MBoneD Working Group                                       Mark Handley
Internet Engineering Task Force                                     ISI
INTERNET-DRAFT                                              Dave Thaler
3 August
7 October 1998                                                Microsoft
Expires February April 1999

           Multicast-Scope Zone Announcement Protocol (MZAP)
                    <draft-ietf-mboned-mzap-01.txt>
                    <draft-ietf-mboned-mzap-02.txt>

                          Status of this Memo

This document is an Internet Draft.  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".

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 two common misconfigurations of administrative scope
zones can be discovered.

Copyright Notice

Copyright (C) The Internet Society (1998).  All Rights Reserved.

Draft                             MZAP                       August                      October 1998

1.  Introduction

IP Multicast groups can be of global scope, or they can be restricted in
scope using a scoping mechanism.  In this document, we only consider
administrative scoping, as defined in RFC 2365 [1].  An administrative
scope zone is defined by a set of routers surrounding a region of the
network.  These "border routers" are configured to not pass multicast
traffic destined for a particular range of multicast addresses to or
from links leaving the scope zone.

Administrative scope zones may be of any size, and a particular host may
be within many administrative scope zones of various sizes. The only
zones a host can assume that it is within are the global zone, and a
"Local Scope".  A Local Scope is defined as being the smallest
administrative scope zone encompassing a host, and the border is
configured for addresses in the range 239.255.0.0 to 239.255.255.255
inclusive.  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."
as well as:
   "administrative scopes that intersect topologically should not
   intersect in address range."

Two problems make administrative scoping difficult to deploy and
difficult to use:

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 border routers were not configured correctly), or
   to intersect in both area and address range.

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

This document defines the Multicast Scope Zone Announcement Protocol

Draft                             MZAP                       August                      October 1998

(MZAP) which will provide applications with information about the scope
zones they are within, and also provide diagnostic information to detect
misconfigured scope zones.

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 5.

2.  Overview

A multicast scope Zone Border Router (ZBR) is a router that is
configured to be a zone border on one or more of its interfaces.  Any
interface that is configured to be a border for any admin scope zone
MUST also be a border for the Local Scope zone, as defined in [1].

Routers SHOULD be configured so that the router itself is within the
scope zone.  This is should in figure 1(a), where router A is inside the
scope zone and has the border configuration.  It is possible for the
first router outside the scope zone to be configured with the border, as
illustrated in figure 1(b) where routers B and C are outside the zone
and have the border configuration, but this is NOT RECOMMENDED.

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

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

  (a) Correct zone border          (b) Incorrect zone border

              Figure 1: Admin scope zone border placement

This rule does not apply for Local Scope borders, but applies for all
other admin scope border routers.

Draft                             MZAP                       August                      October 1998

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.  It can
also send messages into the scope zone, which it SHOULD NOT be able to
do if the router itself is considered outside the scope zone.

Such a ZBR should then send periodic Zone Announcement Messages (ZAMs)
for the zone for which it is configured as a border from one of its
interfaces that go into that scope zone.  These messages are multicast
to the address [MZAP-LOCAL-GROUP] in the Local Scope.

Each ZBR also listens for messages from other ZBRs for the same border.
The ZBR with the lowest interface IP address within the zone from those
ZBRs forming the zone border becomes the zone-id router for the zone.
The combination of this IP address and the first multicast address in
the scoped range serve to uniquely identify the scope zone.

When a ZBR receives a ZAM for some scope zone:

o  If the ZAM was received on an interface with a boundary for the given
   scope, the ZAM is not forwarded.  For example, router D in figure 2
   will not forward the ZAM.

o  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.

o  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 not forwarded.  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.

o  Otherwise, the ZAM is cached for at least [ZAM-DUP-TIME] seconds.

o  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.

Draft                             MZAP                       August                      October 1998

o  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), with 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 added 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.)

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

                     Figure 2: ZAM Flooding Example

The packet also contains a Zones Traveled Limit.  If the number of Local
Zone IDs in the ZAM path becomes equal to the Zones Traveled Limit, the
packet should be dropped. Zones Traveled Limit 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.

Additional messages called Zone Convexity Messages (ZCMs) SHOULD also be
sent to the [ZCM-RELATIVE-GROUP] in the scoped range itself.  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 Local Scope zone ZBRs.  These messages are used to detect
non-convex admin scope zones, as illustrated in figure 3, where the path
between B and D goes outside the scope (through A and E). Here Router B
and Router C originates ZCMs, each reporting each other's presence.
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.

Draft                             MZAP                       August                      October 1998

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

                   Figure 3: Non-convexity detection

3.  Usage

In this section, we summarize how to inform internal entities of scopes
in which they reside, as well as 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.

3.1.  Zone IDs

When a border router first starts up, it uses its lowest IP address
which it considers to be inside a given zone as the Zone ID for that
zone, and schedules the ZCM and ZAM messages to be sent in the future
(it does not send them immedately).  When a ZAM or 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.

3.2.  Informing internal entities of scopes

Any host or application may listen to Zone Announcement Messages to
build up a list of the scope zones that are relevant locally.  However,
listening to Zone Announcement Messages is not the recommended method
for regular applications to discover this information.  These
applications will normally query a local Multicast Address Allocation
Server [3], which in turn listens to Zone Announcement Messages to

Draft                             MZAP                       August                      October 1998

maintain a list of scopes.

3.3.  Detecting non-convex scope zones

Non-convex scope zones can be detected via two 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, or

(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 3.

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.

3.4.  Detecting leaky boundaries for non-local scopes

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 4.

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

                            Figure 4: ZAM Leaking

(2)  If a ZLE message is received.

