wdiff draft-ietf-magma-snoop-02.txt draft-ietf-magma-snoop-03.txt

MAGMA Working Group M. Christensen
Internet Draft morten@jagd-christensen.com
June mjc@jcaps.com
October 2002 F. Solensky K. Kimball
Expiration Date: December 2002 Premonitia April 2003 Hewlett-Packard

Considerations for IGMP and MLD snooping switches
<draft-ietf-magma-snoop-02.txt>
<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¡ 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¡ cov-
ered in this draft although we are not aware of any such implemen¡ 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.

RFC DRAFT October 2002

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

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

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

11.. IInnttrroodduuccttiioonn

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¡ 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.

The problem of wasting bandwidth is even worse when the LAN segment
is not shared, for example in Full Duplex links. Full Duplex is
standard today for most switches operating at 1Gbps or above. In
this case the general, signifi-
cant bandwidth that is can be wasted is proportional to the num¡
ber of attached nodes. 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¡ communica-
tions layers in the ISO model model, and instead utilizes utilize information in
the upper upper- level protocol headers as factors to be considered in
the processing at the lower levels. This is analogous to the manner 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 forwarded 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¡ net-
work where no node has expressed interest in receiving packets
addressed to the group address. This is in contrast to normal
switch behaviour behavior where multicast traffic is typically forwarded on
all interfaces.

RFC DRAFT October 2002

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

The requirements presented here is are based on the following informa¡ informa-
tion sources: The IGMP specifications [RFC112][RFC2236][IGMPv3],
vendor supplied
vendor-supplied technical documents [CISCO], bug reports [MSOFT],
discussions with people invovled 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.

22.. IIGGMMPP SSnnooooppiinngg RReeqquuiirreemmeennttss

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¡ discus-
sion. All implementation discussions are examples only and there
may well be other ways to achieve the same functionality.

22..11.. FFoorrwwaarrddiinngg rruulleess

2.1. Forwarding rules

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

22..11..11.. IIGGMMPP FFoorrwwaarrddiinngg RRuulleess

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¡ Alterna-
tively stated: A a snooping switch SHOULD NOT forward IGMP Mem¡ 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¡ 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 IGMPv3-only network because there is no cancellation of IGMP
Membership reports.

RFC DRAFT October 2002

The administrative control allows IGMP Membership Report mes¡ mes-
sages to be processed by network monitoring equipment such as
packet analysers 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¡ follow-
ing ways:

a) This list SHOULD be built using IGMP Multicast Router Dis¡
covery [MRDISC] by the snooping switch sending
Multicast Router Solicitation messages on its own. 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 where the address is not 0.0.0.0.

c) A list of ports Ports explicitly configured by management as described to be IGMP-for-
warding ports, in addition to or instead of any of the previous step.
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].
An The IGMP proxy-reporting switch would then report its
own state in response to upstream queriers. If the switch does
not
alreay already have an IP address it SHOULD use assigned to it, the address 0.0.0.0 as source in
address for these reports. reports SHOULD be set to all-zeros.

An IGMP proxy-reporting switch may act as Querier for the down¡ 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¡ 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; however, these messages MUST NOT
be included the election process so that a snooping switch does
not elected over an active router. 0.0.0.0.

3) The switch that supports IGMP snooping MUST flood all unrecog¡ 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 particular, messages where any reserved addition, earlier versions of IGMP SHOULD interpret IGMP

RFC DRAFT October 2002

fields in as defined for their versions and MUST NOT alter these
fields when forwarding the message. When generating new mes-
sages, a given IGMP header version should set fields to the appropri-
ate values for its own version. If any fields are non-zero reserved or
otherwise undefined for a given IGMP version, the fields SHOULD
be ignored when parsing the message and MUST NOT be subject to "normal"
snooping since this could indicate an incompatible change set to
the zeroes
when new messages are generated by implementations of that IGMP message format.
version.

4) An IGMP snooping switch SHOULD be aware of link layer topology
changes. Following a topology change the switch SHOULD initi¡ 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
intregity
integrity errors. The switch SHOULD NOT flood such packets but
if it does, it SHOULD take some note of the event (i.e.: incre¡ (i.e., incre-
ment a counter). These errors and their processing are further
discussed in [IGMPv3], [MLD] and [MLDv2].

22..11..22.. DDaattaa FFoorrwwaarrddiinngg RRuulleess

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, today
which does do not Join IP multicast addresses in this range before
sending or listening to IP multicast. 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.

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 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¡ 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 config¡
uration 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¡ 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¡ dis-
carded.

22..22.. IIGGMMPP ssnnooooppiinngg rreellaatteedd pprroobblleemmss

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

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 arise arises in the network networks consisting of IGMPv3 routers
as well as IGMPv2 and IGMPv3 hosts interconnected by a an IGMPv2
snooping switch. IGMPv3 has a mechanism to fall back The router will continue to maintain IGMPv3 even
in the presence of IGMPv2
when receiving IGMPv2 membership reports. This means that hosts, and thus the net¡
work network will converged not
likely converge on IGMPv2. But it is likely that the IGMPv2 eventually. However, snoop-
ing switch will not recognize or process the convergence
time IGMPv3 membership
reports. Groups for these unrecognized reports will lead to supression then either be
flooded (with all of v3 Hosts the problems that may create for several minutes. 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 is be configured to use IGMPv2.

33.. IIPPvv66 CCoonnssiiddeerraattiioonnss

3. IPv6 Considerations

In order to avoid confusion, the previous discussions have been
based on IGMPv3 functionality 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.

