1. Introduction
Considerable interest exists for a set of features that fit within
the general category of "roaming capability" for network access,
including dialup Internet users, Virtual Private Network (VPN) usage,
wireless LAN authentication, and other applications. Interested
parties have included the following:
o Regional Internet Service Providers (ISPs) operating within a
particular state or province, looking to combine their efforts
with those of other regional providers to offer dialup service
over a wider area.
o National ISPs wishing to combine their operations with those of
one or more ISPs in another nation to offer more comprehensive
dialup service in a group of countries or on a continent.
o Wireless LAN hotspots providing service to one or more ISPs.
o Businesses desiring to offer their employees a comprehensive
package of dialup services on a global basis. Those services may
include Internet access as well as secure access to corporate
intranets via a VPN, enabled by tunneling protocols such as the
Point-to-Point Tunneling Protocol (PPTP) [RFC2637], the Layer 2
Forwarding (L2F) protocol [RFC2341], the Layer 2 Tunneling
Protocol (L2TP) [RFC2661], and the IPsec tunnel mode [RFC2401].
In order to enhance the interoperability of roaming services, it is
necessary to have a standardized method for identifying users. This
document defines syntax for the Network Access Identifier (NAI).
Examples of implementations that use the NAI, and descriptions of its
semantics, can be found in [RFC2194].
This document is a revised version of RFC 2486(-> 4282prop) [RFC2486], which
originally defined NAIs. Differences and enhancements compared to
RFC 2486(-> 4282prop) are listed in Appendix A.
1.1. Terminology
This document frequently uses the following terms:
Network Access Identifier
The Network Access Identifier (NAI) is the user identity submitted
by the client during network access authentication. In roaming,
the purpose of the NAI is to identify the user as well as to
assist in the routing of the authentication request. Please note
that the NAI may not necessarily be the same as the user's e-mail
address or the user identity submitted in an application layer
authentication.
Network Access Server
The Network Access Server (NAS) is the device that clients connect
to in order to get access to the network. In PPTP terminology,
this is referred to as the PPTP Access Concentrator (PAC), and in
L2TP terminology, it is referred to as the L2TP Access
Concentrator (LAC). In IEEE 802.11, it is referred to as an
Access Point.
Roaming Capability
Roaming capability can be loosely defined as the ability to use
any one of multiple Internet Service Providers (ISPs), while
maintaining a formal, customer-vendor relationship with only one.
Examples of cases where roaming capability might be required
include ISP "confederations" and ISP-provided corporate network
access support.
Tunneling Service
A tunneling service is any network service enabled by tunneling
protocols such as PPTP, L2F, L2TP, and IPsec tunnel mode. One
example of a tunneling service is secure access to corporate
intranets via a Virtual Private Network (VPN).
In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL",
"RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [RFC2119].
1.3. Purpose
As described in [RFC2194], there are a number of providers offering
network access services, and the number of Internet Service Providers
involved in roaming consortia is increasing rapidly.
In order to be able to offer roaming capability, one of the
requirements is to be able to identify the user's home authentication
server. For use in roaming, this function is accomplished via the
Network Access Identifier (NAI) submitted by the user to the NAS in
the initial network authentication. It is also expected that NASes
will use the NAI as part of the process of opening a new tunnel, in
order to determine the tunnel endpoint.
