Operation Manual – OSPFH3C S9500 Series Routing Switches Chapter 1 OSPF Configuration1-141.3.4 Specifying an Interface to Run OSPFAfter using the ospf command to enable OSPF in system view, you must specify thenetwork to run OSPF. An ABR router can be in different areas, while a network segmentcan only belong to an area. That is, you must specify a specific area for each portrunning OSPF.Perform the following configuration in OSPF area view to enable/disable OSPF on aninterface:To do... Use the command...Specify an interface to run OSPF network ip-address ip-maskDisable OSPF on the interface undo network ip-address ip-maskThe ip-mask argument is IP address wildcard shielded text (similar to the complementof the IP address mask).1.3.5 Configuring OSPF to Import Routes of Other ProtocolsThe dynamic routing protocols on the router can share the routing information. As far asOSPF is concerned, the routes discovered by other routing protocols are alwaysprocessed as the external routes of AS. In the import-route commands, you canspecify the route cost type, cost value and tag to overwrite the default route receiptparameters (refer to “Configuring parameters for OSPF to import external routes”).The OSPF uses the following four types of routes (ordered by priority):z Intra-area routez Inter-area routez External route type 1z External route type 2Intra-area and inter-area routes describe the internal AS topology whereas the externalroutes describe how to select the route to the destinations beyond the AS.External routes type-1 refers to the calculated cost of the external routes. This cost isthe same as the cost of routes within the AS. Also, such route cost and the route cost ofthe OSPF itself are comparable. That is, cost to reach the external route type 1 = cost toreach the corresponding ASBR from the local router + cost to reach the destinationaddress of the route from the ASBR.External routes type-2: OSPF assumes that the cost spent from the ASBR to reach thedestinations beyond the AS is greatly higher than that spent from within the AS to theASBR. So in route cost calculation, the former is mainly considered, that is, the costspent to reach the external route type 2 = cost spent to the destination address of theroute from the ASBR. If the two values are equal, then the cost of the router to thecorresponding ASBR will be considered.
