mboned T. Morin, Ed.
Internet-Draft France Telecom - Orange Labs
Intended status: Experimental B. Haberman
Expires: January 12, 2009 The Johns Hopkins University,
Applied Physics Laboratory
July 11, 2008
IGMP/MLD Error Feedback
draft-morin-mboned-igmpmld-error-feedback-01
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Abstract
This document describes messages and procedures that can optionally
be implemented in IGMP/MLD Queriers and Hosts, to provide information
to multicast receivers on the reason why the IGMP/MLD Querier didn't
take into account a Membership Report message.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. History and problem statement . . . . . . . . . . . . . . . . 3
4. Principle . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Procedures on the IGMP/MLD Querier . . . . . . . . . . . . 4
5.2. Procedures on the IGMP/MLD Host . . . . . . . . . . . . . 5
6. Message encodings . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Feedback message . . . . . . . . . . . . . . . . . . . . . 6
6.2. Error codes . . . . . . . . . . . . . . . . . . . . . . . 9
7. Feedback to the application layer . . . . . . . . . . . . . . 9
8. Impact on IGMP/MLD proxies and equipments doing IGMP/MLD
snooping . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. IGMP/MLD Proxies . . . . . . . . . . . . . . . . . . . . . 11
8.2. Equipments doing IGMP/MLD snooping . . . . . . . . . . . . 12
9. IGMP/MLD Hosts stacks not implementing the Feedback
mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
11. Security Considerations . . . . . . . . . . . . . . . . . . . 12
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
13.1. Normative References . . . . . . . . . . . . . . . . . . . 13
13.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Protocol to carry error feedback messages . . . . . . 15
A.1. ICMP . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
A.2. IGMP/MLD . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 17
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1. Introduction
Requirements have been formulated for means to provide multicast
receivers with error feedback when the IGMP/MLD Querier did not or
could not process an IGMP/MLD Membership Report message
([I-D.ietf-mboned-maccnt-req], section 4). Operator's experience
with IPTV deployments show that introducing such a feedback in IGMP
exchanges between multicast receivers and multicast routing
equipments would help provide a better service (e.g. a liaison
between the IETF mboned working group and the DSLForum was made in
December 2005 to discuss this issue, but didn't lead to a
standardized solution).
An examples case is when an IGMP Querier refuses to take into account
an IGMP Membership Report because the number of multicast channels
would surpass the allowed threshold for the service. Many other
examples of the case where an IGMP error feedback channel would be
useful are presented in Section 6.2.
This document describes new message encodings and the associated
procedures, all of which being optional and preserving full backward
and forward compatibility, and details the impact on the host API for
multicast subscriptions.
This document doesn't state yet whether the messages should be
carried over IGMP, ICMP or another protocol, but tries to document
the pros and cons of the different alternatives, to guide the
decision process.
2. Terminology
The terminology in this document is the terminology used in [RFC3376]
and [RFC3810].
For readability, "Querier" and "Host(s)" will be used throughout this
document, in place of "IGMP or MLD Querier" and "IGMP or MLD
Host(s)".
3. History and problem statement
The DSLForum expressed interest for such a feature, which was
discussed [magma-archive] in a liaison with the Magma IETF Working
group. The specifications described in this document try to address
the comments exchanged on the magma WG mailing-list.
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4. Principle
The procedures described in this memo are fully optional : their only
intent is to carry informative data from the Querier to the Hosts.
Most specifically, the intent is that:
o the procedures don't change the state machine of the Querier or
Host, the information carried is only meant to provide information
to the application subscribed to multicast data
o a Host implementing these specifications will behave correctly in
the absence of these informations.
o the behavior of a Querier implementing these specifications is
unchanged whether or not the hosts implement these specs.
Last, these specifications are not meant to carry information about
transient errors that the network is supposed to recover from, like
network outages.
5. Procedures
5.1. Procedures on the IGMP/MLD Querier
The following procedures introduce a new type of message : the
Feedback message. See section Section 6 for details about message
encodings.
Using these procedures a Querier can OPTIONALLY emmit a Feedback
message after receiving an IGMP or MLD Membership Report message that
it can not process (see Section 6.2 for example reasons on why a
Querier would not process a Membership Report message).
