ripv2 overview€¦ · » path selection and loop prevention via bellman-ford algorithm • best...

RIPv2 Overview

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In This Section

» RIPv2 Overview » Basic RIPv2 Configuration » Basic RIPv2 Verification


What is RIP?

» Routing Information Protocol • Distance Vector IGP • Standards Based

» Three versions • RFC 1058 - Routing Information Protocol • RFC 2453 – RIP Version 2 • RFC 2080 – RIPng for IPv6

http://tools.ietf.org/html/rfc1058




Distance Vector vs. Link State Routing

» Distance Vector • RIP & EIGRP • Routers only know what directly connected neighbors tell

them • I.e. “Routing by Rumor”

• Only routes installed in the RIB are advertised » Link State

• OSPF & IS-IS • Routers know all the topology details within the flooding

domain • i.e. the area or level


Example DV vs. LS Advertisements


How RIPv2 Works

» Routes installed in the RIB are periodically advertised • Convergence is controlled by very basic timers • No active adjacencies, hence no fault detection

» Uses UDP port 520 for transport • Unreliable multicast updates to 224.0.0.9 by default • Can use both broadcast and unicast updates


How RIPv2 Works (cont.)

» Path selection and loop prevention via Bellman-Ford algorithm • Best path has the lowest hop count • Loop prevention via split-horizon, poison reverse, and

holddown timers • Slow to converge and suffers from count-to-infinity

problem

http://en.wikipedia.org/wiki/Bellman%E2%80%93Ford_algorithm

http://en.wikipedia.org/wiki/Bellman%E2%80%93Ford_algorithm


Configuring RIPv2

» Enable the global process • router rip

» Enable the interface process • network [address] • Matches major network only

» Verification • show ip protocols • show ip rip database • debug ip rip


RIP Versions

» Default processing • Send version 1 updates • Listen for versions 1 & 2 updates

» Modifying the version • version process level • ip rip receive version interface level • ip rip send version interface level

» Verification • show ip protocols


RIPv2 Summarization

» RIPv2 is classless • Performs automatic classful summarization by default • Disabled with no auto-summary under process

» With auto-summary on… • VLSM is supported within the same major network • Advertisements between major network boundaries are

summarized to classful boundary • Can result in traffic blackholes


RIPv2 Split-Horizon

» Updates received in an interface will not be sent back out the same interface • Undesirable on partial mesh NBMA networks • E.g. DMVPN

» Enabled by default on all interfaces except main interface in Frame Relay • no ip split-horizon to disable

» Verification • show ip interface


RIPv2 Update Types » Broadcast

• RIPv1 default • RIPv2 optional with ip rip v2-broadcast

» Multicast • RIPv2 default to 224.0.0.9

» Unicast • RIPv1 / RIPv2 optional • neighbor [address]

• Enables unicast update • passive-interface [interface]

• Suppress normal broadcast / multicast updates


RIPv2 Metric Calculation

» RIP uses hop-count as metric • 1 hop per interface • 16 is infinite

» offset-list to modify metric • access-list 0 means all routes


RIPv2 Convergence Timers

» Global • timers basic [update] [invalid] [holddown] [flush]

» Interface level • ip rip advertise [interval]

ripv2 overview€¦ · » path selection and loop prevention via bellman-ford algorithm • best...

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