Re: [OSPF] Question on flodding scope in draft-ietf-ospf-ospfv3-update-17.txt

Hi Adrian,

On Oct 10, 2007, at 9:30 AM, Adrian Farrel wrote:

> Hi,
>
> In section 2.3...
>
>   o  AS scope.  LSA is flooded throughout the routing domain.  Used  
> for
>      AS-external-LSAs.  A router that originates AS scoped LSAs is
>      considered an AS Boundary Router (ASBR) and will set its E-bit in
>      Router-LSAs for regular areas.
>
> I'm concerned about the impact of this statement for future  
> application of text in 3.4.4
>
>   It is expected that new LSAs will be defined that will not be
>   processed during the Shortest Path First (SPF) calculation as
>   described in Section 3.8.  For example, OSPFv3 LSAs corresponding to
>   information advertised in OSPFv2 using opaque LSAs [OPAQUE].
>
> But in 3.4.4 it also says
>
>   To facilitate inter-area reachability validation, any OSPFv3 router
>   originating AS scoped LSAs is considered an AS Boundary Router
>   (ASBR).
>
> You are saying that the only router that cause AS scoped flooding  
> is an ASBR. This limit seems to be unnecessary and overly restrictive.
>
> Further, this seems to be a change from RFC2740 where section 2.3  
> had only
>   o   AS scope. LSA is flooded throughout the routing domain. Used
>       for AS-external-LSAs.
>
> Can you clarify why a non-ASBR is not allowed to originate an AS- 
> scoped LSA?

This is necessary to enforce the "condition of reachability" for all  
LSAs. In other words, in order for an LSA to be considered valid, you  
need to verify that the advertising router is reachable. Hence, a  
router advertising an AS scoped LSA must advertise itself as ASBR so  
that Inter-Area-Router-LSAs are advertised into all regular areas.

We are also respinning RFC 2370 (Opaque LSAs) to enforce this. This  
is  draft-ietf-ospf-rfc2370bis-01.txt.

Thanks,
Acee

>
> Thanks,
> Adrian
>
> PS. I think the I-D header should include "Obsoletes RFC2740"
>
>
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