Internet Engineering Task Force                                 MAGMA WG
INTERNET-DRAFT                                            B. Fenner/AT&T
draft-ietf-magma-msnip-05.txt               B. Haberman/Caspian Networks
                                                       H. Holbrook/Cisco
                                                       I. Kouvelas/Cisco
                                                           10 March 2004
                                                 Expires: September 2004


       Multicast Source Notification of Interest Protocol (MSNIP)



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

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This document is a product of the IETF MAGMA WG.  Comments should be
addressed to the authors, or the WG's mailing list at magma@ietf.org.

                                Abstract


     This document discusses the Multicast Source Interest
     Notification Protocol (MSNIP).  MSNIP is an extension to
     IGMPv3 and MLDv2 that provides membership notification
     services for sources of multicast traffic operating within the
     SSM destination address range.




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                           Table of Contents


     1. Introduction. . . . . . . . . . . . . . . . . . . . . .   3
     2. Routing Protocol Support. . . . . . . . . . . . . . . .   3
     3. Service Interface for Requesting Membership Noti-
     fication . . . . . . . . . . . . . . . . . . . . . . . . .   4
      3.1. Application Operation. . . . . . . . . . . . . . . .   5
     4. MSNIP Managed Address Range Negotiation . . . . . . . .   6
      4.1. Router Coordination. . . . . . . . . . . . . . . . .   6
       4.1.1. MSNIP Operation Option. . . . . . . . . . . . . .   6
       4.1.2. SSM Range Option. . . . . . . . . . . . . . . . .   7
      4.2. Managed Range Discovery by Source Systems. . . . . .   8
     5. Requesting and Receiving Notifications. . . . . . . . .   8
      5.1. Host Interest Solicitation . . . . . . . . . . . . .   9
      5.2. Router Receiver Membership Reports . . . . . . . . .   9
     6. Application Notification. . . . . . . . . . . . . . . .  11
     7. Router Processing . . . . . . . . . . . . . . . . . . .  13
     8. Message Formats . . . . . . . . . . . . . . . . . . . .  14
      8.1. Host Interest Solicitation Message . . . . . . . . .  15
      8.2. Receiver Membership Report Packet. . . . . . . . . .  16
      8.3. IPv4 Header Fields . . . . . . . . . . . . . . . . .  18
      8.4. IPv6 Header Fields . . . . . . . . . . . . . . . . .  18
     9. Constants Timers and Default Values . . . . . . . . . .  18
     10. Possible Optimisations . . . . . . . . . . . . . . . .  19
      10.1. Suppressing HIS Messages. . . . . . . . . . . . . .  19
      10.2. Host Stack Filtering. . . . . . . . . . . . . . . .  19
      10.3. Responding to Unexpected IGMP Queries . . . . . . .  19
      10.4. Host and Router Startup . . . . . . . . . . . . . .  20
     11. Inter-operation with IGMP / MLD Proxying . . . . . . .  20
     12. Security Considerations. . . . . . . . . . . . . . . .  21
      12.1. Receiver Membership Report attacks. . . . . . . . .  21
      12.2. Host Interest Solicitation attacks. . . . . . . . .  22
      12.3. MSNIP Managed Range Discovery . . . . . . . . . . .  22
     13. IANA Considerations. . . . . . . . . . . . . . . . . .  23
     14. Acknowledgments. . . . . . . . . . . . . . . . . . . .  23
     15. Normative References . . . . . . . . . . . . . . . . .  23
     16. Informative References . . . . . . . . . . . . . . . .  24













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1.  Introduction

     The Multicast Source Notification of Interest Protocol (MSNIP) is
an extension to version 3 of the Internet Group Membership Protocol
(IGMPv3 [1]) and version 2 of the Multicast Listener Discovery Protocol
(MLDv2 [2]). MSNIP operates between multicast sources and their first-
hop routers to provide information on the presence of receivers to the
source systems. Using the services offered by MSNIP an application on an
IP system wishing to source multicast data can register to be notified
when receivers join and leave the session. This enables multicast
sources to avoid the work of transmitting packets onto their first-hop
link when there are no joined receivers.

     A common scenario where MSNIP may be useful is one where there is a
multicast server offering a large pool of potential flows that map onto
separate multicast destination addresses but receivers exist only for a
small subset of the flows. If the source were to continuously transmit
data for all the flows that could potentially have receivers,
significant resources would be wasted in the system itself as well as
the first-hop link and first-hop router. Using a higher level control
protocol to determine the existence of receivers for particular flows
may not be practical as there may be many potential receivers in each
active session.

     Information on which multicast destination addresses have receivers
for a particular sender is typically available to the multicast routing
protocol on the first hop router for a source. MSNIP uses this
information to notify the application in the sending system of when it
should start or stop transmitting. This is achieved without any
destination address specific state on the first-hop router for potential
sources without receivers.


2.  Routing Protocol Support

     For reasons described in this section, MSNIP only supports
transmission control for applications that use multicast destination
addresses that are routed using Source Specific Multicast (SSM).

