Ethernet Frame Diverter is mainly used for setting up a bridge with Squid running on it and transparently caching the Web traffic between the LAN and the router. "Transparent" means that no reconfiguration of the router or the clients is required. It also means that, in case of trouble, the machine can be replaced by a simple crossover RJ45 patch cord.
Ethernet Frame Diverter modularized
Ethernet Frame diverter 0.51 is available for both linux kernel 2.2.18 and 2.4.2. It can compile as module for flexibility.