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Re: wiki for IETF71 IPv6 experience Re: IPv6 @ IETF-71, especially Jabber

2008-03-06 04:27:40


Sorry -- I've been on a plane most of the last day.

The problem yesterday was detected & addressed; thanks
for letting me know it's recurring.  I am told that
the problem has been isolated & working on a fix.


Iljitsch van Beijnum wrote:
On 5 mrt 2008, at 16:09, Leslie Daigle wrote:

As mentioned last week -- the wiki is now accessible:

Right, it was accessible yesterday, but not anymore, at least, for me: 
the pages don't load.

Looks like this is hosted on a 6to4 address. This isn't recommended, 
because the quality of 6to4 reachability is highly variable. But 
reachability doesn't seem to be the issue:

$ ping6 -c 4
PING6(56=40+8+8 bytes) 2001:720:410:1001:21b:63ff:fe92:9fbb --> 

--- ping6 statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 133.693/133.840/134.106 ms

So this looks like a path MTU discovery black hole. According to a 
traceroute, the web server is terminating the 6to4 link itself and this 
server is announcing a 1420 byte MSS:

10:54:54.464280 IP6 2002:4e2f:6761::2.http > 
2001:720:410:1001:21b:63ff:fe92:9fbb.49238: S 2106457901:2106457901(0) 
ack 809912022 win 5632 <mss 1420,sackOK,timestamp 1184434509 
542018613,nop,wscale 7>

This is consistent with a 1500 byte IPv4 MTU - 20 bytes IPv4 
encapsulation = a 1480 byte IPv6 MTU. However, the server is unreachable 
(from where I'm sitting) for 1480 byte packets:

$ ping6 -c 4 -s 1432
PING6(1480=40+8+1432 bytes) 2001:720:410:1001:21b:63ff:fe92:9fbb --> 

--- ping6 statistics ---
4 packets transmitted, 0 packets received, 100% packet loss

Can this please be fixed?

In general, people use a 1280 byte MTU for 6to4, which nicely avoids the 
possibility of path MTU discovery black holes.


      Yours to discover."
                                 -- ThinkingCat
Leslie Daigle
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