After an EtherChannel is configured between two Cisco switches, interface port channel 1 is in the down/down state. Switch A is configured with channel-group 1
mode active, while Switch B is configured with channel-group 1 mode desirable. Why is the EtherChannel bundle not working?

A.
The switches are using mismatched EtherChannel negotiation modes.

B.
The switch ports are not configured in trunking mode.

C.
LACP priority must be configured on both switches.

D.
The channel group identifier must be different for Switch A and Switch B.

Explanation:
Here we have a situation where one switch is using active mode, which is an LACP mode, and the other is using desirable, which is a PAGP mode. You can not mix
the LACP and PAGP protocols to form an etherchannel. Here is a summary of the various etherchannel modes:
EtherChannel PagP Modes
Mode
Description
auto
Places a port into a passive negotiating state, in which the port responds to PagP packets it receives but does not start PagP packet negotiation. This setting
minimizes the transmission of

PagP packets.
This mode is not supported when the EtherChannel members are from different switches in the switch stack (cross-stack EtherChannel).
Desirable
Places a port into an active negotiating state, in which the port starts negotiations with other ports by sending PagP packets.
This mode is not supported when the EtherChannel members are from different switches in the switch stack (cross-stack EtherChannel).

EtherChannel LACP Modes
Mode
Description
active
Places a port into an active negotiating state in which the port starts negotiations with other ports by sending LACP packets.
Passive
Places a port into a passive negotiating state in which the port responds to LACP packets that it receives, but does not start LACP packet negotiation. This setting
minimizes the transmission of LACP packets.
http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2960/software/release/12- 2_55_se/configuration/guide/scg_2960/swethchl.html