Dual IP addressing

I have a Unix application server with an internet IP address on it for a gateway and a Unix web server with the Internet IP as well configured for its gateway. Now the problem I have is this: due to these gateways, the application server can't communicate with our internal LAN. Therefore, it isolates the unix servers from the corporate LAN. Someone ones told me that it was possible for IP adresses on a unix server be configured in such a way that it will be accessible for the internet as well as internally. Is this possible and how can it be done. Websites for references are also welcome. Thanks in advance.

P.S I already sent this to Unix for Newbies till I realised that this is a more appropriate platform.

It sounds like your application is on a DMZ - access from the internal WAN would have to be allowed with firewall rules on the firewall - you need to talk to the person/s in charge of your firewalls/network. Realize there are security concerns with opening up your server on the DMZ to both external and internal.

Thanks RTM. Your response actually brought to my memory somethngs. Many thanks.