I have two multisites (and two dev multisites). Each has mapped domains with add-on IPs. I know that my server's primary IP used to get blocked for trying to access itself repeatedly. I had to whitelist the IP address. I'm not sure why it was doing that. I also see lots of hacking attempts, which is why I asked about changing the SSH port #
I don't use SSH to access the server, so it wouldn't matter to me. However, I'm not sure if that port is used by any of the plugins. Do you know if that's common?