Dell Brocade DCX, Configuration Manual

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BigIron RX Series Configuration Guide 677
53-1001810-01
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
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
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.
Router A
Router B
Router C
priority 10
priority 20
priority 5
Designated Backup Router
Designated Router
X
Designated Backup Router
Router C
priority 5
Router B
priority 20
Designated Router
priority 10
Router A