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Difficulty: MediumOSPFv2 Network Types and DR/BDR Selection

A network administrator configures the command `ip ospf network point-to-point` on a GigabitEthernet interface of a Cisco router connected to a switch segment with another router. Previously, the interface operated using default OSPFv2 interface parameters for Ethernet interfaces. Which two operational changes occur on this interface as a result of this configuration change? (Select two.)

  1. OSPF halts the election of Designated Router (DR) and Backup Designated Router (BDR) roles on the interface.Answer
  2. Routers on the segment stop sending and listening to packets on the AllDRouters multicast address (224.0.0.6).Answer
  3. C
    The default Hello and Dead timers automatically increase from 10/40 seconds to 30/120 seconds.
  4. D
    The router automatically forces the interface priority value to 0 to prevent election participation.
  5. E
    Manual neighbor statements using the `neighbor` router configuration command become required to establish adjacencies.

Answer

Configuring an Ethernet interface as an OSPF point-to-point network type stops the DR/BDR election process on that interface and disables the use of the AllDRouters multicast destination address (224.0.0.6).
When an Ethernet interface is converted to an OSPF point-to-point network type, OSPF bypasses the DR and BDR election phase completely because the topology assumes a direct link between two routers. Because no DR or BDR exists, non-DR routers no longer send packets to the 224.0.0.6 (AllDRouters) multicast address; all OSPF control packets are sent exclusively to 224.0.0.5 (AllSPFRouters).

Step-by-Step Solution

1
Identify the default OSPF network type for Ethernet interfaces.
Ethernet interfaces defaults to the Broadcast multiaccess network type, which elects a DR and BDR and uses multicast address 224.0.0.6 for non-DR routers to communicate with the DR/BDR.
Broadcast multiaccess networks reduce adjacencies on shared segments via DR/BDR routers.
2
Analyze the impact of changing the network type to Point-to-Point using `ip ospf network point-to-point`.
Point-to-point network types assume exactly two nodes on the link. Consequently, OSPF DR/BDR election is suppressed, and communication over 224.0.0.6 is disabled since DR/BDR roles are absent.
Point-to-point links form direct peer adjacencies without intermediate designated routers.
3
Evaluate timer and neighbor discovery settings for Point-to-Point interfaces.
Hello/Dead timers remain at 10/40 seconds, and dynamic neighbor discovery using AllSPFRouters (224.0.0.5) is maintained.
Timers only change to 30/120 seconds on Non-Broadcast Multi-Access (NBMA) and Point-to-Multipoint network types.

Key Concept

OSPF Network Types (Broadcast vs. Point-to-Point) and DR/BDR Operational Differences
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Topics

OSPFv2 Network Types and DR/BDR Selection

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