RIP – Routing Information Protocol

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 Format 1: RIPv1 1: request2: response 2: for IP 0…0: request full rou-ting table Address of destination Cost (measured in hops) One RIP message can have up to 25 route entries

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 2: RIPv2 1: request2: response 2: for IP 0…0: request full rou-ting table Address of destination Cost (measured in hops) One RIP message can have up to 25 route entries

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

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RIP – Routing Information Protocol