704 BigIron RX Series Configuration Guide53-1001810-01Configuring OSPF25NOTEFor an external route that is redistributed into OSPF through a route map, the metric value of theroute remains the same unless the metric is set by a set metric command inside the route map. Thedefault-metric command has no effect on the route. This behavior is different from a routethat is redistributed without using a route map. For a route redistributed without using a route map,the metric is set by the default-metric command.Disable or re-enable load sharingBigIron RX can load share among up to eight equal-cost IP routes to a destination. By default, IPload sharing is enabled. The default is 4 equal-cost paths but you can specify from 2 – 8 paths.The router software can use the route information it learns through OSPF to determine the pathsand costs. Figure 108 shows an example of an OSPF network containing multiple paths to adestination (in this case, R1).FIGURE 108 Example OSPF network with four equal-cost pathsIn the example in Figure 108, the BigIron RX has four paths to R1:• BigIron RX ->R3• BigIron RX ->R4• BigIron RX ->R5• BigIron RX ->R6Normally, the device will choose the path to the R1 with the lower metric. For example, if R3’smetric is 1400 and R4’s metric is 600, the device will always choose R4.However, suppose the metric is the same for all four routers in this example. If the costs are thesame, the router now has four equal-cost paths to R1. To allow the router to load share among theequal cost routes, enable IP load sharing. The software supports four equal-cost OSPF paths bydefault when you enable load sharing. You can specify from 2 – 8 paths.OSPF Area 0H1H2H3H4R1R3R4R5R6BigIron RX
