Regardless of the operating system you choose for your gateway, be sure it is installed in a secure manner. Completely disconnect the host from the network and use installation media that you trust. Vendors have different ways to verify their installation media. If you have downloaded an ISO CD image from an FTP server, there should be a checksum file with the ISO image that will allow you to verify the integrity of the data.

Once the operating system is installed, it is imperative that you check with your vendor for security patches. No matter how bug free an operating system was thought to be when it was released, security vulnerabilities will be found and used to create exploits over time. Before connecting your host to the network, download security patches from your vendor, copy them onto a trusted media, and install the patches from that media. This will allow you to have a high degree of assurance in your installation once you place it into production.