path: root/doc/rfc/rfc2776.txt

Network Working Group                                         M. Handley
Request for Comments: 2776                                         ACIRI
Category: Standards Track                                      D. Thaler
                                                               Microsoft
                                                              R. Kermode
                                                                Motorola
                                                           February 2000


           Multicast-Scope Zone Announcement Protocol (MZAP)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

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

Abstract

   This document defines a protocol, the Multicast-Scope Zone
   Announcement Protocol (MZAP), for discovering the multicast
   administrative scope zones that are relevant at a particular
   location.  MZAP also provides mechanisms whereby common
   misconfigurations of administrative scope zones can be discovered.

Table of Contents

   1 Introduction ................................................  2
   2 Terminology .................................................  4
   3 Overview ....................................................  5
   3.1 Scope Nesting .............................................  6
   3.2 Other Messages ............................................  7
   3.3 Zone IDs ..................................................  7
   4 Detecting Router Misconfigurations ..........................  8
   4.1 Detecting non-convex scope zones ..........................  8
   4.2 Detecting leaky boundaries for non-local scopes ...........  9
   4.3 Detecting a leaky Local Scope zone ........................ 10
   4.4 Detecting conflicting scope zones ......................... 10
   5 Packet Formats .............................................. 11
   5.1 Zone Announcement Message ................................. 14
   5.2 Zone Limit Exceeded (ZLE) ................................. 15
   5.3 Zone Convexity Message .................................... 15



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   5.4 Not-Inside Message ........................................ 16
   6 Message Processing Rules .................................... 17
   6.1 Internal entities listening to MZAP messages .............. 17
   6.2 Sending ZAMs .............................................. 18
   6.3 Receiving ZAMs ............................................ 18
   6.4 Sending ZLEs .............................................. 20
   6.5 Receiving ZLEs ............................................ 20
   6.6 Sending ZCMs .............................................. 21
   6.7 Receiving ZCMs ............................................ 21
   6.8 Sending NIMs .............................................. 21
   6.9 Receiving NIMs ............................................ 22
   7 Constants ................................................... 22
   8 Security Considerations ..................................... 23
   9 Acknowledgements ............................................ 24
   10 References ................................................. 25
   11 Authors' Addresses ......................................... 26
   12 Full Copyright Statement ................................... 27

1.  Introduction

   The use of administratively-scoped IP multicast, as defined in RFC
   2365 [1], allows packets to be addressed to a specific range of
   multicast addresses (e.g., 239.0.0.0 to 239.255.255.255 for IPv4)
   such that the packets will not cross configured administrative
   boundaries, and also allows such addresses to be locally assigned and
   hence are not required to be unique across administrative boundaries.
   This property of logical naming both allows for address reuse, as
   well as provides the capability for infrastructure services such as
   address allocation, session advertisement, and service location to
   use well-known addresses which are guaranteed to have local
   significance within every organization.

   The range of administratively-scoped addresses can be subdivided by
   administrators so that multiple levels of administrative boundaries
   can be simultaneously supported.  As a result, a "multicast scope" is
   defined as a particular range of addresses which has been given some
   topological meaning.

   To support such usage, a router at an administrative boundary is
   configured with one or more per-interface filters, or "multicast
   scope boundaries".  Having such a boundary on an interface means that
   it will not forward packets matching a configured range of multicast
   addresses in either direction on the interface.

   A specific area of the network topology which is within a boundary
   for a given scope is known as a "multicast scope zone".  Since the
   same ranges can be reused within disjoint areas of the network, there
   may be many "multicast scope zones" for any given multicast scope.  A



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   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.






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   o  Misconfiguration is easy.  It is difficult to detect scope zones
      that have been configured so as to not be convex (the shortest
      path between two nodes within the zone passes outside the zone),
      or to leak (one or more boundary routers were not configured
      correctly), or to intersect in both area and address range.

   These two barriers are addressed by this document.  In particular,
   this document defines the Multicast Scope Zone Announcement Protocol
   (MZAP) which allows an entity to learn what scope zones it is within.
   Typically servers will cache the information learned from MZAP and
   can then provide this information to applications in a timely fashion
   upon request using other means, e.g., via MADCAP [9].  MZAP also
   provides diagnostic information to the boundary routers themselves
   that enables misconfigured scope zones to be detected.

2.  Terminology

   The "Local Scope" is defined in RFC 2365 [1] and represents the
   smallest administrative scope larger than link-local, and the
   associated address range is defined as 239.255.0.0 to 239.255.255.255
   inclusive (for IPv4, FF03::/16 for IPv6).  RFC 2365 specifies:

      "239.255.0.0/16 is defined to be the IPv4 Local Scope.  The Local
      Scope is the minimal enclosing scope, and hence is not further
      divisible. Although the exact extent of a Local Scope is site
      dependent, locally scoped regions must obey certain topological
      constraints. In particular, a Local Scope must not span any other
      scope boundary. Further, a Local Scope must be completely
      contained within or equal to any larger scope. In the event that
      scope regions overlap in area, the area of overlap must be in its
      own Local Scope.  This implies that any scope boundary is also a
      boundary for the Local Scope."

   A multicast scope Zone Boundary Router (ZBR) is a router that is
   configured with a boundary for a particular multicast scope on one or
   more of its interfaces.  Any interface that is configured with a
   boundary for any administrative scope zone MUST also have a boundary
   for the Local Scope zone, as described above.

