A network access server (NAS) is a group of components that provides remote users with a point of access to a network.
Overview
A NAS concentrates dial-in and dial-out user communications. An access server may have a mixture of analog and digital interfaces and support hundreds of simultaneous users. A NAS consists of a
communications processor that connects asynchronous devices to a
LAN or
WAN through network and
terminal emulation
A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term ''terminal'' covers all remote termi ...
software. It performs both synchronous and asynchronous routing of supported protocols.
The NAS is meant to act as a
gateway to guard access to a protected resource. This can be anything from a
telephone
A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...
network
Network, networking and networked may refer to:
Science and technology
* Network theory, the study of graphs as a representation of relations between discrete objects
* Network science, an academic field that studies complex networks
Mathematics ...
, to
printers
Printer may refer to:
Technology
* Printer (publishing), a person or a company
* Printer (computing), a hardware device
* Optical printer for motion picture films
People
* Nariman Printer ( fl. c. 1940), Indian journalist and activist
* Jam ...
, to the
Internet
The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, pub ...
. A
client
Client(s) or The Client may refer to:
* Client (business)
* Client (computing), hardware or software that accesses a remote service on another computer
* Customer or client, a recipient of goods or services in return for monetary or other valuabl ...
connects to the NAS. The NAS then connects to another resource asking whether the client's supplied
credentials are valid. Based on that answer the NAS then allows or disallows access to the protected resource.
Examples
The above translates into different implementations for different uses. Here are some examples.
*An
Internet service provider
An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise privat ...
which provides network access via common modem or modem-like devices (be it
PSTN
The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...
,
DSL
Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric dig ...
,
cable
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
or
GPRS/
UMTS
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the In ...
) can have one or more NAS (network access server) devices which accept
PPP,
PPPoE or
PPTP
The Point-to-Point Tunneling Protocol (PPTP) is an obsolete method for implementing virtual private networks. PPTP has many well known security issues.
PPTP uses a TCP control channel and a Generic Routing Encapsulation tunnel to encapsulate PP ...
connections, checking credentials and recording accounting data via back-end
RADIUS
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
servers, and allowing users access through that connection.
* The
captive portal
A captive portal is a web page accessed with a web browser that is displayed to newly connected users of a Wi-Fi or wired network before they are granted broader access to network resources. Captive portals are commonly used to present a landin ...
mechanism used by many
WiFi
Wi-Fi () is a family of wireless network protocols, based on the IEEE 802.11 family of standards, which are commonly used for local area networking of devices and Internet access, allowing nearby digital devices to exchange data by radio wa ...
providers: a user wants to access the Internet and opens a
browser. The NAS detects that the user is not currently
authorized
Authorization or authorisation (see spelling differences) is the function of specifying access rights/privileges to resources, which is related to general information security and computer security, and to access control in particular. More for ...
to have access to the Internet, so the NAS prompts the user for their username and password. The user supplies them and sends them back to the NAS. The NAS then uses the
RADIUS
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
protocol to connect to an
AAA
AAA, Triple A, or Triple-A is a three-letter initialism or abbreviation which may refer to:
Airports
* Anaa Airport in French Polynesia (IATA airport code AAA)
* Logan County Airport (Illinois) (FAA airport code AAA)
Arts, entertainment, and me ...
server and passes off the
username
A user is a person who utilizes a computer or network service.
A user often has a user account and is identified to the system by a username (or user name). Other terms for username include login name, screenname (or screen name), accoun ...
and
password
A password, sometimes called a passcode (for example in Apple devices), is secret data, typically a string of characters, usually used to confirm a user's identity. Traditionally, passwords were expected to be memorized, but the large number of ...
. The RADIUS server searches through its resources and finds that the credentials are valid and notifies the NAS that it should grant the access. The NAS then grants the user access to the Internet.
*Another use of a NAS would be in
voice over IP
Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...
(VoIP). However, instead of using a username and password, many times a
phone number
A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices f ...
or
IP Address
An Internet Protocol address (IP address) is a numerical label such as that is connected to a computer network that uses the Internet Protocol for communication.. Updated by . An IP address serves two main functions: network interface ident ...
are used. If the phone number is a valid customer then the call can be completed. Other uses might be to verify whether a phone number has
long distance access or a
telephone card
A telephone card, calling card or phonecard for short, is a credit card-size plastic or paper card, used to pay for telephone services (often international or long-distance calling). It is not necessary to have the physical card except with a st ...
has minutes left.
Associated protocols
Although not required, NASs are almost exclusively used with
authentication, authorization, and accounting (AAA) servers. Of the AAA protocols available,
RADIUS
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
tends to be the most widely used. The
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid fo ...
base protocol extends RADIUS services by providing error handling and inter-domain communications. This protocol is used in networks like the
IP Multimedia Subsystem (IMS).
See also
*
Terminal server
A terminal server connects devices with a serial port to a local area network (LAN). Products marketed as terminal servers can be very simple devices that do not offer any security functionality, such as data encryption and user authentication ...
References
External links
* , Network Access Server Requirements Next Generation (NASREQNG)
Network access
Telephony
Telecommunications infrastructure
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