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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 4541

MAGMA Working Group                                       M. Christensen
Internet Draft                                             mjc@jcaps.com
October 2002                                                  K. Kimball
Expiration Date: April 2003                              Hewlett-Packard


           Considerations for IGMP and MLD snooping switches
                    <draft-ietf-magma-snoop-03.txt>


Status of this Memo

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

Abstract

     This memo describes the requirements for IGMP and MLD snooping
     switches. The requirements for IGMPv2 snooping switches are based
     on best current practices. IGMPv3 and MLDv2 snooping are also cov-
     ered in this draft although we are not aware of any such implemen-
     tations at the time of writing.

     Note that IGMP snooping is related only to IPv4 multicast. Other
     multicast packets, such as IPv6, might be suppressed by the snoop-
     ing functionality if additional care is not taken in the implemen-
     tation.  It is desired not to restrict the flow of non-IPv4 multi-
     casts other than to the degree which would happen as a result of
     regular bridging functions. The same note can be made of MLD snoop-
     ing switches with respect to suppression of IPv4.




Christensen, Kimball, Solensky                                  [Page 1]


RFC DRAFT                                                   October 2002


     Areas which are of relevance to IGMP and MLD snooping switches,
     such as link layer topology changes and Ethernet specific encapsu-
     lation issues, are also considered.

     Interoperability issues that arise between different versions of
     IGMP are not discussed in this document.  Interested readers are
     directed to [IGMPv3] for a thorough description of problem areas.

     This document is intended as an accompanying document to the IGMPv3
     and MLDv2 specifications.


1.  Introduction

     When a packet with a broadcast or multicast destination address is
     received, the switch will forward a copy into each of the remaining
     network segments in accordance with [BRIDGE].  Eventually, the
     packet is made accessible to all nodes connected to the network.

     This approach works well for broadcast packets that are intended to
     be seen or processed by all connected nodes.  In the case of multi-
     cast packets, however, this approach could lead to less efficient
     use of network bandwidth, particularly when the packet is intended
     for only a small number of nodes.  Packets will be flooded into
     network segments where no node has any interest in receiving the
     packet.  While nodes will rarely incur any processing overhead to
     filter packets addressed to unrequested group addresses, they are
     unable to transmit new packets onto the shared media for the period
     of time that the multicast packet is flooded.  In general, signifi-
     cant bandwidth can be wasted by flooding.

     In recent years, a number of commercial vendors have introduced
     products described as "IGMP snooping switches" to the market.
     These devices do not adhere to the conceptual model that provides
     the strict separation of functionality between different communica-
     tions layers in the ISO model, and instead utilize information in
     the upper- level protocol headers as factors to be considered in
     the processing at the lower levels.  This is analogous to the man-
     ner in which a router can act as a firewall by looking into the
     transport protocol's header before allowing a packet to be for-
     warded to its destination address.

     In the case of multicast traffic, an IGMP snooping switch provides
     the benefit of conserving bandwidth on those segments of the net-
     work where no node has expressed interest in receiving packets
     addressed to the group address. This is in contrast to normal
     switch behavior where multicast traffic is typically forwarded on
     all interfaces.



Christensen, Kimball, Solensky                                  [Page 2]


RFC DRAFT                                                   October 2002


     Many switch datasheets state support for IGMP snooping, but no
     requirements for this exist today. It is the authors' hope that the
     information presented in this draft will supply this foundation.

     The requirements presented here are based on the following informa-
     tion sources: The IGMP specifications [RFC112][RFC2236][IGMPv3],
     vendor-supplied technical documents [CISCO], bug reports [MSOFT],
     discussions with people involved in the design of IGMP snooping
     switches, MAGMA mailinglist discussions, and on replies by switch
     vendors to an implementation questionnaire.

     The discussions in this document are based on IGMP which applies to
     IPv4 only. For IPv6 we must use MLD instead. Because MLD is based
     on IGMP we do not repeat the whole discussion and requirements for
     MLD snooping switches. Instead we point out the few cases where
     there is a difference compared to IGMP.


2.  IGMP Snooping Requirements

     The following sections list the requirements for an IGMP snooping
     switch.  The requirement is stated and is supplemented by a discus-
     sion. All implementation discussions are examples only and there
     may well be other ways to achieve the same functionality.


