Every two days or so, my server stops responding entirely to its services. I can ping it, but I cannot use SSH so I have to go into my host's control panel and reset it.
When it comes back up, the last log entry before the crash in /var/log/messages are variations on the following:
named: unexpected RCODE (SERVFAIL) resolving '18.104.22.168.in-addr.arpa/PTR/IN': 22.214.171.124#53
Could this be a part of a DoS attack? I have not configured bind on this server and didn't think I'd need to (however naïve that may be).