Subject: IPv6 path MTU blackhole(?) between WIDE around the meeting network

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Tue, 09 Nov 2004 01:43:33 +0900

(I'm not sure if ietf@ietf is the best place to make a report like
this, but I don't know any other forum.  If this is not the best
please tell me the appropriate place.  And, for that matter, I don't
subscribe to this list)

I found that I could not send IPv6 packets of more than 1428 bytes
from the WIDE IPv6 network (Japan) to the IETF terminal room.  I
suspect this is due to some path MTU blackhole problem.

This is a traceroute result from pc3.yagami.wide.ad.jp
(2001:200:0:1c04::1000:2000) to 2001:468:c12:1::2, which seems to be
the first hop router attached to the IETF terminal room.

pc3# traceroute6 2001:468:c12:1::2
traceroute6 to 2001:468:c12:1::2 (2001:468:c12:1::2) from 2001:200:0:1c04::1000:2000, 30 hops max, 12 byte packets
 1  hitachi1.otemachi.wide.ad.jp (2001:200:0:1c04:240:66ff:fe10:cba9)  1.484 ms
 2  2001:200:0:1800::7660:1 (2001:200:0:1800::7660:1)  1.326 ms
 3  tpr2-ae0-7.jp.apan.net (3ffe:8140:101:6::2)  1.354 ms
 4  transpac-la-tpr2.jp.apan.net (3ffe:8140:101:1::1)  104.972 ms
 5  hstnng-losang.abilene.ucaid.edu (2001:468:ff:1114::1)  136.663 ms
 6  atlang-hstnng.abilene.ucaid.edu (2001:468:ff:e11::1)  156.588 ms
 7  washng-atlang.abilene.ucaid.edu (2001:468:ff:118::2)  172.148 ms
 8  max-washng.abilene.ucaid.edu (2001:468:ff:184c::2)  172.032 ms
 9  clpk-dcne.maxgigapop.net (2001:468:cff:3::1)  172.328 ms
10  2001:468:c12:1::2 (2001:468:c12:1::2)  176.461 ms

We can send 1429 bytes of IPv6 packet to the 8th router.

pc3# ping6 -s 1429 2001:468:ff:184c::2
PING6(1477=40+8+1429 bytes) 2001:200:0:1c04::1000:2000 --> 2001:468:ff:184c::2
1437 bytes from 2001:468:ff:184c::2, icmp_seq=0 hlim=58 time=174.085 ms
^C
--- 2001:468:ff:184c::2 ping6 statistics ---
2 packets transmitted, 1 packets received, 50% packet loss
round-trip min/avg/max/std-dev = 174.085/174.085/174.085/0.000 ms

And we can send 1428 bytes of IPv6 packets to the 9th router, which
seems to be attached to the terminal room network.

pc3# ping6 -s 1428 2001:468:c12:1::2
PING6(1476=40+8+1428 bytes) 2001:200:0:1c04::1000:2000 --> 2001:468:c12:1::2
1436 bytes from 2001:468:c12:1::2, icmp_seq=0 hlim=56 time=179.507 ms
1436 bytes from 2001:468:c12:1::2, icmp_seq=1 hlim=56 time=179.504 ms
^C
--- 2001:468:c12:1::2 ping6 statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/std-dev = 179.504/179.505/179.507/0.002 ms

But we cannot send 1429 bytes to that router.

pc3# ping6 -s 1429 2001:468:c12:1::2
PING6(1477=40+8+1429 bytes) 2001:200:0:1c04::1000:2000 --> 2001:468:c12:1::2
^C
--- 2001:468:c12:1::2 ping6 statistics ---
5 packets transmitted, 0 packets received, 100% packet loss

I suspect MTU between the 8th router and the 9th router is 1428, and,
either
  - the 8th router does not send an ICMPv6 too big error message
or
  - some router(s) between the 8th router and the WIDE IPv6 network
    drops ICMPv6 too big messages (actually, I confirmed that at least
    we cannot send an ICMPv6 too big message from the terminal room to
    the WIDE IPv6 network in a separate attempt.)

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]

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