200-301 Question #192: Real Exam Question with Answer & Explanation

Question

The OSPF Hello protocol performs which of the following tasks? (Choose two.)

Options

• AIt provides dynamic neighbor discovery.
• BIt detects unreachable neighbors in 90 second intervals.
• CIt maintains neighbor relationships.
• DIt negotiates correctness parameters between neighboring interfaces.
• EIt uses timers to elect the router with the fastest links as the designated router.
• FIt broadcasts hello packets throughout the internetwork to discover all routers that are running OSPF.

Explanation

The OSPF Hello protocol is crucial for discovering neighboring OSPF routers and continuously monitoring their reachability to maintain neighbor relationships.

Common mistakes.

• B. OSPF detects unreachable neighbors based on the Dead Interval, which is typically 40 seconds on broadcast networks (4 * 10-second Hello interval), not a fixed 90-second interval.
• D. While Hello packets contain parameters like the network mask, hello/dead intervals, and stub area flag, the negotiation of these parameters is implicit in forming an adjacency if they match, rather than an explicit "negotiation" as per the Hello protocol's primary task.
• E. The Designated Router (DR) election process uses Hello packets to exchange router priorities and router IDs, but the DR is not elected based on link speed.
• F. Hello packets are sent to multicast addresses (224.0.0.5 or 224.0.0.6) on the local segment, not broadcast throughout the entire internetwork to discover all OSPF routers.

Concept tested. OSPF Hello protocol functions

Reference. https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13681-5.html

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