Full form: OSPF Router ID
Also known as: OSPF Router ID, RID
Quick Definition
A 32-bit value that uniquely identifies an OSPF router within an OSPF domain.
The Router ID (RID) is used by OSPF to uniquely identify each router in the domain. It is formatted like an IPv4 address. The Router ID selection order is: (1) manually configured router-id command, (2) highest IP address on any loopback interface, (3) highest IP address on any active physical interface. Configuring a loopback address ensures a stable Router ID that does not change when physical links go down.
router ospf 1 router-id 1.1.1.1 show ip ospf ! shows current Router ID
The Router ID is selected once at OSPF startup and does not change automatically if interface IPs change. To force a change you must clear the OSPF process with 'clear ip ospf process'. A common exam trap is assuming the RID always uses a physical interface.
A virtual IP address on a router that is always up and never tied to a physical interface.
A link-state routing protocol that calculates the best path using cost based on bandwidth.
The elected OSPF router on a multi-access network that collects and distributes LSAs on behalf of all neighbours.
The Router ID (RID) is used by OSPF to uniquely identify each router in the domain. It is formatted like an IPv4 address. The Router ID selection order is: (1) manually configured router-id command, (2) highest IP address on any loopback interface, (3) highest IP address on any active physical interface. Configuring a loopback address ensures a stable Router ID that does not change when physical links go down.
The Router ID is selected once at OSPF startup and does not change automatically if interface IPs change. To force a change you must clear the OSPF process with 'clear ip ospf process'. A common exam trap is assuming the RID always uses a physical interface.
Router ID falls under the Routing domain of the 200-301 exam. Understanding it in context with related terms like ospf and dr is essential for answering scenario-based questions correctly.