The Feedback message carries error type/sub-type field, and
information about the group to which the error pertains. Optionally,
if IGMPv3/MLDv2 is used, and if the error message pertains to some
specific sources, the addresses of the sources to which the error
pertains are included in the message.
The address to which the Feedback message will be sent is determined
as follows:
o if IGMPv3/MLDv2 is used (and if the sender IP address is not
0.0.0.0 or 0::0), the address of the sender of the Membership
Report is used
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o else, the group address specified in the Membership Report message
is used
The source address MUST be the same address as the address used for
Query messages, and the TTL MUST be set to 1.
If IGMPv2/MLDv1 is being used, not more than one Feedback message
should be sent for a said Membership Report message.
If IGMPv3/MLDv2 is being used, multiple feedback message MAY be sent
if the group record of the IGMP/MLD message that triggered the error
contained multiple source addresses.
In any case the amount of Feedback messages sent on a link MUST be
rate-limited,
5.2. Procedures on the IGMP/MLD Host
When a Host receives an Feedback message, it MAY process it.
Processing a Feedback message consists in :
o MANDATORY checking that the TTL is set to 1
o OPTIONALLY checking that the message source address is the address
of a known Querier
o parsing the Feedback message
o determining the network sockets for which the Feedback message is
relevant (G is the group address of the Feedback message)
* if no source address is included in the Feedback message, the
sockets are the sockets that have some active forwarding state
related to G (subscribed to G with a non-null include list)
* if some source addresses are indicated in the Feedback message,
the sockets are the sockets to which traffic from at least one
of these sources, and toward G, would be forwarded
o notifying these sockets of the error (see Section 7)
o OPTIONALLY logging the error and/or doing any local action
depending on policy
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6. Message encodings
6.1. Feedback message
The Feedback message is a subtype of IGMP message when used as a
feedback to an IGMP message, and a subtype of ICMPv6 when used as a
feedback to an MLD message. It contains an error code, the multicast
group address in error (optional), and the source addresses in error
(optional).
The encoding is common to the two types of messages (except the
length of fields specifying addresses).
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = XXX | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Number of Group Records (M) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Group Record [1] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Group Record [2] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
. . .
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Group Record [M] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Type: Identifies this message as a Feedback message. Currently
using:
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* in the case of IPv6/MLD: 0xYY (currently using value 200 as
defined in RFC 4443 "private experimentation value", until
another value is registered with IANA).
* in the case of IPv4/IGMP: 0xZZ (currently using 0xF2, in the
"Reserved for experimentation" range, until another value is
registered with IANA)
Code: One byte, gives additional information about the error that
triggered the feedback message. The possible values are described
in Section 6.2.
Checksum: The standard IGMP checksum.
Reserved: Reserved for future use. Set to zero on transmission;
ignored upon receipt.
Number of Group Records: Indicates the number of group records.
The Feedback message MUST at least include one group record.
It MUST NOT include more than one group record if the Feedback
message is to be sent toward a multicast group address (see section
Section 5).
o the message that triggered the Feedback message is IGMPv3 or MLDv2
and the group record that triggered the error contains no source
address
o the message that triggered the Feedback message is IGMPv2 or MLDv1
and the message contains no source address
Group record encoding:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Multicast Group Address |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Number of Sources (N) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address [1] |
~ ~
+--- ---+
| Source Address [2] |
~ ~
+--- ---+
. . .
. . .
~ ~
+--- ---+
| Source Address [N] |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
Multicast Group Address: IPv4 multicast group address of the group
in error. Possibly set to all zeros. Contains an IPv4 address in
the case of IPv4/IGMP, and an IPv6 address in the case of IPv6/
MLD.
Reserved: Reserved for future use. Set to zero on transmission;
ignored upon receipt.
Number of Sources: Indicates the number of sources in error.
Possibly set to zero.
Source Address [1..n]: Addresses of the multicast sources in error.
In the case of IPv4/IGMP, all these fields are 32-bit fields
containing IPv4 addresses. In the case of IPv6/MLD, all these
fields are 128-bit fields containing IPv6 addresses.