     Many currently deployed multicast routing protocols require data
from an active source to be propagated past the first-hop router before
information on the existence of receivers becomes available on the
first-hop. In addition, such protocols require that this activity is
repeated periodically to maintain source liveness state on remote
routers. All dense-mode protocols fall under this category as well as
sparse-mode protocols that use shared trees for source discovery (such
as PIM-SM [11]). In order to provide receiver interest notification for
such protocols, the default mode of operation would require that the



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source IP system periodically transmits on all potential destination
addresses and the first-hop routers prune the traffic back. Such a
flood-and-prune behaviour on the first-hop link significantly diminishes
the benefits of managing source transmission.

     In contrast, with source-specific sparse-mode protocols such as
PIM-SSM [11] availability of receiver membership information on the
first-hop routers is independent of data transmission. Such protocols
use an external mechanism for source discovery (like source-specific
IGMPv3 membership reports) to build source-specific multicast trees.

     Clearly these two classes of routing protocols require different
handling for the problem MSNIP is trying to solve. In addition the
second type covers the majority of applications that MSNIP is targeted
at. MSNIP avoids the extra complication in supporting routing protocols
that require a flood and prune behaviour.

3.  Service Interface for Requesting Membership Notification

     Applications within an IP system that wish to source multicast
packets and are interested in being notified on the existence of
receivers must register with the IP layer of the system. MSNIP requires
that within the IP system, there is (at least conceptually) a service
interface that can be used to register with the IP layer for such
notifications.  Dual stack systems supporting both IPv4 and IPv6 need to
provide separate service interfaces for each protocol.


     A system's IPv4 or IPv6 service interface must support the
following operation or any logical equivalent:

    IPMulticastSourceRegister (socket, source-address, multicast-address)
    IPMulticastSourceDeregister (socket, source-address, multicast-address)

     In addition the application must provide the following interface
for receiving notifications from the IP system:

    IPMulticastSourceStart (socket, source-address, multicast-address)
    IPMulticastSourceStop (socket, source-address, multicast-address)

where:

socket
     is an implementation-specific parameter used to distinguish amongst
     different requesting entities (e.g., programs or processes) within
     the system; the socket parameter of BSD UNIX system calls is a
     specific example.




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source-address
     is the IP unicast source address that the application wishes to use
     in transmitting data to the specified multicast address. The
     specified address must be one of the IP addresses associated with
     the network interfaces of the IP system. Note that an interface in
     an IP system may be associated with more than one IP address.  An
     implementation may allow a special "unspecified" value to be passed
     as the source-address parameter, in which case the request would
     apply to the "primary" IP address of the "primary" or "default"
     interface of the system (perhaps established by system
     configuration). If transmission to the same multicast address is
     desired using more than one source IP address,
     IPMulticastSourceRegister must be invoked separately for each
     desired source address.

multicast-address
     is the IP multicast destination address to which the request
     pertains.  If the application wishes to transmit data to more than
     one multicast addresses for a given source address,
     IPMulticastSourceRegister must be invoked separately for each
     desired multicast address.


3.1.  Application Operation

     Applications wishing to use MSNIP to control their multicast data
transmission to destination G from source address S operate as follows.

     Initially the application contacts the IP system to obtain the
socket handle for use on all subsequent interactions. The application
invokes IPMulticastSourceRegister for the desired S and G and then waits
without transmitting any packets for the IP system to notify that
receivers for the session exist.

     If and when the IP system notifies the application that receivers
exist using the IPMulticastSourceStart call, the application may start
transmitting data. After the application has been notified to send, if
all receivers for the session leave, the IP system will notify the
application using the IPMulticastSourceStop call. At this point the
application should stop transmitting data until it is notified again
that receivers have joined through another IPMulticastSourceStart call.

     When the application no longer wishes to transmit data it should
invoke the IPMulticastSourceDeregister call to let the IP system know
that it is no longer interested in notifications for this source and
destination. The IPMulticastSourceDeregister call should be implicit in
the teardown of the associated socket state.




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4.  MSNIP Managed Address Range Negotiation

     With current multicast deployment in the Internet, different
multicast routing protocols coexist and operate under separate parts of
the multicast address space. Multicast routers are consistently
configured with information that maps specific multicast address ranges
to multicast routing protocols. Part of this configuration describes the
subset of the address space that is used by source-specific multicast
(SSM) [12]. As described in section 2, MSNIP only tries to control
application transmission within the SSM address range.

     It is desirable for applications within an IP system that supports
MSNIP to have a consistent service interface for multicast transmission
that does not require the application to be aware of the SSM address
range. MSNIP supports this by allowing applications to use the service
interface described in section 3 for multicast destination addresses
that are outside its operating range. When an application registers for
notifications for a destination address that is not managed by MSNIP it
is immediately notified to start transmitting. This is equivalent to the
default behaviour of IP multicast without MSNIP support which forces
multicast applications to assume that there are multicast receivers
present in the network.


4.1.  Router Coordination

     In order for MSNIP to operate on a shared link where two or more
multicast routers may be present, all the multicast routers must be
MSNIP-capable and have an identical configuration for the SSM address
range.  MSNIP enforces these requirements by using two new options for
IPv4 in the Multicast Router Discovery protocol [3] and one new option
for IPv6 in the Neighbour Discovery / ICMPv6 protocol [6].

