RFC 3169 (rfc3169) – Page 2 of 17

Criteria for Evaluating Network Access Server Protocols

Alternative Format: Original Text Document

RFC 3169         Criteria for Evaluating NAS Protocols    September 2001


   carried over a telephony protocol.  Second are broadband pseudo-
   telephony access protocols, which are carried over xDSL or cable
   modems, for example.  These protocols typically support an
   encapsulation method such as PPP over Ethernet [PPPOE].  Finally are
   the virtual access protocols used by NAS's that terminate tunnels.
   One example of this type of protocol is L2TP [L2TP].

   It is a central assumption of the NAS model used here that a NAS
   accepts multiple point-to-point links via one of the above access
   protocols.  Therefore, at a minimum, any NAS access protocol MUST be
   able to carry PPP.  The exception to this requirement is for NAS's
   that support legacy text login methods such as telnet [TELNET],
   rlogin, or LAT.  Only these access protocols are exempt from the
   requirement to support PPP.

4.  Network Protocol Requirements

   The network protocols supported by a NAS depend entirely on the kind
   of network to which a NAS is providing access.  This document does
   not impose any additional requirements on network protocols beyond
   the protocol specifications themselves.  For example, if a NAS that
   serves a routed network includes internet routing functionality, then
   that NAS must adhere to [ROUTING-REQUIREMENTS], but there are no
   additional protocol requirements imposed by virtue of the device
   being a NAS.

5.  AAA Protocol Requirements

5.1.  General protocol characteristics

   There are certain general characteristics that any AAA protocol used
   by NAS's must meet.  Note that the transport requirements for
   authentication/authorization are not necessarily the same as those
   for accounting/auditing.  An AAA protocol suite MAY use the same
   transport and protocol for both functions, but this is not strictly
   required.

5.1.1.  Transport requirements

5.1.1.1.  Transport independence

   The design of the AAA protocol MUST be transport independent.
   Existing infrastructures use UDP-based protocols [RADIUS], gateways
   to new protocols must be practical to encourage migration.  The
   design MUST comply with congestion control recommendations in RFC
   2914 [CONGEST].





Beadles & Mitton             Informational