Introduction to OSPF Configuration Tasks 307■ AS-external-LSA: Type-5 LSA, also called ASE LSA, generated by ASBRs todescribe the routes to other ASs and advertised to the whole AS (excludingstub areas). The default AS route can also be described by AS-external-LSAs.Type-7 LSAsIn RFC 1587 (OSPF NSSA Option), Type-7 LSA, a new LSA type, is added.As described in RFC 1587, Type-7 LSAs and Type-5 LSAs mainly differ in thefollowing two ways:■ Type-7 LSAs are generated and advertised in an NSSA, where Type-5 LSAs willnot be generated or advertised.■ Type-7 LSAs can only be advertised in an NSSA area. When Type-7 LSAs reachan ABR, the ABR can convert part of the routing information carried in theType-7 LSAs into Type-5 LSAs and advertise the Type-5 LSAs. Type-7 LSAs arenot directly advertised to other areas (including the backbone area).OSPF Features Switch 7750 support the following OSPF features:■ Stub area: Stub area is defined to reduce the cost for the routers in the area toreceive ASE routes.■ NSSA area: NSSA area is defined to remove the limit on the topology in a stubarea.■ OSPF multi-process: Multiple OSPF processes can be run on a router.■ Sharing discovered routing information with other dynamic routing protocols:At present, OSPF supports importing the routes of other dynamic routingprotocols (such as RIP), and static routes as OSPF external routes into the AS towhich the router belongs. In addition, OSPF supports advertising the routinginformation it discovered to other routing protocols.■ Authentication key: OSPF supports the authentication of the packets betweenneighboring routers in the same area by using one of the two methods: plaintext authentication key and MD5 authentication key.■ Flexible configuration of router interface parameters: For a router interface, youcan configure the following OSPF parameters: output cost, Hello interval,interface transmission delay, route priority, dead time for a neighboring router,and packet authentication mode and authentication key.■ Virtual link: Virtual links can be configured.Introduction to OSPFConfiguration Tasks Table 230 OSPF configuration tasksConfiguration Task DescriptionRelatedsectionBasic OSPF Configuration Required “Basic OSPFConfiguration”on page 309OSPF Area Attribute Configuration Optional “OSPF AreaAttributeConfiguration”on page 311
