This document describes how to configure the Open Shortest Path First (OSPF) link state routing protocol for Multi-Area Adjacency.
Cisco recommends that you have knowledge of these topics:
- Multi-Area Adjacency
Cisco also recommends that these requirements be met before you attempt the configuration that is described in this document:
- The OSPF link state routing protocol must be pre-configured in the network.
- Only two OSPF speakers use the interface between which OSPF Multi-Area functionality works. Multi-Area OSPF only works on Point-to-Point network types.
The information in this document is based on Multi-Area OSPF.
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
The OSPF link state routing protocol uses the concept of Areas, which are sub-domains within the OSPFv2 domain. A router within an Area maintains the complete topology information of that Area. By default, an interface can only belong to one OSPFv2 Area. This can not only cause sub-optimal routing in the network, but it can also lead to other issues if the network is not designed correctly.
When Multi-Area Adjacency is configured on an interface, the OSPFv2 speakers form more than one Adjacency (ADJ) over that link. The Multi-Area interface is a logical, point-to-point interface over which the ADJ is formed. This document describes a scenario where Multi-Area OSPFv2 ADJ can be used in order to work around a problem and meet the network requirements.
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. In this lesson we will describe how you can configure a multiarea OSPF.