Last week, we enabled IPv6 on our Authoritative DNS Servers and the corresponding Glue Records on our registrar for our domain's name servers, and we added AAAA records for our own website. This roll-out went without a hitch, and we're now serving up our website natively on IPv6.
This weekend, we added an IPv6 address to one of our client's dedicated servers, made sure Apache was configured for IPv6, and added that IP address to their own DNS zone file.
Since then, our Nagios monitoring of the URL (http://www.allgirlsallowed.org) has been complaining with:
CRITICAL - Socket timeout after 10 seconds
We have confirmed that the website is fully operational and that DNS is configured correctly, although external tools (such as Pingdom's website tests and http://www.downforeveryoneorjustme.com) have mixed results (Pingdom says it is working fine, Down for Everyone says it is down).
In our investigation, we've noticed several dozen TIME_WAITs coming from the same IPv6 address (which is in our same /64 block and is an IP operated by the hosting provider).
Now I do understand that a TIME_WAIT status means the connection is actually closed and that the process will go away shortly. That said, this is the only weird thing I've been able to find on the server. We've also seen a sustained increased load (~0.5, even when there's 0 current visitors).
What concerns me is that we haven't seen this behavior on our other IPv6-enabled servers (although granted, our other IPv6 servers probably receive a lot less traffic than this particular client).
Is there anything you would suggest I look into? Obviously I could go back in and disabled IPv6, but that's a crap-out. I want to identify the issue and address it head-on.