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Multicast Routing Protocols

NETE0514

Presented byDr.Apichan an!ana"apastit

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Multicast Routing

# $pti%al Routing& 'hortest Path Trees

( The process o) opti%al interdo%ain routing e"entually

results in the )inding o) the shortest path tree

( The root o) the tree is the source and the lea"es arethe potential destinations

( The path )ro% the root to each destination is the

shortest path

( *o+e"er, the nu%ber o) trees and the )or%ation o)the trees in unicasting and %ulticast routing are

di))erent

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-nicast Routing

# n unicast routing, +hen a router recei"es apac/et to )or+ard, it needs to )ind the shortestpath to the destination o) the pac/et

# The nethop entry in the routing tablecorresponding to the destination is the start o)the shortest path tree

# Each line o) the routing table is a shortest path2the +hole routing table is a shortest path

# Each router needs only one shortest path tree to)or+ard a pac/et2 ho+e"er, each router has itso+n shortest path tree

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-nicast Routing 3cont.

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Multicast Routing

# A %ulticast pac/et %ay ha"e destinationsin %ore than one net+or/

# or+arding o) a single pac/et to %e%berso) a group re6uires a shortest path tree

# ) +e ha"e ngroups, +e %ay need nshortest path trees

# T+o approaches ha"e been used to sol"ethe proble%& source based trees andgroupshared trees

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'ource7ased Tree

# n the sourcebased tree approach, each router needs toha"e one shortest path tree )or each group

# The shortest path tree )or a group de)ines the net hop

)or each net+or/ that has loyal %e%ber3s )or that group

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8roup'hared Tree

# n the groupshared tree approach, instead o) eachrouter ha"ing mshortest path trees, only onedesignated router called the center core or rende9"ousrouter ta/es the responsibility o) distributing %ulticast

tra))ic# The core has mshortest path trees in its routing table.

The rest o) the routers in the do%ain ha"e none

# ) a router recei"es a %ulticast pac/et, it encapsulates

the pac/et in a unicast pac/et and sends it to the core# The core router re%o"es the %ulticast pac/et )ro% its

capsule, and consults its routing table to route thepac/et

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8roup'hared Tree

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Multicast Routing Protocols

# During the last )e+ decades, se"eral %ulticast

routing protocols ha"e e%erged

# 'o%e o) these protocols are etensions o)

unicast routing protocols2 so%e are totally ne+

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Multicast :in/ 'tate Routing

# Multicast lin/ state routing is a direct etension o) unicastrouting and uses a sourcebased tree approach

# A node ad"ertises e"ery group +hich has any loyal %e%beron the lin/

# The in)or%ation about the group co%es )ro% 8MP. Eachrouter running 8MP solicits the hosts on the lin/ to )ind outthe %e%bership status

# ;hen a router recei"es all :'Ps, it creates n 3n is the nu%bero) groups topologies, )ro% +hich n shortest path trees are%ade using Di!/stra

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Multicast $pen 'hortest Path irst

3M$'P

# M$'P protocol is an etension o) the $'Pprototol that uses %ulticast lin/ state routing tocreate sourcebased trees

# The protocol re6uires a ne+ lin/ state updatepac/et to associate the unicast address o) a host+ith the group address

# This pac/et is called the group %e%bership :'A# M$'P is a datadri"en protocol2 the )irst ti%e

an M$'P router sees a datagra% +ith a gi"ensource and group address, the router constructsthe Di!/stra shortest path tree

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Multicast Distance =ector Routing

# Multicast distance "ector routing uses sourcebased trees, but the router ne"er actually %a/esa routing table

# ;hen a router recei"es a %ulticast pac/et, it)or+ards the pac/et as though it is consulting arouting table

# ;e can say that the shortest path tree ise"anescent. A)ter its use 3a)ter a pac/et is

)or+arded the table is destroyed# To acco%plish this, the %ulticast distance "ector

algorith% uses a process based on 4 decision%a/ing strategies

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looding

# A router recei"es a pac/et and +ithout e"enloo/ing at the destination group address, sends itout )ro% e"ery inter)ace ecept the one )ro%+hich it +as recei"ed

