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Difficulty: MediumOSPFv2 Network Types and DR/BDR Selection

A network engineer is auditing OSPFv2 interface configurations across a corporate network topology. On a multi-access Ethernet segment connecting five routers (R1 through R5), R1 must be configured so that it never becomes a Designated Router (DR) or Backup Designated Router (BDR). Additionally, on a separate point-to-point serial/Ethernet link between R1 and R2, the engineer converts the default OSPF network type to `point-to-point`. Which TWO actions or operational characteristics correctly apply to this OSPFv2 deployment? (Choose two.)

  1. Configuring `ip ospf priority 0` on R1's multi-access interface prevents it from participating in the DR/BDR election, keeping it permanently in the DROTHER state.Answer
  2. Changing the interface network type to `point-to-point` on the link between R1 and R2 eliminates DR/BDR election overhead while maintaining a default Hello interval of 10 seconds on Ethernet media.Answer
  3. C
    Setting an OSPF interface priority of 0 on R1's interface causes it to yield DR status but forces it to become the BDR if its loopback IP address is higher than all other routers.
  4. D
    Configuring `ip ospf network point-to-point` on an Ethernet interface automatically changes the default OSPF Hello interval from 10 seconds to 30 seconds.
  5. E
    Adding a new router with an OSPF interface priority of 255 to an active multi-access segment immediately preempts and replaces the currently elected DR.

Answer

Configuring an OSPF priority of 0 prevents a router from participating in DR/BDR elections (keeping it DROTHER), and configuring a point-to-point network type suppresses DR/BDR elections while preserving the default 10-second Hello timer on Ethernet.
Configuring an interface priority of 0 ensures a router will never assume the role of DR or BDR on a multi-access network segment. Furthermore, configuring the point-to-point network type eliminates DR/BDR elections entirely on that interface while retaining the standard 10-second Hello interval on Ethernet.

Step-by-Step Solution

1
Evaluate the requirement for R1 on the multi-access Ethernet segment.
Setting `ip ospf priority 0` on the interface completely excludes R1 from becoming either DR or BDR.
In OSPFv2, a router priority of 0 signifies non-participation in elections.
2
Analyze the operational properties of the OSPF point-to-point network type.
Point-to-point interfaces form adjacencies without electing a DR or BDR, and default Hello/Dead timers on Ethernet media remain 10s/40s.
DR/BDR elections are unnecessary on links limited to two endpoints.
3
Evaluate incorrect assertions regarding DR preemption, election override, and timer changes.
Reject claims that priority 0 allows BDR election, that point-to-point on Ethernet uses 30s timers, or that higher priority preempts an active DR.
Priority 0 excludes both DR and BDR roles; timer default is 10s; elections are non-preemptive.

Key Concept

OSPFv2 DR/BDR Election Rules and Network Type Timer Defaults
Estimated Time:1m 30s
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Topics

OSPFv2 Network Types and DR/BDR Selection

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