OSPF Status Process

1) Down status: the router does not exchange any OSPF messages with any other routers; 2) Init status: the receiver router has received the hello packet from the peer router, however, no route id is found in the hello packet of the Peer router .. In this case, the communication is unidirectional; 3) Two-Way status: the user's router-id is found in the received hello packet, indicating that the hello packets are sent to each other. 4) once a router enters the Two-Way state, it is considered as a neighbor. In this case, the election process is required. Select the specified router (DR) and back up the specified router (BDR). 5) the ospf router with the highest priority becomes the DR in the network segment. If the priorities are the same, the router with the highest vroid ID will become DR. By default, all vrouters have 1 priority and the priority range is from (0-255 ); use the ip ospf priority command to configure in the interface sub-configuration mode. After the DR and BDR are selected, other routers form an adjacent relationship with the DR and BDR, but the other routers are still in a neighbor relationship, that is, it is still in the TWO-WAY State; 6) After the DR and BDR are elected, the router continues to generate a hello packet to maintain communication. This is considered as the exstart State. In this state, the ospf router is ready to share the link status information. 7) Exstart status: DR and BDR are adjacent to other ospf routers in the CIDR block. Then, in each adjacent relationship, the routers with the highest router ID become the primary router. Note that DR does not need to be the primary router during the switching process. The remaining vrouters In the joining relationship become the slave vro; 8) Exchang status: the master vro first shares the link status information with the slave vro. That is to say, the master router sends the DBD package. If the link status database is similar to a book, the DBD is equivalent to the directory of the book. Through the DBD package, you can find information that you do not have. The DBD package contains the link status type, the ID of the advertised router, the cost of the advertised link, and the serial number of the link. 9) Loading status: After finding information that you do not have from the vro through the DBD package, the vro will send a link status request packet to the primary vro (LSR package ), the master router then sends a Link status Update packet (LSU packet, Link State Update) with Link details to the slave router ). Merge the information from the vro to its local link status database. The slave router returns an LSACK packet to the master router. 10) Full status: At this time, the LSDB is consistent. At this time, each ospf router can independently calculate the initial route table. 11) route table calculation: Based on LSDB, use LSDB as the raw material and the spf algorithm to independently calculate the tree with no loops and put it into the routing table.

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