   Such routers SHOULD be configured so that the router itself is within
   the scope zone.  This is shown in Figure 1(a), where router A is
   inside the scope zone and has the boundary configuration.









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          ............                     ................
         .            .   +B+-->          .                *B+-->
        .              . /               .                / .
       .                *               .                +   .
       .          <---+A*---+C+->       .          <---+A+---*C+->
       .              + .               .              +     .
       .             /  .               .             /      .
        . zone X  <--  .                 . zone X  <--      .
         ..............                   ..................

        A,B,C - routers    * - boundary interface    + - interface

       (a) Correct zone boundary         (b) Incorrect zone boundary

          Figure 1: Administrative scope zone boundary placement

   It is possible for the first router outside the scope zone to be
   configured with the boundary, as illustrated in Figure 1(b) where
   routers B and C are outside the zone and have the boundary
   configuration, whereas A does not, but this is NOT RECOMMENDED.  This
   rule does not apply for Local Scope boundaries, but applies for all
   other boundary routers.

   We next define the term "Zone ID" to mean the lowest IP address used
   by any ZBR for a particular zone for sourcing MZAP messages into that
   scope zone.  The combination of this IP address and the first
   multicast address in the scope range serve to uniquely identify the
   scope zone.  Each ZBR listens for messages from other ZBRs for the
   same boundary, and can determine the Zone ID based on the source
   addresses seen.  The Zone ID may change over time as ZBRs come up and
   down.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [2].

   Constants used by this protocol are shown as [NAME-OF-CONSTANT], and
   summarized in section 7.

3.  Overview

   When a ZBR is configured correctly, it can deduce which side of the
   boundary is inside the scope zone and which side is outside it.

   Such a ZBR then sends periodic Zone Announcement Messages (ZAMs) for
   each zone for which it is configured as a boundary into that scope
   zone, containing information on the scope zone's address range, Zone
   ID, and textual names.  These messages are multicast to the well-



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   known address [MZAP-LOCAL-GROUP] in the Local Scope, and are relayed
   across Local Scope boundaries into all Local Scope zones within the
   scope zone referred to by the ZAM message, as shown in Figure 2.

    ###########################
    # Zone1      =      Zone2 #    ##### = large scope zone boundary
    *E-----+--->A*-----+-x    #
    #      |     =     v      #    ===== = Local Scope boundaries
    #      |     ======*===*==#
    #      |     =     B   F  #    ----> = path of ZAM originated by E
   G*<-----+--->C*->   |   ^  #
    #      v     =   <-+---+  #    ABCDE = ZBRs
    #      D     =      Zone3 #
    #######*###################        * = boundary interface

                   Figure 2: ZAM Flooding Example

   Any entity can thus listen on a single well-known group address and
   learn about all scopes in which it resides.

3.1.  Scope Nesting

   MZAP also provides the ability to discover the nesting relationships
   between scope zones.  Two zones are nested if one is comprised of a
   subset of the routers in the other, as shown in Figure 3.

     +-----------+       +-----------+      +-------------+
     | Zone 1    |       | Zone 3    |      | Zone 5      |
     |   +------+|       |    +------+      |    .........|..
     |   |Zone 2||       |    |Zone 4|      |    : Zone 6 | :
     |   +--A---+|       |    C      |      |    D        | :
     +-----------+       +----+--B---+      +--------E----+ :
                                                 :..........:

   (a) "Contained"    (b) "Common Border"  (c) "Overlap"
        Zone 2 nests       Zone 4 nests         Zones 5 and 6
        inside Zone 1      inside Zone 3        do not nest

                   Figure 3: Zone nesting examples

   A ZBR cannot independently determine whether one zone is nested
   inside another.  However, it can determine that one zone does NOT
   nest inside another.  For example, in Figure 3:

   o  ZBR A will pass ZAMs for zone 1 but will prevent ZAMs from zone 2
      from leaving zone 2.  When ZBR A first receives a ZAM for zone 1,
      it then knows that zone 1 does not nest within zone 2, but it
      cannot, however, determine whether zone 2 nests within zone 1.



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   o  ZBR B acts as ZBR for both zones 3 and 4, and hence cannot
      determine if one is nested inside the other.  However, ZBR C can
      determine that zone 3 does not nest inside zone 4 when it receives
      a ZAM for zone 3, since it is a ZBR for zone 4 but not zone 3.

   o  ZBR D only acts as ZBR zone 6 and not 5, hence ZBR D can deduce
      that zone 5 does not nest inside zone 6 upon hearing a ZAM for
      zone 5.  Similarly, ZBR E only acts as ZBR zone 5 and not 6, hence
      ZBR E can deduce that zone 6 does not nest inside zone 5 upon
      hearing a ZAM for zone 6.

   The fact that ZBRs can determine that one zone does not nest inside
   another, but not that a zone does nest inside another, means that
   nesting must be determined in a distributed fashion.  This is done by
   sending Not-Inside Messages (NIMs) which express the fact that a zone
   X is not inside a zone Y.  Such messages are sent to the well-known
   [MZAP-LOCAL-GROUP] and are thus seen by the same entities listening
   to ZAM messages (e.g., MADCAP servers).  Such entities can then
   determine the nesting relationship between two scopes based on a
   sustained absence of any evidence to the contrary.

