6to4 relay at AS26943 (Your.org) blackholing >1280B traffic

Kevin - Your.Org kevin at your.org
Mon Feb 25 21:30:04 CET 2008

On Feb 25, 2008, at 11:27 AM, Pekka Savola wrote:

> Hi,
> Today I noticed that traffic that goes through a relay one of my  
> colo server ISP's uses appears to be blackholing traffic through  
> their 6to4 relay that's bigger than 1280 bytes.  ICMPv6 Packet too  
> Big message is not returned..
> The 6to4 relay in question appears to reside at AS26943 (Your.org).  
> Please fix it ASAP.

Hey, Pekka!

I'm not completely sure the problem is on our end from what I've just  
looked at, but I'll gladly look into this further with you. Testing  
from another v6 native host on our network(2001:4978:2:410::ffff) to  

20:06:52.555427 IP6 (hlim 64, next-header: ICMPv6 (58), length: 1248)  
2001:4978:2:410::ffff > 2002:5872:3460::1: [icmp6 sum ok] ICMP6, echo  
request, length 1248, seq 0
20:06:52.555513 IP6 (hlim 64, next-header: ICMPv6 (58), length: 1240)  
2001:4978:2:410:211:43ff:fee8:2c76 > 2001:4978:2:410::ffff: [icmp6 sum  
ok] ICMP6, packet too big, length 1240, mtu 1280

If you'd like to contact me off list with the source IP you're trying  
from, I'll set a tcpdump running to capture what's going on with our  
end, and trace it as far towards you as possible while you're running  

The asymmetric and anycast nature of 6to4 makes troubleshooting this  
sort of thing really difficult if you don't have people on all sides  
of the equation involved, so I'm happy to help.

-- Kevin

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