OSPF (Open Shortest Path First)
AD 110
Tcp 89
multicast address: 224.0.0.5 224.0.0.6
Send hello packets once every 10 seconds
Link state routing protocol: link information (port speed, link state) with SPF algorithm to calculate the optimal path
The three tables of OSPF
Neighbor table
Topology table
Routing table
Five OSPF packets
1 HELLO 1, used to discover neighbors 2, establish adjacency relationship 3, maintain adjacency relationship 4, ensure two-way communication 5, elect DR and BDR
2 Database Description DBD is reliable
3 Link-state Request LSR is reliable
4 Link-state Update Link state update package LSU is reliable
5 Link-state Acknowledgment LSACK
OSPF's eight neighbor states (there are also seven states, and Attempt is not listed):
Down: The state when the Hello packet sent by the neighbor router is not received within the dead time interval;
Attempt: The state after the Hello packet has not been sent out, but the Hello packet sent by a neighbor router has been received;
Initiat: Initialization state, the neighbor's Hello packet has been received, but its state is not found in the Hello packet, or the state when the Hello parameter does not match;
Two-Way: Two-way state, the state when your RID is found in the Hello packet sent by the neighbor, the Hello parameter matches and the verification is passed;
ExStart: pre-start state, the state after sending the first DBD packet to 224.0.0.5, until the router with the higher RID becomes the main router;
Exchange: Exchange state, the state entered after the election of the main router is completed, the two routers continue to exchange DBD packets until the L SID learned by both parties is the same;
Loading: Loading state, switch to loading state after all DBD packet exchange is completed, at this time send L.SR/LSU/L.SA to start detailed LSA exchange;
Full: After the full adjacency state is sent and received and all LSAs are confirmed, the LSAs of both routers are exactly the same and enter the final full adjacency state.