# *o+e"er, )looding is a broadcast, not a %ulticast# There is another proble%& it create loops. A

pac/et that has le)t the router %ay co%e bac/again )ro% another inter)ace or the sa%e

inter)ace and be )or+arded again# 'o%e )looding protocols /eep a copy o) the

pac/et )or a +hile and discard any duplicates toa"oid loops

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Re"erse Path or+arding 3RP

# RP is a %odi)ied )looding strategy. To pre"ent loops,only one copy is )or+arded2 the other copies are dropped

# n RP, a router )or+ards only the copy that has tra"eledthe shortest path )ro% the source to the router

# To )ind this copy, RP uses the unicast routing table. Therouter recei"es a pac/et and etracts the source address3a unicast address

# t consults its unicast routing table as though it +ants tosend a pac/et to the source address

# The routing table tells the router the net hop. ) the%ulticast pac/et has !ust co%e )ro% the hop de)ined inthe table, the pac/et has tra"eled the shortest path )ro%the source and it )or+ards the pac/et2 it discards itother+ise

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Re"erse Path or+arding 3RP

3cont.

# This strategy pre"ents loops because there is

al+ays one shortest path )ro% the source to the

router

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Re"erse Path 7roadcasting 3RP7

# RP guarantees that each net+or/ recei"es a copy o) the %ulticastpac/et +ithout )or%ation o) loops

# *o+e"er, RP does not guarantee that each net+or/ recei"es onlyone copy2 a net+or/ %ay recei"e > or %ore copies

# The reason is that RP is not based on the destination address 3agroup address2 )or+arding is based on the source address

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Re"erse Path 7roadcasting 3RP7

3cont.

# To eli%inate duplication, +e %ust de)ine onlyone parent router )or each net+or/

# A net+or/ can recei"e a %ulticast pac/et )ro% aparticular source only through a designatedparent router

# This policy is called re"erse path broadcasting3RP7

# The designated parent router can be the router

+ith the shortest path to the source. ) %ore thanone router 6uali)ies, the router +ith the s%allestP address is selected

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RP "s RP7

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Re"erse Path Multicasting 3RPM

# To increase e))iciency, the %ulticast pac/et %ust reach onlythose net+or/s that ha"e acti"e %e%bers )or the particulargroup

# This is called re"erse path %ulticasting 3RPM. The protocoluses > procedures, pruning and gra)ting

# Pruning. The designated parent router o) each net+or/ isresponsible )or holding the %e%bership in)or%ation. Theprocess starts +hen a router connected to a net+or/ )indsthat there is no interest in a %ulticast pac/et. The routersends a prune %essage to the upstrea% router so that it

can prune the corresponding inter)ace. The upstrea% routercan stop sending %ulticast %essages )or this group throughthat inter)ace. ) this router recei"es prune %essages )ro%all do+n strea% routers, it in turn sends a prune %essageto its upstrea% router

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Re"erse Path Multicasting 3RPM

3cont.# Grafting. ;hat i) a lea) router has sent a prune

%essage but suddenly reali9es that one o) its net+or/s isagain interested in recei"ing the %ulticast pac/et

# t can send a gra)t %essage. The gra)t %essage )orces

the upstrea% router to resu%e sending the %ulticast%essage

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?ore7ased Tree 3?7T Protocol

# The ?7T protocol is a groupshared protocol

that uses a core as the root o) the tree

# The autono%ous syste% is di"ided into regions

an a core 3center router or rende9"ous router ischosen )or each region

# There is a procedure in this protocol

( 'electing the Rende9"ous Router

( or%ation o) the Tree

( 'ending Multicast Pac/ets

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or%ation o) the Tree

# A)ter the rende9"ous point is selected, e"ery router isin)or%ed o) the unicast address o) the selected router

# Each router then sends a unicast !oin %essage to sho+that it +ants to !oin the group

# This %essage passes through all routes that are locatedbet+een the sender and the rende9"ous router# Each inter%ediate router etracts the necessary

in)or%ation )ro% the %essage, such as the unicastaddress o) the sender and the inter)ace, and )or+ards

the %essage to the net router in the path# ;hen the rende9"ous router has recei"ed all !oin%essages )ro% e"ery %e%ber o) the group, the tree is)or%ed

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or%ation o) the Tree 3cont.

