3Com SuperStack 4, Configuration Manual

Page: 125 / 432

OSPF Configuration 137
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. A router can be a
DR on one interface, and a BDR or DROther on another interface.
■
DR election is only required for the broadcast or NBMA interfaces. For P2P or
P2MP interfaces, DR election is not required.
Perform the following configuration in Interface View:
By default, the priority of the Interface is 1 in the DR election. The value can be
taken from 0 to 255.
Setting the Peer
In an NBMA network, some special configurations are required. Since an NBMA
interface on the network cannot discover the adjacent router through
broadcasting 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.
Perform the following configuration in OSPF View.
By default, the preference for the neighbor of NBMA interface is 1.
Setting the Interval of Hello Packet Transmission
Hello packets are the most frequently sent packets. They 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.
Table 137 Setting the Interface Priority for DR Election
Operation Command
Configure the interface with a priority for DR
election
ospf dr-priority
priority_num
Restore the default interface priority
undo ospf dr-priority
Table 138 Configuring the peer
Operation Command
Configure a peer for the NBMA interface
peer
ip_address
[ dr-priority
dr_priority_number ]
Remove the configured peer for the NBMA
interface
undo peer
ip_address