The Routing Information Protocol (RIP) is one of the oldest

distance-vector routing protocol A distance-vector routing protocol in data networks determines the best route for data packets based on distance. Distance-vector routing protocols measure the distance by the number of routers a packet has to pass; one router counts as one hop ...

s which employs the

hop count In wired computer networking, including the Internet, a hop occurs when a packet is passed from one network segment to the next. Data packets pass through Router (computing), routers as they travel between source and destination. The hop count ...

as a routing metric. RIP prevents

routing loops A routing loop is a common problem with various types of networks, particularly computer networks. They are formed when an error occurs in the operation of the routing algorithm, and as a result, in a group of nodes, the path to a particular destin ...

by implementing a limit on the number of

hops Hops are the flowers (also called seed cones or strobiles) of the hop plant ''Humulus lupulus'', a member of the Cannabaceae family of flowering plants. They are used primarily as a bittering, flavouring, and stability agent in beer, to whi ...

allowed in a path from source to destination. The largest number of hops allowed for RIP is 15, which limits the size of networks that RIP can support. RIP implements the

split horizon In computer networking, split-horizon route advertisement is a method of preventing routing loops in distance-vector routing protocols by prohibiting a router from advertising a route back onto the interface from which it was learned. The concep ...

route poisoning Route poisoning is a method to prevent a router from sending packets through a route that has become invalid within computer networks. Distance-vector routing protocols in computer networks use route poisoning to indicate to other routers that a ro ...

, and

holddown Holddown works by having each router start a timer when they first receive information about a network that is unreachable. Until the timer expires, the router will discard any subsequent route messages that indicate the route is in fact reachable ...

mechanisms to prevent incorrect routing information from being propagated. In RIPv1 routers broadcast updates with their routing table every 30 seconds. In the early deployments,

routing table In computer networking, a routing table, or routing information base (RIB), is a data table stored in a router or a network host that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with tho ...

s were small enough that the traffic was not significant. As networks grew in size, however, it became evident there could be a massive traffic burst every 30 seconds, even if the routers had been initialized at random times. In most networking environments, RIP is not the preferred choice of

routing protocol A routing protocol specifies how routers communicate with each other to distribute information that enables them to select routes between nodes on a computer network. Routers perform the traffic directing functions on the Internet; data packets ...

, as its time to converge and

scalability Scalability is the property of a system to handle a growing amount of work by adding resources to the system. In an economic context, a scalable business model implies that a company can increase sales given increased resources. For example, a ...

are poor compared to

EIGRP Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietary ...

OSPF Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks. It uses a link state routing (LSR) algorithm and falls into the group of interior gateway protocols (IGPs), operating within a single autonomous syst ...

, or

IS-IS Intermediate System to Intermediate System (IS-IS, also written ISIS) is a routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes this b ...

. However, it is easy to configure, because RIP does not require any parameters, unlike other protocols. RIP uses the

User Datagram Protocol In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network. ...

(UDP) as its transport protocol, and is assigned the reserved

port number In computer networking, a port is a number assigned to uniquely identify a connection endpoint and to direct data to a specific service. At the software level, within an operating system, a port is a logical construct that identifies a specific ...

520.

Development of distance-vector routing

Based on the

Bellman–Ford algorithm The Bellman–Ford algorithm is an algorithm that computes shortest paths from a single source vertex to all of the other vertices in a weighted digraph. It is slower than Dijkstra's algorithm for the same problem, but more versatile, as it is ...

and the Ford–Fulkerson algorithm,

s started to be implemented from 1969 onwards in

data networks A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...

such as the

ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite. Both technologies became the technical fou ...

and

CYCLADES The Cyclades (; el, Κυκλάδες, ) are an island group in the Aegean Sea, southeast of mainland Greece and a former administrative prefecture of Greece. They are one of the island groups which constitute the Aegean archipelago. The nam ...

. The predecessor of RIP was the Gateway Information Protocol (GWINFO) which was developed by

Xerox Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and electronic document, digital document products and services in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut (ha ...

in the mid-1970s to route its experimental network. As part of the

Xerox Network Systems Xerox Network Systems (XNS) is a computer networking protocol suite developed by Xerox within the Xerox Network Systems Architecture. It provided general purpose network communications, internetwork routing and packet delivery, and higher level f ...