3.2.  Other Messages

   Two other message types, Zone Convexity Messages (ZCMs) and Zone
   Limit Exceeded (ZLE) messages, are used only by routers, and enable
   them to compare their configurations for consistency and detect
   misconfigurations.  These messages are sent to MZAP's relative
   address within the scope range associated with the scope zone to
   which they refer, and hence are typically not seen by entities other
   than routers.  Their use in detecting specific misconfiguration
   scenarios will be covered in the next section.

   Packet formats for all messages are described in Section 5.

3.3.  Zone IDs

   When a boundary router first starts up, it uses its lowest IP address
   which it considers to be inside a given zone, and which is routable
   everywhere within the zone (for example, not a link-local address),
   as the Zone ID for that zone.  It then schedules ZCM (and ZAM)
   messages to be sent in the future (it does not send them
   immediately).  When a ZCM is received for the given scope, the sender
   is added to the local list of ZBRs (including itself) for that scope,
   and the Zone ID is updated to be the lowest IP address in the list.
   Entries in the list are eventually timed out if no further messages
   are received from that ZBR, such that the Zone ID will converge to
   the lowest address of any active ZBR for the scope.




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   Note that the sender of ZAM messages MUST NOT be used in this way.
   This is because the procedure for detecting a leaky Local scope
   described in Section 4.3 below relies on two disjoint zones for the
   same scope range having different Zone IDs.  If ZAMs are used to
   compute Zone IDs, then ZAMs leaking across a Local Scope boundary
   will cause the two zones to converge to the same Zone ID.

4.  Detecting Router Misconfigurations

   In this section, we cover how to detect various error conditions.  If
   any error is detected, the router should attempt to alert a network
   administrator to the nature of the misconfiguration.  The means to do
   this lies outside the scope of MZAP.

4.1.  Detecting non-convex scope zones

   Zone Convexity Messages (ZCMs) are used by routers to detect non-
   convex administrative scope zones, which are one possible
   misconfiguration.  Non-convex scope zones can cause problems for
   applications since a receiver may never see administratively-scoped
   packets from a sender within the same scope zone, since packets
   travelling between them may be dropped at the boundary.

   In the example illustrated in Figure 4, the path between B and D goes
   outside the scope (through A and E).  Here, Router B and Router C
   send ZCMs within a given scope zone for which they each have a
   boundary, with each reporting the other boundary routers of the zone
   from which they have heard.  In Figure 4, Router D cannot see Router
   B's messages, but can see C's report of B, and so can conclude the
   zone is not convex.

    #####*####========
    #    B   #       =         ##### = non-convex scope boundary
    #    |->A*       =
    #    |   #       =         ===== = other scope boundaries
    #    |   ####*####
    #    |       E   #         ----> = path of B's ZCM
    #    v          D*
    #    C           #             * = boundary interface
    #####*############

                Figure 4: Non-convexity detection









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   Non-convex scope zones can be detected via three methods:

   (1) If a ZBR is listed in ZCMs received, but the next-hop interface
       (according to the multicast RIB) towards that ZBR is outside the
       scope zone,

   (2) If a ZBR is listed in ZCMs received, but no ZCM is received from
       that ZBR for [ZCM-HOLDTIME] seconds, as illustrated in Figure 4,
       or

   (3) ZAM messages can also be used in a manner similar to that for
       ZCMs in (1) above, as follows: if a ZAM is received from a ZBR on
       an interface inside a given scope zone, and the next-hop
       interface (according to the multicast RIB) towards that ZBR is
       outside the scope zone.

   Zone Convexity Messages MAY also be sent and received by correctly
   configured ordinary hosts within a scope region, which may be a
   useful diagnostic facility that does not require privileged access.

4.2.  Detecting leaky boundaries for non-local scopes

   A "leaky" boundary is one which logically has a "hole" due to some
   router not having a boundary applied on an interface where one ought
   to exist.  Hence, the boundary does not completely surround a piece
   of the network, resulting in scoped data leaking outside.

   Leaky scope boundaries can be detected via two methods:

   (1) If it receives ZAMs originating inside the scope boundary on an
       interface that points outside the zone boundary.  Such a ZAM
       message must have escaped the zone through a leak, and flooded
       back around behind the boundary.  This is illustrated in Figure
       5.

        =============#####*########
        = Zone1      #    A Zone2 #       C   = misconfigured router
        =      +---->*E   v       #
        =      |     #    B       #     ##### = leaky scope boundary
        =======*=====#====*=======#
        =      D     #    |       #     ===== = other scope boundaries
        =      ^-----*C<--+       #
        = Zone4      #      Zone3 #     ----> = path of ZAMs
        =============##############

                        Figure 5: ZAM Leaking





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   (2) If a Zone Length Exceeded (ZLE) message is received.  The ZAM
       packet also contains a Zones Traveled Limit.  If the number of
       Local Scope zones traversed becomes equal to the Zones Traveled
       Limit, a ZLE message is generated (the suppression mechanism for
       preventing implosion is described later in the Processing Rules
       section).  ZLEs detect leaks where packets do not return to
       another part of the same scope zone, but instead reach other
       Local Scope zones far away from the ZAM originator.

   In either case, the misconfigured router will be either the message
   origin, or one of the routers in the ZBR path list which is included
   in the message received (or perhaps a router on the path between two
   such ZBRs which ought to have been a ZBR itself).

