OSPF Characteristics

OSPF
Hello/dead time10/40,30/1 20
Cisco or IETFI ETF
UpdatesMulticast (224.0.0.5, 224.0.0.6)
Load balancingEqual paths
Routed protocolsIP

 

OSPF
Hello/dead time10/40,30/1 20
Cisco or IETFI ETF
UpdatesMulticast (224.0.0.5, 224.0.0.6)
Load balancingEqual paths
Routed protocolsIP

 

OSPF is a link-state routing protocol that automatically discovers its neighbors by sending hello messages to 224.0.0.5. After the neighbors are discovered, they form an adjacency by syn­chronizing their databases. This database lists all possible routes that the neighbor is aware ofin the topology. Each subnet learned has a cost associated with it, which is calculated by tak­ing 1 08/bandwidth. The paths with the lowest cost to a destination are put in the routing table.

TCost Values Based on Bandwidth
BandwidthOSPF Cost
56Kbps1785
64Kbps1562
T1 (1 .544 Mbps)64
E1 (2048 Mbps)48
Ethernet (10 Mbps)10
Fast Ethernet (100 Mbps)Gigabit Ethernet (1000 Mbps)11

 

 Verifying and Troubleshooting OSPF Commands

CommandOutput
show ip routeThe routing table with OSPF entries represented as “O.” Routes learned from other areas also have an interarea indicator ( “ IA”).
show ip protocolsOSPF process ID and advertised networks.
show ip ospf interfaceLocal router’s router ID, interface topology type, link cost and priority, router ID for the DR and BDR on the segment, hello/dead intervals, and a count of how many neighbors and adjacencies.
show ip ospf neighborNeighbor table to verify neighbor IDs and if neighbor is DR or BDR.
showip ospf databaseOSPF subnets and advertising routers in the topology table.
debug ip ospf eventsReal-time display of LSAs and LSUs being sent and received.

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