Contents
What is the backbone area in OSPF?
ID 0.0.0.0
An OSPF backbone area consists of all networks in area ID 0.0. 0.0, their attached routing devices, and all ABRs. The backbone itself does not have any ABRs. The backbone distributes routing information between areas.
What is an ABR and what purpose does it serve in an OSPF network?
An area border router (ABR) is a kind of router that is located near the border between one or more Open Shortest Path First (OSPF) areas. It is used to establish a connection between backbone networks and the OSPF areas.
What is ABR in OSPF?
Well Abr stands for Area border router. Area 0 is a very special area in ospf which has the capability of sharing inter area routes. Abr is some thing in which at least one of its interface is connected to area 0.
Is a backbone area compulsory in OSPF?
All OSPF areas must connect to the backbone area. This connection, however, can be through a virtual link. Stub Area The stub area is an area that does not receive external routes except the default route, but does receive inter-area routes.
What is the main 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.
Why areas are used in OSPF?
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.
How many types of OSPF areas are there?
five types
There are five types of OSPF areas: Backbone area (area 0), Standard area, Stub area, Totally stubby area, and No so stubby area (NSSA).
Do you need an area 0 router in OSPF?
If running single area OSPF any area can be used, there is no requirement to have area 0. When running multi area OSPF, an ABR must be used. An ABR is a router with adjacency in area 0 and at least one other area. ABRs take type 1 and 2 LSAs and announce them as type 3 summary LSAs in other areas.
How does OSPF prevent inter-area routing loops?
OSPF prevents inter-area routing loops by implementing a split-horizon mechanism, allowing ABRs to inject into the backbone only Summary-LSAs derived from the intra-area routes, and limiting ABRs’ SPF calculation to consider only Summary-LSAs in the backbone area’s link-state database. OSPF is usually considered a link-state protocol.
Why does OSPF carry non-backbone routes through the backbone?
When OSPF must carry non-backbone routes through the backbone, it uses some distance-vector behavior (i.e. parts of the Bellman Ford algorithm) to propagate Type3 LSA metrics into non-backbone areas. Consider what happens to a /32 Loopback route for R5.
Is it possible to advertise OSPF as an E2 route?
If this router is in the backbone or a normal area, “redistribute connected” is possible and OSPF will advertise 172.16.1.0/24 as E2 route (default). In the case of the router being in a stub or totally stubby area, “redis conn” is not feasible as ASBR is not allowed in a stub area.