4.1.1.  MSNIP Operation Option

     A multicast router advertises that it is participating in MSNIP
using the MSNIP Operation option in either the Multicast Router
Discovery protocol for IPv4 or the Neighbour Discovery / ICMPv6 protocol
for IPv6. This option MUST be included in all router advertisement
messages of a router that is configured for MSNIP. The format of the
option is as follows:










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 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |    Length     |           Padding             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            Padding                            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Type The type field is set to WW (TBD by IANA) for IPv4 and ZZ (TBD by
     IANA) for IPv6.

Length
     The length field is set to 0 for IPv4 and 1 for IPv6.

Padding
     The six extra bytes of padding are only present in IPv6 and are
     required to bring the size of the option up to the eight octet
     boundary. The value of the padding bytes must be set to zero on
     transmission and ignored on receipt.

     A multicast router uses received Multicast Router Advertisement and
Neighbour Discovery / ICMPv6 messages to determine if all live neighbour
multicast routers on each interface are participating in MSNIP. When a
router advertisement message not containing an MSNIP option is received
by a router participating in MSNIP, the mis-configuration SHOULD be
logged to the operator in a rate-limited manner.

     If even one multicast router on a link does not have MSNIP
capability then ALL routers on that link MUST be configured to not
provide MSNIP services and to not advertise the MSNIP Operation option.


4.1.2.  SSM Range Option

     The SSM Range Multicast Router Discovery option advertises the IPv4
SSM Range with which the router is configured. The option is defined in
[4]. This option is only valid in IPv4.

     The SSM range for IPv6 is well defined for all valid scopes [15]
and a mechanism to allow additional ranges to operate in SSM mode on a
per-link bases is not required.








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4.2.  Managed Range Discovery by Source Systems

     When an application in an IP system uses the MSNIP service
interface to register for notification, the IP system must behave
differently depending on whether or not the destination address for
which the application registered is operating under SSM (and is being
managed by MSNIP). For SSM channels, the IP system should only instruct
the application to transmit when there are receivers for the multicast
destination. For non-SSM destination addresses the IP system will not be
able to determine if there are receivers and should immediately instruct
the application to transmit. In addition, an MSNIP-capable IP system
must be able to detect if there are multicast routers on its connected
links and if they support MSNIP operation. If no multicast routers are
present or if the multicast routers are not MSNIP-capable then the IP
system MUST default to flooding and immediately instruct applications to
transmit.

     An IP system controls transmission behaviour under the different
possible conditions by adapting its definition of the MSNIP-managed
multicast destination address range:

     o On a link with multicast routers operating the MSNIP protocol the
       IP system MUST use the SSM multicast destination address range as
       the MSNIP-managed range. IPv4 systems MUST use the contents of
       the SSM Range option in received Multicast Router Advertisement
       messages [4] to discover the configured SSM range. SSM range
       discovery is not needed in IPv6 where the SSM destination address
       range is fixed.

     o On a link not connected to a multicast routed infrastructure or
       on a link with multicast routers that do not support MSNIP
       operation, the IP system MUST use an empty range as its MSNIP-
       managed range. This forces applications transmitting to any
       multicast destination address to default to flooding thus
       providing backward compatibility.

     As described in 4.1.1, an IP system can determine the status of a
link and distinguish between the above two cases through the reception
of IPv4 Multicast Router Advertisement and Neighbour Discovery / ICMPv6
messages.

5.  Requesting and Receiving Notifications

     Like IGMP, MSNIP is an asymmetric protocol specifying different
behaviour for systems wishing to source traffic and for multicast
routers. Host IP systems multicast Host Interest Solicitation messages
to register for notification with their first-hop routers. Routers
unicast Router Receiver Membership Reports to IP systems to notify them



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of the arrival of the first or departure of the last receiver for a
session. Note that a system may perform at the same time both of the
above functions. An example is a router that wishes to source traffic.


5.1.  Host Interest Solicitation

     Source systems that wish to be managed by MSNIP periodically
transmit a Host Interest Solicitation message. This message is multicast
with a multicast destination address of ALL_IGMPv3_ROUTERS (224.0.0.22)
or ALL_MLDv2_ROUTERS (TBA) and is transmitted every [Interest
Solicitation Interval] seconds. The Host Interest Solicitation message
contains a holdtime which is set to [Interest Solicitation Holdtime] and
instructs the multicast first-hop routers to maintain MSNIP state for
this IP system for the specified period.  Systems with multiple
interfaces or multiple IP addresses per interface must originate
separate Host Interest Solicitation messages from each of their IP
addresses that they wish to have managed by MSNIP. In practice a system
with more than one IP address is treated by MSNIP as multiple IP
systems.

     When an IP system first comes up it transmits [Robustness Variable]
Host Interest Solicitation messages spaced by [Initial Interest
Solicitation Interval] seconds.

