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350-401 · Question #1279

Refer to the exhibit. An administrator configures two switches with LACP EtherChannels, but packets are not being exchanged between the switches. What is the reason, and what fixes the issue? S1> enab

The correct answer is C. S2 is configured with PAgP. Change the channel group mode to active.. The EtherChannel fails because Switch 1 is configured for LACP active while Switch 2 is configured for PAgP desirable, creating an incompatible negotiation protocol mismatch.

Submitted by lars.no· Mar 6, 2026Infrastructure

Question

Refer to the exhibit. An administrator configures two switches with LACP EtherChannels, but packets are not being exchanged between the switches. What is the reason, and what fixes the issue? S1> enable S1# configure terminal S1(config)# interface port-channel 1 S1(config-if)# ip address 10.1.1.1 255.2 S1(config-if)# interface g2/0/0 S1(config-if)# no ip address S1(config-if)# channel-group 1 mode active S1(config-if)# exit S1(config)# interface g4/0/0 S1(config-if)# no ip address S1(config-if)# channel-group 1 mode active S2> enable S2# configure terminal S2(config)# interface port-channel 1 $2(config-if)# ip address 10.1.1.2 255.255.255.0 S2(config-if)# interface g2/0/0 $2(config-if)# no ip address $2(config-if)# channel-group 1 mode desirable S2(config-if)# exit S2(config)# interface g4/0/0 S2(config-if)# no ip address S2(config-if)# channel-group 1 mode desirable

Options

  • AS1 is configured as PAgP. Change the channel group mode to desirable.
  • BS2 is configured as LACP. Change the channel group mode to passive.
  • CS2 is configured with PAgP. Change the channel group mode to active.
  • DS1 is configured with LACP. Change the channel group mode to on.

How the community answered

(29 responses)
  • A
    24% (7)
  • B
    7% (2)
  • C
    55% (16)
  • D
    14% (4)

Why each option

The EtherChannel fails because Switch 1 is configured for LACP `active` while Switch 2 is configured for PAgP `desirable`, creating an incompatible negotiation protocol mismatch.

AS1 is configured as PAgP. Change the channel group mode to desirable.

S1 is configured with LACP `active`, not PAgP, so the premise is incorrect.

BS2 is configured as LACP. Change the channel group mode to passive.

S2 is configured with PAgP `desirable`, not LACP, so the premise is incorrect; while changing to LACP passive on S2 would be a valid fix if S2 was already LACP, it's not the correct identification of the current problem.

CS2 is configured with PAgP. Change the channel group mode to active.Correct

The exhibit shows S1 configured with `channel-group 1 mode active`, which is an LACP mode, while S2 is configured with `channel-group 1 mode desirable`, which is a PAgP mode. For an EtherChannel to form, both sides must use the same negotiation protocol (LACP or PAgP), so changing S2's `mode desirable` (PAgP) to `mode active` (LACP) will resolve the incompatibility.

DS1 is configured with LACP. Change the channel group mode to on.

While S1 is LACP, changing its mode to `on` would remove LACP negotiation on S1 and still leave S2 attempting PAgP negotiation, failing to resolve the protocol mismatch.

Concept tested: LACP and PAgP EtherChannel negotiation modes

Source: https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3750/software/release/12-2_55_se/configuration/guide/scg/swethchl.html

Topics

#LACP#PAgP#EtherChannel#channel-group mode

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