RFC 2907 (rfc2907) - Page 2 of 13

MADCAP Multicast Scope Nesting State Option

RFC 2907      MADCAP Multicast Scope Nesting State Option September 2000


   10. References. . . . . . . . . . . . . . . . . . . . . .   11
   11. Author's Address. . . . . . . . . . . . . . . . . . .   12
   12. Full Copyright Statement. . . . . . . . . . . . . . .   13

1. Introduction

   The Multicast Address Dynamic Client Allocation Protocol (MADCAP)
   [RFC 2730] affords client applications the ability to request
   multicast address allocation services from multicast address
   allocation servers.  As part of the Multicast Address Allocation
   Architecture [RFC 2908], MADCAP gives clients the ability to reserve,
   request, and extend leases on multicast addresses.

   A new MADCAP option, the "Multicast Scope Nesting State" option is
   proposed to allow clients to learn not only which scopes exist via
   the existing "Multicast Scope List" option, but how these scopes nest
   inside each other. This new option will also afford clients the
   ability to make better scope selections for a given session and also
   to construct hierarchies of administratively scoped zones. These
   hierarchies may then be used to perform expanding scope searches
   instead of the expanding ring or increasing-TTL searches. Expanding
   scope searches do not suffer from the Split-Horizon Effect present in
   expanding ring searches, and therefore both simplify protocol design
   and provide better localization.

1.1 Time-To-Live (TTL) Scoping Split Horizon Effect

   Multicast searching and localized recovery transport techniques that
   rely on TTL scoping are known to suffer when deployed in a wide scale
   manner. The failing lies in the split horizon effect shown below in
   Figure 1. Here a requestor and responder must each use a TTL that is
   sufficiently large that they will reach the other. When they are
   separated by many hops the TTL becomes large and the number of
   receivers within the multicast tree that only receive either the
   request or the response can become very large.
















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