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

Hi Nitin,

On Oct 10, 2007, at 2:02 PM, Nitin Kakkar wrote:

> Adrian> You are saying that the only router that cause AS scoped  
> flooding is an ASBR. This limit seems to be unnecessary and overly  
> restrictive.
>
> Adrian> Can you clarify why a non-ASBR is not allowed to originate  
> an AS-scoped LSA?
>
>
>
> Acee> 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.
>
>
>
> IMHO> It is quite possible in many scenario’s that  a router  
> originated AS scope LSA’s and then changed from ASBR to Non ASBR,  
> leaving older ASE LSA’s in domain.
>
> 1)     If we use implict definition of ASBR (independent of E bit)  
> it will result in incorrect  Routes
>
> 2)     This statement also tries to prevent unnecessary origination  
> of unusable lsa’s (If router originate ASE lsa’s and does not  
> advertise it self as ASBR, what would be the use of those LSA’s?   
> these LSA’s will only occupy space in LSDB & result into  
> unnecessary flooding but won’t contribute to routing, this is very  
> similar to  )
So, I'll take this as agreement.

Thanks,
Acee
>
>
> Regards
>
> Nitin
>
> From: Acee Lindem [mailto:acee@redback.com]
> Sent: Wednesday, October 10, 2007 8:19 AM
> To: Adrian Farrel
> Cc: ospf@ietf.org
> Subject: Re: [OSPF] Question on flodding scope indraft-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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