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Point-to-Point Protocol

In networking , the Point-to-Point Protocol , or PPP , is a data link protocol commonlyused in establishing a direct connection between two networking nodes . It can provideconnection authentication , transmission encryption privacy, and compression .

PPP is used over many types of physical networks including serial cable , phone line , trunk line , cellular telephone , specialized radio links, and fiber optic links such asSONET . Most Internet service providers (ISPs) use PPP for customer dial-up access tothe Internet . Two encapsulated forms of PPP, Point-to-Point Protocol over Ethernet (PPPoE) and Point-to-Point Protocol over ATM (PPPoA), are used most commonly byInternet Service Providers (ISPs) to establish a Digital Subscriber Line (DSL) Internetservice connection with customers.

PPP is commonly used as a data link layer protocol for connection over synchronous andasynchronous circuits, where it has largely superseded the older Serial Line InternetProtocol (SLIP) and telephone company mandated standards (such as Link AccessProtocol, Balanced (LAPB) in the X.25 protocol suite). PPP was designed to work withnumerous network layer protocols, including Internet Protocol (IP), Novell's Internetwork Packet Exchange (IPX), NBF and AppleTalk .

PPP is also used over broadband connections. RFC 2516 describes Point-to-PointProtocol over Ethernet (PPPoE), a method for transmitting PPP over Ethernet that issometimes used with DSL . RFC 2364 describes Point-to-Point Protocol over ATM

(PPPoA), a method for transmitting PPP over ATM Adaptation Layer 5 (AAL5), whichis also a common alternative to PPPoE used with DSL.

PPP is specified in RFC 1661 .[1]
http://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Data_Link_Layerhttp://en.wikipedia.org/wiki/Data_Link_Layerhttp://en.wikipedia.org/wiki/Protocol_(computing)http://en.wikipedia.org/wiki/Protocol_(computing)http://en.wikipedia.org/wiki/Node_(networking)http://en.wikipedia.org/wiki/Authenticationhttp://en.wikipedia.org/wiki/Encryptionhttp://en.wikipedia.org/wiki/Data_compressionhttp://en.wikipedia.org/wiki/Serial_cablehttp://en.wikipedia.org/wiki/Phone_linehttp://en.wikipedia.org/wiki/Phone_linehttp://en.wikipedia.org/wiki/Trunkinghttp://en.wikipedia.org/wiki/Cellular_telephonehttp://en.wikipedia.org/wiki/Cellular_telephonehttp://en.wikipedia.org/wiki/SONEThttp://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Dial-up_accesshttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_Ethernethttp://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_ATMhttp://en.wikipedia.org/wiki/Digital_Subscriber_Linehttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Synchronizationhttp://en.wikipedia.org/wiki/Asynchronyhttp://en.wikipedia.org/wiki/Serial_Line_Internet_Protocolhttp://en.wikipedia.org/wiki/Serial_Line_Internet_Protocolhttp://en.wikipedia.org/wiki/LAPBhttp://en.wikipedia.org/wiki/LAPBhttp://en.wikipedia.org/wiki/LAPBhttp://en.wikipedia.org/wiki/X.25http://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internetwork_Packet_Exchangehttp://en.wikipedia.org/wiki/Internetwork_Packet_Exchangehttp://en.wikipedia.org/wiki/Internetwork_Packet_Exchangehttp://en.wikipedia.org/wiki/NetBIOS_Frames_protocolhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/Broadbandhttp://en.wikipedia.org/wiki/Broadbandhttp://tools.ietf.org/html/rfc2516http://tools.ietf.org/html/rfc2516http://tools.ietf.org/html/rfc2516http://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_Ethernethttp://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_Ethernethttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Digital_Subscriber_Linehttp://tools.ietf.org/html/rfc2364http://tools.ietf.org/html/rfc2364http://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_ATMhttp://en.wikipedia.org/wiki/Asynchronous_Transfer_Modehttp://en.wikipedia.org/wiki/Request_for_Commentshttp://en.wikipedia.org/wiki/Point-to-Point_Protocol#cite_note-0http://en.wikipedia.org/wiki/Point-to-Point_Protocol#cite_note-0http://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Data_Link_Layerhttp://en.wikipedia.org/wiki/Protocol_(computing)http://en.wikipedia.org/wiki/Node_(networking)http://en.wikipedia.org/wiki/Authenticationhttp://en.wikipedia.org/wiki/Encryptionhttp://en.wikipedia.org/wiki/Data_compressionhttp://en.wikipedia.org/wiki/Serial_cablehttp://en.wikipedia.org/wiki/Phone_linehttp://en.wikipedia.org/wiki/Trunkinghttp://en.wikipedia.org/wiki/Cellular_telephonehttp://en.wikipedia.org/wiki/SONEThttp://en.wikipedia.org/wiki/Internet_service_providerhttp://en.wikipedia.org/wiki/Dial-up_accesshttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_Ethernethttp://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_ATMhttp://en.wikipedia.org/wiki/Digital_Subscriber_Linehttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Synchronizationhttp://en.wikipedia.org/wiki/Asynchronyhttp://en.wikipedia.org/wiki/Serial_Line_Internet_Protocolhttp://en.wikipedia.org/wiki/Serial_Line_Internet_Protocolhttp://en.wikipedia.org/wiki/LAPBhttp://en.wikipedia.org/wiki/LAPBhttp://en.wikipedia.org/wiki/X.25http://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internetwork_Packet_Exchangehttp://en.wikipedia.org/wiki/Internetwork_Packet_Exchangehttp://en.wikipedia.org/wiki/NetBIOS_Frames_protocolhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/Broadbandhttp://tools.ietf.org/html/rfc2516http://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_Ethernethttp://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_Ethernethttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Digital_Subscriber_Linehttp://tools.ietf.org/html/rfc2364http://en.wikipedia.org/wiki/Point-to-Point_Protocol_over_ATMhttp://en.wikipedia.org/wiki/Asynchronous_Transfer_Modehttp://en.wikipedia.org/wiki/Request_for_Commentshttp://en.wikipedia.org/wiki/Point-to-Point_Protocol#cite_note-0


