What are the types of areas in OSPF?
There are five types of OSPF areas: Backbone area (area 0), Standard area, Stub area, Totally stubby area, and No so stubby area (NSSA).
How many areas are in OSPF?
These connecting routing devices are called (ABRs). Figure 1 shows an OSPF topology of three areas connected by two ABRs. Because all areas are adjacent to the backbone area, OSPF routers send all traffic not destined for their own area through the backbone area.
What does an OSPF area contain?
An OSPF area contains one set of link-state information, although each router within the area will process that information individually to form its own SPF tree. OSPF process IDs are locally significant and are created by the administrator.
Is OSPF Area 0 required?
Albeit OSPF is a link state protocol, the way OSPF handles inter-area traffic leaves it prone to routing loops. This is why OSPF must connect back to area 0 – to avoid routing loops.
What is the purpose of OSPF?
The OSPF (Open Shortest Path First) protocol is one of a family of IP Routing protocols, and is an Interior Gateway Protocol (IGP) for the Internet, used to distribute IP routing information throughout a single Autonomous System (AS) in an IP network.
How does OSPF area work?
Each OSPF router passes along information about the routes and costs they’ve heard about to all of their adjacent OSPF routers, called neighbors. OSPF routers rely on cost to compute the shortest path through the network between themselves and a remote router or network destination.
What are the different types of OSPF areas?
Standard areas can contain LSAs of type 1, 2, 3, 4, and 5, and may contain an ASBR. The backbone is considered a standard area. Stub areas can contain type 1, 2, and 3 LSAs. A default route is substituted for external routes. Totally stubby areas can only contain type 1 and 2 LSAs, and a single type 3 LSA.
What is the purpose of OSPF in multiarea?
OSPF uses areas to simplify administration and optimize traffic and resource utilization. An area is simply a logical grouping of contiguous networks and routers. All routers in the same area have the same topology table and don’t know about routers in the other areas.
What kind of link state advertisements are used in OSPF?
Each area is connected to a central backbone, area zero. OSPF relies on several types of Link State Advertisements (LSAs) to communicate link state information between neighbors. A brief review of the most applicable LSA types: LSA types 1 and 2 are found in all areas, and are never flooded outside of an area.
How are LSAs injected into the OSPF backbone?
These LSAs are injected into the backbone by the ABR of an area which contains an ASBR. This is to ensure all other routers in the OSPF domain can reach the ASBR. Standard areas work fine and ensure optimal routing since all routers know about all routes.
