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