School Papers

OSPF an added advantage because it enhances the

OSPF Area is a feature that can be used to limit memory and CPU requirements that the protocol can put on routers. OSPF communicates routing updates by flooding them via links to other routers, and one way to control this is to divide the network into logical segments called Areas. By dividing the network into areas, LSA flooding is limited to an area and this consequently limits LSDB formation to links within areas. Routers connected together in an area are identified by that area ID. This area ID must be the same for all the routers. Also all routers within an area have the same topology table. Area ID is assigned to specific interface on the router since a router can belong to more than one area at a time. When configuring more than one OSPF area there must be an area 0 which is a reserved area configured on any router that forms the backbone of the network. Designing the network in a hierarchical fashion using areas is an added advantage because it enhances the scalability of OSPF (Lammle, 2007). In OSPFv3, Area ID is still a 32–bit value that can be expressed as a decimal number or in dotted decimal notation. For example, Area 0 can also be configured as Area 0.0.0.0 (Islam et al., 2010). The use of OSPF area in a routing domain (autonomous system) allows some routers to be designated for specific purposes. These routers are used when the network is divided into multiple areas. According to Rousinnos (2014), OSPF router types include the following: • Internal router (IR): A router that has all its interfaces belonging to the same area is referred to as an IR. • Area border router (ABR): An ABR is a router used to connect at least one area to the backbone area. An ABR is considered a member of each area it connects to. It stores multiple copies of LSAs for each area it is connected to. The ABR forwards type 3 LSAs received from one area to the backbone area. For example in Figure 2.2, ABR2 and ABR1 will send type 3 LSAs from areas 1 and 2 to the backbone area (Area 0). The backbone area also uses the ABR to send summarized information about an area to another area. For example in Figure 2.2, Area 0 will send summarized information about Area 2 to Area 1 • Backbone router (BR): A backbone router is the router that has its interface connected to the backbone area. • Autonomous system boundary router (ASBR): An ASBR connects an OSPF area to another autonomous system. This allows OSPF to redistribute its routing information into or receive redistributed routes from that autonomous system. 

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