Creating Etherchannel group on live network

I can't recall exactly, but I think if you keep the additional ports shutdown, configure the trunks, configure the virtual port channels and add the interfaces, and then 'no shut' the interfaces, you should be ok. If you turn up the trunk first, spanning-tree will need to run and it could take down your active link, especially if it is a non- preferred path.

While I think this will work without outage, I would never recommend messing with trunks and not scheduling and outage. Spanning tree is a nasty beast, and without knowing your whole network design, nothing can be promised.

I guess if these aren't trunks and are simple access ports with crossovers (no trunks), then you could do the above with portfast, but again need to be VERY careful here.

As mentioned it's not really the way to have a long and happy life however I have the idea that this might work. I am not at all sure.

Use 2 new ports for the channel on each end. Configure it all up (shutdown).

Configure STP costs such that the existing link is preferred. Note that you will have to do this for *all* vlans that cross the port channel.

Bring up the new links.

If the channel works you may not end up with a loop:-)

To transfer the traffic to the new links change the costs on them such that they are lower than the existing link. I think that the fail over should lose few packets. Maybe a one second outage.

Yeah that is why I said turn up the new configuration on a single port that you are going to channel with the existing, to hopefully avoid spanning tree having to run. I believe if the channel is pre- configured, and you simply bring up the second port, it will treat it as a down link in an etherchannel and simply add it back into the channel. You'd probably want to lab this first though.