     All MSNIP capable routers that receive a Host Interest Solicitation
message from an IP system, maintain a system interest record of the
form:

     (IP system address, holdtime timer)

Each time a Host Interest Solicitation message is received from the IP
system, the holdtime timer is reset to the holdtime in the received
message.  In addition the router may respond to the solicitation message
with a Receiver Membership Report message described in section 5.2. The
message contains a TRANSMIT record for each of the multicast destination
addresses within the MSNIP-managed range for which the routing protocol
indicates there are receivers for this source system.

     The holdtime timer of a record counts down to zero. When the
holdtime timer of a specific system interest record expires, the record
is deleted.


5.2.  Router Receiver Membership Reports

     Receiver Membership Report messages are used by routers to
communicate the receiver membership status of particular multicast



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destination addresses to a specific IP system. Each message contains a
list of transmission control records of either TRANSMIT or HOLD type
that instruct a system to respectively start or stop sending traffic on
this link to the specified multicast destination address.  Receiver
Membership Report messages are unicast to the target system.

     In addition to reports sent in response to Host Interest
Solicitation messages, routers send unsolicited Receiver Membership
Reports to IP systems when the receiver membership status reported by
the multicast routing protocol changes for a specific source and
multicast destination. Such reports are only sent if the multicast
destination address is managed by MSNIP and the router has a system
interest record created by a previously received Host Interest
Solicitation message with an IP system address equal to the source
address. If the source / destination pair satisfy these conditions then
[Robustness Variable] Receiver Membership Reports are sent out spaced by
[Unsolicited Membership Report Interval] seconds.  If the membership
status changes again for the same destination address and source system
while transmission of Receiver Membership Reports is still pending then
the pending report messages are canceled and a new set of [Robustness
Variable] messages indicating the new state are scheduled.

     When an IP system receives a Receiver Membership Report message,
for each of the TRANSMIT records listed in the message, it creates or
updates a transmission record of the form:

     (router address, source address, multicast address, holdtime timer)

The router address is obtained from the source address on the IP header
of the received message. The source address is obtained from the
destination address of the IP header of the received message. The
multicast address is obtained from the information in the TRANSMIT
record. The holdtime timer is set to the value of the holdtime field in
the received Receiver Membership Report message.

     For each HOLD record present in the message, the system deletes the
matching previously created transmission record from its state.

     The holdtime timer of a record counts down to zero. When the
holdtime timer of a specific transmission record expires, the record is
deleted.

     Note that creation and deletion of transmission records in an IP
system's state may cause local applications to be notified to start and
stop transmitting data (see section 6).






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6.  Application Notification

     This section describes the relation between protocol events and
notifications to source applications within an IP system. The state
machine below is specific to each source address of the IP system and
each multicast destination address. The initial state is the No Info
state.


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

     Figure 1: Per source-address (S) and multicast destination address (G)
     state machine at an IP system

In tabular form, the state-machine is:

+-------------------+---------------------------------------------------+
|                   |                    Prev State                     |
| Event             +----------------+------------------+---------------+
|                   |   No Info      |   Hold           |  Transmit     |
+-------------------+----------------+------------------+---------------+
| New Register      |   -            |   -              |  -            |
|                   |   Start new    |                  |  Start new    |
+-------------------+----------------+------------------+---------------+
|                   |   -> Hold      |   -              |  -            |
| Start Manage      |   Stop ALL     |                  |               |
|                   |   registered   |                  |               |
+-------------------+----------------+------------------+---------------+
|                   |   -            |   -> No Info     |  -> No Info   |
| Stop Manage       |                |   Stop ALL       |               |
|                   |                |   registered     |               |
+-------------------+----------------+------------------+---------------+
|                   |   -            |   -> Transmit    |  -            |
| Recv TRANSMIT     |                |   Start ALL      |               |
|                   |                |   registered     |               |
+-------------------+----------------+------------------+---------------+
| Recv last HOLD    |   -            |   -              |  -> Hold      |
| or timeout        |                |                  |  Stop ALL     |
|                   |                |                  |  registered   |
+-------------------+----------------+------------------+---------------+

The events in the state machine above have the following meaning:


New register
     A new application has registered through a call to



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     IPMulticastSourceRegister for this S and G.


Start manage
     We received a SSM Range option in an MRD packet on the interface
     that S belongs to that changed the status of G from a non-managed
     to a MSNIP-managed destination address.  The SSM Range option is
     only valid in IPv4.


Stop manage
     We received a SSM Range option in an MRD packet on the interface
     that S belongs to that changed the status of G from a MSNIP-managed
     to a non-managed destination address or the mapping state that
     caused this destination address to be managed expired.  The SSM
     Range option is only valid in IPv4.


Receive TRANSMIT
     We received a Receiver Membership Report with S as the IP
     destination address that contains a TRANSMIT record for G.


Receive last HOLD or timeout
     We either received a Receiver Membership Report with S as the IP
     destination address that contains a HOLD record for G or the
     holdtime timer in a transmission record for S and G expired and
     there are no other transmission records for S and G. This means
     that the last router that was reporting receivers no longer does so
     and there are no routers left wishing to receive traffic from this
     S to destination address G.


The state machine actions have the following meaning:


Start new
     Send an IPMulticastSourceStart notification to the application that
     just registered for this S and G.