2.1.  Forwarding rules

     The IGMP snooping functionality is here separated into a control
     section (IGMP forwarding) and a data section (Data forwarding).


2.1.1.  IGMP Forwarding Rules

     1)  A snooping switch SHOULD forward IGMP Membership Reports only
         to those ports where multicast routers are attached.  Alterna-
         tively stated: a snooping switch SHOULD NOT forward IGMP Mem-
         bership Reports to ports on which only hosts are attached.  An
         administrative control MAY be provided to override this
         restriction, allowing the report messages to be flooded to
         other ports.

         This is the main IGMP snooping functionality.  Sending member-
         ship reports (as described in IGMP versions 1 and 2) to other
         hosts can result in unintentionally preventing a host from
         joining a specific multicast group.  This is not a problem in
         an IGMPv3-only network because there is no cancellation of IGMP
         Membership reports.



Christensen, Kimball, Solensky                                  [Page 3]


RFC DRAFT                                                   October 2002


         The administrative control allows IGMP Membership Report mes-
         sages to be processed by network monitoring equipment such as
         packet analyzers or port replicators.

         The switch supporting IGMP snooping MUST maintain a list of
         multicast routers and the ports on which they are attached.
         This list can be constructed in any combination of the follow-
         ing ways:

         a)  This list SHOULD be built by the snooping switch sending
             Multicast Router Solicitation messages as described in IGMP
             Multicast Router Discovery [MRDISC].  It MAY also snoop
             Multicast Router Advertisement messages sent by and to
             other nodes.

         b)  The arrival port for IGMP Queries (sent by multicast
             routers) where the source address is not 0.0.0.0.

         c)  Ports explicitly configured by management to be IGMP-for-
             warding ports, in addition to or instead of any of the
             above methods to detect router ports.

     2)  IGMP snooping switches MAY also implement "proxy-reporting" in
         which reports received from downstream hosts are summarized and
         used to build internal membership states as described in
         [PROXY].  The IGMP proxy-reporting switch would then report its
         own state in response to upstream queriers.  If the switch does
         not already have an IP address assigned to it, the source
         address for these reports SHOULD be set to all-zeros.

         An IGMP proxy-reporting switch may act as Querier for the down-
         stream hosts while proxy reporting to the 'real' upstream
         queriers.

         It should be noted that there may be multiple IGMP proxy-
         reporting switches in the network all using the 0.0.0.0 source
         IP address. In this case the switches can be uniquely identi-
         fied through their link layer source MAC address.

         IGMP membership reports MUST NOT be rejected because of a
         source IP address of 0.0.0.0.

     3)  The switch that supports IGMP snooping MUST flood all unrecog-
         nized IGMP messages to all other ports and MUST NOT attempt to
         make use of any information beyond the end of the network layer
         header.

         In addition, earlier versions of IGMP SHOULD interpret IGMP



Christensen, Kimball, Solensky                                  [Page 4]


RFC DRAFT                                                   October 2002


         fields as defined for their versions and MUST NOT alter these
         fields when forwarding the message.  When generating new mes-
         sages, a given IGMP version should set fields to the appropri-
         ate values for its own version.  If any fields are reserved or
         otherwise undefined for a given IGMP version, the fields SHOULD
         be ignored when parsing the message and MUST be set to zeroes
         when new messages are generated by implementations of that IGMP
         version.

     4)  An IGMP snooping switch SHOULD be aware of link layer topology
         changes.  Following a topology change the switch SHOULD initi-
         ate the transmission of a General Query on all ports in order
         to reduce network convergence time.  If the switch is not the
         Querier, it SHOULD use the 'all-zeros' IP Source Address in
         these proxy queries.  When such proxy queries are received,
         they MUST NOT be included in the Querier election process.

     5)  An IGMP snooping switch MUST NOT make use of information in
         IGMP packets where the IP or IGMP headers have checksum or
         integrity errors.  The switch SHOULD NOT flood such packets but
         if it does, it SHOULD take some note of the event (i.e., incre-
         ment a counter).  These errors and their processing are further
         discussed in [IGMPv3], [MLD] and [MLDv2].

