Probably a stupid question but...

bwillford

So if a switch seperates each port into a different collision domain and eliminates collisions, why is there a collision light on the switch?

xza

I believe collisions can still occur in a half duplex network. Like if the switch and pc transmit at the same time. I haven't looked into it much, but I'm almost positive I've read they can occur at half duplex.

MrXpert

Each switchport is its own collision domain so this means that a pc connected to a switchport can only collide with itself which isn't going to happen.

If you are having collisons using a switch then could be due to one end being Full duplex and other side half or half duplex on both sides. I'd check what you have and hard code the correct speed and duplex if needed.