MULTIMOB Working Group H. Asaeda
Internet-Draft Y. Uchida
Expires: April 28, 2011 Keio University
October 25, 2010
Tuning the Behavior of IGMP and MLD for Mobile Hosts and Routers
draft-asaeda-multimob-igmp-mld-optimization-04
Abstract
IGMP and MLD are the protocols used by hosts to report their IP
multicast group memberships to neighboring multicast routers. This
document describes the ways of IGMPv3 and MLDv2 protocol optimization
for mobility, mainly for a query timer tuning.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 28, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Asaeda & Uchida Expires April 28, 2011 [Page 1]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Explicit Tracking of Membership Status . . . . . . . . . . . . 5
4. IGMP/MLD Query Processing . . . . . . . . . . . . . . . . . . 7
5. Interoperability . . . . . . . . . . . . . . . . . . . . . . . 9
6. Timers, Counters, and Their Default Values . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
Asaeda & Uchida Expires April 28, 2011 [Page 2]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
1. Introduction
The Internet Group Management Protocol (IGMP) [2] for IPv4 and the
Multicast Listener Discovery Protocol (MLD) [3] for IPv6 are the
standard protocols for hosts to initiate joining or leaving multicast
sessions. These protocols must be also supported by multicast
routers or IGMP/MLD proxies [12] that maintain multicast membership
information on their downstream interfaces. Conceptually, IGMP and
MLD work on wireless networks. However, wireless access technologies
operate on a shared medium or a point-to-point link with limited
frequency and bandwidth. In many wireless regimes, it is desirable
to minimize multicast-related signaling to preserve the limited
resources of battery powered mobile devices and the constrained
transmission capacities of the networks. A mobile host may cause
initiation and termination of a multicast service in the new or the
previous network upon its movement. Slow multicast service
activation following a join may degrade reception quality. Slow
service termination triggered by IGMP/MLD querying or by a rapid
departure of the mobile host without leaving the group in the
previous network may waste network resources.
To create the optimal multicast membership management condition, IGMP
and MLD protocols could be tuned to "ease a mobile host's processing
cost or battery power consumption by IGMP/MLD Query transmission
timing coordination by routers" and "realize fast state convergence
by successive monitoring whether downstream members exist or not".
This document describes the ways of tuning the IGMPv3 and MLDv2
protocol behavior for mobility, including a query and other timers
tuning. The selective optimization that provides tangible benefits
to the mobile hosts and routers is given by "keeping track of
downstream hosts' membership status" and "varying IGMP/MLD Query
types and values to tune the number of responses". A source
filtering mechanism in a lightweight manner is also described for
enabling Source-Specific Multicast. The proposed behavior
interoperates with the IGMPv3 and MLDv2 protocols.
Asaeda & Uchida Expires April 28, 2011 [Page 3]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
2. Terminology
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 [1].
Asaeda & Uchida Expires April 28, 2011 [Page 4]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
3. Explicit Tracking of Membership Status
Mobile hosts use IGMP and MLD to request to join or leave multicast
sessions. When the adjacent upstream routers receive the IGMP/MLD
Report messages, they recognize the membership status on the link.
To update the membership status, the routers send IGMP/MLD Query
messages periodically as a soft-state approach does, and the member
hosts reply IGMP/MLD Report messages upon reception. IGMP/MLD Query
is therefore necessary to obtain the up-to-date membership
information, but a large number of the reply messages sent from all
member hosts may cause network congestion or consume network
bandwidth.
The "explicit tracking function" [9] is the possible approach to
reduce the transmitted number of IGMP/MLD messages and contribute to
mobile communications. It enables the router to keep track of the
membership status of the downstream IGMPv3 or MLDv2 member hosts.
