network protocols handbook.pdf

184Protocols GuideWAN - PPP ProtocolsProtocol NamePPP NCP: Point to Point ProtocolNetwork Control ProtocolsProtocol DescriptionThe Network Control Protocol (NCP) phase in the PPP link connectionprocess is used for establishing and configuring differentnetwork-layer protocols such as IP, IPX or AppleTalk.After a NCP has reached the Opened state, PPP will carry thecorresponding network-layer protocol packets. Any supportednetwork-layer protocol packets received when the correspondingNCP is not in the Opened state MUST be silently discarded.During this phase, link traffic consists of any possible combinationof LCP, NCP, and network-layer protocol packets.The most common layer 3 protocol negotiated is IP. The routersexchange IP Control Protocol (IPCP) messages negotiating optionsspecific to the protocol. The corresponding network controlprotocol for IPv6 is IPv6CP.IPCP negotiates two options: compression and IP address assignments.However, IPCP is also used to pass network relatedinformation such as primary and backup Windows Name Service(WINS) and Domain Name System (DNS) servers.Protocol StructureNetwork Control Protocols such as IPCP and IPv6CP use thesame packet format as the Link Control Protocols.Configuration Option format:Packet format:8 16 32bitType Length Configuration Option8 16 32bit VariableCode Identifier Length Data• Code - The Code field is one octet and identifies thetype of the packet.• Identifier - The Identifier field is one octet and aids inmatching requests and replies.• Length - The Length field is two octets and indicatesthe length of the packet.• Data - The Data field is zero or more octets. Theformat of the Data field is determined by the Codefield.Related protocolsPPP, NCP, IPCP, IPv6CP, LCP, IP, IPX, DECnet, AppleTalkSponsor SourcePPP Network Control Protocols are defined by IETF (http://www.ietf.org) .Referencehttp://www.javvin.com/protocol/rfc1661.pdfThe Point-to-Point Protocol (PPP)http://www.javvin.com/protocol/rfc1332.pdfThe PPP Internet Protocol Control Protocol (IPCP).http://www.javvin.com/protocol/rfc2472.pdfIP Version 6 over PPPhttp://www.javvin.com/protocol/rfc3241.pdfRobust Header Compression (ROHC) over PPP.http://www.javvin.com/protocol/rfc3544.pdfIP Header Compression over PPP.