Re: IPv6 day and tunnels

[Jeroen Massar <jeroen () unfix org>]

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/ )