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Configuring OSPF
Designated Router Election
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
8.2
Designated Backup Router
Router A
priority 10
priority 5
priority 20
Designated Router
Router C
Router B
Figure 8.2 Designated and backup router election
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 8.3.
NOTE: Priority is a configurable option at the interface level. You can use this parameter to help bias one
routing switch as the DR.
Designated Router
Router A
priority 10
priority 5
priority 20
Designated
Backup
Router
X
Router C
Router B
Figure 8.3 Backup designated router becomes designated router
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.
NOTE: By default, the HP router ID is the IP address configured on the lowest numbered loopback interface. If
the routing switch does not have a loopback interface, the default router ID is the lowest numbered IP address
configured on the device. For more information or to change the router ID, see “Changing the Router ID” on
page 6-25.
When multiple routing switches on the same network are declaring themselves as DRs, then both priority and
router ID are used to select the designated router and backup designated routers.
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