rfc2328 OSPF

  1. OSPF is a link-state routing protocol.
  2. Each OSPF router maintains an identical db describing the AS’ topology. From this db, a routing table is calculated by constructing a shortest-path tree.
  3. OSPF recalculates routes quickly in the face of topological changes, utilizing a minimum of routing protocol traffic.
  4. Networks can be either transit or stub networks.
  5. stub networks: 桩网络,又叫末端网络,是指仅有一单个同路通过路由器连接到其他子网,或者仅有一个通路连接到其他网络。(https://www.2cto.com/net/201208/147516.html)
  6. Interfaces to point-to-point networks need not be assigned IP address. When interface addresses are assigned, they are modeled as sub links, with each router advertising a stub connection to the other router’s interface address.
  7. LSA: Link-State Advertisement(链路状态通告)
  8. SPF: short path first
  9. The topology of an area is invisible from the outside of the area. Conversely, routers internal to a given area know nothing of the detailed topology external to the area. This isolation of knowledge enables the protocol to effect a marked reduction in routing traffic as compared to treating the entire Autonomous System as a single link-state domain.
  10. Each area border router in an area summarizes for the area its cost to all networks external to the area. After the SPF tree is calculated for the area, routes to all inter-area destinations are calculated by examining the summaries of the are border routers.
  11. IP TOS field set to 0.
  12. The IP multicast datagrams used by OSPF never travel more than on hop.
  13. Supernetting has been proposed as one way to improve the scaling of IP routing in the worldwide Internet.
  14. OSPF simplifies this by requiring only adjacent routers to remain synchronized.
  15. The Designated Router is elected by the Hello Protocol.
  16. two-way receive: https://zhidao.baidu.com/question/1883741654782230828.html
  17. OSPF packet types:
    • Hello Discover/maintain neighbors
    • Database Description Summarize database contents
    • Link State Request Database download
    • Link State Update Database update
    • Link State Ack Flooding ackownledgment