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Re: OSPFv3 and IPv6 on-link router advertisements

From: Yasuhiro Ohara (yasuSFC.WIDE.AD.JP)
Date: Mon Mar 31 2003 - 12:01:56 CST

Hi Mike,

> I don't think my question was precise enough. I have been through RFC
> 2740, and as far as I can tell, it does cover the interaction I am asking
> about.

I don't think so, which part is it mentioned ?

> I am asking about interaction between OSPFv3 and the IPv6 Neighbor
> Discovery protocol, which is described in RFC 2461 . Part of the IPv6
> Neighbor Discovery protocol is the ability of routers to send ICMPv6 Router
> Advertisement messages to on-link hosts, advertising on-link prefixes.
> These advertised prefixes can be used in stateless autoconfiguration,
> and/or they can also be simply advertised as on-link.
>
> With that background, hopefully these questions are better phrased and
> more to the point:
>
> 1. If a router is running OSPFv3, does it still advertise on-link prefixes
> via Neighbor Discovery ICMPv6 messages,or does it only use link-LSA's, or
> does it use both?

I guess that all depends on the configuration of the router. A router
can know his on-link prefix either Link-LSA or RA, or both. Even if
the router receives both Link-LSA and RA, there won't be any problem,
at least protocol level.

One interesting case will be when the router receives RA,
and the router's interface is "passive" or something that
makes OSPFv3 to advertise attached address prefix on that interface.
Then the router will advertise the prefix in the Intra-Area-Prefix-LSA
referring the router's Router-LSA.

> 2. If a host or router running OSPFv3 receives an ICMPv6 Neighbor Discovery
> message advertising an on-link prefix, and that prefix is not also received
> in a link-LSA, does it treat it as OSPF internal or OSPF external?

Usually OSPFv3 do not advertise the address prefix on the interface
which is not included in OSPF domain (in other words the interface
that does neither speak OSPF nor form OSPF adjacency), I believe.
So in your case, OSPF will have nothing to do with the address prefix,
except for the case I mentioned above.

regards,
yasu