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

From: SUBSCRIBE OSPF vishnuvardhan B <[email-masked]>
Date: Tue, 14 Feb 2006 18:51:44 -0500

Hi Acee,
Thanks for the response, i am little bit worried about the spf calculatio
n 
on broadcast networks. Let me explain my problem with the help of diagram

Assume R1,R2,R3,R4 are on broadcast medium.

   R1(DR)        R2           R3    R4 
    |             |            |     |
 -----------------------------------------

 During SPF suppose R4 is root, when i extend from R4  i reach R1(since R
1 
is DR), so i copy all the prefixes from type-9 ref-network LSA genereated
 
by DR. so i need to set for all the prefixes nexthop as R1?[Is this the 

correct way?] 
                          OR
should i use each routers link-lsa's to copy the global prefixes on the 

link and set the next hops as the individual link-local addresses?   

If i follow the second approach where should i use the prefixes copied by
 
the DR into type-9 LSA?

---

From: Acee Lindem <[email-masked]>
Date: Tue, 14 Feb 2006 19:04:28 -0500

Vishnu,
Please remove SUBSCRIBE OSPF from your mail alias for this list. Also, 
sending a
single copy to this list is sufficient (I'm subscribed :^).

Anyway, in answer to your question, there are 2 cases:

      1) You are directly connected to the network referenced by the 
intra-area prefix LSA. In
           this case, this excerpt from RFC 2328, section 16.1.1 applies.

            If the destination is a
            directly connected network, or a router which connects to
            the calculating router via a point-to-point interface, no
            next hop IP address is required. 

       2) You are one or more hops away. Then this cause from RFC 2328 
applies.

            If there is at least one intervening router in the current
            shortest path between the destination and the root, the
            destination simply inherits the set of next hops from the
            parent.  

Hope this helps,
Acee