Pppd
Encyclopedia
PPPD is the Point-to-Point Protocol
daemon
which is used to
manage network connections between two nodes on Unix-like
operating systems. It is configured using command-line arguments and configuration file
s.
While it has initially been used to manage only dial-up access
, it is also used to manage broadband
connections such as DSL
, if Point-to-Point Protocol over Ethernet
(PPPoE) or Point-to-Point Protocol over ATM
(PPPoA) is used.
The role of pppd is managing PPP session establishment and session termination.
During session establishment, pppd has the role of:
pppd terminates a PPP link when:
Some newer versions of pppd are also capable of handling Dial-on-demand routing
, where pppd sets up a virtual network, captures the packages it receives and establishes a PPP connection and forwards the captured and not-yet transmitted packages over the link.
Point-to-Point Protocol
In networking, the Point-to-Point Protocol is a data link protocol commonly used in establishing a direct connection between two networking nodes...
daemon
Daemon (computer software)
In Unix and other multitasking computer operating systems, a daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user...
which is used to
manage network connections between two nodes on Unix-like
Unix-like
A Unix-like operating system is one that behaves in a manner similar to a Unix system, while not necessarily conforming to or being certified to any version of the Single UNIX Specification....
operating systems. It is configured using command-line arguments and configuration file
Configuration file
In computing, configuration files, or config files configure the initial settings for some computer programs. They are used for user applications, server processes and operating system settings. The files are often written in ASCII and line-oriented, with lines terminated by a newline or carriage...
s.
While it has initially been used to manage only dial-up access
Dial-up access
Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network to establish a dialled connection to an Internet service provider via telephone lines...
, it is also used to manage broadband
Broadband
The term broadband refers to a telecommunications signal or device of greater bandwidth, in some sense, than another standard or usual signal or device . Different criteria for "broad" have been applied in different contexts and at different times...
connections such as DSL
Digital Subscriber Line
Digital subscriber line is a family of technologies that provides digital data transmission over the wires of a local telephone network. DSL originally stood for digital subscriber loop. In telecommunications marketing, the term DSL is widely understood to mean Asymmetric Digital Subscriber Line ,...
, if Point-to-Point Protocol over Ethernet
Point-to-Point Protocol over Ethernet
The Point-to-Point Protocol over Ethernet is a network protocol for encapsulating Point-to-Point Protocol frames inside Ethernet frames. It is used mainly with DSL services where individual users connect to the DSL modem over Ethernet and in plain Metro Ethernet networks...
(PPPoE) or Point-to-Point Protocol over ATM
Point-to-Point Protocol over ATM
The Point-to-Point Protocol over ATM is a network protocol for encapsulating PPP frames in AAL5. It is used mainly with DOCSIS and DSL carriers....
(PPPoA) is used.
The role of pppd is managing PPP session establishment and session termination.
During session establishment, pppd has the role of:
- Looped link detection: PPP detects looped links using magic numbersMagic number (programming)In computer programming, the term magic number has multiple meanings. It could refer to one or more of the following:* A constant numerical or text value used to identify a file format or protocol; for files, see List of file signatures...
. When PPPD sends PPP LCP messages, these messages include a magic number. If a line is looped, the node receives an LCP message with its own magic number, instead of getting a message with the peer's magic number. - Automatic self configuration: Using Link Control ProtocolLink Control ProtocolIn computing, the Link Control Protocol forms part of the Point-to-Point Protocol. In setting up PPP communications, both the sending and receiving devices send out LCP packets to determine the standards of the ensuing data transmission...
it has to negotiate protocol features like Address-and-Control-Field-Compression (ACFC), escaped characters, and the compression, encryption (like MPPEMPPEMicrosoft Point-to-Point Encryption is a protocol for encrypting data across Point-to-Point Protocol and virtual private network links. It uses the RSA RC4 encryption algorithm. MPPE supports 40-bit, 56-bit and 128-bit session keys, which are changed frequently to improve security...
) and authentication methods to use. - Access control and authentication: Using protocols like Challenge-handshake authentication protocolChallenge-handshake authentication protocolIn computing, the Challenge-Handshake Authentication Protocol authenticates a user or network host to an authenticating entity. That entity may be, for example, an Internet service provider. CHAP is specified in RFC 1994....
