Transparent proxy on dd-wrt

Using dd-wrt firmware v24-sp2

edit /tmp/.rc_firewall

iptables -t nat -A PREROUTING -s -d client_ip_address $(nvram get lan_ipaddr) -p tcp --dport 80 -j DNAT --to $(nvram get lan_ipaddr)
iptables -t nat -A PREROUTING -s client_ip_address -p tcp --dport 80 -j DNAT --to proxy_ip_address:proxy_port