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Difficulty: MediumOSPFv2 Network Types and DR/BDR Selection

An administrator modifies the OSPFv2 network type on a GigabitEthernet interface shared by two routers from the default BROADCAST to POINT_TO_POINT using the command `ip ospf network point-to-point`. Which two statements correctly describe the operational changes resulting from this configuration? (Select two.)

  1. Designated Router (DR) and Backup Designated Router (BDR) elections are bypassed on the interface.Answer
  2. OSPF packets continue to be sent to the AllSPFRouters multicast address (224.0.0.5), but the AllDRouters address (224.0.0.6) is no longer used.Answer
  3. C
    The router interface priority must be explicitly changed to 0 to prevent a DR election from occurring.
  4. D
    The default OSPF Hello and Dead timers automatically adjust from 10/40 seconds to 30/120 seconds.
  5. E
    Neighbors must now be statically configured using the `neighbor` command under the OSPF router configuration process.

Answer

On an OSPFv2 Point-to-Point network link, DR/BDR elections are entirely bypassed, and routers communicate using the AllSPFRouters multicast address (224.0.0.5) while discontinuing the use of 224.0.0.6.
Configuring `ip ospf network point-to-point` changes OSPF operating behavior such that DR and BDR elections are omitted because the link connects only two endpoints. In addition, all OSPF traffic (Hello, DBD, LSU, LSAck) on a point-to-point link uses the 224.0.0.5 multicast destination address, omitting 224.0.0.6.

Step-by-Step Solution

1
Analyze DR/BDR requirements for Point-to-Point network types.
Recognize that Point-to-Point links connect exactly two routers, making DR/BDR election unnecessary.
DR and BDR roles exist solely to reduce adjacency flood overhead on multiaccess networks.
2
Evaluate OSPF multicast address usage on Point-to-Point links.
Identify that 224.0.0.5 (AllSPFRouters) is used for all OSPF packet exchanges on Point-to-Point links, while 224.0.0.6 (AllDRouters) is unused.
Since there is no DR present on the segment, packets destined to DRs (224.0.0.6) are unnecessary.
3
Compare default timers and neighbor discovery behavior between Broadcast and Point-to-Point modes.
Confirm that both network types default to 10-second Hello and 40-second Dead timers and both dynamically discover neighbors via multicast.
Only NBMA and Point-to-Multipoint modes use 30/120 second default timers or require static neighbor statements.

Key Concept

OSPFv2 Point-to-Point vs Broadcast Network Type Characteristics
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Topics

OSPFv2 Network Types and DR/BDR Selection

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