network protocols handbook.pdf

97Protocols GuideTCP/IP - Data Link Layer ProtocolsData Link Layer ProtocolsProtocol NameARP and InARP: Address ResolutionProtocol and InverseARPProtocol DescriptionAddress Resolution Protocol (ARP) performs mapping of an IPaddress to a physical machine address (MAC address for Ethernet)that is recognized in the local network. For example, in IPVersion 4, an address is 32 bits long. In an Ethernet local areanetwork, however, addresses for attached devices are 48 bitslong. A table, usually called the ARP cache, is used to maintaina correlation between each MAC address and its correspondingIP address. ARP provides the rules for making this correlationand providing address conversion in both directions.Since protocol details differ for each type of local area network,there are separate ARP specifications for Ethernet, Frame Relay,ATM, Fiber Distributed-Data Interface, HIPPI, and other protocols.InARP is an addition to ARP to address ARP in FrameRelay environment.There is a Reverse ARP (RARP) for host machines that don’tknow their IP address. RARP enables them to request their IPaddress from the gateway’s ARP cache. Details of RARP arepresented in a separate document.Protocol StructureARP and InARP have the same structure:7 Dynamic RARP error.8 InARP request.9 InARP reply.• Sender hardware address -HLen bytes in length.• Sender protocol address - PLen bytes in length.• Target hardware address - HLen bytes in length.• Target protocol address - PLen bytes in length.Related protocolsARP, RARP, InARPSponsor SourceARP/IARP are defined by IETF (http://www.ietf.org) in RFC 826,2390, 2625.Referencehttp://www.javvin.com/protocol/rfc826.pdfAn Ethernet Address Resolution Protocolhttp://www.javvin.com/protocol/rfc2390.pdfInverse Address Resolution Protocol (Frame Relay)http://www.javvin.com/protocol/rfc2625.pdfIP and ARP over Fibre Channel16 32 bitHardware TypeProtocol TypeHLen Plen OperationSender Hardware AddressSender Protocol AddressTarget Hardware AddressTarget Protocol Address• Hardware type - Specifies a hardware interface type forwhich the sender requires a response.• Protocol type - Specifies the type of high-level protocoladdress the sender has supplied.• Hlen - Hardware address length.• Plen - Protocol address length.• Operation - The values are as follows:1 ARP request.2 ARP response.3 RARP request.4 RARP response.5 Dynamic RARP request.6 Dynamic RARP reply.