strange iptable rules - at a loss

Howdy -- hmm, do you by chance have any non-default or third party software installed that might automatically configure firewall rules?

You don't actually need a firewall, and in most cases one isn't enabled by default. So one solution would be to disable your firewall altogether. Or you could just remove those entries relating to vibr0.

However, if you don't actually have a vibr0 interface, that may mean that there's some non-default software on your server that tried to add a set of rules -- and if that's the case, you may need to disable/remove that software.

Some of those rules look like the default firewall on CentOS/RHEL systems, mostly harmless. Some of them are our allow rules that get added during install. Some look unfamiliar (but there may be new stuff in the default CentOS firewall that I haven't looked at lately).

If it is not interfering with services, it's probably not a problem to leave the rules in place. I usually leave the CentOS firewall alone and just open up the ports I need for my services. But, as Eric said, a firewall is less interesting/useful on a server than on a client machine, as most of your active ports have to be open to actually provide service to the world. They only get useful if you have something like a database or other service that you want to be accessible to other servers you control, but not the world at large, for example.

Do you know if you installed any non-default software?

Nothing installed on CentOS by default would do such a thing. I don't see anything in that list which is an obvious culprit.

Some folks install third party tools such as CSF, which can modify firewall rules automatically.

You may want to review your process list, using 'ps auxw', to see if anything there stands out.

Ah, it looks like you're running a desktop version of CentOS, and there's a number of processes running that I'm not familiar with.

However, of what I see, my best guess is that it may be related to Fail2ban.

Could you try disabling that, and see if the rules stop being modified?

I haven't used Microsoft Hyper-V previously, and hadn't attempted running any VM's within it. However, Googling that particular package name, it appears that all it does is provide a set of kernel modules that enables Linux to run as a Hyper-V VPS guest.

Typically, kernel modules don't add firewall rules, though I suppose that it's technically possible.

I suspect that the culprit is elsewhere though, as there wouldn't be a simple way to configure those kernel modules with what firewall parameters to use.