RIP – Routing Information Protocol

Syeda Momina Tabish

MIT - 7

Outline Introduction History Version

RIP v1 RIP v2 RIPng

Functioning

RIP – Introduction

One of Interior gateway protocol (IGP) routing protocols on internal networks.

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.

Its made obsolete by OSPF and IS-IS. Also sometimes called Rest in Pieces.

RIP – Introduction A simple intradomain protocol Straightforward implementation of Distance Vector

Routing Each router advertises its distance vector every 30

seconds (or whenever its routing table changes) to all of its neighbors

RIP always uses 1 as link metric Maximum hop count is 15, with “16” equal to “” Routes are timeout (set to 16) after 3 minutes if they

are not updated

RIP – History

Late 1960s : Distance Vector protocols were used in the ARPANET

Mid-1970s: XNS (Xerox Network system) routing protocol is the precursor of RIP in IP (and Novell’s IPX RIP and Apple’s routing protocol)

1982 Release of routed for BSD Unix 1988 RIPv1 (RFC 1058)

- classful routing 1993 RIPv2 (RFC 1388)

- adds subnet masks with each route entry

- allows classless routing 1998 Current version of RIPv2 (RFC 2453)

RIP – Message Format

Two Message Types Request (sent by devices after initialization to

request a unicast copy of a neighbor’s routing table

Response (sent by RIP speaking devices by broadcasting every 30 seconds to IP 255.255.255.255)

Send via UDP/520 up to 25 routes per packet that include IP network, metric, but no subnet mask

RIP – Normal Operation

For every active RIP interface Announce known RIP routes out RIP enabled interfaces

every 30s Process received RIP annoucements by placing routes in

routing table if better than existing route and add 1 to the hop count

Do not announce things learned on an interface out the same interface (split horizon)

Only announce if reachable with hop count <- 15

RIP Timers

Router rip

timers basic update invalid hold down flush Update 30s (when to broadcast response) Invalid 180s (when haven’t heard annoucements for

180s, do not use) Holddown 180s (when neighbor increases metric for

a network, do not accept immediately Flush 240s (after invalid timer expires, mark as

unreachable metric 16 until time to flush)

RIP v1

RIPv1, defined in RFC 1058 Uses classful routing Routing updates do not carry subnet

information Lacking support for variable length subnet

masks No Support for Router Authentication

RIPv1 Packet FormatIP header UDP header RIP Message

Command Version Set to 00...0

32-bit address

Unused (Set to 00...0)

address family Set to 00.00

Unused (Set to 00...0)

metric (1-16)

one

rout

e en

try(2

0 by

tes)

Up to 24 more routes (each 20 bytes)

32 bits

One RIP message can have up to 25 route entries

1: request2: response

2: for IP0…0: request full rou-ting table

Address of destination

Cost (measured in hops)

1: RIPv1

RIP v2

Developed in 1994 Included the ability to carry subnet information, thus

supporting Classless Inter-Domain Routing (CIDR) 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

RIPv2 Packet Format

IP header UDP header RIP Message

Command Version Set to 00...0

32-bit address

Unused (Set to 00...0)

address family Set to 00.00

Unused (Set to 00...0)

metric (1-16)

one

rout

e en

try(2

0 by

tes)

Up to 24 more routes (each 20 bytes)

32 bits

One RIP message can have up to 25 route entries

1: request2: response

2: for IP0…0: request full rou-ting table

Address of destination

Cost (measured in hops)

2: RIPv2

RIP Security

Issue: Sending bogus routing updates to a router RIPv1: No protection RIPv2: Simple authentication scheme

IP header UDP header RIPv2 Message

Command Version Set to 00.00

Password (Bytes 0 - 3)

Password (Bytes 4 - 7)

0xffff Authentication Type

Password (Bytes 8- 11)

Password (Bytes 12 - 15) Auth

etic

atio

n

Up to 24 more routes (each 20 bytes)

32 bits

2: plaintext password

RIP Problems

RIP takes a long time to stabilize Even for a small network, it takes several minutes

until the routing tables have settled after a change RIP has all the problems of distance vector

algorithms, e.g., count-to-Infinity RIP uses split horizon to avoid count-to-infinity

The maximum path in RIP is 15 hops

Thanks