OSPF Router ID

Every router in an OSPF topology will be identified using a Router ID (RID). The RID provides a unique identification for the router in the entire OSPF topology. So, how does a router decide what its RID would be?

There are certain conditions deciding what the RID for a router would be. 

1. The highest IP address assigned to the physical interfaces of a router will be the RID
2. However if the router has been configured with loopback addresses, then the highest IP address assigned to a loopback interface takes priority. The physical IP addresses are ignored
3. If the RID is configured manually using the CLI of the router, then the manual RID configured takes the highest precedence. Both the loopback interface and the physical interface is ignored.

Referring to the exhibit, take a guess as to what the RID for the routers will be

RID for R1 will be 192.168.1.1
RID for R2 will be 1.1.3.1
RID for R3 will be 192.168.1.3
Lets say we manually configure the RID for R4 to be 4.4.4.4. This manual configuration will become the RID for R4
RID for R5 will be 172.16.1.1