4.3.  Detecting a leaky Local Scope zone

   A local scope is leaky if a router has an administrative scope
   boundary on some interface, but does not have a Local Scope boundary
   on that interface as specified in RFC 2365.  This can be detected via
   the following method:

   o  If a ZAM for a given scope is received by a ZBR which is a
      boundary for that scope, it compares the Origin's Scope Zone ID in
      the ZAM with its own Zone ID for the given scope.  If the two do
      not match, this is evidence of a misconfiguration.  Since a
      temporary mismatch may result immediately after a recent change in
      the reachability of the lowest-addressed ZBR, misconfiguration
      should be assumed only if the mismatch is persistent.

   The exact location of the problem can be found by doing an mtrace [5]
   from the router detecting the problem, back to the ZAM origin, for
   any group within the address range identified by the ZAM.  The router
   at fault will be the one reporting that a boundary was reached.

4.4.  Detecting conflicting scope zones

   Conflicting address ranges can be detected via the following method:

   o  If a ZBR receives a ZAM for a given scope, and the included start
      and end addresses overlap with, but are not identical to, the
      start and end addresses of a locally-configured scope.

   Conflicting scope names can be detected via the following method:

   o  If a ZBR is configured with a textual name for a given scope and
      language, and it receives a ZAM or ZCM with a name for the same
      scope and language, but the scope names do not match.




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   Detecting either type of conflict above indicates that either the
   local router or the router originating the message is misconfigured.
   Configuration tools SHOULD strip white space from the beginning and
   end of each name to avoid accidental misconfiguration.

5.  Packet Formats

   All MZAP messages are sent over UDP, with a destination port of
   [MZAP-PORT] and an IPv4 TTL or IPv6 Hop Limit of 255.

   When sending an MZAP message referring to a given scope zone, a ZBR
   MUST use a source address which will have significance everywhere
   within the scope zone to which the message refers.  For example,
   link-local addresses MUST NOT be used.

   The common MZAP message header (which follows the UDP header), is
   shown below:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Version    |B|    PTYPE    |Address Family |   NameCount   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Message Origin                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Zone ID Address                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Zone Start Address                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Zone End Address                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Encoded Zone Name-1 (variable length)                         |
   +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |     . . .                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  . . .        | Encoded Zone Name-N (variable length)         |
   +-+-+-+-+-+-+-+-+               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                               |     Padding (if needed)       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Version:
      The version defined in this document is version 0.









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   "Big" scope bit (B):
      If clear, indicates that the addresses in the scoped range are not
      subdividable, and that address allocators may utilize the entire
      range.  If set, address allocators should not use the entire
      range, but should learn an appropriate sub-range via another
      mechanism (e.g., AAP [7]).

   Packet Type (PTYPE):
      The packet types defined in this document are:
         0: Zone Announcement Message (ZAM)
         1: Zone Limit Exceeded (ZLE)
         2: Zone Convexity Message (ZCM)
         3: Not-Inside Message (NIM)

   Address Family:
      The IANA-assigned address family number [10,11] identifying the
      address family for all addresses in the packet.  The families
      defined for IP are:
         1: IPv4
         2: IPv6

   Name Count:
      The number of encoded zone name blocks in this packet.  The count
      may be zero.

   Zone Start Address: 32 bits (IPv4) or 128 bits (IPv6)
      This gives the start address for the scope zone boundary.  For
      example, if the zone is a boundary for 239.1.0.0 to 239.1.0.255,
      then Zone Start Address is 239.1.0.0.

   Zone End Address: 32 bits (IPv4) or 128 bits (IPv6)
      This gives the ending address for the scope zone boundary.  For
      example, if the zone is a boundary for 239.1.0.0 to 239.1.0.255,
      then Zone End Address is 239.1.0.255.

   Message Origin: 32 bits (IPv4) or 128 bits (IPv6)
      This gives the IP address of the interface that originated the
      message.

   Zone ID Address: 32 bits (IPv4) or 128 bits (IPv6)
      This gives the lowest IP address of a boundary router that has
      been observed in the zone originating the message.  Together with
      Zone Start Address and Zone End Address, it forms a unique ID for
      the zone.  Note that this ID is usually different from the ID of
      the Local Scope zone in which the origin resides.






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   Encoded Zone Name:
      +--------------------+
      |D| Reserved (7 bits)|
      +--------------------+
      | LangLen (1 byte)   |
      +--------------------+-----------+
      | Language Tag (variable size)   |
      +--------------------+-----------+
      | NameLen (1 byte)   |
      +--------------------+-----------+
      | Zone Name (variable size)      |
      +--------------------------------+

      The first byte contains flags, of which only the high bit is
      defined.  The other bits are reserved (sent as 0, ignored on
      receipt).

   "Default Language" (D) bit:
      If set, indicates a preference that the name in the following
      language should be used if no name is available in a desired
      language.

   Language tag length (LangLen): 1 byte
      The length, in bytes, of the language tag.

   Language Tag: (variable size)
      The language tag, such as "en-US", indicating the language of the
      zone name.  Language tags are described in [6].

   Name Len:
      The length, in bytes, of the Zone Name field.  The length MUST NOT
      be zero.

   Zone Name: multiple of 8 bits
      The Zone Name is an ISO 10646 character string in UTF-8 encoding
      [4] indicating the name given to the scope zone (eg: "ISI-West
      Site").  It should be relatively short and MUST be less than 256
      bytes in length.  White space SHOULD be stripped from the
      beginning and end of each name before encoding, to avoid
      accidental conflicts.

   Padding (if needed):
      The end of the MZAP header is padded with null bytes until it is
      4-byte aligned.







