router-id 1.1.1.1 ---->>>I dont have interface with address 1.1.1.1 , but i see it works

[Ibrahim Jamil]

Hello overseas Freinds

Greeting

I have small Queries

router ospf 1

router-id 1.1.1.1    ---->>>I dont have interface with address 1.1.1.1 , but i see it works ,

pls explain

thanks

[Troy Jackson]

A router-id is an identifier, not an IP address.  If you do not have a router-id set it will take the IP address of an interface. But it's just a unique 32-bit number.

https://www.cisco.com/c/m/en_us/techdoc/dc/reference/cli/nxos/commands/ospf/router-id-ospf.html

[Predrag Jovic]

If manually configured router-id under ospf router will use that ID to identify itself to other routers while advertising ospf routes.

Only if router-id is not configured router will need to go through router id selection to choose which IP address it will use as its ID.

The same as your name is Ibrahim. You could have any other name and still be alive. If you did not get your name at your birth at some point you would have to choose name for yourself (but router has some limited number of options to choose from). :)

[balaji.bandi]

OSPF Router ID selection algorithm works as below.

• Any manually configured OSPF Router ID in OSPF Process is selected as the OSPF Router ID.

• If there is no OSPF Router ID configured, the highest IP address on any of the Routers Loopback Interfacesis selected as the OSPF Router ID.

• If there is no Loopback Interfacesconfigured, the highest IP address on its active interfaces is selected as the OSPF Router ID.

BB

[Richard Burts]

The important thing about the router ID in OSPF is that it is an identifier used in OSPF routing updates. An OSPF process must have a router ID which can be manually configured or can be dynamically determined. The router ID is expressed as an IP address, but there is no requirement that the router ID be an address of an interface on the router. It can be any IP address. And there is not any requirement that the address used as router ID be reachable in the network.

HTH

Rick