The Multicast Group Address field MAY be set to all zeros (for
instance, if the error is not specific to a said multicast group).
A group record MAY include zero Source Address (it can be the case,
for instance, for a feedback that is not specific to particular
sources, or that relates to an ASM subscription). It MUST NOT
include any source in the following cases:
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o the message that triggered the Feedback message is IGMPv3 or MLDv2
and the group record that triggered the error contains no source
address
o the message that triggered the Feedback message is IGMPv2 or MLDv1
6.2. Error codes
This section describes some proposed error codes:
o improper message : the Membership Report message is improper (the
group address is not in the 224/0 or FF00::/8 range, or specified
sources are improper addresses)
o IGMP or MLD version is not supported by querier
o wildcard on an SSM group : IGMPv2 or IGMPv3/MLDv2 with an Exclude
source filter mode was used in the Report, but the group address
is not in the SSM range of the Querier
o exclude source filter mode not supported by the Querier
o group administratively prohibited
o source(s) administratively prohibited
o resource limit reached
o multicast reception is disabled on the link
o multicast routing protocol issue
[ This section will later be completed to include error code numbers
]
Remember that the Feedback message is NOT meant to carry information
about transient errors that the network is supposed to recover from,
like for instance network outages.
7. Feedback to the application layer
This section gives an example of how the information from Feedback
messages is supplied to applications subscribed to multicast streams,
and which expect the reception of multicast datagrams on a socket,
based on Linux extensions to the POSIX [posix] network socket API.
A first requirement is full backward compatibility with applications
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not supporting these specifications : an application not supporting
these specifications must not be affected by a Feedback message. For
instance, a wrong solution would be to return an error on a read() or
recv() call.
A second requirement is to allow an application to keep receiving
data on a socket, even if some error was reported through a Feedback
message, for a group or channel joined on this socket. This is
needed, for instance, in two cases : when a socket is used to join
multiple distinct group or channels and only one of them is subject
to an error ; when a socket is used to join only one multicast group,
for which the Querier sends a Feedback message, but there are members
for this group sending data on a directly connected link.
The proposed solution is to rely on the use of the MSG_ERRQUEUE flag
of the recvmsg()/recvfrom() POSIX calls. This call allows the socket
user to retrieve the network errors queued for the socket.
The MLD component receiving an MLD Feedback message containing error
condition reports the error to the application via the MSG_ERRQUEUE
flag in the recvmsg()/recvfrom() calls. The MSG_ERRQUEUE flag
indicates the presence of a sock_extended_err data structure. When
the sock_extended_err data structure is passed to the application,
the ee_origin field is set to 3 (SO_EE_ORIGIN_ICMP6) in the case of
an MLD Feedback message, and XX (SO_EE_ORIGIN_YYYY) in the case of an
IGMP Feedback message [XX and YYY is to be determined in compliance
with the relevant standard, 4 and SO_EE_ORIGIN_IGMP are proposed as
interim values]. The Type and Code fields from the MLD Feedback
message are copied into the ee_type and ee_code field of the
sock_extended_err data structure.
The addresses of the multicast group and sources in error can be
retrieved as follows:
o in the IPv4 case, the group address and source address are stored,
respectively, in the ee_info and ee_data fields,
o the group address and source address can be retrieved, in all
cases, by calling functions returning a sockaddr pointer and which
take into argument a sock_extended_err pointer (similarly as
SOCK_EE_OFFENDER) and called SOCK_EE_MCAST_FEEDBACK_GRP and
SOCK_EE_MCAST_FEEDBACK_SRC
If the Feedback contains multiple sources addresses, a
sock_extended_err will be added to the message queue for each such
sources.
An application receiving a sock_extended_err message from the MLD
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component MUST NOT terminate the multicast subscription to the group
or source/group address in error, except possibly if it can be
ascertained that the Feedback message comes from a legitimate Querier
(e.g. thanks to a mechanism like SEND [RFC3971]), and if multicast
traffic for the said group or channel is not expected from any host
attached to a directly-connected link.
