CentOS 7 Router and IPv6
I use a CentOS machine as my router at the data center. Its doesn't do any NAT. It just routes my public ips. The DC routes my blocks of ips to the WAN interface and the router passes them through to the LAN interface. All has been going well for many years using IPv4.
I recently was given a block of IPv6 addresses and I set up the same router very similarly. I can ping ipv6 on the outside from the router. I can ping ipv6 on the inside from the router. I can ping ipv6 on router from the inside.
However when I try to ping the outside from the inside it pings either 5 or 6 times and then pauses for 27 seconds. It does this over and over again. I have tried it from different machines on the inside and they all ping and pause at the exact same time. And it always pings 5 or 6 times and pauses for 27 seconds.
I have run tcpdump on the router to watch for the traffic. When I run it against the LAN interface I continually see the ping traffic trying to get through. When I run tcpdump on the WAN interface I only see the ping traffic get through when there is successful pings.
Its not just pings. I tried using wget to retrieve a ipv6 web site and same thing happens. Sometimes its successful immediately and sometimes it has to wait until the router allows it.
So something on the router is blocking ipv6 traffic for 27 seconds at a time. I have no idea what that could be. I don't think I have anything special running on it. I have turned off everything I could think of. I turned off the firewall just to check.
I do have in /etc/sysctl.conf and reloaded it:
Is there a problem with routing ipv4 and ipv6 at the same time? Any help would be appreciated.
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