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OSPF part 2

LSA Types

There are 6 common used (by Cisco) LSA types:

LSA type 1 updates describe the router itself: interfaces (in the area), list of neighbor routers and the router ID (RID). The RID is transmited by a linkstate-ID in this hello packet. The linkstate-ID is equal to the RID.

LSA type 2 updates represent a transit subnet for which a DR is elected. The LSID are the RID of the DR IP’s address on that particular subnet. I’ts only active on subnets with a active DR. For subnets without a DR (like a point-to-point), type 1 packets are enough for creating the topology database. Inside one area, only LSA types 1 and 2 are send out. All the routers can create a topology table with only these type 1 and 2 LSA’s. A “show ip ospf database” lists all the received LSA types.

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