Dell PowerConnect B-RX BigIron RX Series Configuration Guide v02.7.02 - Page 749

Overview of OSPF (Open Shortest Path First) 25 Designated router election in multi-access networks In a network with no designated router and no backup designated router, the neighboring router with the highest priority is elected as the DR, and the router with the next largest priority is elected as the BDR, as shown in Figure 102 FIGURE 102 Designated and backup router election Designated Backup Router priority 10 Router A priority 5 Designated Router priority 20 Router C Router B If the DR goes off-line, the BDR automatically becomes the DR. The router with the next highest priority becomes the new BDR. This process is shown in Figure 103. NOTE Priority is a configurable option at the interface level. You can use this parameter to help bias one router as the DR. FIGURE 103 Backup designated router becomes designated router Designated Router priority 10 Router A Designated Backup Router priority 5 X priority 20 Router C Router B If two neighbors share the same priority, the router with the highest router ID is designated as the DR. The router with the next highest router ID is designated as the BDR. BigIron RX Series Configuration Guide 677 53-1001810-01