rfc2908.txt

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   exclude any addresses which have been or will be allocated by other
   MAAS's within its domain.

   When a client needs a multicast address, it first needs to decide
   what the scope of the intended session should be, and locate a MAAS
   capable of allocating addresses within that scope.

   To pick a scope, the client will either simply choose a well-known
   scope, such as the global scope, or it will enumerate the available
   scopes (e.g., by sending a MADCAP query, or by listening to MZAP
   messages over time) and allow a user to select one.






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   Locating a MAAS can be done via a variety of methods, including
   manual configuration, using a service location protocol such as SLP
   [12], or via a mechanism provided by a Layer 1 protocol itself.
   MADCAP, for instance, includes such a facility.

   Once the client has chosen a scope and located a MAAS, it then
   requests an address in that scope from the MAAS located.  Along with
   the request it also passes the acceptable range for the lifetimes of
   the allocation it desires.  For example, if the Layer 1 protocol in
   use is MADCAP, the client sends a MADCAP REQUEST message to the MAAS,
   and waits for a NAK message or an ACK message containing the
   allocated information.

   Upon receiving a request from a client, the MAAS then chooses an
   unused address in a range for the specified scope, with a lifetime
   which both satisfies the acceptable range specified by the client,
   and is within the lifetime of the actual range.

   The MAAS uses the Layer 2 mechanism/protocol to ensure that such an
   address does not clash with any addresses allocated by other MAASs.
   For example, if Layer 2 uses manual configuration of non-overlapping
   ranges, then this simply consists of adhering to the range configured
   in the local MAAS.  If, on the other hand, AAP is used at Layer 2 to
   provide less address space fragmentation, the MAAS advertises the
   proposed allocation domain-wide using AAP.  If no clashing AAP claim
   is received within a short time interval, then the address is
   returned to the client via the Layer 1 protocol/mechanism.  If a
   clashing claim is received by the MAAS, then it chooses a different
   address and tries again.  AAP also allows each MAAS to pre-reserve a
   small "pool" of addresses for which it need not wait to detect
   clashes.

   If a domain ever begins to run out of available multicast addresses,
   a Prefix Coordinator in that domain uses the Layer 3
   protocol/mechanism to acquire more space.

6.  Security Considerations

   The architecture described herein does not prevent an application
   from just sending to or joining a multicast address without
   allocating it (just as the same is true for unicast addresses today).
   However, there is no guarantee that data for unallocated addresses
   will be delivered by the network.  That is, routers may drop data for
   unallocated addresses if they have some way of checking whether a
   destination address has been allocated.  For example, if the border
   routers of a domain participate in the Layer 2 protocol/mechanism and
   cache the set of allocated addresses, then data for unallocated




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   addresses in a range allocated by that domain can be dropped by
   creating multicast forwarding state with an empty outgoing interface
   list and/or pruning back the tree branches for those groups.

   A malicious application may attempt a denial-of-service attack by
   attempting to allocate a large number of addresses, thus attempting
   to exhaust the supply of available addresses.  Other attacks include
   releasing or modifying the allocation of another party.  These
   attacks can be combatted through the use of authentication with
   policy restrictions (such as a maximum number of addresses that can
   be allocated by a single party).

   Hence, protocols/mechanisms that implement layers of this
   architecture should be deployable in a secure fashion.  For example,
   one should support authentication with policy restrictions, and
   should not allow someone unauthorized to release or modify the
   allocation of another party.

7.  Acknowledgments

   Steve Hanna provided valuable feedback on this document.  The members
   of the MALLOC WG and the MBone community provided the motivation for
   this work.

8.  References

   [1]  Meyer, D., "Administratively Scoped IP Multicast", BCP 23, RFC
        2365, July 1998.

   [2]  Mark Handley, "Multicast Session Directories and Address
        Allocation", Chapter 6 of PhD Thesis entitled "On Scalable
        Multimedia Conferencing Systems", University of London, 1997.

   [3]  Mark Handley, "An Analysis of Mbone Performance", Chapter 4 of
        PhD Thesis entitled "On Scalable Multimedia Conferencing
        Systems", University of London, 1997.

   [4]  Hanna, S., Patel, B. and M. Shah, "Multicast Address Dynamic
        Client Allocation Protocol (MADCAP)", RFC 2730, December 1999.

   [5]  Handley, M. and S. Hanna, "Multicast Address Allocation Protocol
        (AAP)", Work in Progress.

   [6]  Estrin, D., Govindan, R., Handley, M., Kumar, S., Radoslavov, P.
        and D. Thaler, "The Multicast Address-Set Claim (MASC)
        Protocol", RFC 2909, September 2000.





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   [7]  Deering, S., "Host Extensions for IP Multicasting", STD 5, RFC
        1112, August 1989.

   [8]  Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
        RFC 1771, March 1995.

   [9]  Handley, M., Thaler, D. and R. Kermode, "Multicast-Scope Zone
        Announcement Protocol (MZAP)", RFC 2776, February 2000.

   [10] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", RFC 2770,
        February 2000.

   [11] Finlayson, R., "Abstract API for Multicast Address Allocation",
        RFC 2771, February 2000.

   [12] Guttman, E., Perkins, C., Veizades, J. and M. Day, "Service
        Location Protocol, Version 2", RFC 2608, June 1999.

   [13] Mills, D., "Network Time Protocol (Version 3) Specification,
        Implementation and Analysis", RFC 1305, March 1992.

9.  Authors' Addresses

   Dave Thaler
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052-6399

   EMail: [e-mail]


   Mark Handley
   AT&T Center for Internet Research at ICSI
   1947 Center St, Suite 600
   Berkeley, CA 94704

   EMail: [e-mail]


   Deborah Estrin
   Computer Science Dept/ISI
   University of Southern California
   Los Angeles, CA 90089

   EMail: [e-mail]






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10.  Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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