Subject: Re: [OSPF] Re:Generating type5 LSA in ospfv3

From: "Pat Murphy - (650)329-4044" <[email-masked]>
Date: Tue, 02 May 2006 07:57:27 -0700 (PDT)

Acee,

>I think that NSSA ABRs should either be precluded from installing an
>NSSA internal default (as they are when summaries are suppressed) or
>have them not advertise a type 7 default when an internal NSSA
>default is installed.

The first option would be problematic if folk are already using the 
feature of RFC 1587 and RFC 3101 that allows one to translate an NSSA 
type 7 default LSA for use by the full OSPF domain. As for the latter 
suggestion, a backup default is just too important to take away from 
an NSSA that uses an internal default; since, more often that not, the 
only backup default is the one originating from the NSSA border.

However yesterday evening I when I wrote 

>Clearly an NSSA ABR's self originated type 7 default LSA can be 
>configured, via metrics, as the NSSA's default path of last resort;

I realized that perhaps a default metric for the NSSA routers' self 
originated type 7 default LSAs was never defined. This seemed like an 
omission to me. I checked this morning and could not find one in RFC 
3101. Why not just add the following in an appropriate location:

  The default metric for any type 7 default LSA originated by any
  configured NSSA border router (regardless of its running ABR status)
  is type 2 and should have the largest possible reachable metric. The
  default metric for any type 7 default LSA originated by an NSSA
  non-border router is type 2 with a value of 1. 

I realize folk can configure around this. But if they do so it is done 
with intent and they must accept the risk. This would seem to 
accomplish what you want with minimal recoding effort. The type 2 
metric with a value of 1 seems consistent with what I have seen done 
by most implementations, so this change should just be a subtle twist 
of the spec. I could add it to another minor errata suggested sometime 
back. I actually plan to send the old errata to the working group in 
the next couple of weeks.  They are both very short and would seem 
appropriate as errata.

Pat

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