( Another proposal would be to allow the setsockopt() and
set(ipv4)sourcefilter() calls [RFC3678] to return an error. That
would require the local network stack to wait for some time after
sending a Membership Report message, before being able to return from
the setsockopt()/set(ipv4)sourcefilter() call, and would not easily
allow to carry detailed information about the specific group or
channel in error. Consequently, this approach doesn't seem a viable
one. )
8. Impact on IGMP/MLD proxies and equipments doing IGMP/MLD snooping
8.1. IGMP/MLD Proxies
To support this Feedback mechanism, an IGMP or MLD proxy [RFC4605]
SHOULD send Feedback messages received on its Host side toward its
Querier side(s) that have matching multicast memberships. The
procedures for sending the Feedback messages are then the same as for
a normal Querier, as specified in Section 5: in particular the IGMP/
MLD proxy MUST use its own address as the source address of the
Feedback message.
A new member of a multicast group already forwarded by the proxy on
its Querier side, will have to wait for some time before having a
chance to receive a Feedback message : timers will have to trigger
before the Querier on the Host side of the proxy sends a Query,
causing the proxy to send a Membership Report that may then cause the
Querier on the Host side to send a Feedback message, and this
Feedback message to be propagated to the new receiver.
To quickly provide Feedback messages to receivers on its Querier
side, the proxy MAY cache the Feedback messages that it receives on
the Host side to later match them with Membership Report messages
received on its Querier side, and send relevant Feedback messages in
reaction to these. If doing Feedback message caching, the proxy MUST
keep only one Feedback message per (S,G) entry or (*,G) entry. It
MUST also remove a Feedback message from its cache, if a same
Feedback message hasn't been sent in the last <> seconds by the
Querier on its Host side.
Last, an IGMP/MLD proxy MAY produce its own Feedback messages. In
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that case it MUST still respect procedures of Section 5.
8.2. Equipments doing IGMP/MLD snooping
IGMP/MLD snooping equipments are expected to transparently
interoperate with the procedures described in this document, given
that RFC 4541 section 2.2.1(3) [RFC4541] states that "[a] switch that
supports IGMP snooping must flood all unrecognized IGMP messages to
all other ports".
9. IGMP/MLD Hosts stacks not implementing the Feedback mechanism
To allow applications running on an IGMP/MLD Host, whose networking
stack or API does not implement the Feedback mechanism described in
this spec, it is proposed that IGMP/MLD Querier implementing this
specification can, when configured to do so, send each Feedback
message twice : once with the encoding described in these
specifications, and another time encapsulated in a UDP packet.
The UDP message uses port xxx [TBD], with a payload identical to the
IGMP or MLD Feedback message, except that the checksum is set to zero
(the UDP message having its own checksum).
10. IANA Considerations
Request to IANA for IGMP and ICMPv6 type allocation will be needed
for the messages defined in this document.
[Whether or not it is needed to define a registry for the error codes
used in IGMP/MLD Feedback messages will be later determined.]
[Note to RFC Editor: this section may be removed on publication as an
RFC.]
11. Security Considerations
Given that the specifications in this document do not change nor the
state machine of the IGMP/MDLD Querier and Host stack, nor the
datagrams that will be received by an application, they are not
expected to introduce security issues not already existing with IGMP/
MLD or the protocol used to carry the Feedback message.
A possible issue would be to have wrong Feedback sent toward
multicast applications. Such an issue could arise if spoofed
Feedback messages are sent and interpreted by multicast receiver
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hosts. This issue is mitigated by the fact that IGMP/MLD Hosts MUST
check that the TTL of the Feedback messages is 1, and MAY also check
the source IP of the Feedback message against a list of known
Queriers.
Another possible issue is denial of service of the Querier function,
that would be due to having the IGMP/MLD Querier be overloaded by
Feedback messages to send. This is mitigated by allowing the Querier
to rate-limit the flow of Feedback messages. On a LAN, such a rate-
limiting would possibly result in some receivers not receiving the
feedback message that they would have, which is a form of denial of
service, but only on the Feedback function by itself, with no impact
on the rest of the multicast group membership control protocol
infrastructure. This later type of denial of service might be
mitigated by doing rate-limiting based on the source address of the
receivers (the source address of the Membership Report triggering the
Feedback message); but such mechanism may themselves be subject to
weaknesses due to Membership Report spoofing.
