Catalyst 3550 and WCCP

To enable WCCP on Cisco Catalyst 3550 switch, first, you need to enable the SDM for routing with extended-match:
sdm prefer routing extended-match

Secondly, enable wccp globly:
ip wccp web-cache

Thirdly, WCCP on 3550 can only run inbound redirect, so under the user interface, run
ip wccp web-cache redirect in