(XNS) protocol suite GWINFO transformed into the XNS Routing Information Protocol. This XNS RIP in turn became the basis for early routing protocols, such as

Novell Novell, Inc. was an American software and services company headquartered in Provo, Utah, that existed from 1980 until 2014. Its most significant product was the multi-platform network operating system known as Novell NetWare. Under the lead ...

's IPX RIP,

AppleTalk AppleTalk is a discontinued proprietary suite of networking protocols developed by Apple Computer for their Macintosh computers. AppleTalk includes a number of features that allow local area networks to be connected with no prior setup or the n ...

's Routing Table Maintenance Protocol (RTMP), and the IP RIP. The 1982

Berkley Software Distribution The Berkeley Software Distribution or Berkeley Standard Distribution (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berke ...

of the

UNIX Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...

operating system implemented RIP in the ''routed''

daemon Daimon or Daemon (Ancient Greek: , "god", "godlike", "power", "fate") originally referred to a lesser deity or guiding spirit such as the daimons of ancient Greek religion and Greek mythology, mythology and of later Hellenistic religion and Hell ...

. The 4.2BSD release proved popular and became the basis for subsequent UNIX versions, which implemented RIP in the ''routed'' or ''gated'' daemon. Ultimately, RIP had been extensively deployed before the standard, written by Charles Hedrick, was passed as RIPv1 in 1988.

The RIP hop count

The routing metric used by RIP counts the number of routers that need to be passed to reach a destination IP network. The hop count 0 denotes a network that is directly connected to the router. 16 hops denote a network that is unreachable, according to the RIP hop limit.

Versions

There are three standardized versions of the Routing Information Protocol: ''RIPv1'' and ''RIPv2'' for

IPv4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version de ...

, and ''RIPng'' for

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...

RIP version 1

The original specification of RIP was published in 1988. When starting up, and every 30 seconds thereafter, a router with RIPv1 implementation

broadcasts Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum (radio waves), in a one-to-many model. Broadcasting began wi ...

to a request message through every RIPv1 enabled interface. Neighbouring routers receiving the request message respond with a RIPv1 segment, containing their

. The requesting router updates its own routing table, with the reachable IP network address, hop count and next hop, that is the router interface IP address from which the RIPv1 response was sent. As the requesting router receives updates from different neighbouring routers it will only update the reachable networks in its routing table, if it receives information about a reachable network it has not yet in its routing table or information that a network it has in its routing table is reachable with a lower hop count. Therefore, a RIPv1 router will in most cases only have one entry for a reachable network, the one with the lowest hop count. If a router receives information from two different neighbouring router that the same network is reachable with the same hop count but via two different routes, the network will be entered into the routing table two times with different next hop routers. The RIPv1 enabled router will then perform what is known as equal-cost load balancing for IP packets. RIPv1 enabled routers not only request the routing tables of other routers every 30 seconds, they also listen to incoming requests from neighbouring routers and send their own routing table in turn. RIPv1 routing tables are therefore updated every 25 to 35 seconds. The RIPv1 protocol adds a small random time variable to the update time, to avoid routing tables synchronizing across a LAN. It was thought, as a result of random initialization, the routing updates would spread out in time, but this was not true in practice. Sally Floyd and Van Jacobson showed in 1994 that, without slight randomization of the update timer, the timers synchronized over time. RIPv1 can be configured into silent mode, so that a router requests and processes neighbouring routing tables, and keeps its routing table and hop count for reachable networks up to date, but does not needlessly send its own routing table into the network. Silent mode is commonly implemented to hosts. RIPv1 uses classful routing. The periodic routing updates do not carry

subnet A subnetwork or subnet is a logical subdivision of an IP network. Updated by RFC 6918. The practice of dividing a network into two or more networks is called subnetting. Computers that belong to the same subnet are addressed with an identical ...

information, lacking support for variable length subnet masks (VLSM). This limitation makes it impossible to have different-sized

s inside of the same network class. In other words, all subnets in a network class must have the same size. There is also no support for router authentication, making RIP vulnerable to various attacks.

RIP version 2

Due to the deficiencies of the original RIP specification, RIP version 2 (RIPv2) was developed in 1993, published in 1994, and declared

Internet Standard In computer network engineering, an Internet Standard is a normative specification of a technology or methodology applicable to the Internet. Internet Standards are created and published by the Internet Engineering Task Force (IETF). They allow ...

