CCNP Network Route OSPF Part -II Open Shortest Path First OSPF Cost: OSPF’s metric is known as cost. Formula: Cost = 100/BW-IN-MBPS Common Cost of OSPF: 56k = 1785 64k = 1562 T1 (1.544) = 65 E1 (2.048) = 48 Ethernet = 10 Fast Ethernet, gigabit, 10 gigabit = 1 Note: OSPF forgets the backup paths if reboots or restart, It keep the road map , they remain in the topology table but it need to re-run the OSPF algorithm.

CCNP Network Route OSPF Part -II Designated and Backup Designated Routers They are also known as DR or BDR Backup Router only works when Designated Routers goes down. DR and BDR work on a shared Network segment. If one of the Router goes down, the update is sent to DR and to BDR. OSPF uses multicast for all of its communication. On shared network the update will always go to 224.0.0.6 Only DR and BDR will listen to this frequency. Then DR sends update to everyone with the multicast address of 224.0.0.5. Eigrp only uses 224.0.0.10, where as OSPF uses 2 multicast addresses. This eliminates huge traffic between all routers. DR and BDR is only for every shared segment not for a whole area.

CCNP Network Route OSPF Part -II On point to point type of network , Router will not become DR and BDR because there are only two routers and they communicate on 224.0.0.6   Election of DR and BDR: Basically Router’s priority play the important role. Router priority is in the hello header. By default its 1. If priority ties, then the Router ID is checked. Not to worry about neighbor relations that are marked as two way because on shared segment a max of 2 neighbor relationship will be formed one with DR and other with DBR

CCNP Network Route OSPF Part -II OSPF Process Packets:   Hello DataBase Description (DBD) Link-State Request (LSR) Link –State Advertisement (LSA) Link – State Update ( LSU) Link-State Acknowledgement (LSACK)