Cisco configure SSH

Prerequisites

The Cisco IOS image used must be a k9(crypto) image in order to support SSH.

Configure using aaa new-model

!--- The aaa new-model command causes the local username and password on the router
!--- to be used in the absence of other AAA statements.
aaa new-model
username cisco password 0 cisco
!--- Instead of aaa new-model, you can use the login local command.

!--- assign domain name to the router/switch, this will be used to sign off SSH key
ip domain-name rtp.cisco.com
ip ssh version 2
ip ssh port 22

!--- Generate an SSH key to be used with SSH here 1024bit long
crypto key generate rsa modulus 1024
ip ssh time-out 60
ip ssh authentication-retries 2

line vty 0 4 
!--- Prevent non-SSH Telnets.
transport input ssh

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

This feature is only supported in IOS 15.0(1)M and later versions.

The below need to be reworked..........WIP.........

Paste your public key

R2#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#ip ssh pubkey-chain
R2(conf-ssh-pubkey)#username tech
R2(conf-ssh-pubkey-user)#key-string
R2(conf-ssh-pubkey-data)#$AAQEA6jYlf9MBskhkWov+ZOUDKun0ExQIRj1zfWA/YciO02VS  
R2(conf-ssh-pubkey-data)#$XsxM7SqNkRSQOR7y7HBMoxTHV7o+R/uS6A8/mF0A3P/ScRjct  
R2(conf-ssh-pubkey-data)#$JrNGACGaFy1njD9PrrvrU4o4hx6XDr6xVXF4sP4OCSXIn+Cp8  
R2(conf-ssh-pubkey-data)#$bCnZLmv908AeDb1Ac4nPdsn1OhCPIg6fxZjB7DvAMB8Dbr+7Y  
R2(conf-ssh-pubkey-data)#$apEbGE94luIqnBc61HsMd6JCWbQ== tech@admin.us     
R2(conf-ssh-pubkey-data)#exit
R2(conf-ssh-pubkey-user)#^Z

Verify

R2#show run | section ssh
ip ssh rsa keypair-name SSH
ip ssh version 2
ip ssh pubkey-chain
 username pipi
  key-hash ssh-rsa C20B739F2645D6850C591C6A11780CB5 tech@admin.us

Disable authentication (not tested)

You can actually use the below listed command. It basically disables authentication and won't prompt for username and password. Remember, we are using default and not any method list so it will disable authentication on all lines including console.

r1(config)#aaa authentication login default none

If you would only like to disable authentication on a specific line then create a method list and apply it on that line.

r1(config)#aaa authentication login SSH none
r1(config)# line vty 0 15
r1(config-line)#login authentication SSH
r1(config-line)#exit

References

• Configuring Secure Shell on Routers and Switches Running Cisco IOS
• Secure Shell Version 2 Support Last Updated: March 31st 2011, Sections: Secure Shell Version 2 Enhancements for RSA Keys & Configuring the Cisco IOS SSH Server to Perform RSA-Based User Authentication
• SSH with key authentication on Cisco IOS devices
• SSH access without password Cisco forum
• SSH Publickey accepted but still prompted for username/password? Cisco forum
• Network Management Configuration Guide Library, Cisco IOS Release 15M&T Last Updated: November 29, 2012