google path mtu?

Artem Viklenko artem at
Mon Jan 19 18:03:28 CET 2015

On 19.01.2015 18:42, Brielle Bruns wrote:
> On 1/19/15 5:52 AM, Artem Viklenko wrote:
>> 19.01.2015 13:12, Mikael Abrahamsson написав(ла):
>>> On Mon, 19 Jan 2015, Ignatios Souvatzis wrote:
>>>> I had some problems at home, which is not tunneled, but a
>>>> less-than-1500-octet-mtu PPPoE DSL line, so - thinking it's tunnels
>>>> only ignores an increasing number of native private users.
>>> Well, PPPoE is a tunnel, but I guess that's splitting hairs.
>>> But regardless, I had trouble this morning with Youtube that might be
>>> related to the same issue.
>> One possible solution to force TCP MSS. For example on my FreeBSD
>> router at home i used PF's scrub rule for ipv6 tunnel to set
>> mss to 1220 bytes.
>> If you use PPPoE as underlying technology, decrease this vale little
>> bit more - 1212 or less.
> Min MTU size allowable for ipv6 is 1280 according to RFC.  Wouldn't
> setting the MSS size to 1212 or 1220 essentially break that RFC as well
> (1220+40 < 1280) or does the RFC only explicitly state the MTU has to be
> at least 1280?

I'm not shure about RFC right now. But spending time trying to fugure
out why one or the other host can't be successfully reached using ipv6
finnally I stopped on this value. It may be not optimal, but it works
for me.

And indeed the main cause of this is the blocking ICPMv6 at the far end.

Sincerely yours,
 Artem Viklenko.

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