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RFC 1994 describes Challenge-handshake authentication protocol (CHAP), which ispreferred for establishing dial-up connections with ISPs. Although deprecated, Passwordauthentication protocol (PAP) is still sometimes used.

Another option for authentication over PPP is Extensible Authentication Protocol (EAP).[2]

After the link has been established, additional network ( layer 3 ) configuration may takeplace. Most commonly, the Internet Protocol Control Protocol (IPCP) is used, althoughInternetwork Packet Exchange Control Protocol (IPXCP) and AppleTalk ControlProtocol (ATCP) were once very popular. [citation needed ] Internet Protocol Version 6 ControlProtocol (IPv6CP) will see extended use in the future, when IPv6 replaces IPv4 's positionas the dominant layer-3 protocol.

Multiple network layer protocols

PPP permits multiple network layer protocols to operate on the same communicationlink. For every network layer protocol used, a separate '''Network Control Protocol'''(NCP) is provided in order to encapsulate and negotiate options for the multiple network layer protocols.

For example, Internet Protocol (IP) uses the IP Control Protocol ( IPCP ), and Internetwork Packet Exchange (IPX) uses the Novell IPX Control Protocol ( '''IPX/SPX''' ). NCPsinclude fields containing standardized codes to indicate the network layer protocol typethat the PPP connection encapsulates.

Looped link detection

PPP detects looped links using a feature involving magic numbers . When the node sendsPPP LCP messages, these messages may include a magic number. If a line is looped, thenode receives an LCP message with its own magic number, instead of getting a messagewith the peer's magic number.

Most important features

Link Control Protocol initiates and terminates connections gracefully, allowinghosts to negotiate connection options. It also supports both byte- and bit-orientedencodings. [citation needed ]

Network Control Protocol is used for negotiating network-layer information, e.g.network address or compression options, after the connection has beenestablished.

