Subject: Question about default route wrt new nssa draft

From: Mani Devarajan <[email-masked]>
Date: Tue, 24 Sep 2002 15:09:15 -0700

Hi,
 Thanks to Pat,Acee and Manral for answering my previous
 questions.

 I have one more question with respect to ospf-nssa-draft-11,

 Section 2.3:
 ============
 In addition, an NSSA border router should originate a default LSA (IP
 address of 0.0.0.0) into the NSSA.

 Does NSSA ABR should always orginate default LSA or only when
 none of the internal NSSA ASBR doesnt generate default route.
 I read in one of the mails sent by Pat, that

 "By default, all of an NSSA ABRs, such as R4, are expected to
 originate a type 7 LSA for default when none of the NSSA's internal
 such as R5, orignate a Type 7 LSA for default"

 If NSSA ABR and NSSA ASBR both orginate a type-7 default in to
 NSSA, which will one be considered while calculating routes.I havent
 tested this scenario, but curious to know how it is handled.

Thanks in advace,
-Mani

---

From: Acee Lindem <[email-masked]>
Date: Thu, 26 Sep 2002 10:14:22 -0400

Hi Mani,

>  I have one more question with respect to ospf-nssa-draft-11,

Follow draft-ietf-ospf-nssa-update-11.txt.
Excepted from section 2.3:

    In addition, an NSSA border router should originate a default LSA (IP
    address of 0.0.0.0) into the NSSA.  Default routes are necessary
    because NSSAs do not receive full routing information and must have a
    default route in order to route to AS-external destinations.  Like
    stub areas, NSSAs may be connected to the backbone at more than one
    area border router, but may not be used as a transit area.  Note that
    a Type-7 default route originated by an NSSA border router is never
    translated into a Type-5 LSA, however, a Type-7 default route
    originated by an NSSA internal AS boundary router (one that is not
    also an area border router) may be translated into a Type-5 LSA.

Also note that many implementations make it configurable as to whether
or not an NSSA ABR will originate a type 7 default.

>  such as R5, orignate a Type 7 LSA for default"

This is incorrect.

>  tested this scenario, but curious to know how it is handled.

There are a number of cases here. The best is too follow section 3.5 in
draft-ietf-ospf-nssa-update-11.txt. In short,  routers internal to
the NSSA will install the default route with the lowest cost. NSSAs ABRs
will not install type 7 default unless the P bit is set in the LSA
options.

--
Acee