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Lectures notes for 2010 - KTH

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IGMP: Internet Group Management Protocol<br />

IGMP: Internet Group Management Protocol (RFC 1112) [2]:<br />

• Used by hosts and routers to know which hosts currently belong to<br />

which multicast groups.<br />

• multicast routers have to know which interface to <strong>for</strong>ward datagrams to<br />

• IGMP like ICMP is part of the IP layer and is transmitted using IP<br />

datagrams (protocol = 2) l<br />

4 bit<br />

20 bytes 8 bytes<br />

Figure 5: Encapsulation of IGMP message in IP datagram (see Stevens, Vol. 1, figure 13.1, pg. 179)<br />

IGMP<br />

version<br />

(1)<br />

4-bit<br />

IGMP<br />

type<br />

(1-2)<br />

Unused<br />

IP header<br />

IGMP message<br />

32 bit group address (class D IP address)<br />

16 bit checksum<br />

• type =1 ⇒ query sent by a router, type =2 ⇒ response sent by a host<br />

Maguire IGMP: Internet Group Management Protocol 8: 19 of 78<br />

maguire@kth.se <strong>2010</strong>.03.21 Internetworking/Internetteknik

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