Multicast Support for Nimrod : Requirements and Solution Approaches
RFC 2102
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RFC - Informational
(February 1997; No errata)
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Author |
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Ram Ramanathan
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2013-03-02
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IETF
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RFC 2102 (Informational)
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Network Working Group R. Ramanathan
Request for Comments: 2102 BBN Systems and Technologies
Category: Informational February 1997
Multicast Support for Nimrod : Requirements and Solution Approaches
Status of this Memo
This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
Abstract
Nimrod does not specify a particular solution for multicasting.
Rather, Nimrod may use any of a number of emerging multicast
techniques. We identify the requirements that Nimrod has of a
solution for multicast support. We compare existing approaches for
multicasting within an internetwork and discuss their advantages and
disadvantages. Finally, as an example, we outline the mechanisms to
support multicast in Nimrod using the scheme currently being
developed within the IETF - namely, the Protocol Indpendent Multicast
(PIM) protocol.
Table of Contents
1 Introduction................................................. 2
2 Multicast vs Unicast......................................... 3
3 Goals and Requirements....................................... 4
4 Approaches................................................... 6
5 A Multicasting Scheme based on PIM........................... 10
5.1 Overview ................................................ 10
5.2 Joining and Leaving a Tree .............................. 12
5.2.1 An Example ........................................ 15
5.3 Establishing a Shared Tree .............................. 16
5.4 Switching to a Source-Rooted Shortest Path Tree.......... 18
5.5 Miscellaneous Issues..................................... 20
6 Security Considerations...................................... 21
7 Summary...................................................... 21
8 References................................................... 22
9 Acknowledgements............................................. 23
10 Author's Address............................................. 23
Ramanathan Informational [Page 1]
RFC 2102 Nimrod Multicast Support February 1997
1 Introduction
The nature of emerging applications such as videoconferencing, remote
classroom, etc. makes the support for multicasting essential for any
future routing architecture. Multicasting is performed by using a
multicast delivery tree whose leaves are the multicast destinations.
Nimrod does not propose a solution for the multicasting problem.
There are two chief reasons for this. First, multicasting is a non-
trivial problem whose requirements are still not well understood.
Second, a number of groups (for instance the IDMR working group of
the IETF) are studying the problem by itself and it is not our
intention to duplicate those efforts.
This attitude towards multicasting is consistent with Nimrod's
general philosophy of flexibility, adaptability and incremental
change.
While a multicasting solution per se is not part of the "core" Nimrod
architecture, Nimrod does require that the solution have certain
characteristics. It is the purpose of this document to discuss some
of these requirements and evaluate approaches towards meeting them.
This document is organized as follows. In section 2 we discuss why
multicasting is treated a little differently than unicast despite the
fact that the former is essentially a generalization of the latter.
Following that, in section 4 we discuss current approaches toward
multicasting . In section 5, we give an example of how Nimrod
multicasting may be done using PIM [DEF+94a]. For readers who do not
have the time to go through the entire document, a summary is given
at the end.
This document uses many terms and concepts from the Nimrod
Architecture document [CCS96] and some terms and concepts (in section
5) from the Nimrod Functionality document [RS96]. Much of the
discussion assumes that you have read at least the Nimrod
Architecture document [CCS96].
Ramanathan Informational [Page 2]
RFC 2102 Nimrod Multicast Support February 1997
2 Multicast vs Unicast
We begin by looking at the similarities and differences between
unicast routing and multicast routing. Both unicast and multicast
routing require two phases - route generation and packet forwarding.
In the case of unicast routing, Nimrod specifies modes of packet
forwarding; route generation itself is not specified but left to the
particular routing agent. For multicasting, Nimrod leaves both route
generation and packet forwarding mechanisms unspecified. To explain
why, we first point out three aspects that make multicasting quite
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