OSPF. Резюме
В этой главе рассказывается о протоколе OSPF. Глава сфокусирована на следующих темах:
- Характеристики протоколов маршрутизации с учётом состояния каналов, таких как OSPF, включая таблицы (таблица соседей, топологическая LSDB и таблица маршрутизации.
- Иерархическая двухуровневая зонная структура с магистральной и немагистральными зонами.
- Различные типы маршрутизаторов OSPF: internal маршрутизаторы, магистральные маршрутизаторы, ABR, ASBR.
Characteristics of link-state routing protocols such as OSPF, including the OSPF tables—the neighbor table (also called the adjacency database), the topology table (also called the topology database or the LSDB), and the routing table (also called the forwarding database). ■ OSPF’s two-tier hierarchical area structure, with a backbone area 0 and regular areas. ■ The different types of OSPF routers: internal routers, backbone routers, ABRs, and ASBRs. ■ How OSPF routers use the Hello protocol to build adjacencies. After two routers establish neighbor adjacency using hello packets, they synchronize their LSDBs by exchanging LSAs and confirming the receipt of LSAs from the adjacent router. Routers on point-to-point links form a full adjacency with each other, whereas routers on LAN links only form a full adjacency with the DR and BDR. ■ The OSPF metric calculation on Cisco routers, which is based on the link bandwidth by default. If interfaces that are faster than 100 Mbps are being used, you should use the auto-cost reference-bandwidth ref-bw router configuration command on all routers. To override the default cost, manually define the cost using the ip ospf cost interface-cost interface configuration command. ■ The five types of OSPF packets—hello, DBD, LSR, LSU, and LSAck. Hello packets are used to discover neighbor and build adjacencies. DBDs are used to synchronize the LSDBs. LSRs are used to request specific link-state records, and LSUs are used to send the requested records. LSAck is used to acknowledge the other packet types. OSPF packets are sent in IP packets with protocol 89.
