Which statement about OSPF multiaccess segments is true?
A.
The designated router is elected first.
B.
The designated and backup designated routers are elected at the same time.
C.
The router that sent the first hello message is elected first.
D.
The backup designated router is elected first.
step 1 . A router starting the ospf process and listen for ospf hellos, if none are heard with in the dead time, it declare itself the DR.
step 2 . If hellos from other routers are heard , the router with the highest ospf priority is elected DR, and election process start again for BDR. A priority of zero removes a router from the election.
step 3. If two or more routers have the same ospf priority , the router with the highest router-id is elected DR, and the election process start again for BDR. After a DR is elected , election do not take place again unless the DR or BDR are lost. default priority is 1.
BUT
reading the RFC (RFC 2328 – OSPF Version 2) does help understand the process. Look at section 9.4 – Electing the Designated Router. According to the RFC, the BDR is actually elected first, followed by the DR. The RFC explains why:
“The reason behind the election algorithm’s complexity is the desire for an orderly transition from Backup Designated Router to Designated Router, when the current Designated Router fails. This orderly transition is ensured through the introduction of hysteresis: no new Backup Designated Router can be chosen until the old Backup accepts its new Designated Router responsibilities.”