HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Routing Confi - Page 78
Configuring OSPF areas, Configuration prerequisites
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Configuring OSPF areas After splitting an OSPF AS into multiple areas, configure some areas as stub areas or NSSA areas as needed. If no connection can be achieved between the backbone and a non-backbone area, or within the backbone itself, you can configure virtual links to solve it. Configuration prerequisites Before you configure an OSPF area, complete the following tasks: • Configure IP addresses for interfaces, and make sure that all neighboring nodes can reach each other at the network layer. • Configure OSPF basic functions. Configuring a stub area Configure a non-backbone area at the AS edge as a stub area by configuring the stub command on all the routers attached to the area. In this way, Type-5 LSAs will not be flooded within the stub area, reducing the routing table size. The ABR generates a default route into the stub area so all packets destined outside of the AS are sent through the default route. To further reduce the routing table size and routing information exchanged in the stub area, configure it as a totally stub area by using the stub [ no-summary ] command on the ABR. In this way, neither AS external routes nor inter-area routing information will be distributed into the area. All the packets destined outside of the AS or area will be sent to the ABR for forwarding. To configure OSPF areas: Step Command Remarks 1. Enter system view. system-view N/A 2. Enter OSPF view. ospf [ process-id | router-id router-id | vpn-instance vpn-instance-name ] N/A * 3. Enter area view. area area-id N/A 4. Configure the area as a stub stub area. [ default-route-advertise-always | no-summary ] * Not configured by default. You must use the stub command on routers attached to a stub area. The backbone area cannot be a totally stub area. A (totally) stub area cannot have an ASBR because AS external routes cannot be distributed into the stub area. 5. Specify a cost for the default route advertised to the stub default-cost cost area. Optional. 1 by default. The default-cost command takes effect only on the ABR of a stub area. 68