network protocols handbook.pdf

99Protocols GuideTCP/IP - Data Link Layer ProtocolsProtocol NameRARP: Reverse Address ResolutionProtocolProtocol DescriptionReverse Address Resolution Protocol (RARP) allows a physicalmachine in a local area network to request its IP address froma gateway server’s Address Resolution Protocol (ARP) table orcache. A network administrator creates a table in a local areanetwork’s gateway router that maps the physical machines’ (orMedia Access Control - MAC) addresses to corresponding InternetProtocol addresses. When a new machine is set up, itsRARP client program requests its IP address from the RARPserver on the router. Assuming that an entry has been set up inthe router table, the RARP server will return the IP address tothe machine, which can store it for future use.RARP is available for Ethernet, Fiber Distributed-Data Interface,and Token Ring LANs.Protocol StructureThe protocol header for RARP is the same as for ARP:Related protocolsARP, RARP, InARPSponsor SourceRARP is defined by IETF (http://www.ietf.org) in RFC 903.Referencehttp://www.javvin.com/protocol/rfc903.pdfReverse Address Resolution Protocol16 32bitHardware 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.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.