     6)  The snooping switch MUST NOT rely exclusively on IGMP announce-
         ments to determine when entries should be removed from the for-
         warding table.  The reason for this is that changes in the
         local topology may cause the snooping switch to fall off the
         path between the router and recipient system.  As a result, the
         switch cannot be assured of seeing an annoucement message asso-
         ciated with the recipient leaving the group.



2.1.2.  Data Forwarding Rules

     1)  Packets with a destination IP (DIP) address in the 224.0.0.X
         range which are not IGMP MUST be forwarded on all ports.

         This requirement is based on fact that many hosts exist today
         which do not Join IP multicast addresses in this range before
         sending or listening to IP multicasts.  Furthermore since the
         224.0.0.X address range is defined as link local (not to be
         routed) it seems unnecessary to keep state for each address in
         this range.  Additionally, some vendors' applications, which
         are not IGMP, use this 224.0.0.X address range, and these
         applications would break if the switch were to prune them due
         to not seeing a Join.



Christensen, Kimball, Solensky                                  [Page 5]


RFC DRAFT                                                   October 2002


     2)  Packets with a destination IP address outside 224.0.0.X which
         are not IGMP SHOULD be forwarded according to group-based port
         membership tables and MUST also be forwarded on router ports.

         This is the core IGMP snooping requirement for the data path.

         Discussion: An implementation could maintain separate member-
         ship and multicast router tables in software and then "merge"
         these tables into a current forwarding cache.

     3)  If a switch receives a non-IGMP IPV4 multicast packet without
         having first processed Membership Reports for the group
         address, it MAY forward the packet on all ports, but it MUST
         forward the packet on router ports.  A switch MAY forward an
         unregistered packet only on router ports, but the switch MUST
         have a configuration option that suppresses this restrictive
         operation and forces flooding of unregistered packets on all
         ports.  In environments with v3 hosts where the snooping switch
         does not support v3, failure to flood unregistered streams
         could prevent v3 hosts from receiving their traffic.  Alterna-
         tively, in environments where the snooping switch supports all
         of the IGMP versions that are present, flooding unregistered
         streams may cause IGMP hosts to be overwhelmed by multicast
         traffic, even to the point of not receiving Queries and failing
         to issue new membership reports for their own groups.

     4)  All non-IPv4 multicast packets SHOULD be flooded, except where
         normal IEEE bridging operation would result in filtering multi-
         cast packets.  Discussion: This ensures that enabling IGMP
         snooping does not break, for example, IPv6 multicast.

     5)  IGMP snooping switches MAY maintain forwarding tables based on
         either MAC addresses or IP addresses.  If a switch supports
         both types of forwarding tables then the default behavior
         SHOULD be to use IP addresses.

         Discussion: Forwarding based on MAC addresses is subject to the
         problem associated with the 32-fold IP address to 1 MAC address
         mapping.

     6)  Switches which rely on information in the IP header SHOULD ver-
         ify that the IP header checksum is correct.  If the checksum
         fails, the information in the packet MUST NOT be incorporated
         into the forwarding table.  Further, the packet SHOULD be dis-
         carded.

     7)  The "include source" and "exclude source" options in IGMPv3 do
         not work on shared segments. These options are used to register



Christensen, Kimball, Solensky                                  [Page 6]


RFC DRAFT                                                   October 2002


         for multicast traffic only from certain senders, or from all
         except certain senders.  On shared segments, if one host has
         registered to receive a multicast data stream but has used the
         "include source" or "exclude source" option, any additional
         hosts that later request membership for that same multicast
         group must accept the restrictions issued in the first host's
         request.


2.2.  IGMP snooping related problems

     A special problem arises in networks consisting of IGMPv3 routers
     as well as IGMPv2 and IGMPv3 hosts interconnected by an IGMPv2
     snooping switch.  The router will continue to maintain IGMPv3 even
     in the presence of IGMPv2 hosts, and thus the network will not
     likely converge on IGMPv2. But it is likely that the IGMPv2 snoop-
     ing switch will not recognize or process the IGMPv3 membership
     reports.  Groups for these unrecognized reports will then either be
     flooded (with all of the problems that may create for hosts in a
     network with a heavy multicast load) or pruned by the snooping
     switch.

