IP Masquerade has been in the Linux kernels for several years now and is quite mature as the kernel enters the 2.4.x stage. Kernels since Linux 1.3.x have had MASQ support built-in. Today, many individuals and commercial businesses are using it with excellent results.
2.4.x kernel users:
The 2.4.x kernel hosts an entirely re-written set of NAT code which is both far superior, faster, and more secure than any previous versions written for Linux. Unfortunately, several kernel modules that were written for the 2.2.x kernel to support things like UDP-based RealAudio, etc. have not been ported to 2.4.x yet. Because of this, some people should consider NOT upgrading if these network applications are critical to them. But, at the same time, some of these programs have been updated and now use different, NAT-friendly protocols. Thus special NAT treatment is no longer required. As always, please see the http://ipmasq.webhop.net/: The IP Masquerade Resources site for updated news, etc.
Common network functionalities like Web browsing, telnet, ssh, ping, traceroute, etc. work well over stock IP Masquerade setups. Other network applications such as ftp, irc, and Real Audio work well with the appropriate additional IP MASQ modules loaded into the kernel as modules. Other network-specific programs like streaming audio (MP3s, True Speech, etc) should work too without any special module. Some users on the mailing list also had good results with video conferencing software.
It should be noted that running IP Masquerade with only ONE network card (NIC) to MASQ between internal and external Ethernet networks is NOT recommended. For more details, please see Section 7.28 FAQ section.
Anyways, please refer to Section 6.3 for a more complete listing of software supported by IP Maquerade all kernel versions.
IP Masquerade works well as a server to other 'client machines' running various operating systems and hardware platforms. Here is a sampling of successful reports with internal MASQed systems running :
UNIX: Sun Solaris, [Net,Free,Open,*i]-BSD, Hp-UX, Linux, IBM AIX, Digital UNIX, Ultrix, etc.
Microsoft Windows 2000, NT (3.x and 4.x), 95/98/ME, Windows for Workgroups (with the TCP/IP package)
IBM OS/2
Apple Macintosh MacOS machines running either MacTCP or Open Transport
DOS-based systems with packet drivers and the NCSA Telnet package
VAXen
Compaq/Digital Alpha running Linux and NT
Amiga computers with AmiTCP or AS225-stack.
The list goes on and on but the point is, if your OS platform talks TCP/IP, it should work with Linux's IP Masquerade!