Etherchannel

I nearly failed to add Etherchannel to the discussion of STP. The essence of fast etherchannel is that, when you have multiple links between switches STP will set all but one in a blocking state. This is a waste of bandwidth as the blocked ports simply wait for a failure. Fast etherchannel allows you to bind all links between switches together to load-balance across the available connections and combine their bandwidth into a virtual interface that you administer as a single physical link. If one of the links in an etherchannel group fails, the rest of the group continues to work together.

That's cool, I think.