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5.1.  Zone Announcement Message

   A Zone Announcement Message has PTYPE=0, and is periodically sent by
   a ZBR for each scope for which it is a boundary, EXCEPT:

   o  the Local Scope

   o  the Link-local scope

   The format of a Zone Announcement Message is shown below:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                               MZAP Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ZT       |     ZTL       |           Hold Time           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Local Zone ID Address 0                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Router Address 1                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Local Zone ID Address 1                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                .....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Router Address N                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Local Zone ID Address N                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields are defined as follows:

   Zones Traveled (ZT): 8 bits
      This gives the number of Local Zone IDs contained in this message
      path.

   Zones Traveled Limit (ZTL): 8 bits
      This gives the limit on number of local zones that the packet can
      traverse before it MUST be dropped.  A value of 0 indicates that
      no limit exists.

   Hold Time:
      The time, in seconds, after which the receiver should assume the
      scope no longer exists, if no subsequent ZAM is received.  This
      should be set to [ZAM-HOLDTIME].





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   Zone Path: multiple of 64 bits (IPv4) or 256 bits (IPv6)
      The zone path is a list of Local Zone ID Addresses (the Zone ID
      Address of a local zone) through which the ZAM has passed, and IP
      addresses of the router that forwarded the packet.  The origin
      router fills in the "Local Zone ID Address 0" field when sending
      the ZAM.  Every Local Scope router that forwards the ZAM across a
      Local Scope boundary MUST add the Local Zone ID Address of the
      local zone that the packet of the zone into which the message is
      being forwarded, and its own IP address to the end of this list,
      and increment ZT accordingly.  The zone path is empty which the
      ZAM is first sent.

5.2.  Zone Limit Exceeded (ZLE)

   The format of a ZLE is shown below:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                               MZAP Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      ZT       |     ZTL       |         Hold Time             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Local Zone ID Address 0                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Router Address 1                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Local Zone ID Address 1                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                .....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Router Address N                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Local Zone ID Address N                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All fields are copied from the ZAM, except PTYPE which is set to one.

5.3.  Zone Convexity Message

   A Zone Announcement Message has PTYPE=2, and is periodically sent by
   a ZBR for each scope for which it is a boundary (except the Link-
   local scope).  Note that ZCM's ARE sent in the Local Scope.

   Unlike Zone Announcement Messages which are sent to the [MZAP-LOCAL-
   GROUP], Zone Convexity Messages are sent to the [ZCM-RELATIVE-GROUP]
   in the scope zone itself.  The format of a ZCM is shown below:





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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                               MZAP Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     ZNUM      |  unused       |           Hold Time           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ZBR Address 1                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                .....
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          ZBR Address N                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields are as follows:

   Number of ZBR addresses (ZNUM): 8 bits
      This field gives the number of ZBR Addresses contained in this
      message.

   Hold Time:
      The time, in seconds, after which the receiver should assume the
      sender is no longer reachable, if no subsequent ZCM is received.
      This should be set to [ZCM-HOLDTIME].

   ZBR Address: 32 bits (IPv4) or 128 bits (IPv6)
      These fields give the addresses of the other ZBRs from which the
      Message Origin ZBR has received ZCMs but whose hold time has not
      expired.  The router should include all such addresses which fit
      in the packet, preferring those which it has not included recently
      if all do not fit.

5.4.  Not-Inside Message

   A Not-Inside Message (NIM) has PTYPE=3, and is periodically sent by a
   ZBR which knows that a scope X does not nest within another scope Y
   ("X not inside Y"):

   The format of a Not-Inside Message is shown below:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                               MZAP Header
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Not-Inside Zone Start Address                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   The fields are as follows:

   MZAP Header:  Header fields identifying the scope X.  The Name Count
      may be 0.

   Not-Inside Zone Start Address: 32 bits (IPv4) or 128 bits (IPv6) This
      gives the start address for the scope Y.

6.  Message Processing Rules

6.1.  Internal entities listening to MZAP messages

   Any host or application may join the [MZAP-LOCAL-GROUP] to listen for
   Zone Announcement Messages to build up a list of the scope zones that
   are relevant locally, and for Not-Inside Messages if it wishes to
   learn nesting information.  However, listening to such messages is
   not the recommended method for regular applications to discover this
   information.  These applications will normally query a local
   Multicast Address Allocation Server (MAAS) [3], which in turn listens
   to Zone Announcement Messages and Not-Inside Messages to maintain
   scope information, and can be queried by clients via MADCAP messages.

   An entity (including a MAAS) lacking any such information can only
   assume that it is within the Global Scope, and the Local Scope, both
   of which have well-known address ranges defined in [1].

   An internal entity (e.g., an MAAS) receiving a ZAM will parse the
   information that is relevant to it, such as the address range, and
   the names.  An address allocator receiving such information MUST also
   use the "B" bit to determine whether it can add the address range to
   the set of ranges from which it may allocate addresses (specifically,
   it may add them only if the bit is zero).  Even if the bit is zero,
   an MAAS SHOULD still store the range information so that clients who
   use relative- addresses can still obtain the ranges by requesting
   them from the MAAS.

   An internal entity (e.g., an MAAS) should assume that X nests within
   Y if:

   a) it first heard ZAMs for both X and Y at least [NIM-HOLDTIME]
      seconds ago, AND

   b) it has not heard a NIM indicating that "X not inside Y" for at
      least [NIM-HOLDTIME] seconds.







