Introduction to IP Multicast Routing

Introduction to IP Multicast Routing

2002.01.31Yun Chan Phill

[email protected]

POSTECHNetworking and Distributed Systems Lab. - 2 -

References

Introduction to IP Multicast Routing-An IP Multicast Initiative White Paper

Stardust Technologies, Inc Multicast Routing Algorithms and Protocols:A Tutorial

Laxman H. Sahasrabuddhe & Biswanath Mukerjee IEEE Network, Jan./Feb. 2000

Intra- And Inter- Domain Multicast Routing Protocols: A Survey And Taxonmy

Maria Ramalho IEEE Communications Surveys & Tutorials, vol.3, no.1, 2000.


Contents

Introduction Multicast Routing Tree Multicast Routing Protocols

Intra-Domain Inter-Domain

Conclusion


What is Multicasting

Ability of Communication Networks Send packets from a source To a group of Receivers at different

locations With shared routes


Multicast

Why Multicasting Better bandwidth Less Host/Router processing

Applications video/audio conferencing for remote meetings News feed/ File distribution Interactive games service advertisement


Compare To Unicast

Unicast

Multicast

Source D

C

B

A

Source D

C

B

A


Multicast Group Address

Multicasting uses group address for Identify

Managed by IGMP protocols Use Class D IP address

224.0.0.2 –239.255.255.255 224.0.0.0 – not assigned to any group 224.0.0.1 – assigned to permanent

group(IGMP query)


Contents-MR Tree

Properties Classification Steiner Tree Problem


Multicast Routing Tree

an acyclic(loopless) spanning tree for support multicasting routing

All Route Multicasting Tree Route


Properties of Good MR Tree

High Priority Low cost Low delay Scalability Support for dynamic multicast groups

Low Priority Survivability Fairness


Classes of MR Trees

Source-based Tree One Source for each MR Tree Dense Mode, Not Scalable App: real time multimedia

Group Shared Tree Multi Source exist for each MR Tree Sparse Mode, Scalable App: software distribution


Source Based Tree

A Tree Required per Source Flood and Prune

Not scalable Heavy control message Hard to manage group

Dense mode DVMRP,MOSPF, PIM-DM


Source Based Tree



Group Shared Tree

A Tree Required per Group Center based Tree Constructing

Scalable Light control message Easy to Manage group Traffic Concentration Steiner Tree Problem occurred

Sparse Mode CBT, PIM-SM


Group Shared Tree



Steiner Tree Problem

The Optimization Problem in MR Group shared multicast tree STP is a NP-complete problem Steiner node

A MR tree nodes which do not belongs to multicast group(e.g.:node D, E in fig)


Two Steiner Trees

All Route 1st Steiner Tree Route2nd Steiner Tree Route


Properties of Good MR Protocols

Efficiency

Scalability

Easy to Implement

Incrementally deployable


Classes of MR Protocols

Host–to–Router IGMP

Intra-Domain DVMRP, MOSPF, PIM-DM/SM, MIP

Inter-Domain YAM, QosMIC, BGMP, PTMR-, EXPRESS


Example of MR protocols


Internet Group Management Protocol

Exist at IP module of host IGMP messages

Enables a MR to keep track of group Host membership query Host membership reply Join-group report Leave-group report


ContentsIntra Domain MR Protocol

RPF DVMRP MOSPF CBT PIM-DB PIM-SM


Reverse Path Forwarding

A method to Find shortest path from one source to many receivers

flood & prune Uses unicast routing table Employed in many MR protocol

DVMRP, MOSPF, PIM-DM, etc.


Steps of RPF

Unicast Route

All Route

F irst F looding

Second F loodiing

Third F loodiing

Fourth F loodiing

MR1

MR2 MR3

MR5

MR6

MR4

MR7 MR8

MR9


Distance-Vector Multicast Routing Protocol

Intra-Domain Protocol of Dense Mode

Construct source-based multicast tree

Depends on RIP, the Unicast protocol

Flood & Prune for construct tree by the first packet


Constructing DVMRP Tree

Unicast Route

All Route

F irst F looding

Second F loodiing

Third F loodiing

Fourth F loodiing

MR1

MR2 MR3

MR5

MR6

MR4

MR7 MR8

MR9


Resulting Spanning Tree

MR1

MR3

MR5MR4

MR7


Merits of DVMRP

Minimize the packet delivery costs No routing loops Support incremental deployment

Use DVMRP Tunnel for inter domain Easy to implement Low computational complexity


Drawbacks of DVMRP

Big memory usage Poor scalability Waste bandwidth Hard to Mange Group(flooding)


Multicast Open Shortest Path First

Intra-Domain Protocol of Dense Mode Depends on OSPF, Unicast Protocol Tree is built on demand by First Packet Every routers knows complete routing top

ology Make Source-based Tree Dijkstra Algorithm for computing Paths


Constructing MOSPF Tree

Unicast Route

All Route

F irst Step

Second Step

Third Step

MR1

MR2 MR3

MR5

MR6

MR4

MR7 MR8

MR9


Resulting Spanning Tree

MR1

MR3

MR5MR4

MR7


Merits of MOSPF

Tree state required only on tree node


Drawbacks of MOSPF

Heavy computation Poor Scalability Not support incremental

deployment No tunnels nor any feature for support

it Hard to Mange Group(flooding)


Core Based Trees

Intra-Domain Protocol of Sparse Mode

Uses only one tree per group To Overcome the scalability Do not use RPF


Joining a CBT Group

existing route

added routesource path

join REQ

join AC K


Merits of CBT

Small Usage of router’s memory space Independent of unicast routing protocol Scalable Easy to manage Multicast Group


Drawbacks of CBT

Concentrates traffic(e.g.: Core Node)

Can occur routing loop Include NP-complete problem

Selecting Core


Protocol Independent Multicast

To overcome the drawbacks of DVMRP, CBT DVMRP: protocol dependant CBT: traffic concentration

Two modes of operations PIM- Dense Mode PIM – Sparse Mode


PIM-DM

Similar to DVMRP RPF checks Construct source-based tree Data driven

Differences from DVMRP Do not save the packet routes Independent of unicast routing protocol


Constructing PIM-DM Tree

Unicast Route

All Route

F irst F looding

Second F loodiing

Third F loodiing

Fourth F loodiing

MR1

MR2 MR3

MR5

MR6

MR4

MR7 MR8

MR9

Differs from DVMRP

P run message


PIM-SM

Similar to CBT Construct group shared tree with core

Differences from CBT PIM-SM can construct source-based

tree Semi-soft state

Wide deployed


Construct PIM-SM SB Tree

existing route

added routesourc e path

join REQ

prune message

deleted route


Result of Tree


Inter-Domain MR Protocols

For Communicate Between different ASes Most Protocols in research only steps Based on Sparse Mode assumption


Border Gateway Multicast Protocol

for inter-operate with any intra-domain MR protocols

Similar to PIM-SM Two Components

MIGP – Intra-Domain MR part BGMP – Join/Prune etc.

Use TCP for Control message


BGMP Simplification


Conclusion

“What is a multicast tree, how does one construct it?”

Design choice Network performance

considerations


IP Address Classes


Tunnel


Terminologies

IGMP: Internet Group Management Protocols

Domain: Routers run the same routing protocols(ex: postech)

Introduction to IP Multicast Routing

Documents

mr tree nodes

mr protocoldvmrp

multicast groupe

group shared treea tree

ip multicast routing2002

group shared treeggggg

mr treesparse mode

mr treedense mode