Traffic Interception with WCCP
WCCP is a tunneling method. Since a tunnel could be built using any two devices. The configurations have been broken into endpoint configurations.
Router WCCP end-point
Squid WCCP end-point
Traffic Interception by Policy Routing
Alternative to tunneling. Policy Routing is a method of passing traffic directly to the interceptor unaltered.
Traffic Interception capture into Squid
Once the packets reach the Squid box they still need passing into Squid. This is done by the NAT infrastructure of the operating system firewall.