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Routing Information Protocol

Background

RIP is the most common protocol used to maintain the routing table used in intranets. The Routing Information Protocol (RIP) is a routing protocol initially designed for Xerox PARC Universal Protocol and used in the Xerox Network Systems (XNS) protocol suite.

RIP became associated with both UNIX and Transmission Control Protocol/Internet Protocol (TCP/IP) when the Berkeley Software Distribution (BSD) version of UNIX began shipping with a RIP implementation referred to as "route dee" in 1982. RIP is formally defined in the XNS Internet Transport Protocols publication (1981) and in Request for Comments (RFC) 1058 (1988).

It has been widely implemented by PC manufacturers for use in their networking products, like in AppleTalk's routing protocol and are also the basis for the routing protocols of Novell, 3Com, Ungermann-Bass, and Banyan. The Novell and 3Com RIPs are mainly standard Xerox RIP while Ungermann-Bass and Banyan made minor alterations to RIP to cater to their own requirements.


Routing Table Format

RIP is a distance vector routing protocol, which means it represents the routing information in terms of the cost of reaching the specific destination. Circuit priorities are represented using numbers between 1 and 15. This scale establishes the order of use of links. The router decides the path to use base on the priority list.

Once the priorities are established, the information is stored in a RIP routing table. Each entry in a RIP routing table provides a variety of information, including the ultimate destination, the next hop on the way to that destination, and a metric. The metric indicates the distance in number of hops to the destination. Other information can also be present in the routing table, including various timers associated with the route.

RIP maintains only the best route to a destination thus whenever new information provides a better route, it would replaces the old route information. Network topology alterations can provoke changes to routes, causing, for example, a new route to become the best route to a particular destination.

When network topology changes occur, they are reflected in routing update messages. For example, when a router detects a link or router failure, it recalculates its routes and sends routing update messages. Each router receiving a routing update message that includes a change updates its tables and propagates the change.


Routing Information Protocol, Routing Table Format
Routing Table Format, Stability Features - Hop-Count Limit
Stability Features - Hop Count Limits, Hold-Downs, Split Horizons
Stability Features - Poison Reverse Updates, RIP Version 2 (RIPv2)