56 in 1998. It included the ability to carry subnet information, thus supporting

Classless Inter-Domain Routing Classless Inter-Domain Routing (CIDR ) is a method for allocating IP addresses and for IP routing. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous classful network addressing architecture on the Internet. Its g ...

(CIDR). To maintain backward compatibility, the hop count limit of 15 remained. RIPv2 has facilities to fully interoperate with the earlier specification if all ''Must Be Zero'' protocol fields in the RIPv1 messages are properly specified. In addition, a ''compatibility switch'' feature allows fine-grained interoperability adjustments. In an effort to avoid unnecessary load on hosts that do not participate in routing, RIPv2 ''

multicast In computer networking, multicast is group communication where data transmission is addressed to a group of destination computers simultaneously. Multicast can be one-to-many or many-to-many distribution. Multicast should not be confused with ...

s'' the entire routing table to all adjacent routers at the address , as opposed to RIPv1 which uses

broadcast Broadcasting is the distribution of audio or video content to a dispersed audience via any electronic mass communications medium, but typically one using the electromagnetic spectrum ( radio waves), in a one-to-many model. Broadcasting began ...

Unicast Unicast is data transmission from a single sender (red) to a single receiver (green). Other devices on the network (yellow) do not participate in the communication. In computer networking, unicast is a one-to-one transmission from one point in ...

addressing is still allowed for special applications. ( MD5) authentication for RIP was introduced in 1997. Route tags were also added in RIP version 2. This functionality allows a distinction between routes learned from the RIP protocol and routes learned from other protocols.

RIPng

RIPng (RIP next generation) is an extension of RIPv2 for support of

, the next generation Internet Protocol. The main differences between RIPv2 and RIPng are: * Support of IPv6 networking. * While RIPv2 supports RIPv1 updates authentication, RIPng does not. IPv6 routers were, at the time, supposed to use

IPsec In computing, Internet Protocol Security (IPsec) is a secure network protocol suite that authenticates and encrypts packets of data to provide secure encrypted communication between two computers over an Internet Protocol network. It is used in ...

for authentication. * RIPv2 encodes the next-hop into each route entry, RIPng requires specific encoding of the next hop for a set of route entries. RIPng sends updates on UDP port 521 using the multicast group .

RIP messages between routers

RIP messages use the

on port 520 and all RIP messages exchanged between routers are encapsulated in a UDP segment.

RIPv1 Messages

RIP defined two types of messages: ;Request Message :Asking a neighbouring RIPv1 enabled router to send its routing table. ;Response Message :Carries the routing table of a router.

Timers

The routing information protocol uses the following timers as part of its operation: ;Update Timer :Controls the interval between two gratuitous Response Messages. By default the value is 30 seconds. The response message is broadcast to all its RIP enabled interface. ;Invalid Timer :The invalid timer specifies how long a routing entry can be in the routing table without being updated. This is also called as expiration Timer. By default, the value is 180 seconds. After the timer expires the hop count of the routing entry will be set to 16, marking the destination as unreachable. ;Flush Timer :The flush timer controls the time between the route is invalidated or marked as unreachable and removal of entry from the routing table. By default the value is 240 seconds. This is 60 seconds longer than Invalid timer. So for 60 seconds the router will be advertising about this unreachable route to all its neighbours. This timer must be set to a higher value than the ''invalid timer.'' ;Holddown Timer :The hold-down timer is started per route entry, when the hop count is changing from lower value to higher value. This allows the route to get stabilized. During this time no update can be done to that routing entry. This is not part of the RFC 1058. This is Cisco's implementation. The default value of this timer is 180 seconds.

Limitations

* The hop count cannot exceed 15, or routes will be dropped. * Variable Length Subnet Masks are not supported by RIP version 1 (which is obsolete). * RIP has slow convergence and count to infinity problems.

Implementations

Cisco IOS The Internetworking Operating System (IOS) is a family of proprietary network operating systems used on several router and network switch models manufactured by Cisco Systems. The system is a package of routing, switching, internetworking, and ...

