OSPF Operational States
Now that you know about the OSPF link-state packets, this topic explains how they work with OSPF-enabled routers. When an OSPF router is initially connected to a network, it attempts to:
- Create adjacencies with neighbors
- Exchange routing information
- Calculate the best routes
- Reach convergence
The table details the states OSPF progresses through while attempting to reach convergence:
|ExStart State||On point-to-point networks, the two routers decide which router will initiate the DBD packet exchange and decide upon the initial DBD packet sequence number.|
|Full State||The link-state database of the router is fully synchronized.|
Establish Neighbor Adjacencies
When OSPF is enabled on an interface, the router must determine if there is another OSPF neighbor on the link. To accomplish this, the router sends a Hello packet that contains its router ID out all OSPF-enabled interfaces. The Hello packet is sent to the reserved All OSPF Routers IPv4 multicast address 188.8.131.52. Only OSPFv2 routers will process these packets. The OSPF router ID is used by the OSPF process to uniquely identify each router in the OSPF area. A router ID is a 32-bit number formatted like an IPv4 address and assigned to uniquely identify a router among OSPF peers.
When a neighboring OSPF-enabled router receives a Hello packet with a router ID that is not within its neighbor list, the receiving router attempts to establish an adjacency with the initiating router.