channel groups are sets of ports that can form a channel. They default to sets of 4 consecutive ports on every card. If you want a channel on ports 3/1-4 or any part of that (3/1-2,3/2-3...it will work. If you want to form a channel using ports that are not already grouped, like 3/4-5 then you need to create a new group. This is the command on a 6500 running cat OS. I think the 4006 is the same. You do not enter the "335" it is assigned automatically. As you can see I used the command to make a channel span two cards so it would stay up if a card went down. I don't know if the 4000 can do that.
set port channel 4/16,6/16 335
