This lesson introduces OSPF, its place in IP networking, and how it selects routes. Understanding these fundamentals explains why OSPF is widely used in large enterprise networks.
Open Shortest Path First (OSPF) is an interior gateway protocol (IGP), used to route IP packets within a single routing domain, such as an autonomous system. It is a link-state routing protocol: routers share information about their links so participating routers can construct a map of the network topology.
All flashcards
What does an OSPF area border router (ABR) do?
It connects the backbone to other areas, maintains a separate LSDB for each area, and can summarize routes between them.
What does an OSPF autonomous system boundary router (ASBR) do?
It introduces routes from another routing domain or source into OSPF and advertises external reachability.
What is an OSPF router ID?
A 32-bit value that identifies a router in OSPF; it need not be a reachable network address.
What distinguishes OSPF External Type 1 from Type 2?
Type 1 includes external cost and internal cost to the ASBR; Type 2 is based on external cost alone.
What information does an OSPF link-LSA provide?
It communicates link-local addresses and IPv6 prefixes associated with a link in OSPFv3.
Quiz questions
What is required of an OSPF area other than area 0?Answer: It must connect to area 0 directly or through an appropriate virtual link.
In OSPF, what does the Two-way neighbor state confirm?Answer: Each router sees its own router ID in the other's Hello packet.
What is the primary purpose of an OSPF Database Description (DBD) packet?Answer: To summarize LSDB contents so neighboring routers can compare information.
How do OSPFv3 neighbors generally exchange packets, except over virtual links?Answer: They use IPv6 link-local addresses.
Which statement about OSPF on a point-to-point link is correct?Answer: It forms neighbor adjacencies without electing a DR or BDR.