RADIUS, which provides centralized authentication and access control services to various network access and application layer devices, is implemented in many products. RADIUS is bundled into popular server-class OSs and sold as its own software and appliances. Various technologies are available that organizations can use for implementation of remote user authentication vary, but RADIUS is probably the default selection for most over the next few years. The Internet Engineering Task Force (IETF) is also promoting Diameter as the next-generation replacement for RADIUS, but few implementations are available as yet. Broad-based use of virtual private networks (VPNs) and per user tunneling has led to development that allows RADIUS to provide expected authorization and access control functionality needed for remote VPN admittance systems. Sometimes more link-specific RADIUS attributes are required, and most are defined in RFC 2868. Another example of the direction is 802.1x, with which devices block all traffic except for special L2 frames that carry user authentication requests inside Extensible Authentication Protocol (EAP) messages. An access request received is forward to an authentication server that in practice is usually a RADIUS server, and the RADIUS server returns an accept or reject response. RADIUS is well-understood and implementations are available. Among products available are free RADIUS servers bundled into Windows and Linux server platforms and commercial software from Funk Software and Interlink Networks. Hardware-enabled RADIUS appliances include ZyXEL Communications Vantage Radius 50, and Infoblox's RADIUSone. Topics covered include improved RADIUS topology support (including the addition of more RADIUS attributes and values defined in RFC 3580) and ongoing enhancements from the Internet Engineering Task Force (IETF) that include standardization of the Network Access Identifier attribute value.