Why Network LSA needed depite of having Router LSA

[shrikarchalki]

                Can anybody give logical explanation  to this Quetion related to ospf - Why Network LSA is nedded ? when router lsa is already there , I know that router LSA are sent by every ospf capable router and network lsa are sent by DR on behalf mutiaccess network but As router lsa will already flodded to all router within area,  so why there is  sepearte need of Network lsa  again ? Thanks in advance

[InayathUlla Sharieff]

Shrikar,

This explains the reason:-

• Type 1 - Router LSA - the router announces its presence and lists the links to other routers or networks in the same area, together with the metrics to them. Type 1 LSAs are flooded across their own area only. The link-state ID of the type 1 LSA is the originating router ID.
• Type 2 - Network LSA - the designated router (DR) on a broadcast segment (e.g. Ethernet) lists which routers are joined together by the segment. Type 2 LSAs are flooded across their own area only. The link-state ID of the type 2 LSA is the IP interface address of the DR.

Simple term :

1- Router LSA are sent by every router in the same area you are correct.

2- But what happens in the Ethernet segment of the same area? You are aware that there comes the concept of DR and BDR, Who is responsible to send/advertise/send the infomration of DR and BDR to all the routers belongs to that segment?  The router LSA would not be having the infomration of DR and BDR right....

http://en.wikipedia.org/wiki/Link-state_advertisement

If you still not convinced let me know and I will try to explain in other way than technical terms.

Regards

Inayath

*Plz rate all usefull posts.

[Rolf Fischer]

Hi,

In addition to Inayath's posting which explains the advantages in database synchronization, network LSAs are also much more efficient in terms of how they are represented in the link state database.

John Moy's "Anatomy of an Internet Routing Protocol" gives a very good explanation with illustrations:

http://books.google.de/books?id=YXUWsqVhx60C&pg=PA101&hl=de&source=gbs_toc_r&cad=4#v=onepage&q&f=false

(=> 5.2.3 - Abstraction, I hope the Link works)

HTH

Rolf