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Zorluk: ZorOSPFv2 Network Types and DR/BDR Selection

An network engineer is analyzing how OSPFv2 resolves Designated Router (DR) selection on a multiaccess Ethernet segment when multiple candidate routers initialize simultaneously. Arrange the tie-breaking criteria in order of evaluation precedence, starting with the primary criterion evaluated first (highest precedence) at the top down to the final fallback tie-breaker at the bottom.

  1. 1Highest OSPF interface priority value (1–255)
  2. 2Explicitly configured OSPF router ID (`router-id` command)
  3. 3Highest IP address among active loopback interfaces
  4. 4Highest IP address among active physical interfaces

Cevap

The correct evaluation sequence for OSPF DR selection precedence is: 1. Highest OSPF interface priority value (1–255), 2. Explicitly configured OSPF router ID (`router-id` command), 3. Highest IP address among active loopback interfaces, and 4. Highest IP address among active physical interfaces.
During an OSPF DR/BDR election on a broadcast multiaccess segment, routers first compare interface priority values (1 to 255). If priorities are tied, the election uses the OSPF Router ID as the tie-breaker. The Router ID selection hierarchy itself evaluates an explicitly configured router ID first, followed by the highest active loopback IP address, and finally the highest active physical interface IP address.

Adım Adım Çözüm

1
Identify the primary parameter evaluated during OSPF DR/BDR elections on multiaccess networks.
OSPF interface priority is evaluated first. Priority values range from 0 to 255, where priority 0 disables election participation and higher values win.
Interface priority explicitly allows network administrators to control DR/BDR roles regardless of IP addressing.
2
Determine the highest precedence method for tie-breaking using the OSPF Router ID when interface priorities match.
An explicitly configured `router-id` under the OSPF router process is evaluated first.
Manual CLI configuration overrides all dynamic IP address collection logic.
3
Identify the dynamic fallback method for Router ID derivation when no manual Router ID is set.
The highest IPv4 address on any active (up/up) loopback interface is chosen.
Loopback interfaces are preferred over physical interfaces due to their logical stability.
4
Identify the final fallback method for Router ID derivation.
The highest IPv4 address on any active (up/up) physical interface is chosen.
Physical interface IP addresses serve as the last-resort tie-breaker when no explicit router ID or loopbacks are present.

Anahtar Kavram

OSPF DR/BDR election logic prioritizes interface priority first, using Router ID (derived via explicit CLI > highest loopback IP > highest physical IP) as a sequential tie-breaker.
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OSPFv2 Network Types and DR/BDR Selection

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