on means force channelling on, but do not negotiate with the other side.
desirable means try and negotiate with the other side, and if he agrees, then enable the channel.
If you have on on one side and desirable on the other, then it will not form a channel because no negotiation will take place. In fact, it is likel?y to cause problems because one side will think it's channelling, and the other side will think it's not.
Use on when you are talking to a switch that does not understand negotiation but which has channel configured on, or if you want to bypass the negotiation to make the link come up quicker.
In addition to Kevin's post, you often use 'on' when the device in the remote end does not support etherchanneling negotiation. You often see this configuration when channeling server ports or non-cisco devices. The channeling mode on both devices must be 'on/on' in order to work.
The desirable option is often used between Cisco switches. Desirable employs the PAgP protocol which is Cisco proprietary. When you use Desirable, the remote end must be set to Desirable or Auto. Those are the only compatible settings (Desirable/Desirable or Desirable/Auto).
There is also another channeling option, LACP. LACP is industry standard and it's supported widely on most 3rd party switches and certain server NICs. LACP uses the Active/Active or Active/Passive modes.
Hi everyone, I would like to thank you in advance for any help you can provide a newcomer like myself!
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