Subject: Question regarding the P bit in type-7 LSA

From: Sunil Patro <[email-masked]>
Date: Wed, 8 Mar 2006 12:33:12 -0800

From section 3.4 of rfc 1587(The OSPF NSSA Option),

  "If a router is attached to another AS and is also an NSSA area border
   router, it may originate a both a type-5 and a type-7 LSA for the
   same network.  The type-5 LSA will be flooded to the backbone (and
   all attached type-5 capable areas) and the type-7 will be flooded
   into the NSSA.  If this is the case, the P-bit must be reset in the
   type-7 NSSA so the type-7 LSA isn't again translated into a type-5
   LSA by another NSSA area border router."

Can someone throw some light on why the P bit must be clear in the case
when an ASBR originates both a type 7 and type 5 LSA for the same
network?

Thanks in advance.
Sunil

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From: Roch Guerin <[email-masked]>
Date: Wed, 8 Mar 2006 15:48:41 -0500

The NSSA ABR that originates both the T5 and T7 may not be the 
designated translator for the NSSA and it would be superfluous to have 
another translation of the T7 flooded as a T5 in the backbone.

Note:  You should be looking at RFC 3101 which obsoltes RFC 1587.

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From: Vishwas Manral <[email-masked]>
Date: Wed, 8 Mar 2006 12:49:39 -0800

Hi Sunil,

Acee may not be able to reply till the evening, so let me give it a try in
the mean while.

"If this is the case, the P-bit must be reset in the  type-7 NSSA so the
type-7 LSA isn't again translated into a type-5 LSA by another NSSA area
border router."

Isnt the reason embedded in the question you ask?

I guess we do not want to originate multiple Type-5 LSA's for the same
destination and that is the reason for the P-bit setting.

Thanks,
Vishwas