Brocade Communications Systems FastIron SX 800 Configuration Manual page 226

Designated router election in multi-access networks
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.
FIGURE 20 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 Brocade device's router ID is the IP address configured on the lowest numbered loopback interface. If the device
does not have a loopback interface, the default router ID is the lowest numbered IP address configured on the device.
When multiple routers 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.
When only one router on the network claims the DR role despite neighboring routers with higher priorities or router IDs, this router
remains the DR. This is also true for BDRs.
The DR and BDR election process is performed when one of the following events occurs:
• an interface is in a waiting state and the wait time expires
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FastIron Ethernet Switch Layer 3 Routing
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