--On Monday, January 01, 2024 1:01 PM +0100 lejeczek via CentOS centos@centos.org wrote:

-> $ ssh box5.proxmox.mine hostname -i 10.3.1.78

-> $ ssh box5 hostname -i Warning: the RSA host key for 'box5' differs from the key for the IP address '10.3.1.78' Offending key for IP in /root/.ssh/known_hosts:2 Matching host key in /etc/ssh/ssh_known_hosts:2 Are you sure you want to continue connecting (yes/no)? yes 10.3.1.78

This is same one host I _ssh_ to. Is this purely _ssh_ and way to fix it would be 'configuration' or perhaps (ssh &) something else? I don't quite get what exactly is happening here.

When you create a new ssh host (ie. run sshd) for the first time, a host key is created that uniquely identifies the host. When a client connects to that host for the first time, it caches that key in its ssh_known_hosts file. It's just a line of text with the host name (or IP address if no name)and its key. If the client later connects and discovers a different key, that's a clue that someone is trying to scam you and pretend to be that trusted host. If you know the host is ok, then something changed its key. The simple fix for that is to remove any lines in ssh_known_hosts for that host and let the client re-learn the new key. But be sure you're really connecting to the host you think you're connecting to. On a corporate network, an evil machine might be using ARP spoofing to pretend to be the IP you want.

On 1/1/24 23:01, lejeczek via CentOS wrote:

I don't quite get what exactly is happening here.

I'd say that box5 was most likely associated with a different IP Address at one time in the past.  SSH obviously knows that box5 resolves to the current IP.

You can make use of ssh-keygen and ssh-keyscan (man is your friend in this endeavor) to help make sense of what's in your known_hosts file.