[Docs] [txt|pdf] [Tracker] [WG] [Email] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 5059

Internet Engineering Task Force                                   PIM WG
INTERNET-DRAFT                                          Bill Fenner/AT&T
draft-ietf-pim-sm-bsr-00.txt                          Mark Handley/ACIRI
                                                  David Thaler/Microsoft
                                                        23 February 2001
                                                    Expires: August 2001


          Bootstrap Router (BSR) Mechanism for PIM Sparse Mode



Status of this Document

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 draft documents 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 "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.

This document is a product of the IETF PIM WG.  Comments should be
addressed to the authors, or the WG's mailing list at
pim@catarina.usc.edu.

                                Abstract


     This document specifies the Bootstrap Router (BSR) mechanism
     for PIM Sparse Mode.  BSR is one way that a PIM-SM router can
     learn the set of group-to-RP mappings required in order to
     function.  The mechanism is dynamic, largely self-configuring,
     and robust to router failure.




Fenner/Handley/Thaler                                           [Page 1]

INTERNET-DRAFT            Expires: August 2001             February 2001


                           Table of Contents


     1. Introduction. . . . . . . . . . . . . . . . . . . . . .   3
      1.1. Overview of Bootstrap and RP Discovery . . . . . . .   3
      1.2. Administratively Scoped Multicast. . . . . . . . . .   4
     2. BSR State and Timers. . . . . . . . . . . . . . . . . .   6
     3. Bootstrap Router Election and RP-Set
     Distribution . . . . . . . . . . . . . . . . . . . . . . .   7
      3.1. Sending Candidate-RP-Advertisements. . . . . . . . .  15
      3.2. Creating the RP-Set at the BSR . . . . . . . . . . .  16
      3.3. Forwarding Bootstrap Messages. . . . . . . . . . . .  17
      3.4. Receiving and Using the RP-Set . . . . . . . . . . .  17
     4. Message Formats . . . . . . . . . . . . . . . . . . . .  18
      4.1. Bootstrap Message Format . . . . . . . . . . . . . .  20
      4.2. Candidate-RP-Advertisement Format. . . . . . . . . .  23
     5. Default Values for Timers . . . . . . . . . . . . . . .  25
     6. Authors' Addresses. . . . . . . . . . . . . . . . . . .  26
     7. References. . . . . . . . . . . . . . . . . . . . . . .  27
     8. Acknowledgments . . . . . . . . . . . . . . . . . . . .  27































Fenner/Handley/Thaler                                           [Page 2]

INTERNET-DRAFT            Expires: August 2001             February 2001


1.  Introduction

For correct operation, every PIM router within a PIM domain must be able
to map a particular multicast group address to the same RP.  If this is
not the case then black holes may appear, where some receivers in the
domain cannot receive some groups.  A domain in this context is a
contiguous set of routers that all implement PIM and are configured to
operate within a common boundary defined by PIM Multicast Border Routers
(PMBRs). PMBRs connect each PIM domain to the rest of the internet.

A notable exception to this is where a PIM domain is broken up into
multiple administrative scope regions - these are regions where a border
has been configured so that a range of multicast groups will not be
forwarded across that border.  For more information on Administratively
Scoped IP Multicast, see RFC 2365.  The modified criteria for admin-
scoped regions are that the region is convex with respect to forwarding
based on the MRIB, and that all PIM routers within the scope region map
a particular scoped group to the same RP within that region.

The PIM-SM specification does not mandate the use of a single mechanism
to provide routers with the information to perform the group-to-RP
mapping.  This document describes the Bootstrap Router (BSR) mechanism.
BSR was first defined in RFC 2362, which has since been obsoleted.  This
document provides an updated specification of the BSR mechanism from RFC
2362, and also extends it to cope with administratively scoped region
boundaries.



1.1.  Overview of Bootstrap and RP Discovery

A small set of routers from a domain are configured as candidate
bootstrap routers (C-BSRs) and, through a simple election mechanism, a
single BSR is selected for that domain. A set of routers within a domain
are also configured as candidate RPs (C-RPs); typically these will be
the same routers that are configured as C-BSRs.  Candidate RPs
periodically unicast Candidate-RP-Advertisement messages (C-RP-Advs) to
the BSR of that domain, advertising their willingness to be an RP. A C-
RP-Adv message includes the address of the advertising C-RP, as well as
an optional list of group addresses and a mask length fields, indicating
the group prefix(es) for which the candidacy is advertised. The BSR then
includes a set of these Candidate-RPs (the RP-Set), along with their
corresponding group prefixes, in Bootstrap messages it periodically
originates.  Bootstrap messages are distributed hop-by-hop throughout
the domain.

All the PIM routers in the domain receive and store Bootstrap messages
originated by the BSR.  When a DR gets a indication of local membership



Fenner/Handley/Thaler                             Section 1.1.  [Page 3]

INTERNET-DRAFT            Expires: August 2001             February 2001


from IGMP or a data packet from a directly connected host, for a group
for which it has no forwarding state, the DR uses a hash function to map
the group address to one of the C-RPs from the RP-Set whose group-prefix
includes the group (see RFC xxxx).  The DR then sends a Join message
towards that RP if the local host joined the group, or it Register-
encapsulates and unicasts the data packet to the RP if the local host
sent a packet to the group.

A Bootstrap message indicates liveness of the RPs included therein.  If
an RP is included in the message, then it is tagged as `up' at the
routers; RPs not included in the message are removed from the list of
RPs over which the hash algorithm acts. Each router continues to use the
contents of the most recently received Bootstrap message from the BSR
until it receives a new Bootstrap message.

