network protocols handbook.pdf

75Protocols GuideTCP/IP - Network Layer ProtocolsProtocol NameRIP: Routing Information Protocol(RIP2)Protocol DescriptionRouting Information Protocol (RIP) is a standard for exchangeof routing information among gateways and hosts. This protocolis most useful as an “interior gateway protocol”. In a nationwidenetwork such as the current Internet, there are many routingprotocols used for the whole network. The network will be organizedas a collection of “autonomous systems”. Each autonomoussystem will have its own routing technology, which maywell be different for different autonomous systems. The routingprotocol used within an autonomous system is referred to as aninterior gateway protocol, or “IGP”. A separate protocol is usedto interface among the autonomous systems. The earliest suchprotocol, still used in the Internet, is “EGP” (exterior gatewayprotocol). Such protocols are now usually referred to as inter-ASrouting protocols. RIP is designed to work with moderate-sizenetworks using reasonably homogeneous technology. Thus itis suitable as an IGP for many campuses and for regional networksusing serial lines whose speeds do not vary widely. It isnot intended for use in more complex environments.RIP2, derives from RIP, is an extension of the Routing InformationProtocol (RIP) intended to expand the amount of usefulinformation carried in the RIP2 messages and to add a measureof security. RIP2 is a UDP-based protocol. Each host that usesRIP2 has a routing process that sends and receives datagramson UDP port number 520.RIP and RIP2 are for the IPv4 network while the RIPng is designedfor the IPv6 network. In this document, the details of RIPand RIP2 will be described.Protocol Structure8 16 32bitCommand Version UnusedAddress family identifier Route tag (only for RIP2; 0 for RIP)IP addressSubnet mask (only for RIP2; 0 for RIP)Next hop (only for RIP2; 0 for RIP)Metricbecause RIP2 may carry routing information for severaldifferent protocols. The address family identifierfor IP is 2.• Route tag -- Attribute assigned to a route which mustbe preserved and readvertised with a route. Theroute tag provides a method of separating internalRIP routes (routes for networks within the RIP routingdomain) from external RIP routes, which may havebeen imported from an EGP or another IGP.• IP address -- The destination IP address.• Subnet mask -- Value applied to the IP address toyield the non-host portion of the address. If zero, thenno subnet mask has been included for this entry.• Next hop -- Immediate next hop IP address to whichpackets to the destination specified by this route entryshould be forwarded.• Metric -- Represents the total cost of getting a datagramfrom the host to that destination. This metric isthe sum of the costs associated with the networksthat would be traversed in getting to the destination.Related protocolsIP, IPv6, IGP, EGP, RIPng, UDP, TCPSponsor SourceRIP is defined by IETF (http://www.ietf.org) RFC1058,RFC2453.Referencehttp://www.javvin.com/protocol/rfc1058.pdfRouting Information Protocol Specification (Version 1)http://www.javvin.com/protocol/rfc2453.pdfRIP Version 2 Specification.• Command -- The command field is used to specifythe purpose of the datagram. There are five commands:Request, Response, Traceon (obsolete),Traceoff (Obsolete) and Reserved.• Version -- The RIP version number. The current versionis 2.• Address family identifier -- Indicates what type of addressis specified in this particular entry. This is used