Enabling internal connections to transparently connect via external IP address

[Chris Willis <chris@castellan.net>]

Environment:
Windows XP laptop machine, part of domain acme.int, IP 192.168.1.150
Windows 2003 Server running Exchange 2003 (exchange.acme.int, 192.168.1.10)
External Domain: acme.com (T1 line, firewall external IP & MX record 
mail.acme.com 60.60.60.60)
Firewall: PC running Fedora Core 6, IPTables, using FWBuilder to create a 
ruleset, 2 NICs (eth0 192.168.1.1, eth1 60.60.60.60)

Problem: when a laptop user (works in office and remotely) goes to 
https://mail.acme.com, it works fine from the outside, but not from the inside.

Goal: when an internal (192.168.1.X) client goes to https://mail.acme.com, the 
firewall should accept the packets, route them to the exchange box, and then 
route return packets back to the client.

This works just fine on a netscreen firewall I tested with at the client site 
(same IP addresses as  linux box above).



Chris Willis