     Therefore it is recommended that in such a network, the multicast
     router be configured to use IGMPv2.


3.  IPv6 Considerations

     In order to avoid confusion, the previous discussions have been
     based on the IGMP protocol which only applies to IPv4 multicast.
     In the case of IPv6 most of the above discussions are still valid
     with a few exceptions which we will describe here.

     The control and data forwarding rules in the IGMP section can with
     a few considerations also be applied to MLD. This means that the
     basic functionality of intercepting MLD packets, building member-
     ship lists and multicast router lists is the same as for IGMP.

     In IPv6, the data forwarding rules are more straight forward
     because MLD is mandated for addresses with scope 2 (link-scope) or
     greater. The only exception is the address FF002::1 which is the
     all hosts link-scope address for which MLD messages are never sent.
     Packets with the all hosts link-scope address should be forwarded
     on all ports.

     MLD messages are also not sent to packets in the address range
     FF00X::/16 when X is 0 or 1 which are reserved and node-local
     respectively, and these addresses should never appear in packets on



Christensen, Kimball, Solensky                                  [Page 7]


RFC DRAFT                                                   October 2002


     the link.

     The three main differences between IPv4 and IPv6 in relation to
     multicast are:

     -  The IPv6 protocol for multicast group maintenance is called Mul-
        ticast Listener Discovery (MLDv2). MLDv2 uses ICMPv6 message
        types instead of IGMP message types.

     -  The ethernet encapsulation is a mapping of 32 bits of the 128
        bit DIP addresses into 48 bit DMAC addresses [IPENCAPS].

     -  Multicast router discovery is done using Neighbor Discovery Pro-
        tocol (NDP) for IPv6. NDP uses ICMPv6 message types.

     The IPv6 packet header does not include a checksum field.  Never-
     theless, the switch SHOULD detect other packet integrity issues.
     When the snooping switch detects such an error, it MUST NOT include
     information from the corresponding packet in the MLD forwarding ta-
     ble.  The forwarding code SHOULD drop the packet and take further
     reasonable actions as advocated above.

     The fact that MLDv2 is using ICMPv6 adds new requirements to a
     snooping switch because ICMPv6 has multiple uses aside from MLD.
     This means that it is no longer sufficient to detect that the next-
     header field of the IP header is ICMPv6 in order to identify pack-
     ets relevant for MLD snooping.

     Discussion: If an implementation was software based, wrongly iden-
     tifying non-MLD packets as candidates for MLD snooping, would
     potentially fill the CPU queue with irellevant packets thus pre-
     venting the snooping functionality. Furthermore, ICMPv6 packets
     destined for other hosts would not reach their destinations.

     A solution is either to require that the snooping switch looks fur-
     ther into the packets, or to be able to detect a multicast DMAC
     address in conjunction with ICMPv6.  The first solution is desir-
     able only if it is configurable which message types should trigger
     a CPU redirect and which should not. The reason is that a hardcod-
     ing of message types is unflexible for the introduction of new mes-
     sage types.  The second solution introduces the risk of new proto-
     cols, which are not related to MLD but use ICMPv6 and multicast
     DMAC addresses, wrongly being identified as MLD. It is suggested
     that solution one is the preferred if the switch is capable of
     triggering CPU redirects on individual ICMPv6 message types.  If
     this is not the case, then use solution two.

     The mapping from IP multicast addresses to multicast DMAC addresses



Christensen, Kimball, Solensky                                  [Page 8]


RFC DRAFT                                                   October 2002


     introduces a potentially enormous overlap. The structure of an IPv6
     multicast address is shown in the figure below.  Theoretically
     2**80, two to the power of 80 (128 - 8 - 4 - 4 - 32) unique DIP
     addresses could map to one DMAC address. This should be compared to
     2**5 in the case of IPv4.

