IPv6 routing /48s

Christopher Morrow morrowc.lists at gmail.com
Wed Nov 19 23:26:15 UTC 2008

On Wed, Nov 19, 2008 at 6:03 PM, Jack Bates <jbates at brightok.net> wrote:
> Christopher Morrow wrote:
>> 6to4 v6 addrs are just regular v6 addrs as far as the network is
>> concerned. if you put a 6to4 addr on your server you are saying that
>> you don't have native v6 transport to that host(s) and that you are
>> reachable via the 6to4 tunnel your host presumably has configured.
> Sure it's just another address, except the anycast portion of it for dealing
> with tunnels. It's also usually set to a different label and priority in
> windows prefix policies (and at least some linux setups). I was referring to
> the matter of if a windows box will even choose to use 6to4.

sure... address selection on new connections, standard ipv6 foo for
end-hosts. routers in the middle don't care, they route to the /16
route for 2002::/16, or they route to ... anycast'd on
their respective sides of the version#.

>> 6to4 is just an ip, 128bits long, but an ip... no differentiation is
>> made in the network for 6to4 vs 'normal v6'... unless someone's
>> putting up acls, or blackholing 6to4's /16, of course.
> Windows and several other end systems use prefix policies to determine if
> they use IPv6 or IPv4 and even when using IPv6, if they should use the 6to4
> tunnel or not.

right, normal address selection rules.

>> can you explain this a little more? is it possible your v6 packets hit
>> something like 6pe inside HE and exit to NTT without hitting a
> If a router does not a) know how to encapsulate 6to4 and send it over ipv4

routers in the middle shouldn't/won't do this.. once it's encap'd it
rides (on v4) to the device that does the 4->6 majics,
then on to the v6 destination where it rides back to the 'local'
2002::/16 endpoint where 6->4 encap majics happen then over the v4 to
you again.

> to the destination or b) know how to reach a 6to4 anycast address where the
> packet can be encapsulated into IPv4, the packet is going to get dropped. Of
> course, you could be right. he.net could be purposefully not sending icmp
> replies back to 6to4 addresses for other reasons while replying to my
> non-6to4 addresses. I hesitate to say filter, as it does push the 6to4
> sourced packets on to other networks.

hopefully mike's message gets it worked out :)

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