On 2/22/10 5:07 PM, "Ole Troan" <[email protected]> wrote:
> Reinaldo,
>
>> I would be interested to know how traceroute from an IPv4 and IPV6 hosts
>> behind a CPE would work on 6rd in general and specifically with IPv4/IPv6
>> anycast addresses. I would be interested on actual details on source
>> addresses used for answers, what happens if different answers for the same
>> TTL traverse different BRs coming back based on the stateless nature, etc.
>>
>> If there is an impact on the current way a client and an admin interprets
>> results, that should be documented.
>>
>> Not sure if this was already discussed on the list. Given the widespread use
>> of traceroute as a diagnostic tool shouldn't at least some of these details
>> be covered on the draft?
>>
>> In ds-lite there is a little discussion on that but given the stateful
>> nature of NAT that would be a different topic.
>
> I can't think of anything which would affect traceroute. 6rd of course only
> affects IPv6 traceroute.
> with multiple BRs it will appear like you have multiple output paths as well
> as inbound paths. so you may get asymmetric traffic, that's of course not
> uncommon.
Ole,
Thanks for the answer. There seems to be some differences here that you can
help clarify in the context of anycast.
These questions are based on the following from the draft (and section
around it) that in my reading advances an idea of fully stateless
deployment.
"As 6rd is stateless, any BR may be used at any time. "
In 6rd although one can use anycast, there is a need for the IGP to be
stable, correct? It cannot be fully stateless otherwise different packets
for the same (source, destination, protocol) tuple would use different BRs.
Traceroute packets with the same TTL, source and destination taking
different paths would be a subset of a more general problem.
But in general what are the anycast affinity requirements for such a
deployable solution? But more specifically when connection based protocols
like TCP that react to delay are used on top of it.
I'm familiar with the use of anycasting for DNS where request and responses
are idempotent, short-lived and over a connectionless protocol, therefore
not much an issue.
And also use of TCP anycast as in this presentation
http://www.nanog.org/meetings/nanog37/presentations/matt.levine.pdf where
there are discussions on use and stability requirements.
Thanks,
Reinaldo
> the access network will look like a single hop across the 6rd
> domain. the IPv6 SA that the BR uses will be a normal IPv6 unicast address.
>
> we've recommended that the IPv6 subnet router anycast address is supported,
> but I wouldn't expect that one to be used as an SA.
>
> to summarize, I don't think there is any impact here.
>
> cheers,
> Ole
>
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