Generating or erasing the switch public/private host key pair

A public and private host key pair must be generated on the switch. The switch uses this key pair along with a dynamically generated session key pair to negotiate an encryption method and session with an SSH client trying to connect to the switch.

The host key pair is stored in the switch flash memory, and only the public key in this pair is readable. The public key should be added to a "known hosts" file (for example, $HOME/.ssh/known_hosts on UNIX systems) on the SSH clients which should have access to the switch. Some SSH client applications automatically add the switch public key to a "known hosts" file. Other SSH applications require you to manually create a known hosts file and place the switch public key in the file. See the documentation for your SSH client application for more details.

(The session key pair mentioned above is not visible on the switch. It is a temporary, internally generated pair used for a particular switch/client session, and then discarded.)


When generating a host key pair on the switch, the switch places the key pair in flash memory and not in the running-config file. Also, the switch maintains the key pair across reboots, including power cycles. Consider this key pair to be "permanent" and avoid re-generating the key pair without a compelling reason. Otherwise, you must re-introduce the switch public key on all management stations you have set up for SSH access to the switch using the earlier pair.

Removing (zeroing) the switch public/private key pair renders the switch unable to engage in SSH operation and automatically disables IP SSH on the switch. To verify whether SSH is enabled, execute show ip ssh. However, any active SSH sessions will continue to run, unless explicitly terminated with the CLI kill command.

Because the host key pair is stored in flash instead of the running-config file, it is not necessary to use write memory to save the key pair. Erasing the key pair automatically disables SSH.

  • To generate the key, enter the appropriate crypto key generate command.

    For the complete syntax, see crypto key generate.

  • To show the key, enter the show crypto host-public-key command.

    For the complete syntax, see show crypto host-public-key.

    If you compare switch key to the key stored in your client's known-hosts file, note that the formatting and comments need not match.

  • To erase the key, enter the appropriate zeroize command.

    For the complete syntax, see zeroize .