Which PAgP mode combination prevents an EtherChannel from forming?
Click on the arrows to vote for the correct answer
A. B. C. D.D.
https://www.omnisecu.com/cisco-certified-network-associate-ccna/etherchannel-pagp-and-lacp-modes.phpPAgP (Port Aggregation Protocol) is a Cisco proprietary protocol that is used to automatically aggregate multiple physical links into a single logical link, called an EtherChannel. PAgP is used to negotiate the creation of an EtherChannel and to maintain its operation.
There are two modes of PAgP operation that can be configured on a port:
Desirable - The port actively tries to negotiate an EtherChannel by sending PAgP packets to the other end of the link.
Auto - The port waits for the other end to initiate PAgP negotiation.
The four possible combinations of PAgP modes are:
Out of these combinations, the combination of Desirable/Desirable enables PAgP negotiation and allows the formation of an EtherChannel. The other three combinations will not form an EtherChannel.
Therefore, the answer to the question is B. desirable/desirable.
Option A (auto/desirable) is a one-way negotiation, and the port configured as desirable will try to negotiate the formation of an EtherChannel. However, the port configured as auto will wait for the other end to initiate PAgP negotiation. Hence, there will be no negotiation and no EtherChannel will be formed.
Option C (desirable/auto) is also a one-way negotiation, and the port configured as auto will not initiate PAgP negotiation. As a result, the port configured as desirable will not receive any PAgP packets, and there will be no EtherChannel formed.
Option D (auto/auto) is similar to option C, where both ports are waiting for the other end to initiate PAgP negotiation. There will be no negotiation, and no EtherChannel will be formed.