The network command determines which interfaces participate in the routing process for an OSPF area. Any interfaces on a router that match the network address in the network command are enabled to send and receive OSPF packets. As a result, the network (or subnet) address for the interface is included in OSPF routing updates.
The basic command syntax is network network-address wildcard-mask area area-id.
The area area-id syntax refers to the OSPF area. When configuring single-area OSPF, the network command must be configured with the same area-id value on all routers. Although any area ID can be used, it is good practice to use an area ID of 0 with single-area OSPF. This convention makes it easier if the network is later altered to support multiarea OSPF.
The figure displays the reference topology.