12. Acknowledgements
Acknowledgments go to DSLForum contributors who provided an initial
proposal, to IETF participants that participated in the discussion on
the magma WG list, from which guidance and inspiration was largely
taken. Thank you to Bill Fenner for providing detailed information
on issues related to ICMP errors in reaction to multicast datagrams.
Thanks to Toerless Eckert for his inputs and who offered a suggestion
on how to handle application running on hosts not implementing the
Feedback mechanism.
Message encodings are largely inspired from Report message encodings
found in[RFC3376].
13. References
13.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3678] Thaler, D., Fenner, B., and B. Quinn, "Socket Interface
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Extensions for Multicast Source Filters", RFC 3678,
January 2004.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC4541] Christensen, M., Kimball, K., and F. Solensky,
"Considerations for Internet Group Management Protocol
(IGMP) and Multicast Listener Discovery (MLD) Snooping
Switches", RFC 4541, May 2006.
[RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick,
"Internet Group Management Protocol (IGMP) / Multicast
Listener Discovery (MLD)-Based Multicast Forwarding
("IGMP/MLD Proxying")", RFC 4605, August 2006.
13.2. Informative References
[I-D.ietf-mboned-maccnt-req]
He, H., "Requirements for Multicast AAA coordinated
between Content Provider(s) and Network Service
Provider(s)", draft-ietf-mboned-maccnt-req-05 (work in
progress), October 2007.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[fenner-icmp-mcast]
"ICMP errors in response to multicast", March 1999,
<http://www.icir.org/fenner/mcast/icmp.html>.
[magma-archive]
"IETF Magma WG mailing-list archives", December 2005, <htt
p://www1.ietf.org/mail-archive/web/magma/current/
msg00815.html>.
[posix] "ISO/IEC 9945 Information technology, Portable Operating
System Interface (POSIX), Part 1: Base Definitions", 2003.
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Appendix A. Protocol to carry error feedback messages
ICMP and IGMP/MLD were possible candidates for carrying the Feedback
message. This section exposes the pros/cons of both alternatives,
and ought to be removed once a decision is made on one of them.
A.1. ICMP
The Feedback message could be an ICMP message that would use a new
ICMP message type (or possibly reusing existing types and codes).
Pros:
o ICMP is already used to carry error messages between routers and
hosts (e.g.. port unreachable message)
o ICMP has an extensible format which could easily be reused for the
Feedback function described in this memo
o Implementations of network socket APIs already take into account
ICMP messages
Cons:
o ICMP has currently nothing to do with multicast today
o some RFC explicitly forbid the sending of ICMP in reaction to
receiving multicast packets, and IGMP/MLD Membership Reports are
multicast packets ([RFC1122] section 7.2 and 3.2.2, [RFC1812]
section 4.3.2.7) (see [fenner-icmp-mcast])
o ICMP messages are (currently) never sent toward multicast
addresses, whereas that would be required to send Feedback
messages to IGMPv2/MLDv1 hostsSo we may say that the generic
argument is that the restriction for ICMP ; this has lead to
practical issues to integrate this approach into existing stacks,
because of the need to work around sanity checks
A.2. IGMP/MLD
The Feedback message could be an IGMP or MLD message that would use
new IGMP/MLD message types.
Pros:
o IGMP and MLD are the protocols used for all operations related to
multicast subscription
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Cons:
o possibly more work to define the encodings
o a new IANA registry might be needed to manage Feedback error codes
o definition of how the network socket API will be used to carry the
information to the applications has to be defined
Authors' Addresses
Thomas Morin (editor)
France Telecom - Orange Labs
2, avenue Pierre Marzin
Lannion 22307
France
Email: thomas.morin@orange-ftgroup.com
Brian Haberman
The Johns Hopkins University, Applied Physics Laboratory
11100 Johns Hopkins Road
Laurel, MD 20723-6099
US
Phone: +1 443 778 1319
Email: brian@innovationslab.net
Morin & Haberman Expires January 12, 2009 [Page 16]
Internet-Draft IGMP/MLD Error Feedback July 2008
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