704 BigIron RX Series Configuration Guide53-1001986-01Configuring OSPF25Modify administrative distanceThe BigIron RX can learn about networks from various protocols, including Border Gateway Protocolversion 4 (BGP4), RIP, ISIS, and OSPF. Consequently, the routes to a network may differ dependingon the protocol from which the routes were learned. The default administrative distance for OSPFroutes is 110. Refer to “Changing administrative distances” on page 757 for a list of the defaultdistances for all route sources.The router selects one route over another based on the source of the route information. To do so,the router can use the administrative distances assigned to the sources. You can bias the device’sdecision by changing the default administrative distance for OSPF routes.Configuring administrative distance based on route typeYou can configure a unique administrative distance for each type of OSPF route. For example, youcan use this feature to prefer a static route over an OSPF inter-area route but you also want toprefer OSPF intra-area routes to static routes.The distance you specify influences the choice of routes when the device has multiple routes forthe same network from different protocols. The device prefers the route with the loweradministrative distance.You can specify unique default administrative distances for the following route types:• Intra-area routes• Inter-area routes• External routesThe default for all these OSPF route types is 110.NOTEThis feature does not influence the choice of routes within OSPF. For example, an OSPF intra-arearoute is always preferred over an OSPF inter-area route, even if the intra-area route’s distance isgreater than the inter-area route’s distance.To change the default administrative distances for inter-area routes, intra-area routes, and externalroutes, enter the following command.BigIron RX(config-ospf-router)# distance external 100BigIron RX(config-ospf-router)# distance inter-area 90BigIron RX(config-ospf-router)# distance intra-area 80Syntax: distance external | inter-area | intra-area The external | inter-area | intra-area parameter specifies the route type for which you are changingthe default administrative distance.The parameter specifies the new distance for the specified route type. Unless youchange the distance for one of the route types using commands such as those shown above, thedefault is 110.To reset the administrative distance to its system default (110), enter a command such as thefollowing.BigIron RX(config-ospf-router)# no distance external 100
