Configuring Area Range

An area range is a form of address summarization that defines a range of addresses to be used by the backbone ABRs when they communicate routes to other areas. Area range is a critical tool that pares the route tables and update traffic, as well as reduces network recalculation by the Dijkstra algorithm. Area range configuration summarizes by aggregating an areas‘ internal networks to advertise a single network. Backbone routers see only one update, representing an entire range of subnets. Area ranges can be configured for purposes of network advertisement as well as summarization of subnets that should not be advertised.

Use the area range command in OSPF configuration command mode to configure an area network summarization.

ABR1(rw)->configure
ABR1(rw-config)->router ospf 1
ABR1(rw-config-ospf-1)->area 1 range 10.2.0.0 255.255.0.0
ABR1(rw-config-ospf-1)->exit
ABR1(rw-config)->

ABR2(rw)->configure
ABR2(rw-config)->router ospf 1
ABR2(rw-config-ospf-1)->area 2 range 10.3.0.0 255.255.0.0
ABR2(rw-config-ospf-1)->area 2 range 10.3.2.0 255.255.255.0 not-advertised
ABR2(rw-config-ospf-1)->exit
ABR2(rw-config)->

Area 3

ABR3(rw)->configure
ABR3(rw-config)->router ospf 1
ABR3(rw-config-ospf-1)->area 3 range 10.1.0.0 255.255.0.0
ABR3(rw-config-ospf-1)->exit
ABR3(rw-config)->

OSPF Summarization Topology