TCPv6 and UPDv6 are dead until server received ICMPv6 ping. Further analysis shows that actually TCP and UDP packets won't even come to the server. But after receiving ICMPv6 ping, everything starts working as expected. What could be causing this? I'm really confused. It's not my network, but servers are mine. I got VPS servers and hardware servers using both Windows Server 2012 and Linux distributions and all of these experience the same issue. So it's clearly networking issue. But what could be causing it? I can't come up with anything reasonable quickly. Why ping does make an difference? Maybe someone has configured some filtering badly or you tell me.
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Is that native IPv6 all the way? – kasperd Jun 13 '15 at 16:17
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Yes, full native IPv6 all the way + dual-stack for v4. – Sami Lehtinen Jul 06 '15 at 15:20
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After checking logs and wondering when this problem occures, it became evident after I contacted the helpdesk that the problem was caused by firewall blocking MLD / ICMPv6 type 130 packets. Normal IPv6 traffic just stops if that query isn't being responded to. Yet stuff like ICMPv6 ping still come through and after address is known also other traffic passes ok. It's just like in the good old days when people used to block DHCP and then complained about connectivity issues. Ha!
Sami Lehtinen
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