If a PIM domain becomes partitioned, each area separated from the old
BSR will elect its own BSR, which will distribute an RP-Set containing
RPs that are reachable within that partition. When the partition heals,
another election will occur automatically and only one of the BSRs will
continue to send out Bootstrap messages. As is expected at the time of a
partition or healing, some disruption in packet delivery may occur. This
time will be on the order of the region's round-trip time and the
bootstrap router timeout value.


1.2.  Administratively Scoped Multicast

Administratively Scoped IP Multicast, as defined in RFC 2365, permits a
network provider to configure scope boundaries at multicast routers.
Such a scope boundary consists of a range of multicast addresses
(expressed as an address and mask) that the router will not forward
across the boundary.  For correct operation, such a scope zone border
must be complete and convex.  By this we mean that there must be no path
from inside the scoped zone to outside it that does not pass through a
configured scope border router, and that the multicast capable path
between any arbitrary pair of multicast routers in the scope zone must
remain in the zone.

For PIM-SM using BSR to function correctly with admin scoping, there
must be a BSR and at least one C-RP within every admin scope region.
Admin scope zone boundaries must be configured at the Zone Border
Routers (ZBRs), as they need to filter PIM Join messages that might
inadvertantly cross the border due to error conditions.  However we do
not wish any other router within the scope zone to require manual
configuration as this creates further possibilities for error, and makes
the configuration of large scope zones difficult.  If all the C-BSR and
C-RP routers within a scope zone are ZBRs, then there is no problem, but
this may not the the desired case.  Thus whilst we also permit interior



Fenner/Handley/Thaler                             Section 1.2.  [Page 4]

INTERNET-DRAFT            Expires: August 2001             February 2001


C-BSRs and C-RPs to be configured for the admin scope zone, we would
also require a mechanism by which all C-BSRs and C-RPs inside an admin
scope zone can automatically learn of the existence of the scope zone.

We do this by requiring all ZBRs to be both C-BSRs and C-RPs for the
scoped group range, although the default priority should be the lowest
possible.  A ZBR that does not know of a higher-priority BSR advertising
RPs for the scope zone will therefore originate its own Bootstrap
message, initially only containing itself as a possible RP for the
scoped group range.  The group-range field in the ZBRs bootstrap message
is marked (using the "Admin Scope" bit, previously a "Reserved" bit) to
indicate that this is an administrative scope range, and not just a
range that a particular set of RPs are configured to handle.  Such a
bootstrap message is flooded in the normal way, but will not be
forwarded by another ZBR across the boundary for that scope zone (see
Section 3.3 for the specifics of this).

When a C-BSR within the scope zone receives such a Bootstrap message, it
stores state for the admin scope range contained in the message.  A
separate BSR election will then take place for every admin scope range
(plus one for the global range).

When a C-RP within the scope zone receives such a Bootstrap message, it
also stores state for the admin scope range contained in the message.
It separately unicasts Candidate-RP-Advertisement messages to the BSR
for every admin scope range within which it is willing to serve as an
RP.  Unless configured otherwise, all candidate RPs are willing to serve
as RPs for all groups in all ranges.

ZBRs are also C-RPs for the admin scope zone; they also learn of the
current BSR for the admin scope range from receiving a Bootstrap
message, and so they must also send a Candidate-RP-Advertisement message
to the BSR for the scope range.  However, unlike an internal C-RP, a ZBR
sets the "Admin Scope" bit in the group-range field in its C-RP
advertisement.  When the BSR receives such a C-RP-Adv message, it
updates the scope zone keepalive timer; if this timer ever expires the
BSR stops being the BSR for that admin scope zone and flushes all state
concerned with the scope zone.  In this way, if all the ZBRs are
configured to no longer be ZBRs, then the BSR will eventually time out
the zone.

Note that so long as at least one reachable internal BSR and C-RP is
configured within the scope zone to have better-than-minimum priority,
then by default the ZBRs themselves will never actually be used as
either the BSR or an RP for the scope zone despite being a C-BSR and C-
RP.





Fenner/Handley/Thaler                             Section 1.2.  [Page 5]

INTERNET-DRAFT            Expires: August 2001             February 2001


2.  BSR State and Timers

A PIM-SM router implementing BSR holds the following state in addition
to the state needed for PIM-SM operation:

     At all routers:

          List of Active Scope Zones

          Per Scope Zone:

               Scope-Zone Expiry Timer: SZT(Z)

               Bootstrap State:

                    o Bootstrap Router's IP Address

                    o BSR Priority

                    o Bootstrap Timer (BST)

                    o List of Scope Group-Ranges for this BSR

          RP Set

     At a Candidate BSR:

          Per Scope Zone:

               o My state: One of "Candidate-BSR", "Pending-BSR",
                 "Elected-BSR"

     At a router that is not a Candidate BSR:

          Per Scope Zone:

               o My state: One of "Accept Any", "Accept Preferred"

Bootstrap state is described in section 3, and the RP Set is described
in section 3.4.

The following timers are also required:

     At the Bootstrap Router only:

          Per Scope Zone (Z):





Fenner/Handley/Thaler                               Section 2.  [Page 6]

INTERNET-DRAFT            Expires: August 2001             February 2001


               Per Candidate RP (C):

                    C-RP Expiry Timer: CET(C,Z)

     At the C-RPs only:

          C-RP Advertisement Timer: CRPT


3.  Bootstrap Router Election and RP-Set Distribution

For simplicity, bootstrap messages (BSMs) are used in both the BSR
election and the RP-Set distribution mechanisms.

