Subject: [OSPF] Functional​ly equivalent AS-Externa​l/NSSA LSA for OSPFv3

From: Gaurav Agrawal <[email-masked]>
Date: Tue, 5 Jun 2012 01:51:33 -0700

Hi,

    I had a question about functionally equivalent AS-External LSA/NSSA LSA
for OSPFv3. There is no mention in RFC 5340 or RFC 2740 in this regard. RFC
2328 and RFC 3101 provides details in context of OSPFv2. Can the same logic
be extended for OSPFv3 as well?

Thanks,

Gaurav

---

From: Acee Lindem <[email-masked]>
Date: Tue, 5 Jun 2012 12:55:44 -0400

Hi Gaurav,
Yes - you can assume the same NSSA logic. From the RFC 5340 Abstract:

   All of OSPF for IPv4's optional capabilities, including demand
   circuit support and Not-So-Stubby Areas (NSSAs), are also supported
   in OSPF for IPv6.

The NSSA-LSA description was missing from RFC 2740 and added to RFC 5340. Also from RFC 5340:

3.3.  NSSA Specification

   This protocol feature was only partially specified in RFC 2740.  The
   level of specification was insufficient to implement the function.
   This document includes an NSSA specification unique to OSPFv3.  This
   specification coupled with [NSSA] provide sufficient specification
   for implementation.  Refer to Section 4.8.5, Appendix A.4.3,
   Appendix A.4.8, and [NSSA].

Thanks,
Acee

On Jun 5, 2012, at 4:51 AM, Gaurav Agrawal wrote:

Hi,

    I had a question about functionally equivalent AS-External LSA/NSSA LSA for OSPFv3. There is no mention in RFC 5340 or RFC 2740 in this regard. RFC 2328 and RFC 3101 provides details in context of OSPFv2. Can the same logic be extended for OSPFv3 as well?

Thanks,

Gaurav

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---

From: Gaurav Agrawal <[email-masked]>
Date: Tue, 5 Jun 2012 10:26:18 -0700

Hi Acee,
             I was not referring to NSSA capabilities. I was referring to
Functionally equivalent LSAs, which applies to AS-external LSAs as well.
There is no mention or reference in OSPFv3 RFC:

It is defined for OSPFv2 in section 12.4.4.1 RFC 2328,

                    RTA and RTB would originate the same set of AS-
                    external-LSAs.  These LSAs, if they specify the same
                    metric, would be functionally equivalent since they
                    would specify the same destination and forwarding
                    address (RTX).  This leads to a clear duplication of
                    effort.  If only one of RTA or RTB originated the
                    set of AS-external-LSAs, the routing would remain
                    the same, and the size of the link state database
                    would decrease.  However, it must be unambiguously
                    defined as to which router originates the LSAs
                    (otherwise neither may, or the identity of the
                    originator may oscillate).  The following rule is
                    thereby established: if two routers, both reachable
                    from one another, originate functionally equivalent
                    AS-external-LSAs (i.e., same destination, cost and
                    non-zero forwarding address), then the LSA
                    originated by the router having the highest OSPF
                    Router ID is used.  The router having the lower OSPF
                    Router ID can then flush its LSA.  Flushing an LSA
                    is discussed in Section 14.1.

Thanks,
Gaurav

---

From: Acee Lindem <[email-masked]>
Date: Tue, 5 Jun 2012 14:43:32 -0400

Hi Gaurav,
I'd like to say this is not applicable to OSPFv3 since it is one of those optimizations that I think is more pain and complexity than it is worth (not to mention the potential convergence delay if one ASBR becomes unreachable). However, the intent is definitely that this behavior is carried over to OSPFv3.
Thanks,
Acee
On Jun 5, 2012, at 1:26 PM, Gaurav Agrawal wrote:

Hi Acee,
             I was not referring to NSSA capabilities. I was referring to Functionally equivalent LSAs, which applies to AS-external LSAs as well. There is no mention or reference in OSPFv3 RFC:

Thanks,
Gaurav

On Tue, Jun 5, 2012 at 9:55 AM, Acee Lindem <[email-masked]<mailto:[email-masked]>> wrote:
Hi Gaurav,
Yes - you can assume the same NSSA logic. From the RFC 5340 Abstract:

3.3.  NSSA Specification

Thanks,
Acee

Hi,

Thanks,

Gaurav

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