Brocade TurboIron 24X Series Configuration Guide - Manual (Page 642)

608 Brocade TurboIron 24X Series Configuration Guide
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Overview of OSPF
In an OSPF point-to-point network, where a direct Layer 3 connection exists between a single pair of
OSPF routers, there is no need for Designated and Backup Designated Routers, as is the case in
OSPF multi-access networks. Without the need for Designated and Backup Designated routers, a
point-to-point network establishes adjacency and converges faster. The neighboring routers
become adjacent whenever they can communicate directly. In contrast, in broadcast and
non-broadcast multi-access (NBMA) networks, the Designated Router and Backup Designated
Router become adjacent to all other routers attached to the network.
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, as shown in
Figure 95
FIGURE 95 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 96 .
Router A
Router B Router C
priority 10
priority 20 priority 5
Designated Backup Router
Designated Router