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MBoneD Working Group                                       Mark Handley
Internet Engineering Task Force                                   ACIRI
INTERNET-DRAFT                                              Dave Thaler
15 December 1999                                              Microsoft
Expires June 2000                                         Roger Kermode
                                                               Motorola



           Multicast-Scope Zone Announcement Protocol (MZAP)
                    <draft-ietf-mboned-mzap-06.txt>





                          Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups.  Note that other groups
may also distribute working documents as Internet-Drafts.

Internet Drafts are valid for a maximum of six months and may be
updated, replaced, or obsoleted by other documents at any time.  It is
inappropriate to use Internet Drafts as reference material or to cite
them other than as a "work in progress".

     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt

     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.
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.

Copyright Notice

Copyright (C) The Internet Society (1999).  All Rights Reserved.













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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 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





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     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.

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.






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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.

      ............                     ................
     .            .   +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





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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-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.

















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    ###########################
    # 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





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   then knows that zone 1 does not nest within zone 2, but it cannot,
   however, determine whether zone 2 nests within zone 1.

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





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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.

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.











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    #####*####========
    #    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

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





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       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


 (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.






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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.

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:












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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    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.

"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





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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.

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.






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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.


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:

















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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      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].

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.





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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:











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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                  Not-Inside Zone Start Address                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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:





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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.


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):







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     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.

(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





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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 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.





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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.


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





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       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.


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.








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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).

[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





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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.

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:







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 (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.


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, October 1999.

[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, November 1997.

[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, October 1999.





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

[9]  Patel, B., Shah, M., and S. Hanna.  "Multicast Address Dynamic
     Client Allocation Protocol (MADCAP)", Work in progress, May 1999.

[10] J. Postel, "Assigned Numbers", RFC 1700, STD 2, 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.


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@email.mot.com


12.  Full Copyright Statement

Copyright (C) The Internet Society (1999).  All Rights Reserved.







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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
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.


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 .............................   11
5 Packet Formats ..................................................   11
5.1 Zone Announcement Message .....................................   14
5.2 Zone Limit Exceeded (ZLE) .....................................   16
5.3 Zone Convexity Message ........................................   16
5.4 Not-Inside Message ............................................   17
6 Message Processing Rules ........................................   18
6.1 Internal entities listening to MZAP messages ..................   18
6.2 Sending ZAMs ..................................................   19





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6.3 Receiving ZAMs ................................................   19
6.4 Sending ZLEs ..................................................   21
6.5 Receiving ZLEs ................................................   22
6.6 Sending ZCMs ..................................................   22
6.7 Receiving ZCMs ................................................   22
6.8 Sending NIMs ..................................................   23
6.9 Receiving NIMs ................................................   23
7 Constants .......................................................   24
8 Security Considerations .........................................   25
9 Acknowledgements ................................................   26
10 References .....................................................   26
11 Authors' Addresses .............................................   27
12 Full Copyright Statement .......................................   27





































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