Subject: Re: RFC ietf Drafe Contradicts in NSSA

From: "Pat Murphy - (650)329-4044" <[email-masked]>
Date: Thu, 8 Aug 2002 17:18:38 -0700

Amit,

Keep in mind that the latest NSSA spec, ietf dratf number 11, is
updating section 3.5 of RFC 1587 to be consistent with the
current OSPFv2 spec, RFC 2328, Section 16.4. Consider an
expanded wording of your snip from RFC 1587:

  When a type-5 LSA and a type-7 LSA are found to have the
  same type and an equal distance, the following priorities
  apply (listed from highest to lowest) for breaking the tie.

         a. Any type 5 LSA.
         b. A type-7 LSA with the P-bit set and the forwarding
            address non-zero.
         c. Any other type-7 LSA.

The biggest problem with this algorithm is the fact it makes a
Type 5 LSA translation of a Type 7 LSA more preferred when it
originates from a different NSSA ABR than the local router. It
also gives Type 5 LSAs preference over equally preferred Type 7
LSAs even when their forwarding addresses are different.

The new NSSA spec (An RFC publication is forthcoming as soon as
I can crank out one last response with edits to the RFC Editor)
resolves this issue more specifically:

  (e) If the current LSA is functionally the same as an
      installed LSA (i.e., same destination, cost and non-zero
      forwarding address) then apply the following priorities in
      deciding which LSA is preferred:

        1. A Type-7 LSA with the P-bit set.

        2. A Type-5 LSA.

        3. The LSA with the higher router ID.

Unlike RFC 1587, multiple Type 5 LSAs and/or Type 7 LSAs which
have the same type and equal metric, but different forwarding
addresses, have equal preference and are all installed. Note
that there are examples where each of these three preferences
is used. Furthermore these preferences always produce a single
installed LSA amongst a set of LSAs which are functionally the
same, regardless of Type.

Pat

---

From: Subhash <[email-masked]>
Date: Thu, 8 Aug 2002 20:38:17 -0700

Hi,

I was going over rfc 2740 section 3.5.1(3) - if the flooding scope of a
received LSA is set to reserved, discard it.  Is such a check required
when a database description packet is received?

The reason why I am asking is because if a router doesnt make such a
check upon receiving the DD, & sends a request for such an LSA, its
request list will never become empty, as per rfc 2328.  Am I right?

Thanks for your feedback.
-Subhash

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