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6.2.  Sending ZAMs

   Each ZBR should send a Zone Announcement Message for each scope zone
   for which it is a boundary every [ZAM-INTERVAL] seconds, +/- 30% of
   [ZAM-INTERVAL] each time to avoid message synchronisation.

   The ZAM packet also contains a Zones Traveled Limit (ZTL).  If the
   number of Local Zone IDs in the ZAM path becomes equal to the Zones
   Traveled Limit, the packet will be dropped.  The ZTL field is set
   when the packet is first sent, and defaults to 32, but can be set to
   a lower value if a network administrator knows the expected size of
   the zone.

6.3.  Receiving ZAMs

   When a ZBR receives a ZAM for some scope zone X, it uses the
   following rules.

   If the local ZBR does NOT have any configuration for scope X:

   (1) Check to see if the included start and end addresses overlap
       with, but are not identical to, the start and end addresses of
       any locally-configured scope Y, and if so, signal an address
       range conflict to a local administrator.

   (2) Create a local "X not inside" state entry, if such an entry does
       not already exist.  The ZBR then restarts the entry's timer at
       [ZAM-HOLDTIME].  Existence of this state indicates that the ZBR
       knows that X does not nest inside any scope for which it is a
       boundary.  If the entry's timer expires (because no more ZAMs for
       X are heard for [ZAM-HOLDTIME]), the entry is deleted.

   If the local ZBR does have configuration for scope X:

   (1) If the ZAM originated from OUTSIDE the scope (i.e., received over
       a boundary interface for scope X):

      a) If the Scope Zone ID in the ZAM matches the ZBR's own Scope
         Zone ID, then signal a leaky scope misconfiguration.

      b) Drop the ZAM (perform no further processing below).  For
         example, router G in Figure 2 will not forward the ZAM.  This
         rule is primarily a safety measure, since the placement of G in
         Figure 2 is not a recommended configuration, as discussed
         earlier.






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   2) If the ZAM originated from INSIDE the scope:

      a) If the next-hop interface (according to the multicast RIB)
         towards the Origin is outside the scope zone, then signal a
         non- convexity problem.

      b) If the Origin's Scope Zone ID in the ZAM does not match the
         Scope Zone ID kept by the local ZBR, and this mismatch
         continues to occur, then signal a possible leaky scope warning.

      c) For each textual name in the ZAM, see if a name for the same
         scope and language is locally-configured; if so, but the scope
         names do not match, signal a scope name conflict to a local
         administrator.

      d) If the ZAM was received on an interface which is NOT a Local
         Scope boundary, and the last Local Zone ID Address in the path
         list is 0, the ZBR fills in the Local Zone ID Address of the
         local zone from which the ZAM was received.

   If a ZAM for the same scope (as identified by the origin Zone ID and
   first multicast address) was received in the last [ZAM-DUP-TIME]
   seconds, the ZAM is then discarded.  Otherwise, the ZAM is cached for
   at least [ZAM-DUP-TIME] seconds.  For example, when router C in
   Figure 2 receives the ZAM via B, it will not be forwarded, since it
   has just forwarded the ZAM from E.

   The Zones Travelled count in the message is then incremented, and if
   the updated count is equal to or greater than the ZTL field, schedule
   a ZLE to be sent as described in the next subsection and perform no
   further processing below.

   If the Zone ID of the Local Scope zone in which the ZBR resides is
   not already in the ZAM's path list, then the ZAM is immediately re-
   originated within the Local Scope zone.  It adds its own address and
   the Zone ID of the Local Scope zone into which the message is being
   forwarded to the ZAM path list before doing so.  A ZBR receiving a
   ZAM with a non-null path list MUST NOT forward that ZAM back into a
   Local Scope zone that is contained in the path list.  For example, in
   Figure 2, router F, which did not get the ZAM via A due to packet
   loss, will not forward the ZAM from B back into Zone 2 since the path
   list has { (E,1), (A,2), (B,3) } and hence Zone 2 already appears.

   In addition, the ZBR re-originates the ZAM out each interface with a
   Local Scope boundary (except that it is not sent back out the
   interface over which it was received, nor is it sent into any local
   scope zone whose ID is known and appears in the path list).  In each
   such ZAM re-originated, the ZBR adds its own IP address to the path



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   list, as well as the Zone ID Address of the Local Scope Zone into
   which the ZAM is being sent, or 0 if the ID is unknown.  (For
   example, if the other end of a point-to-point link also has a
   boundary on the interface, then the link has no Local Scope Zone ID.)

6.4.  Sending ZLEs

   This packet is sent by a local-zone boundary router that would have
   exceeded the Zone Traveled Limit if it had forwarded a ZAM packet.
   To avoid ZLE implosion, ZLEs are multicast with a random delay and
   suppressed by other ZLEs.  It is only scheduled if at least [ZLE-
   MIN-INTERVAL] seconds have elapsed since it previously sent a ZLE to
   any destination.  To schedule a ZLE, the router sets a random delay
   timer within the interval [ZLE-SUPPRESSION-INTERVAL], and listens to
   the [MZAP-RELATIVE-GROUP] within the included scope for other ZLEs.
   If any are received before the random delay timer expires, the timer
   is cleared and the ZLE is not sent.  If the timer expires, the router
   sends a ZLE to the [MZAP-RELATIVE-GROUP] within the indicated scope.

