Multicasting and Multicast Routing Protocols

Chapter 12

Unicasting

R2

R1

N1 N2 N3 N4

1

1

2

2

3

3

4

N5 N6

R3 R4

Recipientis here

Source

Ethernet switch

Point-to-point WAN

Unicast router

Legend

2

Multicasting

R1

R2 R3 R4

Nomember

Nomember

Nomember

At leastsone member

At leastsone member

At leastsone member

Source

1

1 1

2

22

3

33

4

Ethernet switch

Point-to-point WAN

Multicast router

Legend

3

Multicasting versus Multiple Unicasting

D4D1 D2 D3

b. Multiple unicasting

S1

DiGi

Multicast router

Unicast destinationGroup member

Unicast router

Legend

S1

G1 G1 G1G1

a. Multicasting

4

Multicast Applications

Information Dissemination

Teleconferencing

Distance Learning

5

Multicast Addresses

6

Multicast Addresses

Multicast addresses for protocol control traffic

7

Delivery of Multicast Packets at Data Link Layer

Ethernet multicast address range:01:00:5E:00:00:00 to 01:00:5E:7F:FF:FF

8

Tunneling

When network does not support multicast, multicast packet encapsulated in unicast packet and sent through the network (tunneling)

9

Internet Group Management Protocol (IGMP)

Multicast routers need to collect information about members and share it with each other

Information collected locally by multicast router connected to network (IGMP protocol)

Collected information globally propagated to other routers (multicast routing protocols)

10

Internet Group Management Protocol (IGMP)

IGMP is group management protocol Helps multicast router create and update list of

members related to each router interface Provides source-specific multicast

Recipient can choose to receive multicast packets coming from list of predefined sources

11

IGMP Messages

12

Membership Query Message

Sent by router to find active group members in network

Max Response Code: defines maximum time before sending report in response to query

13

Three Forms of Query Messages

Router probes each neighbor to report if it is interested in any multicast group

Router probes each neighbor to report if it is still interested in specific multicast group

Router probes each neighbor to report if it is still interested in receiving packets from specific multicast group, coming from any of N sources

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Membership Report Message

15

Record Type

Each host has record for each multicast group Group record has one of two modes:

Include: List source addresses accepts packets from Exclude: List source addresses does not accept from

Report message has six record types

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IGMP at Host - Socket State

Each process (associated with socket) on host has record for each multicast group

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IGMP at Host - Interface State

Interface connecting host to network has record for each multicast group

Combines socket records with same multicast group

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IGMP at Host - Interface State

19

226.14.5.2 :

228.24.21.4 :

IGMP at Router - Router States

Router maintains state information for each multicast group associated with each network interface

Forwarding (or not forwarding) received packet based on router Interface state

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IGMP Message Encapsulation

IGMP messages encapsulated in IP datagrams Destination IP address depends on message

type

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Multicast Routing

Multicast routers need to collect information about members and share it with each other

information collected by IGMP is disseminated to other routers using multicast routing protocols

In multicast routing, each router constructs shortest path tree for each group

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Unicast Routing

23

Each router has table defines shortest path tree to destinations

Multicast Routing using Source-Based Tree

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Each router has one shortest path tree for each group

Multicast Routing using Group-Shared Tree

25

Only core router has shortest path tree for each group

Multicast Routing Protocols

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Multicast Link State Routing

Uses source-based tree approach Extension of unicast link state routing Node advertises group with members on the link Router creates n shortest path trees (for n groups)

using Dijkstra’s algorithm

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Multicast Open Shortest Path First (MOSPF) Protocol

Extension of OSPF Protocol Uses multicast link state routing to create source-

based trees Uses new link state update packet to associate

source with group (group-membership LSA) Router calculates shortest path trees on demand

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Multicast Distance Vector Routing

Uses source-based tree approach Uses four strategies, each built on its predecessor

Flooding Reverse Path Forwarding (RPF) Reverse Path Broadcasting (RPB) Reverse Path Multicasting (RPM)

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RPF

30

Flooding broadcasts packets, but creates loops RPF eliminates loop in flooding

Problem with RPF

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RPF dose not guarantee each network receives only one copy of packet

RPF versus RPB

32

RPB guarantees each destination receives only one copy of packet

RPF, RPB, and RPM

33

RPM adds pruning and grafting to RPB to create multicast shortest path tree supports dynamic membership changes

Distance Vector Multicast Routing Protocol (DVMRP)

Source-based routing protocol Uses multicast distance vector routing Based on RIP

34

Core-Based Tree (CBT) Protocol

35

Group-shared routing protocol

CBT - Sending Multicast Packets

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Protocol Independent Multicast (PIM)

PIM Dense Mode (PIM-DM) Used in dense multicast environment Source-based routing protocol Uses RPF and pruning/grafting Operates like DVMRP

PIM Sparse Mode (PIM-SM) Used in sparse multicast environment Group-shared routing protocol Operates like CBT

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Multicast Backbone (MBONE)

38

Uses logical tunneling for multicasting between noncontiguous multicast routers

MBONE

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