IPv6 routing /48s

Jack Bates jbates at brightok.net
Wed Nov 19 23:54:36 UTC 2008

Mike Leber wrote:
> We don't operate any 6to4 gateways.

This I suspected, and actually took as evidence based on the results 
from traceroutes.

> However, what is likely happening is a random 6to4 gateway operator may 
> have seen fit to rate limit or filter ICMP.

This may very well be true. I have nothing but love for he.net. However, 
the anycast nature of 6to4 does have it's issues. This was just a 
passing example that I noticed. Packets go through the network, but your 
network couldn't send ICMPv6 back. Actually not a concern for me, but I 
doubt it's the only 6to4 issue seen across the network.

> To properly diagnose 6to4 problems you potentially need as many as 4 
> traceroutes, IPv6 traceroutes from the source and destination endpoints 
> and a IPv4 traceroutes to the 6to4 gateway addresses from the source and 
> destination endpoint.  There a few other tips I'm forgetting at the 
> moment, however if you send us email (to ipv6 at he.net) we will make sure 
> to research it thoroughly.

Will do. Not that I care, but might be something you'll want to check 
into anyways.

> Because 6to4 gateways are *anycast* the gateways you use in any part of 
> the world in any part of a specific network may be different.
> This makes debugging it "interesting".

Definitely, and another reason I am heavily against 6to4 except in cases 
where it's absolutely necessary.

> Jack, it seems you are saying traffic passes end to end just fine, you 
> just don't get ICMP responses from some of the hops in the middle.  Is 
> this correct?

Correct, traceroute and ping find a void on the 2 routers I pass before 
I hit NTT's network in the test case I was doing. I haven't tested this 
in 1/2 a week, though.

> If you would like, please send email to ipv6 at he.net with the detail 
> regarding what you are seeing with all of the endpoint information and 
> the traceroutes and we will work from our side to see where the 
> "interesting" 6to4 gateway is that is affecting your traceroute.  We 
> will probably also need you to have access to the destination side as well.

Will do. Be abit. The "interesting" part is primarily what it was 
mentioned. Though in another response I agreed that anyone using IPv6 
from an end network should consider have 6to4 relays so as not to depend 
  on someone else. In some cases, though, it's just not practical.

FYI: Outside of testing, my link to he.net was to take what little 6to4 
traffic I had on the network to non-6to4 addresses and give it a better 
chance. My nearest IPv4 anycast 6to4 was beyond horrid (major 
isolation). Heaviest traffic load appears to be p2p to teredo destinations.


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