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Difficulty: MediumOSPFv2 Network Types and DR/BDR Selection

Arrange the evaluation steps in the correct order of precedence used by OSPFv2 routers to determine Designated Router (DR) selection on a multiaccess network segment, from the initial eligibility filter to the final tie-breaker.

  1. 1Disqualify any candidate interface configured with an OSPF priority of 0 from participating in the election.
  2. 2Select the candidate router possessing the highest configured OSPF interface priority value.
  3. 3Break priority ties by choosing the router with the highest explicitly configured OSPF Router ID or highest active loopback IPv4 address.
  4. 4Break remaining ties by choosing the router with the highest IPv4 address configured on an active non-loopback physical interface.

Answer

The correct order of precedence for OSPFv2 DR selection is: 1) Disqualify priority 0 interfaces, 2) Select the candidate with the highest OSPF interface priority, 3) Break priority ties using the highest explicit Router ID or loopback IPv4 address, and 4) Break remaining ties using the highest active physical interface IPv4 address.
During an OSPFv2 DR election on a multiaccess network segment, candidate routers first exclude any interfaces configured with an OSPF priority of 0. Next, routers compare interface priorities to select the highest value. If interface priorities tie, OSPF compares Router IDs by selecting the candidate with the highest explicitly configured Router ID or highest loopback IPv4 address. Finally, if no loopback interface is present, the highest active physical interface IPv4 address is used as the tie-breaker.

Step-by-Step Solution

1
Filter out non-eligible candidate interfaces.
Interfaces configured with `ip ospf priority 0` are excluded from DR/BDR candidacy.
A priority of 0 explicitly revokes a router's ability to serve as DR or BDR.
2
Compare candidate interface priority values.
The router with the highest numeric priority value (1 to 255) is preferred.
Interface priority is the primary metric for OSPF DR election.
3
Evaluate Router ID using explicit setting or loopback addresses.
If interface priorities tie, the router with the highest explicit Router ID or highest active loopback IP address is selected.
Router ID serves as the secondary selection criteria when priorities are tied.
4
Evaluate physical interface IP addresses.
If no explicit Router ID or loopback interfaces exist, the highest active physical interface IPv4 address breaks the tie.
Physical interface IPv4 addresses are the final tie-breaker for Router ID assignment and election decisions.

Key Concept

OSPFv2 DR/BDR Election Precedence
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Topics

OSPFv2 Network Types and DR/BDR Selection

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