The state-machine for bootstrap messages depends on whether or not a
router has been configured to be a Candidate-BSR.  The state-machine for
a C-BSR is given below, followed by the state-machine for a router that
is not configured to be a C-BSR.

Candidate-BSR State Machine


                 +-----------------------------------+
                 | Figures omitted from text version |
                 +-----------------------------------+


              Figure 1: State-machine for a candidate BSR


In tabular form this state machine is:

+-----------------------------------------------------------------------+
|                        When in No Info state                          |
+---------+-------------------------------+-----------------------------+
| Event   |  Receive Preferred BSM for    | Receive Non-Preferred BSM   |
|         |  unknown Admin Scope          | for unknown Admin Scope     |
+---------+-------------------------------+-----------------------------+
|         |  -> C-BSR state               | -> P-BSR state              |
| Action  |  Forward BSM;                 | Forward BSM;                |
|         |  Store RP Set;                | Store RP Set;               |
|         |  Set BS Timer to BS Timeout   | Set BS Timer to BS Timeout  |
+---------+-------------------------------+-----------------------------+








Fenner/Handley/Thaler                               Section 3.  [Page 7]

INTERNET-DRAFT            Expires: August 2001             February 2001


+-----------------------------------------------------------------------+
|                         When in C-BSR state                           |
+------------+-------------------+-------------------+------------------+
| Event      |  Receive          |  BS Timer         |  Receive BSM     |
|            |  Preferred BSM    |  Expires          |  from BSR with   |
|            |                   |                   |  Admin Scope     |
|            |                   |                   |  bit cleared     |
+------------+-------------------+-------------------+------------------+
|            |  -> C-BSR state   |  -> P-BSR state   |  -> No Info      |
|            |                   |                   |  state           |
| Action     |  Forward BSM;     |  Set BS Timer     |  cancel timers,  |
|            |  Store RP Set;    |  to               |  clear state     |
|            |  Set BS Timer     |  rand_override    |                  |
|            |  to BS Timeout    |                   |                  |
+------------+-------------------+-------------------+------------------+


+-----------------------------------------------------------------------+
|                         When in P-BSR state                           |
+------------+-------------------+-------------------+------------------+
| Event      |  Receive          |  BS Timer         |  Receive BSM     |
|            |  Preferred BSM    |  Expires          |  from BSR with   |
|            |                   |                   |  Admin Scope     |
|            |                   |                   |  bit cleared     |
+------------+-------------------+-------------------+------------------+
|            |  -> C-BSR state   |  -> E-BSR state   |  -> No Info      |
|            |                   |                   |  state           |
|            |  Forward BSM;     |  Originate BSM;   |  cancel timers,  |
| Action     |  Store RP Set;    |  Set BS Timer     |  clear state     |
|            |  Set BS Timer     |  to BS Period;    |                  |
|            |  to BS Timeout    |  Set SZ Timer     |                  |
|            |                   |  to SZ Period     |                  |
+------------+-------------------+-------------------+------------------+


















Fenner/Handley/Thaler                               Section 3.  [Page 8]

INTERNET-DRAFT            Expires: August 2001             February 2001


+-----------------------------------------------------------------------+
|                         When in E-BSR state                           |
+----------+---------------+--------------+--------------+--------------+
|Event     | Receive       | BS Timer     | SZ Timer     | Receive C-   |
|          | Preferred     | Expires      | Expires      | RP-Adv for   |
|          | BSM           |              |              | this Admin   |
|          |               |              |              | Scope        |
+----------+---------------+--------------+--------------+--------------+
|          | -> C-BSR      | -> E-BSR     | -> No Info   | -> E-BSR     |
|          | state         | state        | state        | state        |
|          | Forward BSM;  | Originate    | Originate    | Set SZ Timer |
|Action    | Store RP      | BSM; Set BS  | BSM with     | to SZ        |
|          | Set; Set BS   | Timer to BS  | Admin Scope  | Timeout      |
|          | Timer to BS   | Period       | bit cleared  |              |
|          | Timeout       |              |              |              |
+----------+---------------+--------------+--------------+--------------+
A candidate-BSR may be in one of four states for a particular scope
zone:

No Info
     The router has no information about this scope zone.  This state
     does not apply if the router is configured to know about this scope
     zone, or for the global scope zone.  When in this state, no state
     information is held and no timers run that refer to this scope
     zone.

Candidate-BSR (C-BSR)
     The router is a candidate to be a BSR, but currently another router
     is the preferred BSR.

Pending-BSR (P-BSR)
     The router is a candidate to be a BSR.  Currently no other router
     is the preferred BSR, but this router is not yet the BSR.  For
     comparisons with incoming BS messages, the router treats itself as
     the BSR.  This is a temporary state that prevents rapid thrashing
     of the choice of BSR during BSR election.

Elected-BSR (E-BSR)
     The router is the elected bootstrap router and it must perform all
     the BSR functions.

On startup, the initial state for this scope zone is "Pending-BSR" for
routers that know about this scope zone, either through configuration or
because the scope zone is the global scope which always exists; the BS
Timer is initialized to the BS Timeout value.  For routers that do not
know about a particular scope zone, the initial state is No Info; no
timers exist for the scope zone.




Fenner/Handley/Thaler                               Section 3.  [Page 9]

INTERNET-DRAFT            Expires: August 2001             February 2001


In addition to the four states, there are two timers:

o The bootstrap timer (BS Timer) - that is used to time out old
  bootstrap router information, and used in the election process to
  terminate P-BSR state.

o The scope zone timer (SZ Timer) - that is used to time out the scope
  zone itself at an Elected BSR if no C-RP-Adv messages arrive from the
  Zone Border Routers.

