What are the main types of ISIS Hello messages? (Multiple choice)

Question

Options

• AP2P LAN IIH
• BLevel-1 LAN IIH
• CLevel-2 LAN IIH
• DLevel-3 LAN IIH

• A
  73% (19)
• B
  8% (2)
• C
  4% (1)
• D
  15% (4)

Explanation

Note: This question appears to contain an error in its answer key. IS-IS (Intermediate System-to-Intermediate System) actually has three real Hello message types: Level-1 LAN IIH, Level-2 LAN IIH, and Point-to-Point (P2P) IIH - making B and C also correct, not distractors.

Here's the accurate breakdown:

• A (P2P IIH): Valid - sent on point-to-point links regardless of IS-IS level. Note that "P2P LAN IIH" as written is a contradictory label; P2P links are not LANs. The real term is simply "P2P IIH."
• B (Level-1 LAN IIH): Also valid - sent on broadcast/LAN segments by Level-1 routers to form intra-area adjacencies.
• C (Level-2 LAN IIH): Also valid - sent on broadcast/LAN segments by Level-2 routers for inter-area routing.
• D (Level-3 LAN IIH): Genuinely wrong - IS-IS only has two levels (L1 and L2); Level-3 does not exist in the protocol.

Memory tip: IS-IS Hellos mirror the topology: two types for LAN (one per level) + one for P2P (level-agnostic). If you see "Level-3" anywhere in IS-IS questions, it's always a trap - IS-IS stops at Level-2.

If this is from an official exam, flag the answer key - B and C should also be marked correct.

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