     Initial allocation of IPv6 multicast addresses, however, uses only
     the lower 32 bits of group ID. This eliminates the address ambigu-
     ity for the time being, but it should be noted that the allocation
     policy may change in the future. Because of the potential overlap
     it is recommended that IPv6 address based forwarding is preferred
     to MAC address based forwarding.


       |   8    |  4 |  4 |             112 bits                  |
       +--------+----+----+---------------------------------------+
       |11111111|flgs|scop|             group ID                  |
       +--------+----+----+---------------------------------------+



4.  Security Considerations

     Security considerations for IGMPv3 are accounted for in [IGMPv3].
     The introduction of IGMP snooping switches adds the following con-
     siderations with regard to IP multicast.

     The exclude source failure which could cause traffic from sources
     that are 'black listed' to reach hosts that have requested other-
     wise.  This can also occur in certain network topologies without
     IGMP snooping.

     It is possible to generate packets which make the switch wrongly
     believe that there is a multicast router on the segment on which
     the source is attached. This will potentially lead to excessive
     flooding on that segment.  The authentication methods discussed in
     [IGMPv3] will also provide protection in this case.

     IGMP snooping switches which rely on the IP header of a packet for
     their operation and which do not validate the header checksum
     potentially will forward packets on the wrong ports. Even though
     the IP headers are protected by the ethernet checksum this is a
     potential vulnerability.

     Generally though, it is worth it to stress that IP multicast must
     so far be considered insecure until the work of for example the
     suggested Multicast Security (MSEC) working group or similar is
     completed or at least has matured.



Christensen, Kimball, Solensky                                  [Page 9]


RFC DRAFT                                                   October 2002


5.  IGMP Questionnaire

     As part of this work the following questions were asked both on the
     MAGMA discussion list and sent to known switch vendors implementing
     IGMP snooping.  The individual contributions have been anonymized
     upon request and do not necessarily apply to all of the vendors'
     products.

     The questions were:

     Q1  Does your switches perform IGMP Join aggregation?  In other
         words, are IGMP joins intercepted, absorbed by the hard-
         ware/software so that only one Join is forwarded to the
         querier?

     Q2  Is multicast forwarding based on MAC addresses?  Would data-
         grams addressed to multicast IP addresses 224.1.2.3 and
         239.129.2.3 be forwarded on the same ports-groups?

     Q3  Is it possible to forward multicast datagrams based on IP
         addresses (not routed)? In other words, could 224.1.2.3 and
         239.129.2.3 be forwarded on different port-groups with unal-
         tered TTL?

     Q4  Are multicast datagrams within the range 224.0.0.1 to
         224.0.0.255 forwarded on all ports whether or not IGMP Joins
         have been sent?

     Q5  Are multicast frames within the MAC address range
         01:00:5E:00:00:01 to 01:00:5E:00:00:FF forwarded on all ports
         whether or not IGMP joins have been sent?

     Q6  Does your switch support forwarding to ports on which IP multi-
         cast routers are attached in addition to the ports where IGMP
         Joins have been received?

     Q7  Is your IGMP snooping functionality fully implemented in hard-
         ware?

     Q8  Is your IGMP snooping functionality partly software imple-
         mented?

     Q9  Can topology changes (for example spanning tree configuration
         changes) be detected by the IGMP snooping functionality so that
         for example new queries can be sent or tables can be updated to
         ensure robustness?





Christensen, Kimball, Solensky                                 [Page 10]


RFC DRAFT                                                   October 2002


     The answers were:

          ---------------------------+-----------------------+
                                     |     Switch Vendor     |
          ---------------------------+---+---+---+---+---+---+
                                     | 1 | 2 | 3 | 4 | 5 | 6 |
          ---------------------------+---+---+---+---+---+---+
          Q1 Join aggregation        | x | x | x |   | x | x |
          Q2 Layer-2 forwarding      | x | x | x | x |(1)|   |
          Q3 Layer-3 forwarding      |(1)|   |(1)|   |(1)| x |
          Q4 224.0.0.X aware         |(1)| x |(1)|(2)| x | x |
          Q5 01:00:5e:00:00:XX aware | x | x | x |(2)| x | x |
          Q6 Mcast router list       | x | x | x | x | x | x |
          Q7 Hardware implemented    |   |   |   |   |   |   |
          Q8 Software assisted       | x | x | x | x | x | x |
          Q9 Topology change aware   | x | x | x | x |   |(2)|
          ---------------------------+---+---+---+---+---+---+
           x  Means that the answer was Yes.
          (1) In some products (typically high-end) Yes, in others No.
          (2) Currently no, but will be really soon.


