OSPF LSA

[vinodbharwani]

Hi

I want to know , what is difference between type LSA 4 and LSA 5. I know both are related to ASBR. I want to know practically scenario , when LSA4 and LSA 5 is generted.

thanks in advance

[jackyoung]

Found in Cisco.

LSA 1

Router Link advertisements. Generated by each router for each area it belongs to. They describe the states of the router's link to the area. These are only flooded within a particular area.

LSA 2

Network Link advertisements. Generated by Designated Routers. They describe the set of routers attached to a particular network. Flooded in the area that contains the network.

LSA 3 or 4

Summary Link advertisements. Generated by Area Border routers. They describe inter-area (between areas) routes. Type 3 describes routes to networks, also used for aggregating routes. Type 4 describes routes to ASBR.

LSA 5

AS external link advertisements. Originated by ASBR. They describe routes to destinations external to the AS. Flooded all over except stub areas.

More info. from design guide.

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml

Hope this helps.

[yan.yong]

ASBR Summary LSAs are also originated by ABRs.Summary LSA will always be a host address because it is a route to a router

then ,Autonomous System External LSAs, or External LSAs, are originated by ASBRs.They advertise either a destination external to the OSPF autonomous system, or a default route external to the OSPF autonomous system .

you can observe the command show ip os database .the AS External LSAs are the only LSA types in the database that are not associated with a particular area; external LSAs are flooded throughout the autonomous system.