squid.conf
acl localusers 192.168.0.0/24
http_access allow localusers

http_accel_host virtual
http_accel_port 80
http_accel_with_proxy on
http_accel_uses_host_header on

iptables -t nat -A PREROUTING -p tcp -s $IP -d ! 192.168.0.0/24 --dport 80 -j REDIRECT --to-ports 3128