# No+ e"ery router /no+s its upstrea% router 3the router that leads tothe root and the do+nstrea% router 3the router that leads to thelea)

# ) a router +ants to lea"e the group, it sends a lea"e %essage to itsupstrea% router

# The upstrea% router re%o"es the lin/s to that router )ro% the treeand )or+ards the %essage to its upstrea% router, and so on

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'ending Multicast Pac/ets

# A)ter )or%ation o) the tree, any source can send a%ulticast pac/et to all %e%bers o) the group

# t si%ply sends the pac/et to the rende9"ous router,using the unicast address o) the rende9"ous router2 the

rende9"ous router distributes the pac/et to all %e%berso) the group

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'u%%ary to ?7T

# n ?7T, a pac/et is sent )ro% the source to

%e%bers o) the group )ollo+ing this precedure&

1. The source, +hich %ay or %ay not be part o) the

tree, encapsulates the %ulticast pac/et inside aunicast pac/et +ith the unicast destination address

o) the core and sends it to the core

>. The core decapsulates the unicast pac/et and

)or+ards it to all interested inter)aces

@. Each router that recei"es the %ulticast pac/et, in

turn, )or+ards it to all interested inter)aces

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Protocol ndependent Multicast

3PM

# PM is the na%e gi"en to t+o independent

%ulticast routing protocols& PM, Dense

Mode 3PMDM and PM, 'parse Mode

3PM'M

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PMDM

# PMDM is used +hen there is a possibility thateach router is in"ol"ed in %ulticasting 3dense%ode

# n this en"iron%ent, the use o) a protocol thatbroadcasts the pac/et is !usti)ied becauseal%ost all routers are in"ol"ed in the process

# PMDM is a sourcebased tree routing protocolthat uses RP and pruninggra)ting strategies )or

%ulticasting# ts operation is li/e D=MRP2 ho+e"er, it does not

depend on a speci)ic unicating protocl

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PM'M

# PM'M is used +hen there is a slight possibility thateach router is in"ol"ed in %ulticasting 3spare %ode

# n this en"iron%ent, the use o) a protocol that broadcaststhe pac/et is not !usti)ied2 a protocol such as ?7T that

uses a groupshared tree is %ore appropriate# PM'M is a groupshared tree routing protocol that has

a rende9"ous point 3RP as the source o) the tree

# ts operation is li/e ?7T2 ho+e"er, it is si%pler because it

does not re6uire ac/no+ledge%ent )ro% a !oin %essage# n addition, it creates a bac/up set o) RPs )or eachregion to co"er RP )ailures

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PM'M 3cont.

# $ne o) the characteristics o) PM'M isthat it can s+itch )ro% a groupshared treestrategy to a sourcebased tree strategy

+hen necessary# This can happen i) there is a dense area

o) acti"ity )ar )ro% the RP. That area can

be %ore e))iciently handled +ith a sourcebased tree strategy instead o) a groupshared tree strategy

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M7$NE

# Multi%edia and realti%e co%%unication ha"e

increased the need )or %ulticasting in the

nternet

# *o+e"er, a %ulticast router %ay not )ind another%ulticast router in the neighborhood to )or+ard

the %ulticast pac/et

# The solution is tunneling. To enabling

%ulticasting, +e %a/e a %ulticast bac/bone

3M7$NE using the concept o) tunneling

Fi 12 28 L i l t li

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Figure 12.28 Logical tunneling

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M7$NE 3cont.

# A logical tunnel is established by encapsulating the%ulticast pac/et inside a unicast pac/et

# The non%ulticast routers )or+ard the pac/et as unicastrouters and deli"er the pac/et )ro% one island to another

# 'o )ar the only protocol that supports M7$NE andtunneling is D=MRP