Which PAgP mode combination prevents an Etherchannel from forming?

Question

Exhibit

Options

• Aauto/auto
• Bdesirable/desirable
• Cauto/desirable
• Ddesirable

• A
  92% (58)
• B
  3% (2)
• C
  2% (1)
• D
  3% (2)

Explanation

PAgP EtherChannel Mode Combinations

Option A (auto/auto) is correct because both switches are in a passive, waiting state - neither side will actively initiate PAgP negotiation, so no EtherChannel will ever form. Think of it like two shy people at a dance, both waiting for the other to ask first - nothing happens.

Why the distractors are wrong:

• B (desirable/desirable): Both sides actively send PAgP packets, so negotiation succeeds and EtherChannel forms
• C (auto/desirable): The desirable side actively initiates, and auto will respond, so EtherChannel forms
• D (desirable): This is incomplete - desirable can pair with either auto or desirable to successfully form an EtherChannel

Memory Tip: Use the phrase "Auto needs a Desirable partner" - auto only responds; it never starts the conversation. If both sides are auto, nobody talks first and no channel forms. Similarly, for LACP (the open standard equivalent), passive/passive has the same problem - memorize both pairs together!

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