(CHAP) or Password authentication protocolPassword authentication protocolA password authentication protocol is an authentication protocol that uses a password.PAP is used by Point to Point Protocol to validate users before allowing them access to server resources. Almost all network operating system remote servers support PAP.PAP transmits unencrypted ASCII passwords...
(PAP) it has to provide and check authentication data. - Layer 3 configuration: If using Internet Protocol Control ProtocolInternet Protocol Control ProtocolIn computer networking, Internet Protocol Control Protocol is a network control protocol for establishing and configuring Internet Protocol over a Point-to-Point Protocol link. IPCP uses the same packet exchange mechanism as the Link Control Protocol...
(IPCP), it will negotiate or determine IPInternet ProtocolThe Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
parameters such as the IP addressIP addressAn Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
es, the maximum transmission unitMaximum transmission unitIn computer networking, the maximum transmission unit of a communications protocol of a layer is the size of the largest protocol data unit that the layer can pass onwards. MTU parameters usually appear in association with a communications interface...
, and name serverName serverIn computing, a name server is a program or computer server that implements a name-service protocol. It maps a human-recognizable identifier to a system-internal, often numeric, identification or addressing component....
addresses. Some versions may also support Internetwork Packet Exchange Control Protocol (IPXCP) and AppleTalk Control Protocol (ATCP) for routing IPXIPXInternetwork Packet Exchange is the OSI-model Network layer protocol in the IPX/SPX protocol stack.The IPX/SPXM protocol stack is supported by Novell's NetWare network operating system. Because of Netware's popularity through the late 1980s into the mid 1990s, IPX became a popular internetworking...
or AppletalkAppleTalkAppleTalk is a proprietary suite of protocols developed by Apple Inc. for networking computers. It was included in the original Macintosh released in 1984, but is now unsupported as of the release of Mac OS X v10.6 in 2009 in favor of TCP/IP networking...
over the link. - After negotiation is complete, it has to setup the required network interfaces and routes, so that the connection is run by the kernel.
pppd terminates a PPP link when:
- too many frames with invalid Frame Check SequenceFrame Check SequenceA frame check sequence refers to the extra checksum characters added to a frame in a communication protocol for error detection and correction. Frames are used to send upper-layer data and ultimately the user application data from a source to a destination. The data package includes the message...
(FCS) field have been received - the link is considered "idle" (if configured)
- another program or the peer requests link termination.
Some newer versions of pppd are also capable of handling Dial-on-demand routing
Dial-on-demand routing
Dial on Demand Routing is a routing technique where a network connection to a remote site is established only when needed. In other words, if the router tries to send out data and the connection is off, then the router will automatically establish a connection, send the information, and close the...
, where pppd sets up a virtual network, captures the packages it receives and establishes a PPP connection and forwards the captured and not-yet transmitted packages over the link.
Frontends and configurators
- kpppKpppkppp is a modem and internet dialer for the KDE system, whose name is an abbreviation for "KDE Point-to-Point Protocol".kppp is generally used to connect to an internet service provider via a modem and phone line, although it can be used in other situations where the PPP protocol is needed...
- A GUIGuiGui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...
frontend for pppd. - gnome-pppGnome-pppGnome-PPP is a front end to the Point-to-Point Protocol dialer Wvdial. It is meant to make it easier to configure a dialup connection, and supports a system tray icon. As of May 2009, the website is dead and the application appears to be discontinued, although it can still be downloaded from...
- A GUIGuiGui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...
frontend for pppd. - pppconfig - It uses the standard ppp configuration files and sets ppp up so that the standard pon and poff commands (to connect and disconnect) and plog (to list the log) can be used to control ppp. It includes modem detection.
- wvdialWvdialWvDial is a utility that helps in making modem-based connections to the Internet that is included in some important Linux distributions. WvDial is a Point-to-Point Protocol dialer: it dials a modem and starts pppd in order to connect to the Internet....
- A CLI tool which is used for modem initialisation before starting pppd.
Further reading
- Linux PPP HOWTO
- FAQ about ppp configuration
- Use of pon, poff and plog
- Understanding debug ppp negotiation Output