6.  IETF IPR Statement



     "The IETF takes no position regarding the validity or scope of any
     intellectual property or other rights that might be claimed to
     pertain to the implementation or use of the technology described in
     this document or the extent to which any license under such rights
     might or might not be available; neither does it represent that it
     has made any effort to identify any such rights.  Information on
     the IETF's procedures with respect to rights in standards-track and
     standards-related documentation can be found in BCP-11.  Copies of
     claims of rights made available for publication and any assurances
     of licenses to be made available, or the result of an attempt made
     to obtain a general license or permission for the use of such pro-
     prietary rights by implementors or users of this specification can
     be obtained from the IETF Secretariat."


7.  References


     [BRIDGE]   IEEE 802.1D, "Media Access Control (MAC) Bridges"

     [CISCO]    Cisco Tech Notes, "Multicast In a Campus Network: CGMP
                and IGMP snooping",



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RFC DRAFT                                                   October 2002


                http://www.cisco.com/warp/public/473/22.html

     [IANA]     Internet Assigned Numbers Authority, "Internet Multicast
                Addresses", http://www.isi.edu/in-notes/iana/assign-
                ments/multicast-addresses

     [IGMPv3]   Cain, B., "Internet Group Management Protocol, Version
                3", draft-ietf-idmr-igmp-v3-11.txt, May 2002.

     [IPENCAPS] Crawford, M., "Transmission of IPv6 Packets over Ether-
                net Networks", RFC2464, December 1998.

     [MLD]      Deering, S., Fenner, B., and Haberman, B.  "Multicast
                Listener Discovery (MLD) for IPv6", RFC2710, October
                1999.

     [MLDv2]    Vida, R., "Multicast Listener Discovery Version 2
                (MLDv2) for IPv6", draft-vida-mld-v2-03.txt, June 2002.

     [MRDISC]   Biswas, S.  "IGMP Multicast Router Discovery", draft-
                ietf-idmr-igmp-mrdisc-08.txt, January 2002.

     [MSOFT]    Microsoft support article Q223136, "Some LAN Switches
                with IGMP Snooping Stop Forwarding Multicast Packets on
                RRAS Startup", http://support.microsoft.com/sup-
                port/kb/articles/Q223/1/36.ASP

     [PROXY]    Fenner, B. et al, "IGMP-based Multicast Forwarding (IGMP
                Proxying)", draft-ietf-magma-igmp-proxy-01.txt, July
                2002.

     [RFC1112]  Deering, S., "Host Extensions for IP Multicasting", RFC
                1112, August 1989.

     [RFC2026]  Bradner, S.  "The Internet Standards Process -- Revision
                3", RFC2026, October 1996.

     [RFC2236]  Fenner, W., "Internet Group Management Protocol, Version
                2", RFC2236, November 1997.

     [RFC2375]  Hinden, R.  "IPv6 Multicast Address Assignments",
                RFC2375, July 1998.


8.  Acknowledgements

     We would like to thank Martin Bak, Les Bell, Yiqun Cai, Ben Carter,
     Paul Congdon, Toerless Eckert, Bill Fenner, Brian Haberman, Edward



Christensen, Kimball, Solensky                                 [Page 12]


RFC DRAFT                                                   October 2002


     Hilquist, Hugh Holbrook, Kevin Humphries, Suzuki Shinsuke, Jaff
     Thomas and Rolland Vida for comments and suggestions on this docu-
     ment.

     Furthermore, the following companies are acknowledged for their
     contributions: 3Com, Alcatel, Cisco Systems, Enterasys Networks,
     Hewlett-Packard, Vitesse Semiconductor Corporation.  The ordering
     of these names do not necessarily correspond to the column numbers
     in the response table.


9.  Revision History
     This section, while incomplete, is provided as a convenience to the
     working group members.  It will be removed when the document is
     released in its final form.



     draft-ietf-magma-snoop-03.txt: October 2002

     IGMP Forwarding rules:
          Add references to and become consistant with the current IGMP
          proxy draft,

          Unrecognized IGMP packets should not be ignored because "mbz"
          fields are not zero since packets from future versions are
          expected to maintain consistency.

