3Com 7700 Configuration Manual page 91

Note that:
The DR on the network is not necessarily the router with the highest priority.
■
Likewise, the BDR is not necessarily the router with the second highest priority.
If a new router is added after DR and BDR election, it is impossible for the
router to become the DR even if it has the highest priority.
The DR is based on the router interface in a certain segment. Maybe a router is
■
a DR on one interface, but it can be a BDR or DROther on another interface.
DR election is only required for broadcast or NBMA interfaces. For the P2P or
■
P2MP interfaces, DR election is not required.
Perform the following configuration in VLAN interface view.
Table 28 Set the Interface Priority for DR Election
Operation
Configure the interface with a
priority for DR election
Restore the default interface
priority
By default, the priority of the interface is 1 in the DR election. The value can be set
from 0 to 255.
Set the Peer
For an NBMA network, some special configurations are required. Since an NBMA
interface on the network cannot discover the adjacent router through
broadcasting the Hello packets, you must manually specify an IP address for the
adjacent router for the interface, and whether the adjacent router is eligible for
election. This can be done by configuring the peer ip-address command. If
dr-priority-number is not specified, the adjacent router will be regarded as
ineligible.
Perform the following configuration in OSPF view.
Table 29 Configure the Peer
Operation
Configure a peer for the NBMA
interface.
Remove the configured peer for the
NBMA interface
By default, the preference for the neighbor of NBMA interface is 1.
Set the Interval of Hello Packet Transmission
Hello packets are the most frequently used packets, which are periodically sent to
the adjacent router for discovering and maintaining adjacency, and for electing a
DR and BDR. The user can set the hello timer.
According to RFC2328, the consistency of hello intervals between network
neighbors should be kept. The hello interval value is in inverse proportion to the
route convergence rate and network load.
Command
ospf dr-priority priority_num
undo ospf dr-priority
Command
peer ip-address [ dr-priority dr-priority-number ]
undo peer ip-address
OSPF 83