Routers that enable the explicit tracking function can unicast IGMP/
MLD General Query messages. This is beneficial especially to mobile
hosts that do not have enough battery power, since flooding IGMP/MLD
messages on a wireless link makes all multicast members pay attention
the messages and induces power consumption to the member hosts. This
also allows the upstream router to proceed fast leaves, because the
router can immediately converge and update the membership
information, ideally. (The usage of unicast General Query is
described in Section 4, and Section 6 show the potential timer
value.)
In addition, the explicit tracking function reduces the chance of
Group-Specific or Group-and-Source Specific Query transmission.
Whenever a router that does not enable the explicit tracking function
receives the State-Change Report, it sends the corresponding Group-
Specific or Group-and-Source Specific Query messages to confirm
whether the Report sender is the last member host or not. However,
if a router enables the explicit tracking function, it does not need
to ask Current-State Report message transmission to the receiver
hosts since the router recognizes the (potential) last member hosts
when it receives the State-Change Report.
This document therefore recommends to enable the explicit tracking
function on adjacent upstream multicast routers. On the other hand,
routers enabling the explicit tracking function may still need to
maintain downstream membership status by sending IGMPv3/MLDv2 Query
messages as IGMPv3/MLDv2 messages may be lost during transmission,
while it gives the possibility to make several timers longer as
described in Section 6. And the explicit tracking function requires
additional processing capability and a possibly large memory for
Asaeda & Uchida Expires April 28, 2011 [Page 5]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
routers to keep all membership status. Especially when a router
needs to maintail a large number of receiver hosts, this resource
requirement may be potentially-impacted. Operators may decide to
disable this function when their routers do not have enough
resources. See [9] for the detail.
Asaeda & Uchida Expires April 28, 2011 [Page 6]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
4. IGMP/MLD Query Processing
IGMP and MLD are non-reliable protocols; to cover the possibility of
a State-Change Report being missed by one or more multicast routers,
a host retransmits the same State-Change Report [Robustness Variable]
- 1 more times, at intervals chosen at random from the range (0,
[Unsolicited Report Interval]) [2][3]. However, this manner does not
guarantee that the State-Change Report is reached to the routers.
The routers still need to refresh the downstream membership
information by receiving Current-State Report periodically solicited
by IGMP/MLD General Query, in order to be robust in front of host or
link failures and packet loss. It supports the situation that mobile
hosts turn off or move from the wireless network to other wireless
network managed by the different router without any notification
(e.g., leave request).
A multicast router periodically transmits IGMP/MLD General Query in
the [Query Interval] sec., whose default value is 125 seconds [2][3].
In general, the all-hosts multicast address (224.0.0.1) or link-scope
all-nodes multicast address (FF02::1) is used as the IP destination
address of IGMP/MLD General Query. Unfortunately, flooding
periodical message whose destination address is the all-hosts/
all-nodes multicast address consumes bettery power of mobile hosts.
Only the active hosts that have been receiving multicast contents
should respond the Query message.
IGMPv3 and MLDv2 specifications [2][3] describe that a host MUST
accept and process any Query whose IP Destination Address field
contains any of the addresses (unicast or multicast) assigned to the
interface on which the Query arrives. According to the scenario, a
router can unicast General Query to tracked member hosts in [Query
Interval] (or [Unicast Query Interval] newly defined in [10]), if the
router keeps track of membership information (Section 3). Unicasting
IGMP/MLD General Query would be effective especially when a wireless
link is heavily loaded.
If a multicast router attached to a wireless link enables an explicit
tracking function and unicasts IGMP/MLD General Query for each member
host, the General Query messages do not affect resources of non-
member hosts. And since the router recognizes the (mostly) actual
member hosts, whether IGMP/MLD General Query messages are transmitted
by unicast or multicast, the router can configure longer [Query
Interval] value and send IGMP/MLD Group-Specific and Group-and-Source
Specific Queries when it recognizes the last member has left from the
network. This will reduce the number of both IGMP/MLD General Query
and Current-State Report messages.
Note that longer query interval may increase join latency and leave
Asaeda & Uchida Expires April 28, 2011 [Page 7]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
latency when an unsolicited message with State-Change Record is not
reached to the router.
