Does anyone have a perfectly functioning IPv6 with an MTU higher than 1280?
It seems that some (AT&T?) routers in communication path are filtering out ICMPv6, specifically 'packet too large' messages. This behavior is not consistent, so it appears that only some routes are affected and not all the time (as in load balancing scenario).
What I am seeing is when I set MTU higher than 1280, sometimes IPv6 works great, with correct ICMPv6 messages at appropriate times. Other times I get connection resets and timeouts on IPv6 pages without receiving any ICMPv6 messages.
The only thing that works all the time is setting MTU on my internal RAs to the lowest possible value of 1280, but that is not how IPv6 is supposed to work, it is an ugly workaround for misconfigured carrier routers.
Does anyone have good IPv6 experience without hardcoding restrictive MTU?
I have not reached out to tech support. I am sure their advice would be to restart the router or disable IPv6.
P.S. I am not using any AT&T RG. My connection is straight from my router to ONT. I am not filtering or throttling ICMPv6 on either my router or my PCs. I am getting /60 with DHCPv6-PD with my subnets receiving /64s. I am not using 6rd.
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