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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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amount of processing involved in receiving these packets presents no significant<br />

cost, the flooding of these packets does have the potential to waste b<strong>and</strong>width.<br />

This problem is documented in RFC 4541, which provides recommendations <strong>and</strong><br />

suggested rules to allow network switches to “snoop” on IGMP traffic. By doing<br />

so, switches can analyze the data contained within the IGMP header <strong>and</strong><br />

determine if the traffic needs to be forwarded to every segment to which the<br />

switch is connected. By doing this, switches can reduce the amount of<br />

unnecessary IGMP traffic flooding uninterested networks, thereby reserving the<br />

segment’s b<strong>and</strong>width for the traffic with which the hosts on those networks are<br />

concerned.<br />

6.3 Multicast delivery tree<br />

IGMP only specifies the communication occurring between receiving hosts <strong>and</strong><br />

their local multicast router. Routing of packets between multicast routers is<br />

managed by a separate routing protocol. We describe these protocols in 6.4,<br />

“Multicast forwarding algorithms” on page 252. Figure 6-6 on page 251 shows<br />

that multicast routing protocols <strong>and</strong> IGMP operate in different sections of the<br />

multicast delivery tree.<br />

250 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong>

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