Subject: Re: Idea behind DR copying the list of prefixes in the Link-LSA

From: vishnuvardhan B <[email-masked]>
Date: Fri, 10 Feb 2006 14:25:41 -0500

Hi,
I am not able to understand the idea behind DR copying the list of 
prefixes in the Link-LSA 
RFC2740 sec 3.4.3.7:
 Each Link-LSA associated with Link L is examined (these are in the
      Designated Router's interface structure for Link L). If the Link-
      LSA's Advertising Router is fully adjacent to the Designated
      Router, the list of prefixes in the Link-LSA is copied into the
      intra-area-prefix-LSA that is being built. 
Since anyway all the routers describe about the prefixes in their own 
intra-area prefix LSA's. So what is the advantage in advertising all the 

prefixes in the link-lsa's by DR. Any replies will be most helpful.
Reagards,
Vishnu

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From: Paul Wells <[email-masked]>
Date: Fri, 10 Feb 2006 20:57:13 -0600

Hi Vishnu,

Only prefixes associated with the router itself (e.g. loopback 
interfaces) and attached stub (non-transit) network segments are 
advertised in the intra-area prefix LSAs associated with the router LSAs.

Prefixes associated with transit network segments are advertised in the 
intra-area prefix LSAs originated by the DR and associated with the 
type-2 LSA for that segment.  The way the DR finds out about the transit 
link prefixes is by looking at the link LSAs.

Regards,
Paul