Qtech QSW-3900-24-SFP-DC Руководство пользователя v1-1 онлайн [229/634] 481617

The priority of router interface determines the competency in

selecting“designated router”. The superior priority is firstly considered in

conflict. Designated router (DR) is not determined by human, but selected

by all routers in the network interface. The router in this network interface

whose Priority > 0 can be the candidate. Choose the one with the superior

priority to be the so called DR. If the priority is the same, choose the one

with larger router ID. The vote is the Hello packet. Each router writes its

own DR into Hello and sends it to each router in the network interface.

When two of them declairing that they are the DR, choose the one with

superior priority. If they have the same priority, choose the one with the

larger router ID. The one with the priority being 0, he will not be selected to

be DR or BDR.

If DR is failure because of some fault, routers must select DR again at the

same time. It costs a long time. During this time, the calculation of router is

not correct. In order to shorten it, BDR（Backup Designated Router）is

brought up. BDR is a abackup for DR. Select BDR at the same time as DR.

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