router ID

[avdheshgautam]

does the interface has to be in the routing process(EIGRP/OSPF) to be considered for router ID selection.

[John Blakley]

No it doesn't. You just have to have the routing process active. In order of preference as to how the router id would be chosen would be:

1. Router ID specified under the routing process

2. Highest ip address of any loopback interface (if you only have 1 loopback, it will choose that one)

3. Highest ip address of a physical interface if no loopback exists.

For example, if you have:

int lo1

ip address 1.1.1.1 255.255.255.0

int fa0/0

ip addre 192.168.1.1 255.255.255.0

int fa0/1

ip addre 192.168.5.1 255.255.255.0

router ospf 1

router-id 15.15.15.15

network 192.168.1.0 0.0.0.255 area 0

The router will choose 15.15.15.15 as the router id because it's specified under the process. If that wasn't there, the next thing it would choose would be int lo1, and finally, if the loopback isn't there, it would choose int fa0/1 as the router id. Notice that I don't have ospf listening, or advertising, the loopback or int fa0/1 interfaces.

HTH,

John

[avdheshgautam]

Thanks! john

[John Blakley · Accepted solution]

You're welcome! If this resolved your question, please mark the question as 'Answered'.

Thanks!

John