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- The show ip protocols EXEC command provides an overview of all running routing
protocols when multiple routing protocols are running on a single router. The following
command output shows the Process ID, Router ID, the number of OSPF areas and their types,
networks and areas configured for OSPF, and OSPF Router IDs of the neighbors.
RT1#sh ip protocols
Routing Protocol is "ospf 1"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Router ID 10.1.3.1
Number of areas in this router is 1. 1 normal 0 stub 0 nssa
Maximum path: 4
Routing for Networks:
10.0.0.0 0.255.255.255 area 0
Routing Information Sources:
Gateway Distance Last Update
10.1.3.1 110 00:02:21
10.1.6.1 110 00:02:21
10.1.5.1 110 00:02:21
Distance: (default is 110)
RT1#
- The debug ip ospf adj privileged command displays the OSPF adjacency events, eg: DR/BDR
election.
- The debug ip ospf events privileged command displays information on OSPF-related events,
eg: adjacency formation, flooding information, DR/BDR election, and SPF calculation.
- The debug ip ospf packet privileged command displays the contents of all sent and received
OSPF packets.
- Cisco OSPF link cost is calculated based on bandwidth, whereas other vendors may use other
methods for link cost / metric calculation. Hence when connecting routers from different
vendors, the OSPF cost might need to be adjusted to match other vendor’s router. Both routers
must have the same cost for a particular link for the OSPF to operate properly.
- Since OSPF cost is based on bandwidth, the OSPF cost of an interface can also be changed with
the bandwidth {bw} interface subcommand. If an interface’s cost is not set, the formula 10 8 /
bandwidth is used by default. Changing an interface’s bandwidth changes its OSPF cost as well.
Cisco OSPF cost calculation 10 8 / bandwidth (in bps). 100Mbps FE 1, 10Mbps 10.
A higher bandwidth indicates a lower cost, making higher speed links more preferable.
- Gigabit Ethernet = 0.1, but since only integer value can be used, so OSPF uses a cost of 1 for
both FE and GE links. The reference bandwidth, which is the value of the numerator in the cost
calculation formula, can be changed with the auto-cost reference-bandwidth 1000 router
subcommand. This command changes the numerator to 1000Mbps (10 9 ), and hence the formula
becomes 10 9 / bandwidth. Finally, the cost calculation will be 1 for GE and 10 for FE.
* 10 8 = 100’000’000 = 100Mbps
* 10 9 = 1’000’000’000 = 1000Mbps = 1Gbps
- The ip ospf cost {cost} interface subcommand manipulates the OSPF cost associated with a
particular interface. This command overrides the default formulated cost. The OSPF cost value
ranges from 1 – 65535. The OSPF cost has no unit of measurement, it is just a number.
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