To Bypass Transperent proxy for local Intranet

Dear All,

We have setup Squid proxy server in transparent mode so that every user is forced to browse the internet through squid proxy on 3128 port.

Configuration is follows

1) Squid and Firewall configured on same box on 172.18.0.51.

2) Done all necessary setting required for Transparent Proxy.
also it is working file.

But my problem is that we have local intranet server on 172.21.0.4:80

In normal case without Transperent proxy manually assingning proxy address in Internet explorer proxy setting and clicking bypass proxy for local address we able to access intranet, but with Transperent proxy we r not able to access the same becuase which I suppose that all request is redirected to 3128 port( transperent proxy feature).

therefore We want to bypass transpernet proxy for local intranet so that
we can able to access 172.21.0.4 : 80 port. I thinks there must be iptable
rule which enables this, can anybody tell me how this is to done.