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Difficulty: EasyOSPFv2 Network Types and DR/BDR Selection

Arrange the criteria used by OSPFv2 to determine Designated Router (DR) election precedence in order from highest precedence (evaluated first) to lowest precedence (evaluated last).

  1. 1Highest OSPF interface priority (range 1–255)
  2. 2Highest explicitly configured OSPF router ID
  3. 3Highest IPv4 address on an active loopback interface
  4. 4Highest IPv4 address on an active physical interface

Answer

The correct sequence from highest to lowest precedence is: Highest OSPF interface priority, followed by Highest explicitly configured OSPF router ID, then Highest IPv4 address on an active loopback interface, and finally Highest IPv4 address on an active physical interface.
OSPFv2 DR/BDR election process evaluates interface priority first. If priorities are equal, it breaks ties using the Router ID, which is selected in the following order of precedence: (1) explicitly configured router ID command, (2) highest IP address on an active loopback interface, and (3) highest IP address on an active physical interface.

Step-by-Step Solution

1
Evaluate the primary election criteria: OSPF Interface Priority
The router with the highest configured OSPF interface priority (1-255) is elected DR. Priority 0 disqualifies a router entirely.
Interface priority provides explicit administrative control over DR/BDR election.
2
Evaluate explicit Router ID configuration
If interface priorities are equal (the default is 1), OSPF uses the Router ID as a tie-breaker, checking for a manually configured 'router-id' first.
Explicit configuration takes precedence over dynamically selected interface IP addresses.
3
Evaluate active loopback interfaces
If no explicit router ID is configured, OSPF selects the highest IPv4 address among all active logical (loopback) interfaces.
Loopback interfaces are preferred over physical interfaces because they are stable and do not go down due to physical line failures.
4
Evaluate active physical interfaces
If no loopback interfaces are configured, OSPF defaults to selecting the highest IPv4 address configured on any up/up physical interface.
Physical interface IP addresses serve as the final tie-breaking mechanism.

Key Concept

OSPFv2 DR/BDR Election Precedence Rules
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Topics

OSPFv2 Network Types and DR/BDR Selection

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