Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 247)

Designated routers in multi-access networks
In a network that has multiple routers attached, OSPF elects one router to serve as the designated
router (DR) and another router on the segment to act as the backup designated router (BDR). This
arrangement minimizes the amount of repetitive information that is forwarded on the network by
forwarding all messages to the designated router and backup designated routers responsible for
forwarding the updates throughout the network.
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.
FIGURE 20 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.
NOTE
Priority is a configurable option at the interface level. You can use this parameter to help bias one router
as the DR.
Designated routers in multi-access networks
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