   The method used to choose a random delay (T) is as follows:

     Choose a random value X from the uniform random interval [0:1]
     Let C = 256
     Set T = [ZLE-SUPPRESSION-INTERVAL] log( C*X + 1) / log(C)

   This equation results in an exponential random distribution which
   ensures that close to one ZBR will respond.  Using a purely uniform
   distribution would begin to exhibit scaling problems as the number of
   ZBRs rose.  Since ZLEs are only suppressed if a duplicate ZLE arrives
   before the time chosen, two routers choosing delays which differ by
   an amount less than the propagation delay between them will both send
   messages, consuming excess bandwidth.  Hence it is desirable to
   minimize the number of routers choosing a delay close to the lowest
   delay chosen, and an exponential distribution is suitable for this
   purpose.

   A router SHOULD NOT send more than one Zone Limit Exceeded message
   every [ZLE-MIN-INTERVAL] regardless of destination.

6.5.  Receiving ZLEs

   When a router receives a ZLE, it performs the following actions:

   (1) If the router has a duplicate ZLE message scheduled to be sent,
       it unschedules its own message so another one will not be sent.

   (2) If the ZLE contains the router's own address in the Origin field,
       it signals a leaky scope misconfiguration.



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6.6.  Sending ZCMs

   Each ZBR should send a Zone Convexity Message (ZCM) for each scope
   zone for which it is a boundary every [ZCM-INTERVAL] seconds, +/- 30%
   of [ZCM-INTERVAL] each time to avoid message synchronisation.

   ZCMs are sent to the [ZCM-RELATIVE-GROUP] in the scoped range itself.
   (For example, if the scope range is 239.1.0.0 to 239.1.0.255, then
   these messages should be sent to 239.1.0.252.)  As these are not
   Locally-Scoped packets, they are simply multicast across the scope
   zone itself, and require no path to be built up, nor any special
   processing by intermediate Local Scope ZBRs.

6.7.  Receiving ZCMs

   When a ZCM is received for a given scope X, on an interface which is
   inside the scope, it follows the rules below:

   (1) The Origin is added to the local list of ZBRs (including itself)
       for that scope, and the Zone ID is updated to be the lowest IP
       address in the list.  The new entry is scheduled to be timed out
       after [ZCM-HOLDTIME] if no further messages are received from
       that ZBR, so that the Zone ID will converge to the lowest address
       of any active ZBR for the scope.

   (2) If a ZBR is listed in ZCMs received, but the next-hop interface
       (according to the multicast RIB) towards that ZBR is outside the
       scope zone, or if no ZCM is received from that ZBR for [ZCM-
       HOLDTIME] seconds, as in the example in Figure 4, then signal a
       non-convexity problem.

   (3) For each textual name in the ZCM, see if a name for the same
       scope and language is locally-configured; if so, but the scope
       names do not match, signal a scope name conflict to a local
       administrator.

6.8.  Sending NIMs

   Periodically, for each scope zone Y for which it is a boundary, a
   router originates a Not-Inside Message (NIM) for each "X not inside"
   entry it has created when receiving ZAMs.  Like a ZAM, this message
   is multicast to the address [MZAP-LOCAL-GROUP] from one of its
   interfaces inside Y.

   Each ZBR should send such a Not-Inside Message every [NIM-INTERVAL]
   seconds, +/- 30% of [NIM-INTERVAL] to avoid message synchronization.





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6.9.  Receiving NIMs

   When a ZBR receives a NIM saying that "X is not inside Y", it is
   forwarded, unmodified, in a manner similar to ZAMs:

   (1) If the NIM was received on an interface with a boundary for
       either X or Y, the NIM is discarded.

   (2) Unlike ZAMs, if the NIM was not received on the interface towards
       the message origin (according to the Multicast RIB), the NIM is
       discarded.

   (3) If a NIM for the same X and Y (where each is identified by its
       first multicast address) was received in the last [ZAM-DUP-TIME]
       seconds, the NIM is not forwarded.

   (4) Otherwise, the NIM is cached for at least [ZAM-DUP-TIME] seconds.

   (5) The ZBR then re-originates the NIM (i.e., with the original UDP
       payload) into each local scope zone in which it has interfaces,
       except that it is not sent back into the local scope zone from
       which the message was received, nor is it sent out any interface
       with a boundary for either X or Y.

7.  Constants

   [MZAP-PORT]:  The well-known UDP port to which all MZAP messages are
   sent.  Value: 2106.

   [MZAP-LOCAL-GROUP]:  The well-known group in the Local Scope to which
   ZAMs are sent.  All Multicast Address Allocation servers and Zone
   Boundary Routers listen to this group.  Value: 239.255.255.252 for
   IPv4.

   [ZCM-RELATIVE-GROUP]:  The relative group in each scope zone, to
   which ZCMs are sent.  A Zone Boundary Router listens to the relative
   group in each scope for which it is a boundary.  Value: (last IP
   address in scope range) - 3.  For example, in the Local Scope, the
   relative group is the same as the [MZAP-LOCAL-GROUP] address.

   [ZAM-INTERVAL]:  The interval at which a Zone Boundary Router
   originates Zone Announcement Messages.  Default value: 600 seconds
   (10 minutes).

   [ZAM-HOLDTIME]:  The holdtime to include in a ZAM.  This SHOULD be
   set to at least 3 * [ZAM-INTERVAL].  Default value: 1860 seconds (31
   minutes).




