• Neighbor table – stores information about OSPF neighbors
• Topology table – stores the topology structure of a network
• Routing table – stores the best routes
Each OSPF router is assigned a router ID. A router ID is determined by using one of the following:
2. using the highest IP address of the router’s loopback interfaces
3. using the highest IP address of the router’s physical interfaces
- area id
- hello and dead interval timers
- area stub flag
OSPF neighbor states
2. 2-way state – the neighbor has received the Hello message and replied with a Hello message of his own
3. Exstart state – beginning of the LSDB exchange between both routers. Routers are starting to exchange link state information.
4. Exchange state – DBD (Database Descriptor) packets are exchanged. DBDs contain LSAs headers. Routers will use this information to see what LSAs need to be exchanged.
5. Loading state – one neighbor sends LSRs (Link State Requests) for every network it doesn’t know about. The other neighbor replies with the LSUs (Link State Updates) which contain information about requested networks. After all the requested information have been received, other neighbor goes through the same process
6. Full state – both routers have the synchronized database and are fully adjacent with each other.
All routers are running OSPF. Routers R1 and R2 are inside the backbone area (area 0). Router R3 is an ABR, because it has interfaces in two areas, namely area 0 and area 1. Router R4 and R5 are inside area 1. Router R6 is an ASBR, because it connects OSFP network to another routing domain (an EIGRP domain in this case). If the R1’s directly connected subnet fails, router R1 sends the routing update only to R2 and R3, because all routing updates all localized inside the area.