Huawei Quidway S6500 Series Operation Manual page 177

Operation Manual - Routing Protocol
Quidway S6500 Series Ethernet Switches
For S6500 series switches,the default cost for running OSPF protocol of on the VLAN
interface is 10.
4.2.7 Setting the Interface Priority for DR Election
The priority of the router interface determines the qualification of the interface in DR
election, and the router of higher priority will be considered first if there is a collision in
the election.
DR is not designated manually; instead, it is elected by all the routers on the segment.
Routers with the priorities > 0 in the network are eligible "candidates". Among all the
routers self-declared to be the DR, the one with the highest priority will be elected. If two
routers have the same priority, the one with the highest router ID will be elected as the
DR. Votes are the hello packets. Each router writes the expected DR in the packet and
sends it to all the other routers on the segment. If two routers attached to the same
segment concurrently declare themselves to be the DR, choose the one with higher
priority. If the priorities are the same, choose the one with greater router ID. If the
priority of a router is 0, it will not be elected as DR or BDR.
If DR fails due to some faults, the routers on the network must elect a new DR and
synchronize with the new DR. The process will take a relatively long time, during which,
the route calculation is incorrect. In order to speed up this process, OSPF puts forward
the concept of BDR. In fact, BDR is a backup for DR. DR and BDR are elected in the
meantime. The adjacencies are also established between the BDR and all the routers
on the segment, and routing information is also exchanged between them. When the
DR fails, the BDR will become the DR instantly. Since no re-election is needed and the
adjacencies have already been established, the process is very short. But in this case,
a new BDR should be elected. Although it will also take a quite long period of time, it will
not exert any influence upon the route calculation.
But please note:
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.
DR is based on the router interface in a certain segment. Maybe a router is a DR
on one interface, but can be a BDR or DROther on the other interface.
DR election is only required for the broadcast or NBMA interfaces. For the p2p or
p2mp interfaces, DR election is not required.
Perform the following configuration in Interface view:
Huawei Technologies Proprietary
4-9
Chapter 4 OSPF Configuration