State-machine for Non-Candidate-BSR Routers


                 +-----------------------------------+
                 | Figures omitted from text version |
                 +-----------------------------------+


      Figure 2: State-machine for a router not configured as C-BSR

In tabular form this state machine is:


+-----------------------------------------------------------------------+
|                        When in No Info state                          |
+--------------------+--------------------------------------------------+
|     Event          |         Receive BSM for unknown Admin Scope      |
+--------------------+--------------------------------------------------+
|                    |         -> AP State                              |
|     Action         |         Forward BSM; Store RP-Set;               |
|                    |         Set BS Timer to BS Timeout;              |
|                    |         Set SZ Timer to SZ Timeout               |
+--------------------+--------------------------------------------------+


+-----------------------------------------------------------------------+
|                       When in Accept Any state                        |
+---------------+-----------------------------+-------------------------+
|   Event       |     Receive BSM             |     SZ Timer Expires    |
+---------------+-----------------------------+-------------------------+
|               |     -> AP State             |     -> No Info state    |
|               |     Forward BSM; Store      |     cancel timers;      |
|   Action      |     RP-Set; Set BS          |     clear state         |
|               |     Timer to BS             |                         |
|               |     Timeout                 |                         |
+---------------+-----------------------------+-------------------------+





Fenner/Handley/Thaler                              Section 3.  [Page 10]

INTERNET-DRAFT            Expires: August 2001             February 2001


+-----------------------------------------------------------------------+
|                   When in Accept Preferred state                      |
+-----------+------------------+-----------------+----------------------+
| Event     |  Receive         |   BS Timer      |  Receive BSM from    |
|           |  Preferred BSM   |   Expires       |  BSR with Admin      |
|           |                  |                 |  Scope bit cleared   |
+-----------+------------------+-----------------+----------------------+
|           |  -> AP State     |   -> AA State   |   -> No Info state   |
|           |  Forward BSM;    |                 |  cancel              |
| Action    |  Store RP-Set;   |                 |  timers;clear        |
|           |  Set BS Timer    |                 |  state               |
|           |  to BS Timeout   |                 |                      |
+-----------+------------------+-----------------+----------------------+

A router that is not a candidate-BSR may be in one of three states:

No Info
     The router has no information about this scope zone.  This state
     does not apply if the router is configured to know about this scope
     zone, or for the global scope zone.  When in this state, no state
     information is held and no timers run that refer to this scope
     zone.

Accept Any (AA)
     The router does not know of an active BSR, and will accept the
     first bootstrap message it sees as giving the new BSR's identity
     and the RP-Set.  If the router has an RP-Set cached from an
     obsolete bootstrap message, it continues to use it.

Accept Preferred (AP)
     The router knows the identity of the current BSR, and is using the
     RP-Set provided by that BSR.  Only bootstrap messages from that BSR
     or from a C-BSR with higher weight than the current BSR will be
     accepted.

On startup, the initial state for this scope zone is "Accept Any" for
routers that know about this scope zone, either through configuration or
because the scope zone is the global scope which always exists; the SZ
Timer is considered to be always running for such scope zones.  For
routers that do not know about a particular scope zone, the initial
state is No Info; no timers exist for the scope zone.

In addition to the three states, there are two timers:

o The bootstrap timer (BS Timer) - that is used to time out old
  bootstrap router information.





Fenner/Handley/Thaler                              Section 3.  [Page 11]

INTERNET-DRAFT            Expires: August 2001             February 2001


o The scope zone timer (SZ Timer) - that is used to time out the scope
  zone itself if BS messages specifying this scope zone stop arriving.

Bootstrap Message Processing Checks

When a bootstrap message is received, the following initial checks must
be performed:

if (BSM.dst_ip_address == ALL-PIM-ROUTERS group) {
  if ( BSM.src_ip_address != RPF_neighbor(BSM.BSR_ip_address) ) {
     drop the BS message silently
  }
} else if (BSM.dst_ip_address is one of my addresses) {
  if ( (No previous BSM received)
       OR (DirectlyConnected(BSM.src_ip_address) == FALSE) ) {
     #the packet was unicast, but this wasn't
     #a quick refresh on startup
     drop the BS message silently
  }
} else {
  drop the BS message silently
}
if (the interface the message arrived on is an Admin Scope
    border for the BSM.first_group_address) {
  drop the BS message silently
}

Basically, the packet must have been sent to the ALL-PIM-ROUTERS group
by the correct upstream router towards the BSR that originated the BS
message, or the router must have no BSR state (it just restarted) and
have received the BS message by unicast from a directly connected
neighbor.  In addition it must not have arrived on an interface that is
a configured admin scope border for the first group address contained in
the BS message.


BS State-machine Transition Events

If the bootstrap message passes the initial checks above without being
discarded, then it may cause a state transition event in one of the
above state-machines.  For both candidate and non-candidate BSRs, the
following transition events are defined:

     Receive Preferred BSM
          A bootstrap message is received from a BSR that has greater
          than or equal weight than the current BSR.  In a router is in
          P-BSR state, then it uses its own weight as that of the
          current BSR.



Fenner/Handley/Thaler                              Section 3.  [Page 12]

INTERNET-DRAFT            Expires: August 2001             February 2001


          The weighting for a BSR is the concatenation in fixed-
          precision unsigned arithmetic of the BSR priority field from
          the bootstrap message and the IP address of the BSR from the
          bootstrap message (with the BSR priority taking the most-
          significant bits and the IP address taking the least
          significant bits).

