ospf-3.LSA类型.ppt

Configuring OSPF Link-State Advertisements Issues with Maintaining a Large OSPF Network The Solution: OSPF Hierarchical Routing Consists of areas and autonomous systems Minimizes routing update traffic Types of OSPF Routers Defining Virtual Links Configuring Virtual Links OSPF Virtual Link Configuration Example The show ip ospf virtual-links Command LSA Types LSA Type 1: Router LSA One router LSA (type 1) for every router in an area Includes list of directly attached links Each link identified by IP prefix assigned to link and link type Identified by the router ID of the originating router Floods within its area only; does not cross ABR LSA Type 2: Network LSA One network (type 2) LSA for each transit broadcast or NBMA network in an area Includes list of attached routers on the transit link Includes subnet mask of link Advertised by the DR of the broadcast network Floods within its area only; does not cross ABR LSA Type 3: Summary LSA Type 3 LSAs are used to flood network information to areas outside the originating area (interarea) Describes network number and mask of link. Advertised by the ABR of originating area. Regenerated by subsequent ABRs to flood throughout the autonomous system. By default, routes are not summarized, and type 3 LSA is advertised for every subnet. LSA Type 4: Summary LSA Summary (type 4) LSAs are used to advertise an ASBR to all other areas in the autonomous system. They are generated by the ABR of the originating area. They are regenerated by all subsequent ABRs to flood throughout the autonomous system. Type 4 LSAs contain the router ID of the ASBR. LSA Type 5: External LSA External (type 5) LSAs are used to advertise networks from other autonomous systems. Type 5 LSAs are advertised and owned by the originating ASBR. Type 5 LSAs flood throughout the entire autonomous system. The advertising router ID (ASBR) is unchanged throughout the autonomous system. Type 4 LSA is needed to find the ASBR. By default, routes are not summarized. Int