Google filtering ICMPv6 type 2?

[Erik Kline]

2010/1/4 Erik Kline <ek at google.com>:
> 2010/1/4 Mark Kamichoff <prox at prolixium.com>:
>> Hi -
>>
>> I noticed today that HTTP requests to ipv6.google.com (and
>> www.google.com with Google-over-IPv6) seemed to be unusually laggy and
>> frequently timing out.  I looked a little deeper and saw that Google may
>> be inadvertently dropping ICMPv6 type 2 (packet too big) messages.  I'm
>> seeing things like this for TCP packets that are attempting to enter a
>> tunnel (MTU 1280) I have setup between me and a box of mine with native
>> IPv6 connectivity:
>>
>> 22:21:44.513137 IP6 2001:4860:800e::69.80 >
>> 2001:48c8:1:105:219:d1ff:fe21:d70d.49530: . 1:1429(1428) ack 119 win 90
>> <nop,nop,timestamp 1528748730 1102342799>
>> 22:21:44.513197 IP6 2001:48c8:1:2::2 > 2001:4860:800e::69: ICMP6, packet
>> too big, mtu 1280, length 1240
>> 22:21:44.513263 IP6 2001:4860:800e::69.80 >
>> 2001:48c8:1:105:219:d1ff:fe21:d70d.49530: . 1429:2857(1428) ack 119 win
>> 90 <nop,nop,timestamp 1528748730 1102342799>
>> 22:21:44.513298 IP6 2001:48c8:1:2::2 > 2001:4860:800e::69: ICMP6, packet
>> too big, mtu 1280, length 1240
>> 22:21:44.513388 IP6 2001:4860:800e::69.80 >
>> 2001:48c8:1:105:219:d1ff:fe21:d70d.49530: P 2857:4280(1423) ack 119 win
>> 90 <nop,nop,timestamp 1528748730 1102342799>
>>
>> Sorry if that's hard to read, the full packet capture is here:
>>
>> http://www.prolixium.com/files/mynews/googleipv6.cap.txt
>>
>> I've tested this from the above setup (in NYC) and from an HE tunnel to
>> Ashburn, VA.  Both experience similar issues.  However, I did another
>> test from a friend's box who has an HE tunnel to Chicago, IL, and didn't
>> see a problem.
>>
>> Anyone else seeing this?  Perhaps Google put an erroneous filter on some
>> of their peering routers, but not others?
>>
>> Hopefully it'll get yanked.  I'd hate to go back to IPv4 for searching
>> the web!
>>
>> - Mark
>>
>> --
>> Mark Kamichoff
>> prox at prolixium.com
>> http://www.prolixium.com/
>>
>
> This is an issue that's been reported and we're looking in to right
> now.  Sometimes pMTUd works, sometimes not, as you note.  Hopefully
> we'll have some useful fix soon.
>
> -Erik
>

I don't know you're exact setup but in the meantime you might set the
MTU in the RA for hosts behind that tunnel; that way they know their
correct MSS...