There is another concern in unicast General Query. If a multicast
router sends General Query "only" by unicast, it cannot discover
potential member hosts whose join requests were lost. Since the
hosts do not send the same join requests (i.e., unsolicited Report
messages) again, they loose the chance to join the channels unless
the upstream router asks the membership information by sending
General Query by multicast. It will be solved by using both unicast
and multicast General Queries and configuring the [Query Interval]
timer value for multicast General Query and the [Unicast Query
Interval] timer value for unicast General Query as proposed by [10].
However, using two different timers for General Queries may require
the protocol extension this document does not focus on.
IGMP/MLD Group-Specific and Group-and-Source Specific Queries defined
in [2][3] are sent to verify whether there are hosts that desire
reception of the specified group or a set of sources or to rebuild
the desired reception state for a particular group or a set of
sources. These specific Queries build and refresh multicast
membership state of hosts on an attached network. These specific
Queries should be sent to each corresponding multicast address (not
the all-hosts/all-nodes multicast address) as their IP destination
addresses, because hosts that do not join the multicast session do
not pay attention these specific Queries, and only active member
hosts that have been receiving multicast contents with the specified
address reply IGMP/MLD reports.
Asaeda & Uchida Expires April 28, 2011 [Page 8]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
5. Interoperability
IGMPv3 [2] and MLDv2 [3] provide the ability for hosts to report
source-specific subscriptions. With IGMPv3/MLDv2, a mobile host can
specify a channel of interest, using multicast group and source
addresses in its join request. Upon its reception, the upstream
router that supports IGMPv3/MLDv2 establishes the shortest path tree
toward the source without coordinating a shared tree. This function
is called the source filtering function and required to support
Source-Specific Multicast (SSM) [8].
Recently, the Lightweight-IGMPv3 (LW-IGMPv3) and Lightweight-MLDv2
(LW-MLDv2) [4] protocols have been proposed in the IETF. These
protocols provide protocol simplicity for mobile hosts and routers,
as they eliminate a complex state machine from the full versions of
IGMPv3 and MLDv2, and promote the opportunity to implement SSM in
mobile communications.
This document assumes multicast routers that deal with mobile hosts
and mobile hosts MUST be IGMPv3/MLDv2 capable, regardless whether the
protocols are the full or lightweight version. However, this
document does not consider interoperability with older version
protocols. The main reason not being interoperate with older IGMP/
MLD protocols is that the explicit tracking function does not work
properly with older IGMP/MLD protocols.
Asaeda & Uchida Expires April 28, 2011 [Page 9]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
6. Timers, Counters, and Their Default Values
The [Query Interval] is the interval between General Queries sent by
the regular IGMPv3/MLDv2 querier, and the default value is 125
seconds [2][3]. By varying the [Query Interval], multicast routers
can tune the number of IGMP messages on the network; larger values
cause IGMP Queries to be sent less often.
This document proposes to inherit the default [Query Interval] value,
125 seconds, in case that a router enables the explicit tracking
function and sends General Query to tracked member hosts by unicast.
Nevertheless, the last-hop router may want to configure longer [Query
Interval] value such as 150 seconds when operators expect the router
will potentially maintains a number of member hosts such as more than
100 hosts on the wireless link.
This document also proposes 180 seconds for the [Query Interval]
value in case that a router enables the explicit tracking function
and sends General Query by multicast. This longer value contributes
to minimizing traffic of Report messages and battery power
consumption for mobile hosts, especially when operators expect the
router will potentially maintains a large number of member hosts such
as more than 500 hosts on the wireless link. Multicast General Query
is necessary to update membership information if it is not correctly
synchronized due to missing Reports.