Start ALL registered
     Send an IPMulticastSourceStart notification to all applications
     that are registered for this S and G.


Stop ALL registered
     Send an IPMulticastSourceStop notification to all applications that



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     are registered for this S and G.

7.  Router Processing

     This section describes the per-source system tracking state machine
operated by each first-hop router. The initial state is No Info.


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

        Figure 2: Per IP source system (S) state machine at a router

In tabular form, the state-machine is:

+----------------------+------------------------------------------------+
|                      |                   Prev State                   |
| Event                +------------------------+-----------------------+
|                      |  Not tracking          |   Tracking            |
+----------------------+------------------------+-----------------------+
|                      |  -> Tracking           |   -                   |
| Receive HIS          |  Set HT to message     |   Set HT to message   |
|                      |  holdtime; Send ALL    |   holdtime; Send ALL  |
|                      |  existing TRANSMITs    |   existing TRANSMITs  |
+----------------------+------------------------+-----------------------+
| HIS timeout          |  -                     |   -> Not tracking     |
|                      |                        |                       |
+----------------------+------------------------+-----------------------+
| Receivers for new    |  -                     |   -                   |
| destination G        |                        |   Send TRANSMIT for   |
|                      |                        |   G                   |
+----------------------+------------------------+-----------------------+
| Receivers of G       |  -                     |   -                   |
| leave                |                        |   Send HOLD for G     |
+----------------------+------------------------+-----------------------+

The events in state machine above have the following meaning:


Receive HIS
     The router has received a Host Interest Solicitation from S.


HIS timeout
     The holdtime timer (HT) in the host interest record associated with
     S has expired.




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Receivers for new destination G
     The routing protocol has informed MSNIP that it now has receivers
     for the MSNIP-managed destination address G and source IP system S.


Receivers of G leave
     The routing protocol has informed MSNIP that all receivers for the
     MSNIP-managed destination address G and source IP system S have
     left the channel.


The state machine actions have the following meaning:


Set HT to message holdtime
     The holdtime timer in the host interest record associated with S is
     restarted to the value of the holdtime field in the received Host
     Interest Solicitation message.


Send ALL existing TRANSMITs
     The router builds and transmits Receiver Membership Reports to S
     that contain a TRANSMIT record for each of the MSNIP-managed
     destination addresses that have receivers for S.


Send TRANSMIT for G
     The router builds and transmits a Receiver Membership Report to S
     that contains a TRANSMIT record for the destination address G.


Send HOLD for G
     The router builds and transmits a Receiver Membership Report to S
     that contains a HOLD record for the destination address G.

8.  Message Formats

     The following packet formats are valid for both IPv4 and IPv6.  IP
version-specific values will be explicitly defined.

     There are two message types of concern to the MSNIP protocol
described in this document:


+-------------------+----------------------------+
| Type Number (hex) | Message Name               |
+-------------------+----------------------------+




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|                   |                            |
| 0xXX              | Host Interest Solicitation |
+-------------------+----------------------------+
| 0xYY              | Receiver Membership Report |
+-------------------+----------------------------+


     Both the Host Interest Solicitation message and the Receiver
Membership Report message MUST not be forwarded by routers (see section
12). The Router Alert option [9] [10] MUST be included in the packet by
the router or host IP system transmitting the message. Routers receiving
Host Interest Solicitation messages and IP systems receiving Receiver
Membership Reports MUST not process a received MSNIP message if the
Router Alert option is not present.


8.1.  Host Interest Solicitation Message

A Host Interest Solicitation message is periodically multicast by MSNIP
capable systems to declare interest in Receiver Membership Reports from
multicast routers on the link. The Host Interest Solicitation message is
multicast with a destination address of ALL_IGMPv3_ROUTERS (224.0.0.22)
or ALL_MLDv2_ROUTERS (TBA).


 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |   Reserved    |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Holdtime            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Type The type field is set to XX (to be assigned by IANA as an IGMP type
     for IPv4 and an ICMPv6 type for IPv6).


Reserved
     Transmitted as zero. Ignored upon receipt.


Checksum
     In IPv4, the Checksum is the 16-bit one's complement of the one's
     complement sum of the whole IGMP message (the entire IP payload).
     In IPv6, the Checksum is the standard ICMPv6 checksum, covering the
     entire MLDv2 message plus a "pseudo-header" of IPv6 header fields
     [5]. For computing the checksum, the Checksum field is set to zero.



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     When receiving packets, the checksum MUST be verified before
     processing a packet.


Holdtime
     The amount of time a receiving router must keep the system interest
     state alive, in seconds. The default value for this field is
     [Interest Solicitation Holdtime].


8.2.  Receiver Membership Report Packet

A Receiver Membership Report packet is unicast by first-hop multicast
routers and targeted at potential sources to inform them of the
existence or not of receivers for the listed multicast destination
addresses.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |   Dest Count  |           Checksum            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Holdtime            |           Reserved            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Record-Type-1 |              Record-Reserved-1                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Destination-Address-1                     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               .                               |
|                               .                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



Type The type field is set to YY (to be assigned by IANA as an IGMP type
     for IPv4 and an ICMPv6 type for IPv6).


