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TCP/IP Tutorial and Technical Overview - IBM Redbooks

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See Figure 6-14 for an overview of MSDP operations.<br />

Figure 6-14 MSDP operations<br />

MSDP limitations<br />

MSDP is currently an experimental RFC, but is deployed in numerous network<br />

environments. Because of the periodic flood <strong>and</strong> prune messages associated<br />

with MSDP, this protocol does not scale to the address the potential needs of the<br />

Internet. It is expected that MSDP will be replaced with the Border Gateway<br />

Multicast Protocol (BGMP). We review this protocol 6.8.2, “Border Gateway<br />

Multicast Protocol” on page 269.<br />

Multiprotocol extensions for BGP-4<br />

When interconnecting multicast domains, it is possible that unicast routing might<br />

select a path containing devices that do not support multicast traffic. This results<br />

in multicast join messages not reaching the intended destination.<br />

To solve this problem, MSDP uses the multiprotocol extensions for BGP-4<br />

(MBGP) defined in RFC 2858. This is a set of extensions allowing BGP to<br />

maintain separate routing tables for different protocols. Therefore, MBGP can<br />

create routes for both unicast <strong>and</strong> multicast traffic. The multicast routes can<br />

traverse around the portions of the environment that do not support multicast. It<br />

permits links to be dedicated to multicast traffic. Alternatively, it can limit the<br />

resources used to support each type of traffic.<br />

The information associated with the multicast routes is used by PIM to build<br />

distribution trees. The st<strong>and</strong>ard services for filtering <strong>and</strong> preference setting are<br />

available with MBGP.<br />

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

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