PPP Configuration Options

The previous section introduced the use of LCP options to meet specific WANconnection requirements. PPP may include the following LCP options:
http://tools.ietf.org/html/rfc1994http://en.wikipedia.org/wiki/Challenge-handshake_authentication_protocolhttp://en.wikipedia.org/wiki/Challenge-handshake_authentication_protocolhttp://en.wikipedia.org/wiki/Password_authentication_protocolhttp://en.wikipedia.org/wiki/Password_authentication_protocolhttp://en.wikipedia.org/wiki/Extensible_Authentication_Protocolhttp://en.wikipedia.org/wiki/Point-to-Point_Protocol#cite_note-1http://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Internet_Protocol_Control_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocol_Control_Protocolhttp://en.wikipedia.org/wiki/IPX/SPXhttp://en.wikipedia.org/wiki/Appletalkhttp://en.wikipedia.org/wiki/Appletalkhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv4http://en.wikipedia.org/wiki/IPv4http://en.wikipedia.org/w/index.php?title=%27%27%27Network_Control_Protocol%27%27%27&action=edit&redlink=1http://en.wikipedia.org/wiki/IPCPhttp://en.wikipedia.org/w/index.php?title=%27%27%27IPX/SPX%27%27%27&action=edit&redlink=1http://en.wikipedia.org/wiki/Magic_number_(programming)http://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://tools.ietf.org/html/rfc1994http://en.wikipedia.org/wiki/Challenge-handshake_authentication_protocolhttp://en.wikipedia.org/wiki/Password_authentication_protocolhttp://en.wikipedia.org/wiki/Password_authentication_protocolhttp://en.wikipedia.org/wiki/Extensible_Authentication_Protocolhttp://en.wikipedia.org/wiki/Point-to-Point_Protocol#cite_note-1http://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Internet_Protocol_Control_Protocolhttp://en.wikipedia.org/wiki/IPX/SPXhttp://en.wikipedia.org/wiki/Appletalkhttp://en.wikipedia.org/wiki/Appletalkhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv4http://en.wikipedia.org/w/index.php?title=%27%27%27Network_Control_Protocol%27%27%27&action=edit&redlink=1http://en.wikipedia.org/wiki/IPCPhttp://en.wikipedia.org/w/index.php?title=%27%27%27IPX/SPX%27%27%27&action=edit&redlink=1http://en.wikipedia.org/wiki/Magic_number_(programming)http://en.wikipedia.org/wiki/Wikipedia:Citation_needed


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Control 1 control byte

Protocol 1 or 2 setting of protocol in information field

Information variable (0 or more) datagram

Padding variable (0 or more) optional padding

FCS 2 (or 4) error check

The Flag field is present when PPP with HDLC-like framing is used.

The Address and Control fields always have the value hex FF (for "all stations") and hex03 (for "unnumbered information"), and can be omitted whenever PPP LCP Address-and-Control-Field-Compression (ACFC) is negotiated.

The Frame Check Sequence (FCS) field is used for determining whether an individualframe has an error. It contains a checksum computed over the frame to provide basic

protection against errors in transmission. This is a CRC code similar to the one used for other layer two protocol error protection schemes such as the one used in Ethernet.According to RFC 1662 , it can be either 16 bits (2 bytes) or 32 bits (4 bytes) in size(default is 16 bits - Polynomial x16 + x12 + x5 + 1).

The FCS is calculated over the Address, Control, Protocol, Information and Paddingfields after the message have been escaped.

PPP line activation and phases

A diagram depicting the phases of PPP according to RFC 1661 .

The phases of the Point to Point Protocol according to RFC 1661 are listed below:

Link Dead . This phase occurs when the link fails, or one side has been told not toconnect (e.g. a user has finished his or her dialup connection.)
http://en.wikipedia.org/wiki/Frame_Check_Sequencehttp://en.wikipedia.org/wiki/Checksumhttp://en.wikipedia.org/wiki/Checksumhttp://en.wikipedia.org/wiki/Cyclic_redundancy_checkhttp://en.wikipedia.org/wiki/Cyclic_redundancy_checkhttp://tools.ietf.org/html/rfc1662http://tools.ietf.org/html/rfc1661http://tools.ietf.org/html/rfc1661http://en.wikipedia.org/wiki/File:PPPPhaseDiagram.svghttp://en.wikipedia.org/wiki/File:PPPPhaseDiagram.svghttp://en.wikipedia.org/wiki/Frame_Check_Sequencehttp://en.wikipedia.org/wiki/Checksumhttp://en.wikipedia.org/wiki/Cyclic_redundancy_checkhttp://tools.ietf.org/html/rfc1662http://tools.ietf.org/html/rfc1661http://tools.ietf.org/html/rfc1661


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Link Establishment Phase . This phase is where Link Control Protocolnegotiation is attempted. If successful, control goes either to the authenticationphase or the Network-Layer Protocol phase, depending on whether authenticationis desired.

Authentication Phase . This phase is optional. It allows the sides to authenticate

each other before a connection is established. If successful, control goes to thenetwork-layer protocol phase. Network-Layer Protocol Phase . This phase is where each desired protocols'

Network Control Protocols are invoked. For example, IPCP is used in establishingIP service over the line. Data transport for all protocols which are successfullystarted with their network control protocols also occurs in this phase. Closingdown of network protocols also occur in this phase.

Link Termination Phase . This phase closes down this connection. This canhappen if there is an authentication failure, if there are so many checksum errorsthat the two parties decide to tear down the link automatically, if the link suddenlyfails, or if the user decides to hang up his connection.