Dest Count
     The number of multicast destination address records present in this
     message.


Checksum
     In IPv4, the Checksum is the 16-bit one's complement of the one's
     complement sum of the whole IGMP message (the entire IP payload).
     In IPv6, the Checksum is the standard ICMPv6 checksum, covering the
     entire MLDv2 message plus a "pseudo-header" of IPv6 header fields



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     [5]. For computing the checksum, the Checksum field is set to zero.
     When receiving packets, the checksum MUST be verified before
     processing a packet.


Holdtime
     The amount of time in seconds that the target host must keep alive
     the transmission record state created or updated by the TRANSMIT
     records in this report. The router originating the Receiver
     Membership Report sets this field to the current value of the
     holdtime timer in the system interest record corresponding to the
     target host. As a result Receiver Membership Reports sent in
     response to the reception of a Host Interest Solicitation message
     have their holdtime set to the value of the holdtime field in the
     received HIS message.


Reserved
     Transmitted as zero. Ignored upon receipt.


Record-Type-1
     The type of the first transmission control record in this message.
     Valid values are:


     +-------------+----------------------------------------------+-------+
     | Record Type | Description                                  | Value |
     +-------------+----------------------------------------------+-------+
     | TRANSMIT    | Request to start transmitting to destination | 1     |
     +-------------+----------------------------------------------+-------+
     | HOLD        | Request to stop transmitting to destination  | 2     |
     +-------------+----------------------------------------------+-------+



Reserved
     Transmitted as zero. Ignored upon receipt.


Destination-Address-1
     The multicast destination address of the first record in the
     message.








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8.3.  IPv4 Header Fields

     Like all IGMP messages, MSNIP messages are encapsulated in IPv4
datagrams, with an IP protocol number of 2. MSNIP messages can be
identified from other IGMP messages by the message types listed in
section 8. Every MSNIP message described in this document is sent with
an IP Time-to-Live of 1, and carries an IP Router Alert option [9] in
its IP header.


8.4.  IPv6 Header Fields

     MLD messages are a sub-protocol of the Internet Control Message
Protocol (ICMPv6 [5]). MSNIP messages are identified in IPv6 packets by
the combination of a preceding Next Header value of 58 and by the MLD
message types listed in section 8. All MSNIP messages described in this
document are sent with a link-local IPv6 Source Address (or the
unspecified address, if a valid link-local address is not available), an
IPv6 Hop Limit of 1, and an IPv6 Router Alert option [10] in a Hop-by-
hop Options header.

9.  Constants Timers and Default Values

Robustness Variable
     The Robustness Variable allows tuning for the expected packet loss
     on a network.  If a network is expected to be lossy, the Robustness
     Variable may be increased.  MSNIP is robust to (Robustness Variable
     - 1) packet losses.  The Robustness Variable MUST NOT be zero, and
     SHOULD NOT be one.  Default: 2

Interest Solicitation Interval
     The interval used by MSNIP capable systems between transmissions of
     Host Interest Solicitation messages. Default: 60 secs

Interest Solicitation Holdtime
     The interval inserted in Host Interest Solicitation messages by
     systems to instruct routers how long they should maintain system
     interest state for.  This MUST be ((the Robustness Variable) times
     (the Interest Solicitation Interval) plus (one second)).

Initial Interest Solicitation Interval
     The interval used by systems to send out the initial Host Interest
     Solicitation messages when they first come up. Default: 1 second.

Unsolicited Membership Report Interval
     The interval used by routers to send out a set of Membership Report
     messages when the receiver membership changes for a specific
     system.  Default: 1 second.



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10.  Possible Optimisations

10.1.  Suppressing HIS Messages

     A possible optimisation for MSNIP is to suppress the transmission
of Host Interest Solicitation messages from the source address of an IP
system for which no local application has registered interest. In
addition to conserving bandwidth, not transmitting HIS messages prevents
remote receivers for groups with no matching source application from
creating transmission record state in the host system.

10.2.  Host Stack Filtering

     Legacy applications that have not been coded with MSNIP support can
still be prevented from wasting first-hop link bandwidth by filtering
transmitted packets at the operating system level. Even though such
applications will not register for MSNIP notifications with the host
operating system, if the OS is MSNIP-capable and the application is
transmitting data to an MSNIP-managed group for which there are no
transmit records, the OS can safely filter the packets and not transmit
them on the wire.

     A problem with the filtering approach is that it cannot be combined
with the HIS message suppression optimisation (see section 10.1). If
there are no registered applications in the system and HIS messages are
being suppressed then the first-hop routers will not send any Receiver
Membership Reports to the system. As a result, knowledge of receiver
membership from the presence of transmit records for groups operated by
legacy applications will not exist. It therefore becomes unsafe to
filter packets from legacy applications.

10.3.  Responding to Unexpected IGMP Queries

     Under steady state the router side of the IGMP protocol elects a
single router on each link that is responsible for issuing IGMP Queries.
Routers other than the acting IGMP querier will send an IGMP Query only
if they restart and have no IGMP querier election state or if the active
Querier crashes and a new election takes place.