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   [ZAM-DUP-TIME]:  The time interval after forwarding a ZAM, during
   which ZAMs for the same scope will not be forwarded.  Default value:
   30 seconds.

   [ZCM-INTERVAL]:  The interval at which a Zone Boundary Router
   originates Zone Convexity Messages.  Default value: 600 seconds (10
   minutes).

   [ZCM-HOLDTIME]:  The holdtime to include in a ZCM.  This SHOULD be
   set to at least 3 * [ZCM-INTERVAL].  Default value: 1860 seconds (31
   minutes).

   [ZLE-SUPPRESSION-INTERVAL]:  The interval over which to choose a
   random delay before sending a ZLE message.  Default value: 300
   seconds (5 minutes).

   [ZLE-MIN-INTERVAL]:  The minimum interval between sending ZLE
   messages, regardless of destination.  Default value: 300 seconds (5
   minutes).

   [NIM-INTERVAL]:  The interval at which a Zone Boundary Router
   originates Not-Inside Messages.  Default value: 1800 seconds (30
   minutes).

   [NIM-HOLDTIME]:   The holdtime to include the state within a NIM.
   This SHOULD be set to at least 3 * [NIM-INTERVAL]. Default value:
   5460 (91 minutes)

8.  Security Considerations

   While unauthorized reading of MZAP messages is relatively innocuous
   (so encryption is generally not an issue), accepting unauthenticated
   MZAP messages can be problematic.  Authentication of MZAP messages
   can be provided by using the IPsec Authentication Header (AH) [12].

   In the case of ZCMs and ZLEs, an attacker can cause false logging of
   convexity and leakage problems.  It is likely that is would be purely
   an annoyance, and not cause any significant problem.  (Such messages
   could be authenticated, but since they may be sent within large
   scopes, the receiver may not be able to authenticate a non-malicious
   sender.)

   ZAMs and NIMs, on the other hand, are sent within the Local Scope,
   where assuming a security relationship between senders and receivers
   is more practical.






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   In the case of NIMs, accepting unauthenticated messages can cause the
   false cancellation of nesting relationships.  This would cause a
   section of the hierarchy of zones to flatten.  Such a flattening
   would lessen the efficiency benefits afforded by the hierarchy but
   would not cause it to become unusable.

   Accepting unauthenticated ZAM messages, however, could cause
   applications to believe that a scope zone exists when it does not.
   If these were believed, then applications may choose to use this
   non-existent administrative scope for their uses.  Such applications
   would be able to communicate successfully, but would be unaware that
   their traffic may be traveling further than they expected.  As a
   result, any application accepting unauthenticated ZAMs MUST only take
   scope names as a guideline, and SHOULD assume that their traffic sent
   to non-local scope zones might travel anywhere.  The confidentiality
   of such traffic CANNOT be assumed from the fact that it was sent to a
   scoped address that was discovered using MZAP.

   In addition, ZAMs are used to inform Multicast Address Allocation
   Servers (MAASs) of names and address ranges of scopes, and accepting
   unauthenticated ZAMs could result in false names being presented to
   users, and in wrong addresses being allocated to users.  To counter
   this, MAAS's authenticate ZAMs as follows:

   (1) A ZBR signs all ZAMs it originates (using an AH).

   (2) A ZBR signs a ZAM it relays if and only if it can authenticate
       the previous sender.  A ZBR MUST still forward un-authenticated
       ZAMs (to provide leak detection), but should propagate an
       authenticated ZAM even if an un-authenticated one was received
       with the last [ZAM-DUP-TIME] seconds.

   (3) A MAAS SHOULD be configured with the public key of the local zone
       in which it resides.  A MAAS thus configured SHOULD ignore an
       unauthenticated ZAM if an authenticated one for the same scope
       has been received, and MAY ignore all unauthenticated ZAMs.

9.  Acknowledgements

   This document is a product of the MBone Deployment Working Group,
   whose members provided many helpful comments and suggestions, Van
   Jacobson provided some of the original ideas that led to this
   protocol.  The Multicast Address Allocation Working Group also
   provided useful feedback regarding scope names and interactions with
   applications.






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10.  References

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

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [3]  Thaler, D., Handley, M. and D. Estrin, "The Internet Multicast
        Address Allocation Architecture", Work in Progress.

   [4]  Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
        2279, January 1998.

   [5]  Fenner, W. and S. Casner, "A `traceroute' facility for IP
        Multicast", Work in Progress.

   [6]  Alvestrand, H., "Tags for the Identification of Languages", RFC
        1766, March 1995.

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

   [8]  Kermode, R. "Scoped Hybrid Automatic Repeat reQuest with Forward
        Error Correction (SHARQFEC)", ACM SIGCOMM 98, September 1998,
        Vancouver, Canada.

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

   [10] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700,
        October 1994.

   [11] IANA, "Address Family Numbers", http://www.isi.edu/in-
        notes/iana/assignments/address-family-numbers

   [12] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
        November 1998.













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11.  Authors' Addresses

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

   EMail: mjh@aciri.org


   David Thaler
   Microsoft
   One Microsoft Way
   Redmond, WA 98052
   USA

   EMail: dthaler@microsoft.com


   Roger Kermode
   Motorola Australian Research Centre
   12 Lord St,
   Botany, NSW 2019
   Australia

   EMail: Roger.Kermode@motorola.com
























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12.  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.

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Handley, et al.             Standards Track                    [Page 27]
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