OSPF router ID significance

mvsheik123 · ‎01-12-2009

Hi all,

Do the router-id in OSPF has anything to do with routing decision..? Or its just an identifier..? I have an ASA enabled for OSPF and 10.100.25.x n/w is advertised via ospf (which is ofcourse we needed) but the ID advertising as 192.168.1.1 (management IP). Just curious to know what is exact significance of the router ID. I also have another location with another ASA picking up 192.168.1.1 as router id.

Also, the Domain id (0.0.0.100) is same as process ID here..?

Below are some of the o/p:

ASA:

************************

ASA1# sh ospf

Routing Process "ospf 100" with ID 192.168.1.1 and Domain ID 0.0.0.100

***********************

ASA1# sh runn | beg router ospf

router ospf 100

network 10.100.25.0 255.255.255.0 area 0

log-adj-changes

*********************************

Core SW adjecent to ASA:

S1#sh ip ospf neighbor (truncated)

(ASA is last entry)

Neighbor ID Pri Address

10.100.199.5 1 10.100.199.5

10.100.25.4 1 10.100.25.4

192.168.1.1 1 10.100.25.11

Thank you

MS

chris.grammer · ‎01-12-2009

Without getting to wordy, the router-id in ospf is used as a tie breaker to a route if all other metrics are the same between 2 routers to a destination.

It is always best to set the router-id with the command:

router osfp 100

router-id 192.168.1.1

If the router id is not set, there is the possibility that it could change if another IP is added to the router configuration and a reboot or reset of the OSPF process occurs. For instance, the router-id is used to configure virtual tunnels and if that ID changes, the virtual tunnels will stop working.

The domain or area is not the same as the ID.

The process ID is not the same as the router ID. The process ID in ospf is locally significant and there can be multiple OSPF processes per router.

The "router ID" is how a router identifies itself in an ospf process to another router.