, ChPass Is Enabled, and the Password Is Changed on First Login

In the following example, a TACACS+ ACS is the backend 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 Backend AAA Server, ChPass Is Enabled, and the Password Expires After Three Logins

In the following example, a TACACS+ ACS is the backend 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>
SNMP Debugging: Example

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#
SSH Debugging Enhancements: Examples
The following is sample output from the debug ip ssh detail command. 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 packet command. 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 Cisco IOS router.

Additional References

The following sections provide references related to Secure Shell Version 2.

Related Documents

Related Topic

Document Title

AAA

Cisco IOS Security Configuration Guide: Securing User Services, Release 15.0.

Configuring a host name and host domain

"Configuring Secure Shell" module.

Configuring Secure Shell

Debugging commands

Cisco IOS Debug Command Reference

Downloading a Cisco software image

Cisco IOS Configuration Fundamentals Guide, Release 12.4T and Cisco IOS Network Management Configuration Guide, Release 15.0.

IOS configuration fundamentals

IPSec

Cisco IOS Security Configuration Guide: Secure Connectivity, Release 15.0.

Security commands

Cisco IOS Security Command Reference

SNMP, configuring traps

"Configuring SNMP Support" module in the Cisco IOS Network Management Configuration Guide, Release 15.0.

Standards

Standards

Title

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

Internet Engineering Task Force website

MIBs

MIBs

MIBs Link

•

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

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

RFCs

RFCs

Title

No new or modified RFCs are supported by this feature.

—

Technical Assistance

Description

Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport

Feature Information for Secure Shell Version 2 Support

Table 1 lists the release history for this feature.

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

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

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

Table 1 Feature Information for Secure Shell Version 2 Support

Feature Name

Releases

Feature Information

Secure Shell Version 2 Support

12.3(4)T
12.2(25)S

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.>>

The following sections provide information about this feature:

•Information About Secure Shell Version 2 Support

•How to Configure Secure Shell Version 2 Support

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

Secure Shell Version 2 Client and Server Support

12.3(7)JA
12.0(32)SY

This feature was integrated into Cisco IOS Release 12.3(7)JA.

Secure Shell Version 2 Client and Server Support

12.4(17)

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

For information about this feature, see the following section:

•"SNMP Trap Generation" section

•"SNMP Debugging: Example" section

SSH Keyboard Interactive Authentication

12.4(18)

12.2(33)SXH3

This 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.

For information about this feature see the following sections:

•"SSH Keyboard Interactive Authentication" section

•"SSH Keyboard Interactive Authentication: Examples" section

Secure Shell SSH Version 2 Client Support

Cisco IOS XE Release 2.1

This feature was introduced on the Cisco ASR 1000 series routers.

Secure Shell Version 2 Enhancements

12.4(20)T
Cisco IOS XE Release 2.4

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.

This feature was implemented on the Cisco ASR 1000 series routers.

For information about this feature see the following sections:

•"Secure Shell Version 2 Enhancements" section

•"Configuring Server-Side SCP: Example" section

Secure Shell Version 2 Enhancements for RSA Keys.

15.0(1)M

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

For information about this feature see the following sections:

•Secure Shell Version 2 Enhancements for RSA Keys

•Configuring a Router for SSH Version 2 Using Private Public Key Pairs

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

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