IPv6 day and tunnels
Jeroen Massar
jeroen at unfix.org
Mon Jun 4 22:04:48 UTC 2012
On 2012-06-04 14:55, Templin, Fred L wrote:
>>> I just want to know if we can expect IPv6 to devolve into 1280 standard
>>> mtu and at what gigabit rates.
>>
>> 1280 is the minimum IPv6 MTU. If people allow pMTU to work, aka accept
>> and process ICMPv6 Packet-Too-Big messages everything will just work.
>>
>> This whole thread is about people who cannot be bothered to know what
>> they are filtering and that they might just randomly block PtB as they
>> are doing with IPv4 today. Yes, in that case their network breaks if the
>> packets are suddenly larger than a link somewhere else, that is the same
>> as in IPv4 ;)
>
> But, it is not necessarily the person that filters the PTBs
> that suffers the breakage. It is the original source that
> may be many IP hops further down the line, who would have
> no way of knowing that the filtering is even happening.
It is not too tricky to figure that out actually:
$ tracepath6 www.nanog.org
1?: [LOCALHOST] 0.078ms pmtu 1500
1: 2620:0:6b0:a::1 0.540ms
1: 2620:0:6b0:a::1 1.124ms
2: ge-4-35.car2.Chicago2.Level3.net 56.557ms asymm 13
3: vl-52.edge4.Chicago2.Level3.net 57.501ms asymm 13
4: 2001:1890:1fff:310:192:205:37:149 61.910ms asymm 10
5: cgcil21crs.ipv6.att.net 92.067ms asymm 12
6: sffca21crs.ipv6.att.net 94.720ms asymm 12
7: cr81.sj2ca.ip.att.net 90.068ms asymm 12
8: sj2ca401me3.ipv6.att.net 90.605ms asymm 11
9: 2001:1890:c00:3a00::11fb:8591 89.888ms asymm 12
10: no reply
11: no reply
12: no reply
and you'll at least have a good guess where it happens.
Not something for non-techy users, but good enough hopefully for people
working in the various NOCs.
Now the tricky part is where to complain to get that fixed though ;)
Greets,
Jeroen
(tracepath6 is available on your favourite Linux, eg in the
iputils-tracepath package for Debian, for the various *BSD's one can use
scamper from: http://www.wand.net.nz/scamper/ )
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