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DYNAMIC HOST REGISTRATION -- INTERNET GROUP MANAGEMENT PROTOCOL

2008.07.26

Yi-Cheng Lin

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Outline INTRODUCTION IGMP MESSAGES IGMPv3 MESSAGES IGMP OPERATION PROTOCOL DETAILS FOR IGMPv2 IGMP SNOOPING SWITCHES

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INTRODUCTION IGMP is used by host receivers to join or leave a

multicast host group.

IGMP is used by IPv4-based receivers.

The latest version at press time was Version 3. IGMPv3 supports receivers that explicitly signal

sources from which they wish to receive traffic.

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INTRODUCTION Specifically, IGMPv3 is employed by hosts to

signal channel access in SSM (Source Specific Multicast ). Benefits of SSM:

Optimized access bandwidth utilization Risk reduction

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IGMP MESSAGES In Version 1 , there are two types of IGMP messages:

MQ and MR.

IGMPv2 message types are MQ,MR, and Leave Group (LG). MQ: generic (general MQ), specific (group-specific MQ).

receiver routerMR

MQ

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IGMP MESSAGES The IGMP messages for IGMPv2

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IGMPv3 MESSAGES Version 3 allows receivers to subscribe to or exclude

a specific set of sources within a multicast group, rather than just an individual source (this is called, as noted, source specific multicast).

With this feature, IGMPv 3 adds support for “source filtering”.

IGMPv3 is not widely implemented as of press time.

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IGMPv3 MESSAGES Receivers signal membership to a multicast h

ost group in the following two modes INCLUDE mode. EXCLUDE mode.

To support this capability the membership query packet (type of 0x11) has been changed; in addition, a new packet type of 0x22 has been added.

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IGMPv3 MESSAGES In IGMPv3 there are the following three varia

nts of the Query message general query group-specific query group-and-source-specific query

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IGMPv3 MESSAGES The Max Resp Code field specifies the maxim

um time allowed before sending a responding report.

Represented in units of 1/10 s and is derived from the maximum response code. < 128, the value of the maximum response time Max Resp Code >=128, Max Resp Code represen

ts a floating-point

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IGMPv3 MESSAGES If Max Resp Code >= 128

Ex: assume that the value of the maximum response code is decimal 178. 10110010 Byte 0= 1 Exp = 011 Mant = 0010 The subsequent calculations are ( Mant | 0x10) = (0010|10000) = 10010 Expt+11 = 011+ 11= 110 (basically, 3 +3= 6 in base 10, or 110 in base 2)

Therefore, when the maximum response code is decimal 178, the maximum response time is 1152 tenths of a second.

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IGMPv3 MESSAGES The QRV field (Querier’s Robustness Variable) carri

es a parameter that is used in tuning timer values for expected packet loss.

The QQIC field (Querier’s Query Interval Code) carries a value specifying the query interval, in seconds, used by the originator of this query.

Number of Sources field indicates how many source addresses are contained within the Query message.

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IGMPv3 MESSAGES As noted earlier, IGMPv3 adds a new type of 0x22 to support

the IGMPv3 MR. MRs are sent by IP systems to report (to neighboring rout

ers) the current multicast reception state.

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IGMPv3 MESSAGES The Record Type field indicates whether the group record

type is a current-state, filter-mode-change, or source-list-change record.

Version 3 reports are sent with an IP destination address of 224.0.0.22, to which all IGMPv3-capable multicast routers listen.

Because of its higher complexity, IGMPv3 is not universally supported by all the receiver hosts, IGMPv2 is more common, especially in IPTV applications

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IGMP OPERATION IGMP is an asymmetric protocol.

Host Operations To receive multicast datagrams, a host must join a

group. To join a group, the host sends an IGMP membership report packet through an attached interface.

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IGMP OPERATION Multicast Router Operations

Multicast routers listen to all multicast addresses to detect membership reports. 1. receiver (host) signals to join a group, 2. creates an entry in the local group database. 3. To verify group membership, multicast routers

regularly send an IGMP Query message.

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IGMP OPERATION Switches Using IGMP Snooping

IGMP snooping utilizes a router to send out IGMP Query messages to identify potentially interested receivers.

Membership reports are returned to the router, which builds a mapping table of the group and associates forwarding filters for the member port.

If no router is available, some switches can take on the query function. RFC 4541 provides mechanisms to allow switches to “snoop” on IGMP traffic. This reduces the amount of unnecessary multicast traffic floodin

g to locally attached networks that have no active receivers.

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IGMP OPERATION Figure 4.5 illustrates the process at a macrole

vel; here receivers seek to access a video multicast from an IPTV source.

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PROTOCOL DETAILS FOR IGMPv2 Receiver (Host)

State Diagram A host may be in one o

f the following three possible states with respect to any single IP multicast group on any single network interface:

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PROTOCOL DETAILS FOR IGMPv2 Router State

Diagram

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PROTOCOL DETAILS FOR IGMPv2 In addition, to keep track

of which groups have members, a router may be in one of the four possible states with respect to any single IP multicast group on any single attached network.

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PROTOCOL DETAILS FOR IGMPv2

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Thank you