     MSNIP can take advantage of this mechanism to quickly populate the
host interest records of a new router starting up. When the router comes
up it will issue an IGMP Query in an attempt to be elected as a Querier.
MSNIP-capable hosts will notice that the sender of the Query is not the
acting Querier. They can use this trigger to respond with Host Interest
Solicitation Messages (with transmission randomised over a small
interval) to quickly bring the new router up-to-date.





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10.4.  Host and Router Startup

     When a host operating system is restarted there may be applications
that are started as part of the initialisation process and want to
source IPv4 multicast traffic. It is possible for the applications to
register through MSNIP with the IP subsystem and to start transmitting
multicast data before the host receives the MSNIP-managed range
definition through the SSM Range option of the Multicast Router
Discovery protocol.

     This temporary flooding can be avoided if the host OS holds off
notifying MSNIP-capable applications that they can transmit until it
receives an MRD advertisement and learns the SSM configuration for the
network. This behaviour has the drawback that it is not compatible with
legacy networks with no MRD deployment. In such a network the host OS
has to be able to determine after a configurable period that MRD is not
enabled and hence all multicast applications wishing to source traffic
should be notified to transmit. A good default value for this period is
the MAX_RESPONSE_DELAY of the Multicast Router Discovery protocol [4].

     Late router startup is harder to deal with. Hosts that start up
before the multicast router may time out waiting for an MRD
advertisement and instruct all MSNIP-capable multicast source
applications to transmit data. One way to work around this problem is to
configure the host OS to wait forever for an MRD advertisement before
instructing MSNIP applications to transmit.

11.  Inter-operation with IGMP / MLD Proxying

     MSNIP is intended for use on networks with multicast servers
offering a large number of potential sessions. Although unlikely, it is
possible to deploy such a server behind an IGMP / MLD Proxy [14]. If the
proxy is not MSNIP-aware and does not implement the extensions described
below then sources behind the proxy will default to flooding.

     If a device performing IGMP / MLD Proxying wishes to proxy MSNIP,
it MUST forward MSNIP Host Interest Solicitation messages that are
received on downstream interfaces to its upstream interface.  No special
treatment is required for MSNIP Receiver Membership Reports as they are
unicast to the target host.

     In addition to the forwarding of MSNIP messages, an IGMP proxy MUST
operate the Multicast Router Discovery protocol [3] on all its
downstream interfaces and advertise the MSNIP capability option (section
4.1.1) and SSM address range option (section 4.1.2). The MSNIP
capability option should be advertised on downstream interfaces only if
it is included in MRD messages received on the upstream interface.  The
address range to be included in the SSM Range option MUST be determined



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by MRD and IGMP messages received on the upstream interface of the proxy
according to the rules in section 4.2.

     In addition to the forwarding of MSNIP messages, an MLD proxy MUST
operate the IPv6 Neighbour Discovery protocol. The MSNIP capability
option should be advertised on downstream interfaces when it is included
in IPv6 Neighbour Discovery messages received on the upstream interface.

12.  Security Considerations

     We consider the ramifications of a forged message of each type.  As
described in [1] and [2], IPSEC AH can be used to authenticate IGMP and
MLD messages if desired.


12.1.  Receiver Membership Report attacks

     A DoS attack on a host could be staged through forged Receiver
Membership Report messages. The attacker can send a large number of
reports, each with a large number of TRANSMIT records and a holdtime
field set to a large value. The host will have to store and maintain the
transmission records specified in all of those reports for the duration
of the holdtime. This would consume both memory and CPU cycles in the
host.

     Forged Receiver Membership Report messages from the local network
can be easily traced. There are three measures necessary to defend
against externally forged reports:

     o Routers SHOULD NOT forward Receiver Membership Reports. This is
       easier for a router to accomplish if the report carries the
       Router-Alert option.

     o Hosts SHOULD ignore Receiver Membership Reports without the
       Router-Alert option.

     Note that a remote attack through the multicast routing protocol is
possible. A remote site can originate join state for a large number of
groups that will propagate through MSNIP to the target source host.
Such attacks are considered a more significant problem for the routers
involved and are left up to the routing protocol security.

     HOLD records in forged Receiver Membership Report messages are not
a significant threat as hosts track the individual interests of each
first-hop router separately. Only by forging the source address of the
report message so that is appears to have originated from a real first-
hop router can the attacker cause the source to stop transmitting to a
group that has valid receivers. Such forged messages can be detected by



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the router itself.


12.2.  Host Interest Solicitation attacks

     Forged Host Interest Solicitation messages can have two effects:

     o When non-existent source addresses are used the solicitation
       messages can create unwanted host record state on attached
       routers for the duration of the holdtime specified in the
       message.

     o When a source address corresponding to an existing host is used
       in the forged HIS message, receipt of the message by attached
       routers will cause them to transmit Receiver Membership Reports
       messages for all MSNIP-managed multicast destination addresses
       with receivers for the target host.  Although no additional state
       will be created in routers or hosts from this attack, bandwidth
       and CPU is wasted in both the first-hop routers and the target
       host.

     Just like for the Receiver Membership Report message, attacks using
the Host Interest Solicitation message can be reduced by requiring the
use of the Router-Alert option on the message.


