When running the OSPF protocol exchange DD messages, which of the following parameters will be used to elect the master-slave relationship?

Question

Options

• AIP address of the interface
• BDR priority of the interface
• CArea ID
• DRouter ID

• A
  3% (1)
• B
  5% (2)
• C
  13% (5)
• D
  79% (30)

Explanation

During OSPF's ExStart state, two neighboring routers exchange Database Description (DD) packets and must elect a master and slave before synchronizing their LSDBs - the router with the higher Router ID wins the master role and controls the DD sequence numbers. Router ID is a unique 32-bit identifier assigned to each OSPF router (typically the highest loopback or interface IP), making it the authoritative tie-breaker for this negotiation.

Why the distractors are wrong:

• A (Interface IP): The Router ID is derived from IP addresses but is a distinct, router-wide value - the specific interface IP facing the neighbor is not what's compared.
• B (DR priority): DR priority governs Designated Router / Backup DR election on multi-access segments, a completely separate process from DD master-slave negotiation.
• C (Area ID): Area ID identifies which OSPF area a link belongs to; it plays no role in the ExStart handshake.

Memory tip: "The Router with the highest Router ID is the Ruler" - it wins both DR elections (when priority ties) and DD master election. If you remember Router ID as OSPF's universal tiebreaker, you'll cover multiple exam scenarios at once.

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