     Receive BSM
          A bootstrap message is received, regardless of BSR weight.

     Receive BSM from BSR with Admin Scope bit cleared
          The scope is not the global scope; it is an admin scope that
          was previously learned from receiving a bootstrap message that
          had the Admin Scope bit set for this scope.  Now a bootstrap
          message is received for this scope range from the BSR, but the
          Admin Scope bit is cleared indicating that the BSR has timed
          out the entire scope zone.

     Receive C-RP-Adv for this Admin Scope
          The scope is not the global scope; it is an admin scope range.
          A C-RP-Adv message arrives with the Admin Scope bit set for
          this scope range.  This indicates that the sender of the C-RP-
          Adv (normally a ZBR for the scope zone) believes the scope
          zone is still active.

BS State-machine Actions

The state-machines specify actions that include setting the BS timer to
the following values:

     BS Period
          The periodic interval with which bootstrap messages are
          normally sent.  The default value is 60 seconds.

     BS Timeout
          The interval after which bootstrap router state is timed out
          if no bootstrap message from that router has been heard.  The
          default value is 2.5 times the BS Period, which is 150
          seconds.

     Randomized Override Interval
          The randomized interval during which a router avoids sending a
          bootstrap message while it waits to see if another router has
          a higher bootstrap weight.  This interval is to reduce control
          message overhead during BSR election.  The following
          pseudocode is proposed as an efficient implementation of this
          "randomized" value:




Fenner/Handley/Thaler                              Section 3.  [Page 13]

INTERNET-DRAFT            Expires: August 2001             February 2001


          Delay = 5 + 2 * log_2(1 + bestPriority - myPriority)
                  + AddrDelay


          where myPriority is the Candidate-BSR's configured priority,
          and bestPriority equals:

          bestPriority = Max(storedPriority, myPriority)

          and AddrDelay is given by the following:

          if ( bestPriority == myPriority) {
              AddrDelay = log_2(bestAddr - myAddr) / 16
          } else {
              AddrDelay = 2 - (myAddr / 2^31)
          }


          where myAddr is the Candidate-BSR's address, and bestAddr is
          the stored BSR's address.

     SZ Period
          The interval after which a router will time out an Admin Scope
          zone that it has dynamically learned.  The interval MUST be
          larger than the C-RP-Adv period and the BS Timeout.  The
          default value is ten times the BS Timeout, which is 1500
          seconds.

In addition to setting the timer, the following actions may be triggered
by state-changes in the state-machines:

     Forward BSM
          The bootstrap message is forwarded out of all multicast-
          capable interfaces except the interface it was received on.
          The source IP address of the message is the forwarding
          router's IP address on the interface the message is being
          forwarded from, the destination address is ALL-PIM-ROUTERS,
          and the TTL of the message is set to 1.

     Originate BSM
          A new bootstrap message is constructed by the BSR, giving the
          BSR's address and BSR priority, and containing the BSR's
          chosen RP-Set.  The message is forwarded out of all multicast-
          capable interfaces.  The IP source address of the message is
          the forwarding router's IP address on the interface the
          message is being forwarded from, the destination address is
          ALL-PIM-ROUTERS, and the TTL of the message is set to 1.




Fenner/Handley/Thaler                              Section 3.  [Page 14]

INTERNET-DRAFT            Expires: August 2001             February 2001


     Originate BSM with Admin Scope Bit Cleared
          The action is the same as "Originate BSM", except that
          although this scope zone is an Admin Scope zone, the group
          range field for the scope zone has the Admin Scope bit
          cleared.  This serves as a signal that the scope zone is no
          longer in existence.

     Store RP Set
          The RP-Set from the received bootstrap message is stored and
          used by the router to decide the RP for each group that the
          router has state for.  Storing this RP Set may cause other
          state-transitions to occur in the router.  The BSR's IP
          address and priority from the received bootstrap message are
          also stored to be used to decide if future bootstrap messages
          are preferred.

In addition to the above state-machine actions, a DR also unicasts a
stored copy of the Bootstrap message to each new PIM neighbor, i.e.,
after the DR receives the neighbor's first Hello message.  It does so
even if the new neighbor becomes the DR.

3.1.  Sending Candidate-RP-Advertisements

Every C-RP periodically unicasts a C-RP-Adv to the BSR for that scope
zone to inform the BSR of the C-RP's willingness to function as an RP.
Unless configured otherwise, it does this for every Admin Scope zone for
which it has state, and for the global scope zone.  If the same router
is BSR for more than one scope zone, the C-RP-Adv for these scope zones
MAY be combined into a single message.

If the C-RP is a ZBR for an admin scope zone, then the Admin Scope bit
MUST be set in the C-RP-Adv messages it sends for that scope zone;
otherwise this bit MUST NOT be set.

The interval for sending these messages is subject to local
configuration at the C-RP, but must be smaller than the HoldTime in the
C-RP-Adv.

A Candidate-RP-Advertisement carries a list of group address and group
mask field pairs.  This enables the C-RP router to limit the
advertisement to certain prefixes or scopes of groups.  If the C-RP
becomes an RP, it may enforce this scope acceptance when receiving
Registers or Join/Prune messages.

The C-RP priority field determines which C-RPs get selected by the BSR
to be in the RP Set.  Note that a value of zero is the highest possible
priority.  C-RPs should by default send C-RP-Adv messages with the
`Priority' field set to `192'.  ZBRs that do not wish to serve as an RP



Fenner/Handley/Thaler                            Section 3.1.  [Page 15]

INTERNET-DRAFT            Expires: August 2001             February 2001


except under failure conditions should default to sending C-RP-Adv
messages with the `Priority' field set to `255'.

