Stub Area Default Route Cost; Example; Ospf Stub Area Topology - Enterasys C5G124-24 Configuration Manual

Configuring OSPF Areas
injected into the stub area to enable other stub routers within the stub area to reach any external
routes that are no longer inserted into the stub area.
A stub area can be configured such that the ABR is prevented from sending type 3 summary LSAs
into the stub area using the no-summary option. In this case, all destinations outside of the stub
area are represented by means of a default route.
There are a couple of restrictions on the use of stub areas. Virtual-links cannot be configured
through stub areas, and AS boundary routers cannot be placed internal to stub areas.
Use the area stub command in router configuration command mode to configure an area as a stub.

Stub Area Default Route Cost

A cost value can be set for the default route that is sent into a stub area by an ABR. Configuration
of the stub area default route cost is restricted to the ABR attached to this stub area.
Use the area default cost command in router configuration command mode on the ABR attached
to this stub area to configure the stub area default route cost.

Example

Figure 22-4
Using the topology shown in
Areas 1 and 2 for a stub area (Routers 1, 2, and 3 for Area 1 and Routers 5, 6, 7, and 8 for Area 2).
Additionally, ABR routers 3, 5, and 6 are also configured with a default-cost to be assigned to the
stub area. Router 5 has a lower metric cost when compared to Router 6, so Router 5 will be the
preferred router for packets to access the area, with Router 6 employed as a backup in case Router
5 fails. Router 3 is configured to prevent it from sending LSAs into the stub area.
Router 1
Router 1(su)->router(Config)#router ospf 1
Router 1(su)->router(Config-router)#area 0.0.0.1 stub
Router 2
Router 2(su)->router(Config)#router ospf 1
Router 2(su)->router(Config-router)#area 0.0.0.1 stub
Router 3
Router 3(su)->router(Config)#router ospf 1
22-10 Configuring OSPFv2

OSPF Stub Area Topology

Area 1
Router 1
Router 3
Router 2
Figure
Backbone
Router 4
22-4, the following code example configures every router in
Area 2
Router 5 Router 7
Router 6 Router 8