Multiclass PPP

MP's monotonically increasing sequence numbering (contiguous numbers are needed for all fragments of a packet) does not allow suspension of the sending of a sequence of fragments of one packet in order to send another packet. The obvious approach toproviding more than one level of suspension with PPP Multilink is to run Multilink multiple times over one link. Multilink as it is defined provides no way for more than oneinstance to be active. Each class runs a separate copy of the mechanism defined i.e. uses aseparate sequence number space and reassembly buffer. See RFC 2686 .

Other featuresNumerous documents on PPP have been published through the RFC process since July1990, including various authentication, encryption, and compression methods, and theuse of PPP in conjunction with other network protocols.

RFC 2615 is also used in Packet over SONET/SDH (PoS) transmissions.

PPTP is a form of PPP between two hosts via GRE . It is often used to set up a VPN , withoptional encryption ( MPPE ) or compression ( MPPC ). PPP can also be used inconjunction with L2TP which tunnels data over IP network. This technique is used with

IPsec (named L2TP/IPsec) to create VPN . One of the reasons to use PPP over L2TP over IPsec is to have virtual IP addresses for connecting clients. Such a scheme is widelystandardized and supported by the industry.

RFCs

PPP is defined in RFC 1661 (The Point-to-Point Protocol, July 1994). RFC 1547 (Requirements for an Internet Standard Point-to-Point Protocol, December 1993)
http://en.wikipedia.org/wiki/Network_Control_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocol_Control_Protocolhttp://tools.ietf.org/html/rfc2686http://tools.ietf.org/html/rfc2686http://tools.ietf.org/html/rfc2686http://tools.ietf.org/html/rfc2615http://en.wikipedia.org/wiki/Packet_over_SONET/SDHhttp://en.wikipedia.org/wiki/Packet_over_SONET/SDHhttp://en.wikipedia.org/wiki/PPTPhttp://en.wikipedia.org/wiki/Generic_Routing_Encapsulationhttp://en.wikipedia.org/wiki/Generic_Routing_Encapsulationhttp://en.wikipedia.org/wiki/VPNhttp://en.wikipedia.org/wiki/VPNhttp://en.wikipedia.org/wiki/Microsoft_Point-to-Point_Encryptionhttp://en.wikipedia.org/wiki/Microsoft_Point-to-Point_Compressionhttp://en.wikipedia.org/wiki/Layer_2_Tunneling_Protocolhttp://en.wikipedia.org/wiki/IPsechttp://en.wikipedia.org/wiki/VPNhttp://en.wikipedia.org/wiki/VPNhttp://en.wikipedia.org/wiki/Virtual_IP_addresshttp://tools.ietf.org/html/rfc1661http://tools.ietf.org/html/rfc1547http://en.wikipedia.org/wiki/Network_Control_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocol_Control_Protocolhttp://tools.ietf.org/html/rfc2686http://tools.ietf.org/html/rfc2615http://en.wikipedia.org/wiki/Packet_over_SONET/SDHhttp://en.wikipedia.org/wiki/PPTPhttp://en.wikipedia.org/wiki/Generic_Routing_Encapsulationhttp://en.wikipedia.org/wiki/VPNhttp://en.wikipedia.org/wiki/Microsoft_Point-to-Point_Encryptionhttp://en.wikipedia.org/wiki/Microsoft_Point-to-Point_Compressionhttp://en.wikipedia.org/wiki/Layer_2_Tunneling_Protocolhttp://en.wikipedia.org/wiki/IPsechttp://en.wikipedia.org/wiki/VPNhttp://en.wikipedia.org/wiki/Virtual_IP_addresshttp://tools.ietf.org/html/rfc1661http://tools.ietf.org/html/rfc1547


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provides historical information about the need for PPP and its development. A series of related RFCs have been written to define how a variety of network control protocols-including TCP/IP , DECnet , AppleTalk , IPX , and others-work with PPP. [3]
http://en.wikipedia.org/wiki/TCP/IPhttp://en.wikipedia.org/wiki/TCP/IPhttp://en.wikipedia.org/wiki/DECnethttp://en.wikipedia.org/wiki/DECnethttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/IPXhttp://en.wikipedia.org/wiki/Point-to-Point_Protocol#cite_note-2http://en.wikipedia.org/wiki/TCP/IPhttp://en.wikipedia.org/wiki/DECnethttp://en.wikipedia.org/wiki/AppleTalkhttp://en.wikipedia.org/wiki/IPXhttp://en.wikipedia.org/wiki/Point-to-Point_Protocol#cite_note-2

Documents

Point point prortocol