When a C-RP is being shut down, it SHOULD immediately send a C-RP-Adv to
the BSR for each scope for which it is currently serving as an RP; the
HoldTime in this C-RP-Adv message should be zero.  The BSR will then
immediately time out the C-RP and generate a new BSR message removing
the shutdown RP from the RPset.


3.2.  Creating the RP-Set at the BSR

Upon receiving a C-RP-Adv, if the router is not the elected BSR, it
silently ignores the message.

If the router is the BSR, then it adds the RP address to its local pool
of candidate RPs.  For each C-RP, the BSR holds the following
information:

     IP address
          The IP address of the C-RP.

     Group Prefix and Mask list
          The list of group prefixes and group masks from the C-RP
          advertisement.

     HoldTime
          The HoldTime from the C-RP-Adv message.  This is included
          later in the RP-set information in the Bootstrap Message.

     C-RP Expiry Timer
          The C-RP-Expiry Timer is used to time out the C-RP when the
          BSR fails to receive C-RP-Advertisements from it.  The expiry
          timer is initialized to the HoldTime from the RP's C-RP-Adv,
          and is reset to the HoldTime whenever a C-RP-Adv is received
          from that C-RP.

     C-RP Priority
          The C-RP Priority is used to determine the subset of possible
          RPs to use in the RP-Set.

When the C-RP Expiry Timer expires, the C-RP is removed from the pool of
available C-RPs.

The BSR uses the pool of C-RPs to construct the RP-Set which is included
in Bootstrap Messages and sent to all the routers in the PIM domain.
The BSR may apply a local policy to limit the number of Candidate RPs
included in the Bootstrap message.  The BSR may override the prefix



Fenner/Handley/Thaler                            Section 3.2.  [Page 16]

INTERNET-DRAFT            Expires: August 2001             February 2001


indicated in a C-RP-Adv unless the `Priority' field from the C-RP-Adv is
less than 128.

The Bootstrap message is subdivided into sets of group-prefix,RP-
Count,RP-addresses.  For each RP-address, the corresponding HoldTime is
included in the "RP-HoldTime" field.  The format of the Bootstrap
message allows `semantic fragmentation', if the length of the original
Bootstrap message exceeds the packet maximum boundaries. However, we
recommend against configuring a large number of routers as C-RPs, to
reduce the semantic fragmentation required.

When an elected BSR is being shut down, it should immediately orginate a
Bootstrap message listing its current RP set, but with the BSR priority
field set to the lowest priority value possible.  This will cause the
election of a new BSR to happen more quickly.


3.3.  Forwarding Bootstrap Messages

Bootstrap messages originate at the BSR, and are forwarded by
intermediate routers if they pass the Bootstrap Message Processing
Check.  Bootstrap messages are multicast to the `ALL-PIM-ROUTERS' group.
When A BS message is forwarded, it is forwarded out of every multicast-
capable interface which has PIM neighbors (excluding the one over which
the message was received).  The exception to this is if the interface is
an adminstrative scope boundary for the admin scope zone indicated in
the first group address in the BS message packet.  Bootstrap messages
are always originated or forwarded with an IP TTL value of 1.


3.4.  Receiving and Using the RP-Set

When a router receives and stores a new RP-Set, it checks if each of the
RPs referred to by existing state (i.e., by (*,G), (*,*,RP), or
(S,G,rpt) entries) is in the new RP-Set.

If an RP is not in the new RP-Set, that RP is considered unreachable and
the hash algorithm (see PIM-SM specification) is re-performed for each
group with locally active state that previously hashed to that RP. This
will cause those groups to be distributed among the remaining RPs.

If the new RP-Set contains a RP that was not previously in the RP-Set,
the hash value of the new RP is calculated for each group covered by the
new C-RP's Group-prefix.  Any group for which the new RP's hash value is
greater than hash value of the group's previous RP is switched over to
the new RP.





Fenner/Handley/Thaler                            Section 3.4.  [Page 17]

INTERNET-DRAFT            Expires: August 2001             February 2001


4.  Message Formats

BSR messages are PIM messages, as defined in RFC xxxx.  The values of
the PIM message Type field for BSR messages are:

4    Bootstrap Message

8    Candidate-RP-Advertisement

In this section we use the following terms defined in the PIM-SM
specification in RFC xxxx:

o    Encoded-Unicast format

o    Encoded-Group format

We repeat these here to aid readability.

Encoded-Unicast address

An Encoded-Unicast address takes the following format:

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Addr Family  | Encoding Type |     Unicast Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...


Addr Family
     The PIM address family of the `Unicast Address' field of this
     address.

     Values of 0-127 are as assigned by the IANA for Internet Address
     Families in [1]. Values 128-250 are reserved to be assigned by the
     IANA for PIM-specific Address Families.  Values 251 though 255 are
     designated for private use.  As there is no assignment authority
     for this space, collisions should be expected.

Encoding Type
     The type of encoding used within a specific Address Family.  The
     value `0' is reserved for this field, and represents the native
     encoding of the Address Family.


Unicast Address
     The unicast address as represented by the given Address Family and
     Encoding Type.



Fenner/Handley/Thaler                              Section 4.  [Page 18]

INTERNET-DRAFT            Expires: August 2001             February 2001


Encoded-Group address

Encoded-Group addresses take the following format:

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Addr Family  | Encoding Type |   Reserved  |Z|  Mask Len     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                Group multicast Address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...


