@johnpoz 'twas not an issue on the HE site. Just had to set 1492 there since I am using PPPoE.
and yes, I can and now have forced it on my end.
Just more than a little surprised to see a default of 1280?!!!
And YES @stephenw10 , I could ping the far end of the tunnel way beyond the MTU. Crazy.
And now, I can ping the far end of the tunnel with 8 bytes more than the outside world.
Here: Near, Far, GoogleBad, GoogleGood ;)
[2.6.0-RELEASE][root@jasmine.ds.org]/root: ping6 -nms 1452 2001:470:39:3c7::2
PING6(1500=40+8+1452 bytes) 2001:470:39:3c7::2 --> 2001:470:39:3c7::2
1460 bytes from 2001:470:39:3c7::2, icmp_seq=0 hlim=64 time=0.180 ms
^C
--- 2001:470:39:3c7::2 ping6 statistics ---
3 packets transmitted, 3 packets received, 0.0% packet loss
round-trip min/avg/max/std-dev = 0.148/0.163/0.180/0.013 ms
[2.6.0-RELEASE][root@jasmine.ds.org]/root: ping6 -nms 1452 2001:470:39:3c7::1
PING6(1500=40+8+1452 bytes) 2001:470:39:3c7::2 --> 2001:470:39:3c7::1
1460 bytes from 2001:470:39:3c7::1, icmp_seq=0 hlim=64 time=5.750 ms
^C
[2.6.0-RELEASE][root@jasmine.ds.org]/root: ping6 -nms 1452 google.com
PING6(1500=40+8+1452 bytes) 2001:470:39:3c7::2 --> 2607:f8b0:400f:802::200e
^C
--- google.com ping6 statistics ---
5 packets transmitted, 0 packets received, 100.0% packet loss
[2.6.0-RELEASE][root@jasmine.ds.org]/root: ping6 -nms 1444 google.com
PING6(1492=40+8+1444 bytes) 2001:470:39:3c7::2 --> 2607:f8b0:400f:802::200e
76 bytes from 2607:f8b0:400f:802::200e, icmp_seq=0 hlim=119 time=6.146 ms