52 lines
2.4 KiB
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52 lines
2.4 KiB
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<H2><A NAME="sect-routing"></A> <A NAME="s8">8. Routing Policies and Forwarding Techniques.</A></H2>
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<P>One trivial algorithm to make worldwide multicast traffic available
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everywhere could be to send it... everywhere, despite someone wants it
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or not. As this does not seem quite optimized, several routing algorithms
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and forwarding techniques have been implemented.
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<P><B>DVMRP</B> (Distance Vector Multicast Routing Protocol) is, perhaps, the one
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most multicast routers use now. It is a <EM>dense mode</EM> routing protocol,
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that is, it performs well in environments with high bandwidth and densely
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distributed members. However, in <EM>sparse mode</EM> scenarios, it suffers
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from scalability problems.
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<P>Together with DVMRP we can find other dense mode routing protocols, such
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as <B>MOSPF</B> (Multicast Extensions to OSPF -Open Shortest Path First-)
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and PIM-DM (Protocol-Independent Multicast Dense Mode).
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<P>To perform routing in sparse mode environments, we have <B>PIM-SM</B>
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(Protocol Independent Multicast Sparse Mode) and <B>CBT</B> (Core Based
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Trees).
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<P>OSPF version 2 is explained in RFC 1583, and MOSPF in RFC 1584.
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PIM-SM and CBT specifications can be found in RFC 2117 and 2201,
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respectively.
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<P>All this routing protocols use some type of multicast forwarding, such
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as <EM>flooding</EM>, <EM>Reverse Path Broadcasting</EM> (RPB), <EM>Truncated
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Reverse Path Broadcasting</EM> (TRPB), <EM>Reverse Path Multicasting</EM> (RPM)
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or <EM>Shared Trees</EM>.
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<P>It would be too long to explain them here and, as short descriptions
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for them are publicly available, I'll just recommend reading the
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<CODE>draft-ietf-mboned-in.txt</CODE> text. You can find it in the
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same places RFCs are available, and it explains in some detail all
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the above techniques and policies.
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