Routing Information Protocol

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This article is chiefly about the Routing Information Protocol (RIP) for the Internet Protocol, but also discusses some other routing information protocols.

The Routing Information Protocol (RIP) is one of the most commonly used interior gateway protocol (IGP) routing protocols on internal networks (and to a lesser extent, networks connected to the Internet), which helps routers dynamically adapt to changes of network connections by communicating information about which networks each router can reach and how far away those networks are.

Although RIP is still actively used, it is generally considered to have been made obsolete by routing protocols such as OSPF and IS-IS. Nonetheless, a somewhat more capable protocol in the same basic family (distance-vector routing protocols), EIGRP, also sees some use.

Contents

1 History

1.1 Technical detail

2 RIP Packet Format
3 Versions
4 Humour
5 See also
6 Further reading

History

The routing algorithm used in RIP, the Bellman-Ford algorithm, was first deployed in a computer network in 1969, as the initial routing algorithm of the ARPANET.

The earliest version of the specific protocol that became RIP was the Gateway Information Protocol, part of Xerox Parc's PARC Universal Packet internetworking protocol suite. A later version, named the Routing Information Protocol, was part of Xerox Network Services.

A version of RIP which supported the Internet Protocol (IP) was later included in the Berkeley Software Distribution (BSD) of the Unix operating system as the routed daemon, and various other vendors would implement their own implementations of the routing protocol. Eventualy RFC 1058 was issued to unify the various implementations under a single standard.

Technical detail

RIP is a distance-vector routing protocol, which employs the hop count as a routing metric. The maximum number of hops allowed with RIP is 15. Each RIP router transmits full updates every 30 seconds by default, generating large amounts of network traffic in lower bandwidth networks. It runs above the network layer of the Internet protocol suite, using UDP port 520 to carry its data. A mechanism called split horizon with limited poison reverse is used to avoid routing loops. Routers of some brands also use a holddown mechanism known as heuristics, whose usefulness is arguable and is not a part of the standard protocol.

In many current networking environments RIP would not be the first choice for routing as its convergence times and scalability are poor compared to EIGRP, OSPF, or IS-IS (the latter two being link-state routing protocols), and the hop limit severely limits the size of network it can be used in. On the other hand, it is easier to configure.

RIP Packet Format

0               1               2               3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| command (1)   | version (1)   |      must be zero (2)         |
+---------------+---------------+-------------------------------+
| address family identifier (2) |      must be zero (2)         |
+-------------------------------+-------------------------------+
|                         IP address (4)                        |
+---------------------------------------------------------------+
|                        must be zero (4)                       |
+---------------------------------------------------------------+
|                        must be zero (4)                       |
+---------------------------------------------------------------+
|                          metric (4)                           |
+---------------------------------------------------------------+

Versions

There are three versions of RIP, RIPv1, RIPv2, and RIPng.

RIPv1, defined in RFC 1058, uses classful routing. The routing updates do not carry subnet information, lacking support for variable length subnet masks. This limitation makes it impossible to have different-sized subnets inside of the same network class. In other words, all subnets in a network class must be the same size. There is also no support for router authentication, making RIPv1 slightly vulnerable to various attacks.

Due to the above deficiencies of RIPv1, RIPv2 was developed in 1994 and included the ability to carry subnet information, thus supporting Classless Inter-Domain Routing. However to maintain backwards compatibility the 15 hop count limit remained. Rudimentary plain text authentication was added to secure routing updates; later, MD5 authentication was defined in RFC 2082.

RIPv2 is specified in RFC 2453 or STD 56.

RIPng, defined in RFC 2080, is an extension of the original protocol to support IPv6.

Humour

Sudden references to the protocol may be found in online discussion groups: typically, the BSD implementation of the protocol is being referenced and only acronyms are being discussed, such as BSD RIP ^{[[Citing sources citation needed]]}. Usually, these messages are posted by anonymous users and consist entirely of the acronym itself, but sometimes even trusted users produce these messages for unknown reasons.