Etherchannel practice question

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Hey ITPro.TV, ran into a test question that is twisting my head a little. Can you clarify? The answer to the question indicated by the practice exam is "A", but if you look at the config of a switch this doesn't make a lot of sense. If you set a channel-group to mode "auto", doesn't that mean it is going to do PAgP only? The only way to get JUST Etherchannel is to use "mode on" at each end. Right?

active Enable LACP unconditionally
auto Enable PAgP only if a PAgP device is detected
desirable Enable PAgP unconditionally
on Enable Etherchannel only
passive Enable LACP only if a LACP device is detected

You have executed the following commands on a switch:

Switch64(config)# interface range gigabitethernet2/0/1 -2
Switch64(config-if-range)# switchport mode access
Switch64(config-if-range)# switchport access vlan 10
Switch64(config-if-range)# channel-group 5 mode auto

In which of the following situations will Switch64 create an Etherchannel?
A. If the other switch is set for desirable mode
B. If the other switch is set for auto mode
C. If the other switch is set for on mode
D. If the other switch is set for passive mode

@Adam-Tyler said in Etherchannel practice question:

Hey ITPro.TV, ran into a test question that is twisting my head a little. Can you clarify? If you set a channel-group to mode "auto", doesn't that mean it is going to do PAgP only?

This can be true or false depending the context you're using it. for the question you posted you have to look at the config on switch64. You've already set one side as:
Switch64(config-if-range)# channel-group 5 mode auto If you set another switch
with an auto, so that both ends are set to auto. PAgP sees this as a passive configuration on both sides so that neither side will attempt to form the PAgP channel group. If you want PAgP to form, one side must actively negotiate for that to happen you must have one side configured to Switch63(config-if-range)# channel-group 5 mode desireable So the correct answer is "A"

The only way to get JUST Etherchannel is to use "mode on" at each end. Right?

This is where the language is confusing when using the keywords. If you want to

• configure LACP you must use Active/Passive as the keywords
• configure PAgP, you must use desireable/auto as the keywords
• configure Etherchannel (that is neither LACP or PAgP) you must use on

The problem is that Etherchannel is not used in the question as describing what they want you to configure but instead used generically to describe how to form up the type of etherchannel (i.e. PAgP or LACP) that is configured on the other side. If you where to choose "C", the Etherchannel still wouldn't form because the other side is not configured as on.

active Enable LACP unconditionally
auto Enable PAgP only if a PAgP device is detected
desirable Enable PAgP unconditionally
on Enable Etherchannel only
passive Enable LACP only if a LACP device is detected

You have executed the following commands on a switch:

Switch64(config)# interface range gigabitethernet2/0/1 -2
Switch64(config-if-range)# switchport mode access
Switch64(config-if-range)# switchport access vlan 10
Switch64(config-if-range)# channel-group 5 mode auto

In which of the following situations will Switch64 create an Etherchannel?
A. If the other switch is set for desirable mode
B. If the other switch is set for auto mode
C. If the other switch is set for on mode
D. If the other switch is set for passive mode

Ah, that was where my confusion was. The term "Etherchannel" can be used to describe bonded links on a Cisco switch no matter if it is using PAgp, LACP, or Etherchannel. Thanks Ronnie.

Regards,
Adam Tyler