Re: [homenet] Redirect and source-specific routing

Hello Juliusz,

Indeed, RFC 4861 is pretty clear and Redirects seem to have a flow when used with sadr.
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Updating RFC 4861 is one way to do it, we could also make hosts sadr-aware. 
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Brian is going to lead a discussion in 6man about the whole hosts&sadr problem.

One interesting fact though is that Open-Source does not wait for IETF to fix IETF’s bugs.
http://lxr.free-electrons.com/source/net/ipv6/route.c#L1285
It looks like Linux looks at the IPv6 header within the redirect and 
only applies the redirect to the given source+dest pair.

- Pierre

> Le 13 juil. 2015 à 09:23, Ole Troan <otroan@employees.org> a écrit :
> 
> Juliusz,
> 
>> I'm wondering if there isn't some interaction between Redirect messages and source-specific routing that we're overlooking.  RFC 4861 Section 8.3 says the following:
>> 
>>  Redirect messages apply to all flows that are being sent to a given
>>  destination.  That is, upon receipt of a Redirect for a Destination
>>  Address, all Destination Cache entries to that address should be
>>  updated to use the specified next-hop, regardless of the contents of
>>  the Flow Label field that appears in the Redirected Header option.
>> 
>> It does not speak of the source address, so I assume that this applies to all sources.  Consider the following topology:
>> 
>>  ---- A ---+--- B ----
>>            |
>>            H
>> 
>> If A and B advertise non-overlapping source-specific default routes and H is multiplexing its traffic over source addresses in both source prefixes (say, it's using MP-TCP), its Destination Cache entry will flap between A and B.
>> 
>> If I'm right, that argues in favour of an update to RFC 4861.
> 
> you are right. these issues are currently being discussed in 6man.
> see http://tools.ietf.org/html/draft-sarikaya-6man-sadr-overview-07
> 
> we haven’t reached a conclusion if a source aware redirect is needed or not (if that’s what you had in mind). by the way, there is also ICMP unreachable code 5 (Source address failed ingress/egress policy), which I would think the router should send, rather than the redirect in this case.
> 
> cheers,
> Ole
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