Addr Family
     described above.


Encoding Type
     described above.


Reserved
     Transmitted as zero. Ignored upon receipt.


Admin Scope [Z]one
     When set, this bit indicates that this group address range is an
     adminstratively scoped range.


Mask Len
     The Mask length field is 8 bits. The value is the number of
     contiguous one bits left justified used as a mask which, combined
     with the group address, describes a range of groups. It is less
     than or equal to the address length in bits for the given Address
     Family and Encoding Type. If the message is sent for a single group
     then the Mask length must equal the address length in bits for the
     given Address Family and Encoding Type.  (e.g. 32 for IPv4 native
     encoding and 128 for IPv6 native encoding).


Group multicast Address
     Contains the group address.








Fenner/Handley/Thaler                              Section 4.  [Page 19]

INTERNET-DRAFT            Expires: August 2001             February 2001


4.1.  Bootstrap Message Format


A bootstrap message is divided up into `semantic fragments', if the
original message exceeds the maximum packet size boundaries.  Basically,
a single bootstrap message can be sent as multiple packets (semantic
fragments), so long as the fragment tage of all the packets comprising
the message is the same.

If the bootstrap message contains information about more than one admin
scope zone, each different scope zone MUST occupy a different semantic
fragment.  This allows Zone Border Routers for an admin scope zone to
not forward only those fragments that should not traverse the admin
scope boundary.

The format of a single `fragment' is given below:



































Fenner/Handley/Thaler                            Section 4.1.  [Page 20]

INTERNET-DRAFT            Expires: August 2001             February 2001


 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Fragment Tag          | Hash Mask len | BSR-priority  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             BSR Address (Encoded-Unicast format)              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address 1 (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Count 1    | Frag RP Cnt 1 |         Reserved              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address 1 (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RP1 Holdtime         | RP1 Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address 2 (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RP2 Holdtime         | RP2 Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address m (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RPm Holdtime         | RPm Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address 2 (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address n (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RP Count n    | Frag RP Cnt n |          Reserved             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address 1 (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RP1 Holdtime         | RP1 Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address 2 (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RP2 Holdtime         | RP2 Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Fenner/Handley/Thaler                            Section 4.1.  [Page 21]

INTERNET-DRAFT            Expires: August 2001             February 2001


|             RP Address m (Encoded-Unicast format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          RPm Holdtime         | RPm Priority  |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Version, Reserved, Checksum
     Described in RFC xxxx.


Type PIM Message Type.  Value is 8 for a Bootstrap Message.


Fragment Tag
     A randomly generated number, acts to distinguish the fragments
     belonging to different Bootstrap messages; fragments belonging to
     same Bootstrap message carry the same `Fragment Tag'.


Hash Mask len
     The length (in bits) of the mask to use in the hash function. For
     IPv4 we recommend a value of 30. For IPv6 we recommend a value of
     126.


BSR priority
     Contains the BSR priority value of the included BSR.  This field is
     considered as a high order byte when comparing BSR addresses.  Note
     that for historical reasons, the highest BSR priority priority is
     255 (the higher the better), whereas the highest RP Priority (see
     below) is 0 (the lower the better).


Unicast BSR Address
     The address of the bootstrap router for the domain.  The format for
     this address is given in the Encoded-Unicast address in RFC xxxx.


Group Address 1..n
     The group prefix (address and mask) with which the Candidate RPs
     are associated.  Format described in RFC xxxx.  In a fragment
     containing admin scope ranges, the first group address in the
     fragment MUST be the group range for the entire admin scope range,
     and this MUST have the Admin Scope bit set.  This is the case even
     if there are no RPs in the RP set for the entire admin scope range
     - in this case the sub-ranges for the RP set are specified later in
     the fragment along with their RPs.




Fenner/Handley/Thaler                            Section 4.1.  [Page 22]

INTERNET-DRAFT            Expires: August 2001             February 2001


RP Count 1..n
     The number of Candidate RP addresses included in the whole
     Bootstrap message for the corresponding group prefix. A router does
     not replace its old RP-Set for a given group prefix until/unless it
     receives `RP-Count' addresses for that prefix; the addresses could
     be carried over several fragments.  If only part of the RP-Set for
     a given group prefix was received, the router discards it, without
     updating that specific group prefix's RP-Set.


Frag RP Cnt 1..m
     The number of Candidate RP addresses included in this fragment of
     the Bootstrap message, for the corresponding group prefix. The
     `Frag RP-Cnt' field facilitates parsing of the RP-Set for a given
     group prefix, when carried over more than one fragment.


RP address 1..m
     The address of the Candidate RPs, for the corresponding group
     prefix.  The format for these addresses is given in the Encoded-
     Unicast address in RFC xxxx.


RP1..m Holdtime
     The Holdtime for the corresponding RP.  This field is copied from
     the `Holdtime' field of the associated RP stored at the BSR.


RP1..m Priority
     The `Priority' of the corresponding RP and Encoded-Group Address.
     This field is copied from the `Priority' field stored at the BSR
     when receiving a Candidate-RP-Advertisement.  The highest priority
     is `0' (i.e. unlike BSR priority, the lower the value of the
     `Priority' field, the better).  Note that the priority is per RP
     per Group Address.
















Fenner/Handley/Thaler                            Section 4.2.  [Page 23]

INTERNET-DRAFT            Expires: August 2001             February 2001


4.2.  Candidate-RP-Advertisement Format

Candidate-RP-Advertisements are periodically unicast from the C-RPs to
the BSR.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|PIM Ver| Type  |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Cnt    |   Priority    |           Holdtime            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             RP Address (Encoded-Unicast format)               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address 1 (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|            Group Address n (Encoded-Group format)             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PIM Version, Reserved, Checksum
     Described in RFC xxxx.


