Which of the following events will cause IS-IS to generate a new LSP? (Multiple choice)

Question

Options

• AAdjacency Up or Down
• BThe imported IP route sends changes
• CPeriodic update
• DThe interface overhead has changed

• A
  100% (49)

Explanation

All four options are correct triggers for IS-IS LSP regeneration. Adjacency changes (A) are the most common trigger - when a neighbor goes up or down, the local router must immediately flood a new LSP to reflect the updated topology. Imported route changes (B) cause a new LSP because IS-IS redistributes external routing information (e.g., from OSPF or BGP) within its LSP payload, so any change to those prefixes must be propagated. Periodic updates (C) are mandatory by design - IS-IS LSPs have a lifetime (default ~1200 seconds) and must be refreshed before expiry to prevent premature purging, even if the topology is stable. Interface metric changes (D) trigger a new LSP because the cost advertised to neighbors is part of the LSP, and SPF recalculations depend on accurate metrics.

Memory tip: Think of IS-IS LSP triggers as "AIRM" - Adjacency change, Imported route change, Refresh (periodic), Metric change. Any event that alters what neighbors need to know about your router forces a new LSP.

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