OSPF RID

[azer.babashov]

when configuring OSPF on any router, RID must be the interface highest IP address or highest ip address of logical interfaces. If you have sub interfaces and loopback interfaces which would be the RID?

[Mark Malone · Accepted solution]

Hi
manual first then loopback if no manual

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 Interfaces is selected as the OSPF Router ID.

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

[azer.babashov]

Thaks sir!

[Peter Paluch · Accepted solution]

Hi Azer,

The OSPF RID selection rules are as follows:

1. If the router-id X.X.X.X command is configured in OSPF, this value will be the OSPF RID.
2. Otherwise, if there is at least one loopback interface, the OSPF RID will be the highest IP address among all loopback interfaces.
3. Otherwise, the OSPF RID will be highest IP address among all other interfaces.

Note: Interfaces that are shutdown are ignored for the RID selection process.

To your question: If your router has both loopbacks and subinterfaces, the Rule 2 above would apply: The router would pick the highest IP configured on any loopback interface and make it its OSPF RID.

Best regards,
Peter

[azer.babashov]

Thanks sir!