POSIX (Portable Operating Systems Interface) is the name used by group of standards sponsored by the IEEE that define a standard API for UNIX-like operating systems. POSIX.1 (IEEE Std1003.1-1990) standardizes the API for C. POSIX.2 (IEEE Std1003.2-1992) standardizes the shell and basic utilities. Other POSIX standards cover Ada and Fortran bindings, real time extensions, conformance testing, etc. NetBSD is extremely close to being POSIX.1 compliant, and somewhat further from being POSIX.2 compliant. There are a few details we know about: some we plan to fix, and others we plan to ignore until a future revision of POSIX fixes them for us. People who use or distribute other free operating systems sometimes claim that their OS is POSIX or Standard C compliant. To our knowledge, none of the freely redistributable operating systems have been certified to be POSIX or Standard C compliant—nor is this likely to change, since certification is quite expensive and must be done for each release. We believe that NetBSD is closer to POSIX and Standard C compliance than any other freely redistributable operating system. To date, no efforts have been made to conform to X/Open Spec 1170, as this is an extremely complex and self-conflicting specification. NetBSD comes with XFree86, a superset of the X Window System Release 6.4 from the MIT X Consortium (now part of the Open Group). This implements the basic X server and client functionality of the X Window System, and provides some useful applications. A large number of additional X11 packages is available through pkgsrc. NetBSD implements many industry standard networking protocols, including TCP/IP, SMTP, NFS, DHCP, NIS and NTP. We also provide ported third party packages which implement HTTP, SMB, Appletalk, and many other protocols. Of particular interest is our TCP/IP implementation. We have identified and fixed a number of performance issues with the 4.4BSD TCP implementation, and work closely with the Internet Engineering Task Force to implement and test new protocol developments. Our TCP/IP implementation is used as a basis for research by some IETF members. In addition, two IPv6 and IPsec implementations have been developed on NetBSD, and another ported. The KAME implementation has been integrated. The industry standard routing system GateD also runs under NetBSD, and several ISPs use GateD under NetBSD to do routing on their networks.