Subject: Re: Mapping between routerlsa and intra-area prefix lsa

From: OSPF vishnuvardhan B <[email-masked]>
Date: Mon, 19 Dec 2005 13:15:01 -0500

Hi All,
Have a query on rfc 2740. The rfc says that ospfv3  router-lsa still 
carries
the info about the links on the router but the addressing info is present 
in
intra-area prefix Lsa. I am not able to understand how can i get the
corresponding prefix for the link in the router-lsa from the intra-area
prefix lsa. This means i am not able to map(there is not one -to-one map)
regarding link info from the router-lsa to the addressing info in intra-
area
prefix LSA. Because the intra-area prefix Lsa carries all the prefixes
configured in the router.I feel its necessary to have mapping since while
computing the spf i.e while adding the candidate vertices from the
router-lsa i need to know the prefixes configured on the corresponding 
link.
Thanks&Regards,
Vishnu

---

From: Acee Lindem <[email-masked]>
Date: Mon, 19 Dec 2005 16:04:23 -0500

>router-lsa i need to know the prefixes configured on the corresponding 
Hi Vishnu,
Why do you think you need this? There are basically 3 cases:

       1. Associated vertex is not directly connected - Doesn't matter
       2. Associated vertex is connected directly and corresponds to a 
network LSA. Assume
           all prefixes advertised by the DR in the intra-area prefix 
LSA are on-link.
       3. Associated vertex is connected directly and corresponds ot a 
router LSA. In this case,
           the assumption is that the connecting network is not 
multi-access and you go through
           the advertising router to get to those prefixes.

Hope this helps,
Acee

---

From: Nitin Kakkar <[email-masked]>
Date: Tue, 20 Dec 2005 11:30:02 +0530

Vishnu,
  For route calculation you need to know (exitIf, NextHop) Pair for a
prefix.
  After Ist stage of route calculation you would have built SPF tree which
would tell indicated (ExitIf, Nexthop) for every router (for Directly
connected routers lookup Link LSa's, non directly connected just borrow this
pair sec 16.1), 

Now lookup IntraPrefix LSA extract prefixes and get (Nexthop, ExitIf) from
the router which originated this LSA. So there is no need for mapping of
prefixes and anything advertised in router LSA.

HTH
Nitin

-----Original Message-----
From: Mailing List [mailto:[email-masked]] On Behalf Of OSPF
vishnuvardhan B
Sent: Monday, December 19, 2005 11:45 PM
To: [email-masked]
Subject: Re: Mapping between routerlsa and intra-area prefix lsa

Hi All,