Subject: Question about the default route in NSSA

From: Mani Devarajan <[email-masked]>
Date: Thu, 12 Sep 2002 20:06:41 -0700

Hi all,

                ASBR
      -----     -----     -----    -----     -----     -----
     |     |   |     |   |     |  |     |   |     |   |     |
     | R1  |   | R2  |   |  R3 |  |  R4 |   | R5  |   |  R6 |
     |     |   |     |   |     |  |     |   |     |   |     |
      -----     -----     -----    -----     -----     -----
          |     |   |      |  |     |  |     |   |     |
           -----     ------    -----    -----     -----
           RIP-I     AREA 1    AREA 0   AREA 2    RIP-II
                                        NSSA

In the above setup, If R2 is configured to redistribute for
RIP-I destination into ospf cloud, the type-5 LSA will not
reach the AREA 2 as it is configured as NSSA.

So the External network RIP-I will be unreachable from AREA2.

So my question is, does NSSA ABR(R4) must inject type7 default
route in to AREA2 or we need manually configure default route
on R4 for the RIP I destination network.

Thanks in advance,
Mani

---

From: "Pat Murphy - (650)329-4044" <[email-masked]>
Date: Fri, 13 Sep 2002 10:35:39 -0700

Mani,

>on R4 for the RIP I destination network.

A default route is not necessary on R4 for it to reach the RIP-I
destinations since R4 can compute their next hops from their Type 5
LSAs. However if R4 originates a default Type 7 LSA into NSSA 2 that R5
prefers, then R5 could reach the RIP-I destinations through R4 via its
default..

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 routers, such as
R5, orignate a Type 7 LSA for default, even when they don't possess an
installed default path. I am not sure about RFC 1587, but this
requirement is explicitly described in the lastest NSSA draft.

Compliments of a suggestion of Alex Zinin's, I posted a draft titled

        Type 5 to Type 7 Translation

which is still available. It would allow the partial import of Type 5
LSAs, such as your RIP I routes, with aggregation. You can also find it
at

        ftp://noc.usgs.net/ietf/draft-ietf-ospf-5to7-01.txt

Quite frankly it seems logical that an NSSA should be able to import a
subset of an OSPF domain's Type 5 external LSAs complete with
aggregation, given that it can import external routes to networks
outside the AS via its external links. While I hope to repost this draft
soon, its current content is fairly clean.

Pat