Configuring Secure Shell (SSH)

• Finding Feature Information, on page 1

• Prerequisites for Configuring Secure Shell, on page 1

• Restrictions for Configuring Secure Shell, on page 2

• Information about SSH, on page 2

• How to Configure SSH, on page 5

• Monitoring the SSH Configuration and Status, on page 8

• Additional References, on page 9

• Feature Information for SSH, on page 10

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 http://www.cisco.com/go/cfn. An account on Cisco.com is not

required.

Prerequisites for Configuring Secure Shell

The following are the prerequisites for configuring the switch for secure shell (SSH):

• To use SSH, you must install the cryptographic (encrypted) software image on your switch.

• For SSH to work, the switch needs an Rivest, Shamir, and Adleman (RSA) public/private key pair. This

is the same with Secure Copy Protocol (SCP), which relies on SSH for its secure transport.

• Before enabling SCP, you must correctly configure SSH, authentication, and authorization on the switch.

• Because SCP relies on SSH for its secure transport, the router must have an Rivest, Shamir, and Adelman

(RSA) key pair.

• SCP relies on SSH for security.

Configuring Secure Shell (SSH)

• SCP requires that authentication, authorization, and accounting (AAA) authorization be configured so

the router can determine whether the user has the correct privilege level.

• A user must have appropriate authorization to use SCP.

• A user who has appropriate authorization can use SCP to copy any file in the Cisco IOS File System

(IFS) to and from a switch by using the copy command. An authorized administrator can also do this

from a workstation.

• The Secure Shell (SSH) server requires an IPsec (Data Encryption Standard [DES] or 3DES) encryption

software image; the SSH client requires an IPsec (DES or 3DES) encryption software image.)

• Configure a hostname and host domain for your device by using the hostname and ip domain-name

commands in global configuration mode.

Related Topics

Secure Copy Protocol, on page 4

Restrictions for Configuring Secure Shell

The following are restrictions for configuring the Switch for secure shell.

• The switch supports Rivest, Shamir, and Adelman (RSA) authentication.

• SSH supports only the execution-shell application.

• The SSH server and the SSH client are supported only on Data Encryption Standard (DES) (56-bit) and

3DES (168-bit) data encryption software. In DES software images, DES is the only encryption algorithm

available. In 3DES software images, both DES and 3DES encryption algorithms are available.

• The Switch supports the Advanced Encryption Standard (AES) encryption algorithm with a 128-bit key,

192-bit key, or 256-bit key. However, symmetric cipher AES to encrypt the keys is not supported.

• This software release does not support IP Security (IPSec).

• When using SCP, you cannot enter the password into the copy command. You must enter the password

when prompted.

• The login banner is not supported in Secure Shell Version 1. It is supported in Secure Shell Version 2.

• The -l keyword and userid :{number} {ip-address} delimiter and arguments are mandatory when

configuring the alternative method of Reverse SSH for console access.

Related Topics

Secure Copy Protocol, on page 4

Information about SSH

Secure Shell (SSH) is a protocol that provides a secure, remote connection to a device. SSH provides more

security for remote connections than Telnet does by providing strong encryption when a device is authenticated.

This software release supports SSH Version 1 (SSHv1) and SSH Version 2 (SSHv2).

Configuring Secure Shell (SSH)

Restrictions for Configuring Secure Shell

SSH and Switch Access

Secure Shell (SSH) is a protocol that provides a secure, remote connection to a device. SSH provides more

security for remote connections than Telnet does by providing strong encryption when a device is authenticated.

This software release supports SSH Version 1 (SSHv1) and SSH Version 2 (SSHv2).

SSH functions the same in IPv6 as in IPv4. For IPv6, SSH supports IPv6 addresses and enables secure,

encrypted connections with remote IPv6 nodes over an IPv6 transport.

SSH Servers, Integrated Clients, and Supported Versions

The Secure Shell (SSH) Integrated Client feature is an application that runs over the SSH protocol to provide

device authentication and encryption. The SSH client enables a Cisco device to make a secure, encrypted

connection to another Cisco device or to any other device running the SSH server. This connection provides

functionality similar to that of an outbound Telnet connection except that the connection is encrypted. With

authentication and encryption, the SSH client allows for secure communication over an unsecured network.

The SSH server and SSH integrated client are applications that run on the switch. The SSH server works with

the SSH client supported in this release and with non-Cisco SSH clients. The SSH client works with publicly

and commercially available SSH servers. The SSH client supports the ciphers of Data Encryption Standard

(DES), 3DES, and password authentication.

The switch supports an SSHv1 or an SSHv2 server.

The switch supports an SSHv1 client.

The SSH client functionality is available only when the SSH server is enabled.

Note

User authentication is performed like that in the Telnet session to the device. SSH also supports the following

user authentication methods:

• TACACS+

• RADIUS

• Local authentication and authorization

Related Topics

Configuring the Switch for Local Authentication and Authorization

TACACS+ and Switch Access

RADIUS and Switch Access

SSH Configuration Guidelines

Follow these guidelines when configuring the switch as an SSH server or SSH client:

• An RSA key pair generated by a SSHv1 server can be used by an SSHv2 server, and the reverse.

• If the SSH server is running on a stack master and the stack master fails, the new stack master uses the

RSA key pair generated by the previous stack master.

Configuring Secure Shell (SSH)

SSH and Switch Access

• If you get CLI error messages after entering the crypto key generate rsa global configuration command,

an RSA key pair has not been generated. Reconfigure the hostname and domain, and then enter the crypto

key generate rsa command. For more information, see Related Topics below.

