Comcast enables 6to4 relays

Jack Bates jbates at
Mon Aug 30 22:45:28 UTC 2010

Others may correct me, but...

Franck Martin wrote:
>     5  2002:7114:4a9d::1  274.299 ms [mtu: 1480]
>     6  2002:7114:4a9d:0:xxxxxxxx  299.939 ms [*mtu: 1422]
> So I suspect on return path I use a HE.Net relay?

Yes, and it appears that your host is replying back to the office.

> And yes I agree it is such a PITA to troubleshoot, I cannot pinpoint the issue. Nor I cannot see if I'm the only one with this kind of troubles, I suspect most just give up immediately...

Given that you seem to complete the trace one direction, but not the 
other, I can think of 2 things,

1) Your originating host may be breaking PMTU (so the packet you send is 
too large and doesn't make it, you never resend a smaller packet, but it 
works when tracerouting from the other side due to PMTU working in that 
direction and you are responding with the same size packet).

2) If hosts in the middle on your traceroute to the destination don't 
have access to 6to4 relay, they won't be able to reply back to you, so 
you may end up with timeout hops before getting to the endpoint.


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