In IPv6

The control and data forwarding rules in the protocol for 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 group maintenance router lists is called Mul¡
ticast Listener Discovery (MLDv2). IPv6 the same as for IGMP.

In IPv6, the data forwarding rules are more straight forward
because MLD is not widely deployed
today and neither mandated for addresses with scope 2 (link-scope) or
greater. The only exception is IPv6 multicast. However, it the address FF002::1 which is anticipated
that at some time IPv6 switches capable of the
all hosts link-scope address for which MLD snooping will
appear. 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

RFC DRAFT October 2002

the link.

The three main differences between IGMPv3 IPv4 and MLDv2 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¡ Pro-
tocol (NDP) for IPv6. NDP uses ICMPv6 message types.

The IPv6 packet header does not include a checksum field. Never¡ 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 IGMP MLD forwarding
table. 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 redirect pack¡ identify pack-
ets to the CPU. relevant for MLD snooping.

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

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

The mapping from IP multicast addresses to multicast DMAC addresses

RFC DRAFT October 2002

introduces a potentially enormous overlap. The structure of an IPv6
multicast address is shown in the figure 5. 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¡ ambigu-
ity for the time being 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 |
+--------+----+----+---------------------------------------+
Figure 5

In the case of IPv6 forwarding can be made on the basis of DMAC
addresses in the forseable future.

Finally, we mention the reserved address range FF02::/96. This
range is similar to 224.0.0.X for IPv4 and is reserved to routing
protocols and resource discovery [RFC2375]. In the case of IPv6 it
is suggested that packets in this range are forwarded on all ports
if they are not MLD packets.

44.. SSeeccuurriittyy CCoonnssiiddeerraattiioonnss

4. Security Considerations

Security considerations for IGMPv3 are accounted for in [IGMPv3].
The introduction of IGMP snooping switches adds the following con¡ 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¡ 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 sug¡
gested
suggested Multicast Security (MSEC) working group or similar is com¡
pleted
completed or at least has matured.

55.. IIGGMMPP QQuueessttiioonnnnaaiirree

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¡ hard-
ware/software so that only one Join is forwarded to the
querier?

Q2 Is multicast forwarding based on MAC addresses? Would data¡ 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). routed)? In other words, could 224.1.2.3 and
239.129.2.3 be forwarded on different port-groups with unal¡ 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¡ 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¡ hard-
ware?

Q8 Is your IGMP snooping functionality partly software imple¡ 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?

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 real really soon.

66.. RReeffeerreenncceess

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", http://www.cisco.com/warp/pub¡
lic/473/22.html

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¡ 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¡ 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¡ 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-proxy-02(?).txt. 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.

77.. AAcckknnoowwlleeddggeemmeennttss

8. Acknowledgements

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

RFC DRAFT October 2002

Hilquist, Hugh Holbrook, Kevin Humphries, Karen Kimball and Suzuki Shinsuke, Jaff
Thomas and Rolland Vida for comments and suggestions on this document. 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.

88.. RReevviissiioonn HHiissttoorryy

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-01.txt: January

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

Extensive restructuring

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 original text. 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:

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¡ 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.

The next revision:

In the interest of getting this version of the draft released
before the deadline (less than seven hours from the moment
this paragraph is being typed), we briefly summarize some

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

Extensive restructuring of the comments on the previous version that need to be included
in the next one. We believe that other comments have been
addressed in this draft; please let the authors know if this
they have either not been included or need to be corrected.

IGMP Forwarding rules:

Add a reference to and become consistant with the next
revision original text.

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

Added several descriptions of the cases where IGMP proxy draft,

In item 'b': include a description on how the switch
determines that a Query came from the router and not
another switch. Is there some way to make this distinc¡
tion beyond the source address?

Proxy reporting: further analysis of the impact on the
election process when using 0.0.0.0 as the source address
in membership report messages. snooping imple-
mentations face problems. Also consider the case
where the switch assumes the role added several network topology

RFC DRAFT October 2002

figures.

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

Initial snooping draft. An overview of Querier when no
routers are detected IGMP snooping and forfeits the role as soon as one
is announced.

Include some discussion about how entries are to be aged
from the list, perhaps similar to spanning tree algorithm
for unicast MAC address processing.

Data Forwarding rules:

Link-local range to mention the problem is due to routing
protocols not sending Report Messages for their respec¡
tive multicast addresses.

Expand discussion of non-IGMP packet forwarding for data
that matches an IGMPv3 record. Do snooping switches add
intelligence
problems to recognize SSM versus ASM groups?

IPv6 Considerations:

Is having MLD a subset of ICMPv6 an issue? Should MLDv2 be a separate protocol?

Add reference to ICMPv6 specification for message pro¡
cessing rules.

99.. AAuutthhoorr''ss AAddddrreesssseess solved.

10. Author's Addresses

Morten Jagd Christensen
jCAPS
email: mjc@jcaps.com

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

Frank Solensky
Premonitia, Inc.
1 Nanog Park
Acton, MA 01720
email: fsolensky@premonitia.com
TTaabbllee ooff CCoonntteennttss solenskyf@acm.org

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 . . . . . . . . . . . . . . 6 7
3. IPv6 Considerations . . . . . . . . . . . . . . . . . . . . 6 7
4. Security Considerations . . . . . . . . . . . . . . . . . . 8 9
5. IGMP Questionnaire . . . . . . . . . . . . . . . . . . 10
6. IETF IPR Statement . . . 8
6. References . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . 11
8. Revision History . . . . . . . . . 12
9. Revision History . . . . . . . . . . . . . 11
9. Author's Addresses . . . . . . 13
10. Author's Addresses . . . . . . . . . . . . . . . 13 . . . 15