[tproxy] please help me

Hi, I setup a debian Squid server as topology as below: INTERNET---- MIKROTIK========SQUID3---CLIENTS My client connect via pppoe tunnel to the mikrotik device for some accounting issue . I ran bridge interface in debian(kernel 2.6.30 and iptables 1.4.8 ), when clients connect via pppoe tunnel to the mikrotik ,debian bidge interface cant redirect traffic to the squid and my squid server can not cache the web traffc but when i set default gateway in my client without pppoe everything works fine and the Squid caching work properly. I wanto know what should i do to redirect traffic to squid when client using pppoe connection. I researched my problem many many times in the intenet without any result,Please help me .