RFC 2776 (rfc2776) - Page 3 of 27


Multicast-Scope Zone Announcement Protocol (MZAP)



Alternative Format: Original Text Document



RFC 2776                          MZAP                     February 2000


   scope zone may have zero or more textual names (in different
   languages) for the scope, for human convenience.  For example, if the
   range 239.192/14 were assigned to span an entire corporate network,
   it might be given (internally) the name "BigCo Private Scope".

   Administrative scope zones may be of any size, and a particular host
   may be within many administrative scope zones (for different scopes,
   i.e., for non-overlapping ranges of addresses) of various sizes, as
   long as scope zones that intersect topologically do not intersect in
   address range.

   Applications and services are interested in various aspects of the
   scopes within which they reside:

   o  Applications which present users with a choice of which scope in
      which to operate (e.g., when creating a new session, whether it is
      to be confined to a corporate intranet, or whether it should go
      out over the public Internet) are interested in the textual names
      which have significance to users.

   o  Services which use "relative" multicast addresses (as defined in
      [1]) in every scope are interested in the range of addresses used
      by each scope, so that they can apply a constant offset and
      compute which address to use in each scope.

   o  Address allocators are interested in the address range, and
      whether they are allowed to allocate addresses within the entire
      range or not.

   o  Some applications and services may also be interested in the
      nesting relationships among scopes.  For example, knowledge of the
      nesting relationships can be used to perform "expanding-scope"
      searches in a similar, but better behaved, manner to the well-
      known expanding ring search where the TTL of a query is steadily
      increased until a replier can be found.  Studies have also shown
      that nested scopes can be useful in localizing multicast repair
      traffic [8].

   Two barriers currently make administrative scoping difficult to
   deploy and use:

   o  Applications have no way to dynamically discover information on
      scopes that are relevant to them.  This makes it difficult to use
      administrative scope zones, and hence reduces the incentive to
      deploy them.






Handley, et al.             Standards Track