OSPF point-to-point links
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.
FIGURE 19 Designated and backup router election
Designated router election in multi-access networks
FastIron Ethernet Switch Layer 3 Routing
53-1003627-04 225
To Next Page
Loading...
Need help?
General
