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Chapter 14

MulticastingAnd

MulticastRouting Protocols

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CONTENTSCONTENTS

• INTRODUCTION• MULTICAST ROUTING• MULTICAST TREES• MULTICAST ROUTING PROTOCOLS• DVMRP• MOSPF• CBT• PIM• MBONE

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INTRODUCTION

14.114.1

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Figure 14-1

Unicasting

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In unicast routing, the router forwards In unicast routing, the router forwards

the received packet through the received packet through

only one of its interfaces.only one of its interfaces.

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Figure 14-2

Multicasting

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In multicast routing, In multicast routing, the router may forward the the router may forward the

received packet received packet through several of its interfaces.through several of its interfaces.

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Figure 14-3:a

Multicasting versus multiple unicasting

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Figure 14-3:b

Multicasting versus multiple unicasting

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Emulation of multicasting through Emulation of multicasting through multiple unicasting is not multiple unicasting is not

efficient and may efficient and may create long delays, create long delays,

particularly with a large group.particularly with a large group.

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MULTICAST ROUTING

14.214.2

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MULTICASTTREES

14.314.3

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In a source-based tree approach, In a source-based tree approach, the combination of source the combination of source

and group determines the tree. and group determines the tree.

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In the group-shared tree approach, In the group-shared tree approach, the group determines the tree.the group determines the tree.

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MULTICASTROUTING

PROTOCOLS

14.414.4

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Figure 14-4

Multicast routing protocols

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DVMRP

14.514.5

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Figure 14-5

Reverse path forwarding

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In reverse path forwarding (RPF), In reverse path forwarding (RPF), the router forwards only the router forwards only

the packets that have traveled the the packets that have traveled the shortest path from the source shortest path from the source

to the router; all other to the router; all other copies are discarded.copies are discarded.

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RPF prevents RPF prevents the formation of loops.the formation of loops.

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Figure 14-6

Reverse path broadcasting

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Figure 14-7

RPF versus RPB

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RPB creates a shortest path RPB creates a shortest path broadcast tree from the source broadcast tree from the source

to each destination. to each destination. It guarantees that each destination It guarantees that each destination

receives one and only receives one and only one copy of the packet. one copy of the packet.

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Figure 14-8

RPF, RPB, and RPM

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RPM adds pruning and grafting to RPB RPM adds pruning and grafting to RPB to create a multicast shortest to create a multicast shortest

path tree that supports path tree that supports dynamic membership changes.dynamic membership changes.

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MOSPF

14.614.6

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Figure 14-9

Unicast tree and multicast tree

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CBT

14.714.7

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Figure 14-10

Shared-group tree with rendezvous router

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Figure 14-11Sending a multicast packet to

the rendezvous router

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In CBT, the source sends the In CBT, the source sends the multicast packet (encapsulated in a multicast packet (encapsulated in a unicast packet) to the core router. unicast packet) to the core router. The core router decapsulates the The core router decapsulates the

packet and forwards it packet and forwards it to all interested hosts. to all interested hosts.

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PIM

14.814.8

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PIM-DM is used in a PIM-DM is used in a dense multicast environment, dense multicast environment, such as a LAN environment.such as a LAN environment.

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PIM-DM uses RPF and pruning/grafting PIM-DM uses RPF and pruning/grafting

strategies to handle multicasting. strategies to handle multicasting. However, it is independent from However, it is independent from the underlying unicast protocol.the underlying unicast protocol.

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PIM-SM is used in a sparse multicastPIM-SM is used in a sparse multicastenvironment such as a WAN.environment such as a WAN.

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PIM-SM is similar to CBT PIM-SM is similar to CBT but uses a simpler procedure. but uses a simpler procedure.

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MBONE

14.914.9

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Figure 14-12

Logical tunneling

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Figure 14-13

MBONE

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DVMRP supports MBONEDVMRP supports MBONE