OSPF Router-ID: Important Details for Network Associates

Key Points About OSPF Router-ID

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Which is true about OSPF router-id? (Choose two .)



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A. B. C. D.


OSPF (Open Shortest Path First) is a popular link-state routing protocol used in computer networks. The router ID (identifier) is a unique 32-bit number that identifies each router running OSPF within a network. It is a critical element in the OSPF protocol and is used in various places within the network. Here are the two true statements regarding the OSPF router-id:

A. It is used for type 1 router LSA:

OSPF uses Link State Advertisements (LSAs) to exchange information between routers about the state of the network. Type 1 LSAs are used to represent the router itself, and they contain information about the router's interfaces and their associated networks. The router ID is used in the creation of these LSAs, as it identifies the router generating the LSA.

B. Router-id needs to be matched on OSPF neighbors:

When OSPF is running between two routers, they need to form a neighbor relationship for proper communication. The OSPF router ID is one of the parameters that are exchanged between neighbors during the process of forming a neighbor relationship. The router ID of each router must be unique within the OSPF domain, and it is recommended that the router ID of each router be manually configured to ensure consistency.

C. Highest IP address of the loopback is used:

This statement is false. While the router ID can be manually configured, OSPF does have an algorithm to automatically select a router ID if one is not configured. OSPF will use the highest IP address of any loopback interface on the router if one is configured. If no loopback interfaces are configured, OSPF will use the highest IP address of any active physical interface on the router.

D. Router-id is 16 bit:

This statement is also false. The OSPF router ID is a 32-bit number and can take any value from to The router ID is configured either manually or automatically and is unique within the OSPF domain.

In conclusion, the OSPF router ID is an essential component of the OSPF protocol, used to identify the router generating the LSA and forming neighbor relationships between routers. The router ID can be manually configured or automatically selected, and it is a 32-bit number.