Lessons · Network switches · what a backup leaves behind
What a backup leaves behind
A configuration carries what was typed. It does not carry the crypto key, the software image, or the VLAN database -- none of which were typed.
Hone is a place to practise programming. This is one of its lessons, written out in full and free to read without an account.
What it is for
A restored switch can read perfectly and still refuse SSH, because the configuration says SSH and the box has no key to do it with. Knowing the list in advance turns a mystery into a checklist.
How to think about it
After any restore, expect three things to need doing by hand: generate the crypto key, check the image, and put the VLAN names back.
Worked example
enableIn.
configure terminalThe things that DO travel.
hostname IDF4Configuration.
ip domain-name works.localConfiguration.
crypto key generate rsaNOT configuration. This makes a key on this box, and it appears nowhere in the file.
endOut.
show running-config | include domainThe domain name is in there.
show running-config | include cryptoAnd the key is not. Nothing comes back.
Your turn
Make the key this switch needs before it can accept SSH.
crypto key rsa
Console into a switch
The trap
Reading the restored configuration, seeing `ip ssh version 2`, and concluding SSH is ready. The line describes an intention, not a key.