Type PIM Message Type.  Value is 4 for a Candidate-RP-Advertisement
     Message.


Prefix Cnt
     The number of encoded group addresses included in the message;
     indicating the group prefixes for which the C-RP is advertising. A
     Prefix Cnt of `0' implies all multicast groups, e.g. for IPv4 a
     prefix of 224.0.0.0 with mask length of 4.  If the C-RP is not
     configured with Group-prefix information, the C-RP puts a default
     value of `0' in this field.


Priority
     The `Priority' of the included RP, for the corresponding Encoded-
     Group Address (if any).  highest priority is `0' (i.e. the lower
     the value of the `Priority' field, the higher the priority). This
     field is stored at the BSR upon receipt along with the RP address
     and corresponding Encoded-Group Address.




Fenner/Handley/Thaler                            Section 4.2.  [Page 24]

INTERNET-DRAFT            Expires: August 2001             February 2001


Holdtime
     The amount of time the advertisement is valid. This field allows
     advertisements to be aged out.


RP Address
     The address of the interface to advertise as a Candidate RP.  The
     format for this address is given in the Encoded-Unicast address in
     RFC xxxx.


Group Address-1..n
     The group prefixes for which the C-RP is advertising.  Format
     described in Encoded-Group-Address in RFC xxxx.


5.  Default Values for Timers

Timer Name: Bootstrap Timer (BST)


+----------------------+------------------------+-----------------------+
| Value Name           |  Value                 |   Explanation         |
+----------------------+------------------------+-----------------------+
| BS Period            |  Default: 60 secs      |   Period between      |
|                      |                        |   bootstrap messages  |
+----------------------+------------------------+-----------------------+
| BS Timeout           |  2 * BS_Period + 10    |   Period after last   |
|                      |  seconds               |   BS message before   |
|                      |                        |   BSR is timed out    |
|                      |                        |   and election        |
|                      |                        |   begins              |
+----------------------+------------------------+-----------------------+
| BS randomized        |  rand(0, 5.0 secs)     |   Suppression period  |
| override interval    |                        |   in BSR election to  |
|                      |                        |   prevent thrashing   |
+----------------------+------------------------+-----------------------+

Timer Name: C-RP Expiry Timer (CET(R))


+----------------+------------------+-----------------------------------+
| Value Name     |  Value           |  Explanation                      |
+----------------+------------------+-----------------------------------+
| C-RP Timeout   |  from message    |  Hold time from C-RP-Adv message  |
+----------------+------------------+-----------------------------------+





Fenner/Handley/Thaler                              Section 5.  [Page 25]

INTERNET-DRAFT            Expires: August 2001             February 2001


C-RP Advertisement messages are sent periodically with period C-RP-Adv-
Period.  C-RP-Adv-Period defaults to 60 seconds.  The holdtime to be
specified in a C-RP-Adv message should be set to (2.5 * C-RP-Adv-Period
).

Timer Name: C-RP Advertisement Timer (CRPT)


+--------------------+--------------------------+-----------------------+
| Value Name         |   Value                  |  Explanation          |
+--------------------+--------------------------+-----------------------+
| C-RP-Adv-Period    |   Default: 60 seconds    |  Period with which    |
|                    |                          |  periodic C-RP        |
|                    |                          |  Advertisements are   |
|                    |                          |  sent to BSR          |
+--------------------+--------------------------+-----------------------+

Timer Name: Scope Zone Expiry Timer (SZT(Z))


+------------------------------------+--------------+-------------------+
|Value Name      Value   Explanation |              |                   |
+------------------------------------+--------------+-------------------+
|SZ Timeout                          |1500 seconds  |Interval after     |
|                                    |              |which a scope zone |
|                                    |              |will be timed out  |
|                                    |              |if the state is    |
|                                    |              |not refreshed      |
+------------------------------------+--------------+-------------------+


6.  Authors' Addresses

     Bill Fenner
     AT&T Labs - Research
     75 Willow Road
     Menlo Park, CA 94025
     fenner@research.att.com


     Mark Handley
     ACIRI/ICSI
     1947 Center St, Suite 600
     Berkeley, CA 94708
     mjh@aciri.org






Fenner/Handley/Thaler                              Section 6.  [Page 26]

INTERNET-DRAFT            Expires: August 2001             February 2001


     David Thaler
     Microsoft Corporation
     One Microsoft Way
     Redmond, WA 98052
     dthaler@Exchange.Microsoft.com



7.  References

[1] IANA, "Address Family Numbers", linked from
     http://www.iana.org/numbers.html

8.  Acknowledgments

PIM-SM was designed over many years by a large group of people,
including ideas from Deborah Estrin, Dino Farinacci, Ahmed Helmy, Steve
Deering, Van Jacobson, C. Liu, Puneet Sharma, Liming Wei, Tom Pusateri,
Tony Ballardie, Scott Brim, Jon Crowcroft, Paul Francis, Joel Halpern,
Horst Hodel, Polly Huang, Stephen Ostrowski, Lixia Zhang, Girish
Chandranmenon, and Pavlin Radoslavov.  This BSR specification draws
heavily on text from RFC 2362.





























Fenner/Handley/Thaler                              Section 8.  [Page 27]


Html markup produced by rfcmarkup 1.107, available from http://tools.ietf.org/tools/rfcmarkup/