Open Shortest Path First (OSPF) Facts Quiz

Answer: Link-State

OSPF is a link-state routing protocol because it builds a complete topology map of all known paths to a destination network. Distance vector routing protocols can only point to destination networks based on distance (hop counts) and metric. Path-vector routing protocol operations allow for a clear path to a destination network by preventing any potential loops. Hybrid routing protocols have elements of both link-state and distance vector protocols.

Answer: 110

A routing protocol's administrative distance (AD) is a number used by a router to select which path is better to a destination network if there are multiple paths to it issued by different routing protocols. Priority is given to lower numbers. OSPF's AD is 110, EIGRP's AD is 90, IS-IS's AD is 115, and RIP's AD is 120.

Answer: OSPFv3

OSPFv3 was created to provide support for IPv6. OSPFv1 was the first version but it was experimental and never implemented. OSPFv2 is the most commonly used version of OSPF in the early twenty-first century, and is usually the version people are referring to when they say OSPF. OSPFv2 only supports IPv4. OSPFv4 does not exist.

Answer: Hello

When forming and maintaining adjacencies, routers using OSPF send out hello packets to their neighbors by default every 10-30 seconds. After the adjacencies have formed, the OSPF router is in the two-way operational state. Link-State Advertisements (LSA) is the name of the overall communication method OSPF routers use. ExStart is the operational state of OSPF that comes after the two-way state. Exchange is the operational state of OSPF that comes after the ExStart state.

Answer: Internal LSA

There are eleven types of LSAs. Router LSA is type 1, network LSA is type 2, summary LSA is type 3, summary ASBR LSA is type 4, external LSA is type 5, multicast LSA is type 6, and the not-so-stubby-area (NSSA) LSA is type 7. Type 8 LSAs are rarely used and types 9-11 are known as opaque LSAs and are reserved for future expansion.

The most frequently used LSAs in an OSPF network are types 1-5.

Answer: priority number, router ID

The DR and BDR are elected first based on the highest priority number. The router with the highest priority number becomes the DR, and the router with the second highest number becomes the BDR. If the priority number is not set, or is the same for two or more routers, the next deciding factor is the router ID.

The router with the highest router ID becomes the DR and the router with the second highest router ID becomes the BDR. CPU speed is not a relevant factor in a DR/BDR election.

Answer: Area 0

The backbone area is a requirement whenever multiple OSPF areas are present, partly in order to prevent routing loops. Areas learn about other area's routing information through the backbone area. In multiarea OSPF, all other areas must connect to the backbone area.

Answer: Autonomous system boundary router

Autonomous system boundary routers (ASBR) connect OSPF autonomous systems with outside networks. Backbone router(s) (BR) are internal routers inside the backbone area. Area border routers (ABR) lie on the border between two OSPF areas. Internal Routers (IR) sit completely inside a single OSPF area.

Answer: Dijkstra's algorithm

OSPF uses Dijkstra's algorithm, also known as the SPF algorithm, which calculates the shortest paths between two nodes. Diffusing update algorithm is used by EIGRP. MENTOR routing algorithm is associated with mesh networks. Symmetric-key algorithm is a cryptographic algorithm.

Answer: Wildcard mask

OSPF uses wildcard masks to specify a range of IP addresses. You would type in the area ID after the wildcard mask. Subnet masks and Router IDs are not used when configuring an interface to use OSPF.