12.3.  MSNIP Managed Range Discovery

     As discussed in [4] it is possible for directly connected systems
to send forged Multicast Router Advertisement messages containing the
SSM Range Discovery option. As the SSM Range Discovery option determines
the MSNIP-managed range under IPv4, such forged messages can temporarily
replace the managed range map with incorrect information in receiving
hosts.  An incorrect mapping can have two effects:

     o Applications using a multicast destination address within the
       real SSM range that have no valid receivers can be tricked into
       thinking that their chosen destination address is no longer an
       SSM address and will therefore start transmitting data.

     o Applications using group addresses outside the valid SSM range
       can be tricked into thinking that they are using an SSM
       destination address and therefore prevented from transmitting
       data.

     The Multicast Router Discovery SSM Range Option specification
suggests that a router receiving a Multicast Router Advertisement with
an inconsistent SSM Range Option log the event to the operator. Such



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logging will enable tracking of this type of attack.


13.  IANA Considerations

     This document introduces the following new types and options that
require allocation by IANA:

     o Two new IGMP messages for Host Interest Solicitation and Receiver
       Membership Report. Each of these messages requires a new IGMP
       type value to be assigned by IANA [13].

     o The new MSNIP Operation option for the Multicast Router Discovery
       protocol. This option requires a new MRD type value to be
       assigned by IANA.

     o The new MSNIP Operation option for the Neighbour Discovery /
       ICMPv6 protocol. This option requires a new NDP / ICMPv6 type
       value to be assigned by IANA.


14.  Acknowledgments

The authors would like to thank Dave Thaler, Jon Crowcroft, Toerless
Eckert, Haixiang He, Pekka Savola and Karen Kimball for their
contribution to this specification.


15.  Normative References

[1] Cain B., Deering S., Fenner W., Kouvelas I. and A. Thyagarajan,
     "Internet Group Management Protocol, Version 3", RFC 3376.

[2] Vida R. and Costa L., "Multicast Listener Discovery Version 2
     (MLDv2) for IPv6", work in progress, <draft-vida-mld-v2-07.txt>,
     June 2003.

[3] Biswas S. and Haberman B., "IGMP Multicast Router Discovery", Work
     In Progress, <draft-ietf-idmr-igmp-mrdisc-10.txt>, January 2003.

[4] Kouvelas I., "Multicast Router Discovery SSM Range Option", work in
     progress, <draft-ietf-magma-mrdssm-03.txt>, June 2003.

[5] Conta A. and Deering S., "Internet Control Message Protocol (ICMPv6)
     for the Internet Protocol Version 6 (IPv6)", RFC 2463.

[6] Narten T., Nordmark E. and Simpson W., "Neighbour Discovery for IP
     Version 6 (IPv6)", RFC 2461.



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[7] Holbrook H. and Cain B., "Source-Specific Multicast for IP", work in
     progress, <draft-ietf-ssm-arch-02.txt>, March 2003.

[8] Kent S. and Atkinson R., "Security Architecture for the Internet
     Protocol.", RFC 2401.

[9] Katz D., "IP Router Alert Option", RFC 2113.

[10] Partridge C. and Jackson A., "IPv6 Router Alert Option", RFC 2711.


16.  Informative References

[11] Fenner W., Handley M., Holbrook H. and Kouvelas I., "Protocol
     Independent Multicast - Sparse Mode (PIM-SM):  Protocol
     Specification (Revised)", Work In Progress, <draft-ietf-pim-sm-
     v2-new-07.txt>, March 2003.

[12] Albanna Z., Almeroth K. and Meyer D., "IANA Guidelines for IPv4
     Multicast Address Allocation", Best Current Practices, <draft-ietf-
     iana-IPv4-mcast-guidelines-00.txt>, 2001.

[13] Fenner W., "IANA Considerations for IGMP",
     http://www.iana.org/assignments/igmp-type-numbers, RFC 3228 (BCP
     57), February 2002.

[14] Fenner W., He H., Haberman B. and Sandick H., "IGMP / MLD-based
     Multicast Forwarding (IGMP / MLD Proxying)" draft-ietf-magma-igmp-
     proxy-02.txt, March 2003.

[15] B. Haberman, D. Thaler, "Unicast-Prefix-based IPv6 Multicast
     Addresses", RFC 3306, August 2002.



















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Authors' Addresses

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


     Brian Haberman
     Caspian Networks
     1 Park Drive, Suite 300
     Research Triangle Park, NC 27709
     brian@innovationslab.net


     Hugh Holbrook
     Cisco Systems
     170 W. Tasman Drive
     San Jose, CA 95134
     holbrook@cisco.com


     Isidor Kouvelas
     Cisco Systems
     170 W. Tasman Drive
     San Jose, CA 95134
     kouvelas@cisco.com



Full Copyright Statement

Copyright (C) The Internet Society (Apr 1 2003). All Rights Reserved.

     This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it or
assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are included
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or references to the Internet Society or other Internet organisations,
except as needed for the purpose of developing Internet standards in
which case the procedures for copyrights defined in the Internet
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languages other than English.




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     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
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NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
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