, software used in Cisco routers (supports version 1, version 2 and RIPng) * Cisco NX-OS software used in Cisco Nexus data center switches (supports RIPv2 only) * Junos software used in Juniper routers, switches, and firewalls (supports RIPv1 and RIPv2) * Routing and Remote Access, a

Windows Server Windows Server (formerly Windows NT Server) is a group of operating systems (OS) for servers that Microsoft has been developing since July 27, 1993. The first OS that was released for this platform was Windows NT 3.1 Advanced Server. With the r ...

feature, contains RIP support *

Quagga The quagga ( or ) (''Equus quagga quagga'') is a subspecies of the plains zebra that was endemic to South Africa until it was hunted to extinction in the late 19th century. It was long thought to be a distinct species, but early genetic ...

, a free

open source software Open-source software (OSS) is computer software that is released under a license in which the copyright holder grants users the rights to use, study, change, and distribute the software and its source code to anyone and for any purpose. Open ...

routing suite based on

GNU Zebra Zebra is a routing software package that provides TCP/IP based routing services with routing protocols support such as RIP, OSPF and BGP. Zebra also supports special BGP Route Reflector and Route Server behavior. In addition to traditional IP ...

BIRD Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

, a free

routing suite *

Zeroshell Zeroshell is a small open-source Linux distribution for servers and embedded systems which aims to provide network services. Its administration relies on a web-based graphical interface; no shell is needed to administer and configure it. Zer ...

, a free

routing suite * A RIP implementation first introduced in

4.2BSD The History of the Berkeley Software Distribution begins in the 1970s. 1BSD (PDP-11) The earliest distributions of Unix from Bell Labs in the 1970s included the source code to the operating system, allowing researchers at universities to modify a ...

, routed, survives in several of its descendants, including

FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

and

NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is a ...

. *

OpenBSD OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD 1.0. According to the website, the OpenBSD project em ...

introduced a new implementation, ripd, in version 4.1 and retired routed in version 4.4. * Netgear routers commonly offer a choice of two implementations of RIPv2; these are labelled RIP_2M and RIP_2B. RIP_2M is the standard RIPv2 implementation using multicasting - which requires all routers on the network to support RIPv2 and multicasting, whereas RIP_2B sends RIPv2 packets using subnet broadcasting - making it more compatible with routers that do not support multicasting, including RIPv1 routers. *

Huawei Huawei Technologies Co., Ltd. ( ; ) is a Chinese multinational technology corporation headquartered in Shenzhen, Guangdong, China. It designs, develops, produces and sells telecommunications equipment, consumer electronics and various smar ...

HG633 ADSL/VDSL routers support passive and active routing with RIP v1 & v2 on the LAN and WAN side.

Similar protocols

Cisco Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...

's proprietary

Interior Gateway Routing Protocol Interior Gateway Routing Protocol (IGRP) is a distance vector interior gateway protocol (IGP) developed by Cisco. It is used by routers to exchange routing data within an autonomous system. IGRP is a proprietary protocol. IGRP was created in ...

(IGRP) was a somewhat more capable protocol than RIP. It belongs to the same basic family of

s. Cisco has ceased support and distribution of IGRP in their router software. It was replaced by the

Enhanced Interior Gateway Routing Protocol Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance-vector routing protocol that is used on a computer network for automating routing decisions and configuration. The protocol was designed by Cisco Systems as a proprietar ...

(EIGRP) which is a completely new design. While EIGRP still uses a distance-vector model, it relates to IGRP only in using the same composite routing metric. Both IGRP and EIGRP calculated a single composite metric for each route, from a formula of five variables:

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

delay Delay (from Latin: dilatio) may refer to: Arts, entertainment, and media * ''Delay 1968'', a 1981 album by German experimental rock band Can * ''The Delay'', a 2012 Uruguayan film People * B. H. DeLay (1891–1923), American aviator and acto ...

reliability Reliability, reliable, or unreliable may refer to: Science, technology, and mathematics Computing * Data reliability (disambiguation), a property of some disk arrays in computer storage * High availability * Reliability (computer networking), a ...

, load, and MTU; though on Cisco routers, by default, only bandwidth and delay are used in this calculation.

Development of distance-vector routing

The RIP hop count

Versions

RIP version 1

RIP version 2

RIPng

RIP messages between routers

RIPv1 Messages

Timers

Limitations

Implementations

Similar protocols

See also

References

Further reading