          Corrections related to IGMP Querier election process.

          Include discussion about aging out entries from the internal
          forwarding table.

          Add clarification to how lists of router ports may be assem-
          bled.

     Data Forwarding rules:
          Added discussion of the problems for different IGMP environ-
          ments in choosing whether to flood or to prune unregistered
          multicasts.

          Added refinements for how to handle NON-IPv4 multicasts, to
          keep IGMP-snooping functionality from interfering with IPv6
          and other multicast traffic. Any filtering for non-IPv4 multi-
          casts should be based on bridge behavior and not IGMP snooping
          behavior.

     IGMP snooping related problems:



Christensen, Kimball, Solensky                                 [Page 13]


RFC DRAFT                                                   October 2002


          Fixed description of interoperability issues in environments
          with v3 routers and hosts, and v2 snooping switches.

          Added discussion of the IGMPv3 "include source" and "exclude
          source" options, and the inability to support them on shared
          segments.

     IPv6 Considerations:
          Clarifications regarding address ranges FF00::, FF01:: and all
          hosts FF02::1 in relation to data forwarding.


     draft-ietf-magma-snoop-02.txt: June 2002

          Status section removes document history; moved into this sec-
          tion instead.

          Introduction restores text from the -00 revision that
          describes snooping and its goals

          IGMP flooding rules eased, allowing management option to
          broaden beyond "routers only".

          Removed a SHOULD/MAY inconsistancy between IPv4 Forwarding and
          IPv6 processing of checksums.

          IGMP Forwarding Rules: clarify text describing processing of
          non-zero reserved fields.

          Data Forwarding Rules, item 3 is changed from "MUST forward to
          all ports" to "MAY"; item 4 default changes from "MUST" to
          "SHOULD use network addresses".

          Added two sets of additional responses to the questionnaire
          and text indicating that responses don't cover all products.

          Removed (commented out) description of IPR issues: IESG is
          aware of them.

     draft-ietf-magma-snoop-01.txt: January 2002

          Extensive restructuring of the original text.


     draft-ietf-idmr-snoop-01.txt:  2001

          Added several descriptions of cases where IGMP snooping imple-
          mentations face problems. Also added several network topology



Christensen, Kimball, Solensky                                 [Page 14]


RFC DRAFT                                                   October 2002


          figures.

     draft-ietf-idmr-snoop-00.txt: 2001

          Initial snooping draft. An overview of IGMP snooping and the
          problems to be solved.



     10.  Author's Addresses

          Morten Jagd Christensen
          jCAPS
          email: mjc@jcaps.com

          Karen Kimball
          Hewlett-Packard
          email: karen.kimball@hp.com

          Frank Solensky
          email: solenskyf@acm.org






























Christensen, Kimball, Solensky                                 [Page 15]


RFC DRAFT                                                   October 2002


                                Table of Contents


          1. Introduction  . . . . . . . . . . . . . . . . . . . . .   2
          2. IGMP Snooping Requirements  . . . . . . . . . . . . . .   3
          2.1. Forwarding rules  . . . . . . . . . . . . . . . . . .   3
          2.1.1. IGMP Forwarding Rules . . . . . . . . . . . . . . .   3
          2.1.2. Data Forwarding Rules . . . . . . . . . . . . . . .   5
          2.2. IGMP snooping related problems  . . . . . . . . . . .   7
          3. IPv6 Considerations . . . . . . . . . . . . . . . . . .   7
          4. Security Considerations . . . . . . . . . . . . . . . .   9
          5. IGMP Questionnaire  . . . . . . . . . . . . . . . . . .  10
          6. IETF IPR Statement  . . . . . . . . . . . . . . . . . .  11
          7. References  . . . . . . . . . . . . . . . . . . . . . .  11
          8. Acknowledgements  . . . . . . . . . . . . . . . . . . .  12
          9. Revision History  . . . . . . . . . . . . . . . . . . .  13
          10. Author's Addresses . . . . . . . . . . . . . . . . . .  15


































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