• When generating the RSA key pair, the message No host name specified might appear. If it does, you

must configure a hostname by using the hostname global configuration command.

• When generating the RSA key pair, the message No domain specified might appear. If it does, you must

configure an IP domain name by using the ip domain-name global configuration command.

• When configuring the local authentication and authorization authentication method, make sure that AAA

is disabled on the console.

Related Topics

Setting Up the Switch to Run SSH, on page 5

Configuring the Switch for Local Authentication and Authorization

Secure Copy Protocol Overview

The Secure Copy Protocol (SCP) feature provides a secure and authenticated method for copying switch

configurations or switch image files. SCP relies on Secure Shell (SSH), an application and a protocol that

provides a secure replacement for the Berkeley r-tools.

For SSH to work, the switch needs an RSA public/private key pair. This is the same with SCP, which relies

on SSH for its secure transport.

Because SSH also relies on AAA authentication, and SCP relies further on AAA authorization, correct

configuration is necessary.

• Before enabling SCP, you must correctly configure SSH, authentication, and authorization on the switch.

• Because SCP relies on SSH for its secure transport, the router must have an Rivest, Shamir, and Adelman

(RSA) key pair.

When using SCP, you cannot enter the password into the copy command. You must enter the password when

prompted.

Note

Secure Copy Protocol

The Secure Copy Protocol (SCP) feature provides a secure and authenticated method for copying switch

configurations or switch image files. The behavior of SCP is similar to that of remote copy (rcp), which comes

from the Berkeley r-tools suite, except that SCP relies on SSH for security. SCP also requires that authentication,

authorization, and accounting (AAA) authorization be configured so the switch can determine whether the

user has the correct privilege level. To configure the Secure Copy feature, you should understand the SCP

concepts.

Related Topics

Prerequisites for Configuring Secure Shell, on page 1

Restrictions for Configuring Secure Shell, on page 2

Configuring Secure Shell (SSH)

Secure Copy Protocol Overview

How to Configure SSH

Setting Up the Switch to Run SSH

Follow these steps to set up your Switch to run SSH:

Before you begin

Configure user authentication for local or remote access. This step is required. For more information, see

Related Topics

SSH Configuration Guidelines, on page 3

Configuring the Switch for Local Authentication and Authorization

Configuring the SSH Server

Follow these steps to configure the SSH server:

This procedure is only required if you are configuring the Switch as an SSH server.

Note

SUMMARY STEPS

1. enable

Configuring Secure Shell (SSH)

Configuring the SSH Server

2. configure terminal

3. ip ssh version [1 | 2]

4. ip ssh {timeout seconds | authentication-retries number}

5. Use one or both of the following:

• line vtyline_number[ending_line_number]

• transport input ssh

6. end

7. show running-config

8. copy running-config startup-config

DETAILED STEPS

PurposeCommand or Action

Enables privileged EXEC mode. Enter your password if

prompted.

enable

Example:

Step 1

Switch> enable

Enters the global configuration mode.configure terminal

Example:

Step 2

Switch# configure terminal

(Optional) Configures the Switch to run SSH Version 1 or

SSH Version 2.

ip ssh version [1 | 2]

Example:

Step 3

• 1—Configure the Switch to run SSH Version 1.

Switch(config)# ip ssh version 1

• 2—Configure the Switch to run SSH Version 2.

If you do not enter this command or do not specify a

keyword, the SSH server selects the latest SSH version

supported by the SSH client. For example, if the SSH client

supports SSHv1 and SSHv2, the SSH server selects SSHv2.

Configures the SSH control parameters:

ip ssh {timeout seconds | authentication-retries number}

Step 4

Example:

• Specify the time-out value in seconds; the default is

120 seconds. The range is 0 to 120 seconds. This

Switch(config)# ip ssh timeout 90

parameter applies to the SSH negotiation phase. After

authentication-retries 2

the connection is established, the Switch uses the

default time-out values of the CLI-based sessions.

By default, up to five simultaneous, encrypted SSH

connections for multiple CLI-based sessions over the

network are available (session 0 to session 4). After

the execution shell starts, the CLI-based session

time-out value returns to the default of 10 minutes.

Configuring Secure Shell (SSH)

Configuring the SSH Server

PurposeCommand or Action

• Specify the number of times that a client can

re-authenticate to the server. The default is 3; the range

is 0 to 5.

Repeat this step when configuring both parameters.

(Optional) Configures the virtual terminal line settings.Use one or both of the following:

Step 5

• line vtyline_number[ending_line_number]

• Enters line configuration mode to configure the virtual

terminal line settings. For line_number and

• transport input ssh

ending_line_number, specify a pair of lines. The range

is 0 to 15.

Example:

Switch(config)# line vty 1 10

• Specifies that the Switch prevent non-SSH Telnet

connections. This limits the router to only SSH

connections.

Switch(config-line)# transport input ssh

Returns to privileged EXEC mode.end

Example:

Step 6

Switch(config-line)# end

Verifies your entries.show running-config

Example:

Step 7

Switch# show running-config

(Optional) Saves your entries in the configuration file.copy running-config startup-config

Example:

Step 8

Switch# copy running-config startup-config

Monitoring the SSH Configuration and Status

This table displays the SSH server configuration and status.

Table 1: Commands for Displaying the SSH Server Configuration and Status

PurposeCommand

Shows the version and configuration information for the SSH server.show ip

ssh

Shows the status of the SSH server.show ssh

Configuring Secure Shell (SSH)

Monitoring the SSH Configuration and Status

Additional References