In either case, the misconfigured router will be either the message
origin, or one of the routers in the path list included in the message received.

Draft                             MZAP                       August                      October 1998

received.

3.5.  Detecting a leaky Local Scope zone

A local scope is leaky if a router has an admin 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 border 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.

3.6.  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 non-empty scope name for a given scope,
   and it receives a ZAM with a non-empty scope name for the same scope,
   and the scope names do not match.

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

Draft                             MZAP                      October 1998

3.7.  Packet Formats

All MZAP messages are sent over UDP, with a destination port of [MZAP-
PORT].  The common MZAP message header (which follows the UDP header),
is show shown below:

Draft                             MZAP                       August                      October 1998

 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 |    NameLen   NameCount   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Message Origin                         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Zone ID Address                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Zone Start Address                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Zone End Address                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoded Zone Name 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)

Address Family:
   This indicates
   The IANA-assigned address family number identifying the format of address
   family for all addresses in the following packet.  The following
   values are families defined by this document:
       0: IPv4 for IP
   are:
       1: IPv4
       2: IPv6

Name Count:

Draft                             MZAP                      October 1998

   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 border.  For example,
   if the zone is a border 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 border.  For
   example, if the zone is a border 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.

Draft                             MZAP                       August 1998

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 NOT the ID of the Local Scope zone in
   which the origin resides.

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

"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): 7 bits
   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].

Draft                             MZAP                      October 1998

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.  All the border routers to the
   same region SHOULD be configured to give the same Zone Name, or a zero
   length string MAY be given.  A zero length string is taken to mean
   that another router is expected to be configured with the zone name.
   Having ALL the ZBRs for a scope zone announce zero length names
   should be considered an error.

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

3.7.1.  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 border, EXCEPT:

o    the Global Scope

o    the Local Scope

o    the Link-local scope

The format of a Zone Announcement Message is shown below:

Draft                             MZAP                       August                      October 1998

 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                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Authentication Block (optional)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 may 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

Draft                             MZAP                       August                      October 1998

   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.

Authentication Block:
   If present, this provides information which can be used to
   authenticate the sender of the ZAM (i.e. Router Address N, if ZT is
   non-zero, or Message Origin, if ZT is zero).  (TBD: any reason not to
   re-use SAP's "Authentication Header" here?)

3.7.2.  Zone Limit Exceeded (ZLE)

This packet is sent by a local-zone border 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 method ensures that close to one ZBR will respond.

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       |              unused           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Local Zone ID Address 0                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Router Address 1                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Local Zone ID Address 1                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                             .....

Draft                             MZAP                       August                      October 1998

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Router Address N                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Local Zone ID Address N                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

A router receiving ZLE messages SHOULD log them and attempt to alert the
network administrator that the scope zone is misconfigured.

3.7.3.  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 border, EXCEPT:

o    the Global Scope

o    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:
 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 may assume the sender

Draft                             MZAP                       August                      October 1998

   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.

4.  Message Timing

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.

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

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

5.  Constants

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

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

[ZCM-RELATIVE-GROUP]:  The relative group in each scope zone, to which
ZCMs are sent.  A Zone Border Router listens to the relative group in
each scope for which it is a border.  Value: TBD by IANA.

[ZAM-INTERVAL]:  The interval at which a Zone Border 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).

Draft                             MZAP                       August                      October 1998

[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 Border 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).

6.  Security Considerations

MZAP does not include authentication in its messages.  Thus it is open
to misbehaving hosts sending spoof ZAMs or ZCMs.

In the case of ZCMs, these spoof messages can cause false logging of
convexity problems.  It is likely that is would be purely an annoyance,
and not cause any significant problem.

In the case of ZAMs, spoof messages can also cause false logging of
configuration problems.  This is also considered to not be a significant
problem.

Spoof zone announcements however might 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 admin scope zone 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, applications 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 of names of scopes, and spoofed ZAMs would result in false names

Draft                             MZAP                       August                      October 1998

being presented to users.  To counter this, ZAMs may be authenticated as
follows:

(1)  A ZBR signs all ZAMs it originates.

(2)  A ZBR signs a ZAM it forwards 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
     autheticated 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.

7.  References

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

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

[3]  Handley, M., Thaler, D., and D. Estrin, "The Internet Multicast
     Address Allocation Architecture", Internet Draft, Dec 1997.

[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", draft-ietf-idmr-traceroute-ipm-02.txt, Internet Draft,
     November 1997.

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

[7]  Handley, M., "Multicast Address Allocation Protocol (AAP)", draft-
     handley-aap-01.txt, Internet Draft, July 1998.

Draft                             MZAP                      October 1998

8.  Full Copyright Statement

Copyright (C) The Internet Society (1998).  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 implmentation 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

Draft                             MZAP                       August 1998
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 Overview ........................................................    3
3 Usage ...........................................................    6
3.1 Zone IDs ......................................................    6
3.2 Informing internal entities of scopes .........................    6
3.3 Detecting non-convex scope zones ..............................    7
3.4 Detecting leaky boundaries for non-local scopes ...............    7
3.5 Detecting a leaky Local Scope zone ............................    8
3.6 Detecting conflicting scope zones .............................    8
3.7 Packet Formats ................................................    8    9
3.7.1 Zone Announcement Message ...................................   10   12
3.7.2 Zone Limit Exceeded (ZLE) ...................................   12   14
3.7.3 Zone Convexity Message ......................................   13   15
4 Message Timing ..................................................   14   16
5 Constants .......................................................   14   16

Draft                             MZAP                      October 1998

6 Security Considerations .........................................   15   17
7 References ......................................................   16   18
8 Full Copyright Statement ........................................   16   19