Dell PowerConnect B-RX BigIron RX Series Configuration Guide v02.8.00 - Page 783

Configuring OSPF 25 The router software can use the route information it learns through OSPF to determine the paths and costs. Figure 108 shows an example of an OSPF network containing multiple paths to a destination (in this case, R1). FIGURE 108 Example OSPF network with four equal-cost paths OSPF Area 0 H1 R3 R1 H2 R4 H3 R5 H4 R6 BigIron RX In the example in Figure 108, the BigIron RX has four paths to R1: • BigIron RX ->R3 • BigIron RX ->R4 • BigIron RX ->R5 • BigIron RX ->R6 Normally, the BigIron RX will choose the path to the R1 with the lower metric. For example, if R3's metric is 1400 and R4's metric is 600, the BigIron RX will always choose R4. However, suppose the metric is the same for all four routers in this example. If the costs are the same, the router now has four equal-cost paths to R1. To allow the router to load share among the equal cost routes, enable IP load sharing. The software supports four equal-cost OSPF paths by default when you enable load sharing. You can specify from 2 - 8 paths. NOTE The BigIron RX is not source routing in these examples. The router is concerned only with the paths to the next-hop routers, not the entire paths to the destination hosts. OSPF load sharing is enabled by default when IP load sharing is enabled. To configure IP load sharing parameters, refer to "Configuring IP load sharing" on page 209. BigIron RX Series Configuration Guide 707 53-1002253-01