Network Working Group M. Christensen
Internet Draft Thrane & Thrane
Expiration Date: July 2003 K. Kimball
Category: Informational Hewlett-Packard
F. Solensky
Bluejavelin
January 2003
Considerations for IGMP and MLD snooping switches
<draft-ietf-magma-snoop-05.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].
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Abstract
This memo describes the requirements for IGMP- and MLD-snooping
switches. These are based on best current practices for IGMPv2,
with further considerations for IGMPv3- and MLDv2-snooping. Addi-
tional areas of relevance, such as link layer topology changes and
Ethernet-specific encapsulation issues, are also considered.
Interoperability issues that arise between different versions of
IGMP are not the focus of this document. Interested readers are
directed to [IGMPv3] for a thorough description of problem areas.
This document is intended to accompany the IGMPv3 and MLDv2
Christensen, et al. [Page 1]
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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.
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 founda-
tion.
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],
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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
only to IPv4. For IPv6, MLD must be used instead. Because MLD is
based on IGMP, we do not repeat the whole discussion and require-
ments for MLD snooping switches. Instead, we point out the few
cases where there are differences from IGMP.
Note that the IGMP snooping function should apply only to IPv4 mul-
ticasts. Other multicast packets, such as IPv6, might be suppressed
by IGMP snooping if additional care is not taken in the implementa-
tion. 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.
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
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an IGMPv3-only network because there is no cancellation of IGMP
Membership reports.
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
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header.
In addition, earlier versions of IGMP should interpret IGMP
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 group
leave announcements to determine when entries should be removed
from the forwarding table. The snooping switch should imple-
ment a membership timeout feature to ensure unneeded forwarding
table entries will be appropriately removed if downstream mem-
bers silently leave the group or become unavailable for any
reason. If the switch implements this timeout behavior, it must
have a feature to override it if the switch is also configured
to forward unregistered multicast packets on all ports. Addi-
tionally, if timeout is implemented, a group's forwarding table
entry should be removed from a port when no IGMP report has
been received for [(Query Interval x Number of Queries) + Query
Response Time] seconds. These variables may be learned dynami-
cally but IGMP snooping switches implementing timeout should
have a configuration option that allows these variables to be
set manually.
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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.
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
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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) When IGMPv3 "include source" and "exclude source" membership
reports are received on shared segments, the switch needs to
forward the superset of all received membership reports onto
the shared segment. Forwarding of traffic from a particular
source S to a group G must happen if at least one host on the
shared segment reports an IGMPv3 membership of the type
INCLUDE(G, Slist1) or EXCLUDE(G, Slist2) where S is an element
of Slist1 and not an element of Slist2.
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.
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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, and building mem-
bership 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 FF02::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
FF0X::/16 when X is 0 or 1 (which are reserved and node-local,
respectively), and these addresses should never appear in packets
on 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 poten-
tially fill the CPU queue with irrelevant packets thus preventing
the snooping functionality. Furthermore, ICMPv6 packets destined
for other hosts would not reach their destinations.
Christensen, et al. [Page 8]
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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 inflexible for the introduction of new mes-
sage types. The second solution introduces the risk of new proto-
cols which use ICMPv6 and multicast DMAC addresses but which are
not related to MLD, wrongly being identified as MLD. It is sug-
gested that solution one is 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
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. Normative References
[BRIDGE] IEEE 802.1D, "Media Access Control (MAC) Bridges"
[IGMPv3] Cain, B., "Internet Group Management Protocol, Version
3", RFC3376, October 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.
Christensen, et al. [Page 9]
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[MLDv2] Vida, R., "Multicast Listener Discovery Version 2
(MLDv2) for IPv6", draft-vida-mld-v2-06.txt, November
2002.
[MRDISC] Biswas, S. "IGMP Multicast Router Discovery", draft-
ietf-idmr-igmp-mrdisc-10.txt, January 2003.
[PROXY] Fenner, B. et al, "IGMP-based Multicast Forwarding
(IGMP Proxying)", draft-ietf-magma-igmp-proxy-01.txt,
November 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.
5. Informative References
[IANA]
Internet Assigned Numbers Authority, "Internet Multicast
Addresses", http://www.isi.edu/in-notes/iana/assignments/mul-
ticast-addresses
[CISCO]
Cisco Tech Notes, "Multicast In a Campus Network: CGMP and
IGMP snooping", http://www.cisco.com/warp/public/473/22.html
[MSOFT]
Microsoft support article Q223136, "Some LAN Switches with
IGMP Snooping Stop Forwarding Multicast Packets on RRAS
Startup", http://support.microsoft.com/support/kb/arti-
cles/Q223/1/36.ASP
6. 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.
Christensen, et al. [Page 10]
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1) The exclude source failure, which could cause traffic from
sources that are 'black listed' to reach hosts that have requested
otherwise. This can also occur in certain network topologies with-
out IGMP snooping.
2) 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.
3) 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.
4) In IGMP, there is no mechanism for denying recipients access to
groups (i.e. no "exclude receiver" functionality). Hence, apart
from IP-level security configuration outside the scope of IGMP, any
multicast stream may be received by any host without restriction.
Generally, IGMP snooping must be considered insecure due to the
issues above. However, none of the these issues are any worse for
IGMP snooping than for IGMP implementations in general.
7. 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
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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?
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.
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8. 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."
9. Acknowledgements
We would like to thank Martin Bak, Les Bell, Yiqun Cai, Ben Carter,
Paul Congdon, Toerless Eckert, Bill Fenner, Brian Haberman, Edward
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 correspond to the column numbers in the
response table.
10. 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-05.txt: January 2003 Changes in wording of
IGMP forwarding rule 6) and Data forwarding rule 7). Corrections
in the references section.
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Apart from above, no substantial changes has occured in the docu-
ment. Several editorial changes, however, have been made to comply
with the rfc editors requirements:
References splitted in normative and informative sections.
Abstract shortened.
Changed all occurances of MUST, MAY etc. to lowercase to reflect
that this is not a standards track document.
Sections moved around so they appear in the required order.
draft-ietf-magma-snoop-04.txt: November 2002 Editorial changes
only.
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.
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 mul-
ticasts should be based on bridge behavior and not IGMP snoop-
ing behavior.
IGMP snooping related problems:
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
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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
figures.
draft-ietf-idmr-snoop-00.txt: 2001
Initial snooping draft. An overview of IGMP snooping and the
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problems to be solved.
11. Author's Addresses
Morten Jagd Christensen
Thrane & Thrane
Lundtoftegaardsvej 93 D
2800 Lyngby
email: mjc@tt.dk
Karen Kimball
Hewlett-Packard
8000 Foothills Blvd.
Roseville, CA 95747
email: karen.kimball@hp.com
Frank Solensky
Bluejavelin, Inc.
3 Dundee Park
Andover, MA 01810
email: fsolensky@bluejavelin.net
Christensen, et al. [Page 16]
RFC DRAFT January 2003
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 . . . . . . . . . . . . . . . 6
2.2. IGMP snooping related problems . . . . . . . . . . . 7
3. IPv6 Considerations . . . . . . . . . . . . . . . . . . 7
4. Normative References . . . . . . . . . . . . . . . . . 9
5. Informative References . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . 10
7. IGMP Questionnaire . . . . . . . . . . . . . . . . . . 11
8. IETF IPR Statement . . . . . . . . . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . 13
10. Revision History . . . . . . . . . . . . . . . . . . . 13
11. Author's Addresses . . . . . . . . . . . . . . . . . . 16
Christensen, et al. [Page i]
