In IS-IS, which of the following describes a purpose of Hellos?

Question

Options

• AKey exchange algorithm used to generate session keys
• BSpanning tree algorithm to prevent communication loops
• CHost protocol used for digital signatures and authentication
• DAlgorithm used for data encryption
• EAlgorithm for data integrity protection

• A
  4% (1)
• B
  78% (18)
• C
  17% (4)

Explanation

There's a significant problem with this question that I need to flag before proceeding.

The answer key appears to be incorrect. IS-IS Hello packets (IIH - IS-IS Hello PDUs) serve these actual purposes:

• Neighbor discovery on a link
• Establishing and maintaining adjacencies with neighboring routers
• Electing the DIS (Designated Intermediate System) on broadcast networks
• Keepalive / holddown timer - if Hellos stop arriving, the adjacency is torn down

None of options B, D, or E describe any of these functions:

• B (spanning tree algorithm) describes STP, a Layer 2 loop-prevention protocol - unrelated to IS-IS Hellos
• D (data encryption algorithm) describes protocols like AES - not a Hello function
• E (data integrity protection) describes hashing like MD5/SHA - not a Hello function

Option A (key exchange to generate session keys) doesn't fit either, but none of the five options correctly describe IS-IS Hellos.

My recommendation: Do not study this question as written. The answer key is wrong and will create a misconception. If this came from a study guide or practice exam, the question is likely corrupted or misattributed (the choices look like they belong to a completely different question, possibly about IPsec or another security protocol).

The memory tip for IS-IS Hellos: think "discover, adjacent, elect, keepalive" - those are the four real purposes.

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