The [Query Response Interval] is the Max Response Time (or Max
Response Delay) used to calculate the Max Resp Code inserted into the
periodic General Queries. Its default value is 10 seconds expressed
by "100" for IGMPv3 [2] and "10000" for [3]. By varying the [Query
Response Interval], multicast routers can tune the burstiness of
IGMP/MLD messages on the network; larger values make the traffic less
bursty as host responses are spread out over a larger interval, but
will increase join latency when State-Change Report is missing.
This document proposes 5 seconds (expressed by "50" for IGMPv3 and
"5000" for MLDv2) for the [Query Response Interval] value in case
that a router enables the explicit tracking function and sends
General Query by unicast. This shorter value introduces quick
response, which is valuable for the use of unicast General Query.
Note that the shorter [Query Response Interval] value may cause
sudden increase in a traffic especially when a large number of member
hosts attaches on the network; therefore it SHOULD NOT be 1 or
smaller second.
In case that a router multicasts General Query, the default [Query
Response Interval] value, 10 seconds, can be reasonablly used.
Asaeda & Uchida Expires April 28, 2011 [Page 10]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
To cover the possibility of unsolicited reports being missed by
multicast routers, unsolicited reports are retransmitted [Robustness
Variable] - 1 more times, at intervals chosen at random from the
defined range [2][3]. The QRV (Querier's Robustness Variable) field
in IGMP/MLD Query contains the [Robustness Variable] value used by
the querier. Routers adopt the QRV value from the most recently
received Query as their own [Robustness Variable] value, whose range
SHOULD be set between "1" to "7". The default [Robustness Variable]
value defined in IGMPv3 [2] and MLDv2 [3] is "2". This document
proposes "2" for the [Robustness Variable] value for mobility. And
whether the explicit tracking function is enabled or not, the
[Robustness Variable] value SHOULD NOT be bigger than "2".
The [Startup Query Interval] is the interval between General Queries
sent by a Querier on startup. The default value is 1/4 of [Query
Interval]; however, this document recommends the use of its
shortended value such as 1 second since the shorter value would
contribute to smooth handover for mobile hosts using e.g., PMIPv6
[13]. Note that the [Startup Query Interval] is a static value and
cannot be changed by any external signal. Therefore operators who
maintain routers and wireless links must properly configure this
value.
Asaeda & Uchida Expires April 28, 2011 [Page 11]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
7. Security Considerations
This document neither provides new functions or modifies the standard
functions defined in [2][3][4]. Therefore there is no additional
security consideration provided.
Asaeda & Uchida Expires April 28, 2011 [Page 12]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
8. Acknowledgements
Marshall Eubanks, Gorry Fairhurst, Behcet Sarikaya, Thomas C.
Schmidt, Stig Venaas, Jinwei Xia, and others provided many
constructive and insightful comments.
Asaeda & Uchida Expires April 28, 2011 [Page 13]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
9. References
9.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to indicate requirement
levels", RFC 2119, March 1997.
[2] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version 3",
RFC 3376, October 2002.
[3] Vida, R. and L. Costa, "Multicast Listener Discovery Version 2
(MLDv2) for IPv6", RFC 3810, June 2004.
[4] Liu, H., Cao, W., and H. Asaeda, "Lightweight IGMPv3 and MLDv2
Protocols", RFC 5790, February 2010.
[5] Deering, S., "Host Extensions for IP Multicasting", RFC 1112,
August 1989.
[6] Fenner, W., "Internet Group Management Protocol, Version 2",
RFC 2236, July 1997.
[7] Deering, S., Fenner, W., and B. Haberman, "Multicast Listener
Discovery (MLD) for IPv6", RFC 2710, October 1999.
[8] Holbrook, H. and B. Cain, "Source-Specific Multicast for IP",
RFC 4607, August 2006.
[9] Asaeda, H. and Y. Uchida, "IGMP/MLD-Based Explicit Membership
Tracking Function for Multicast Routers",
draft-asaeda-mboned-explicit-tracking-01.txt (work in
progress), October 2010.
9.2. Informative References
[10] Asaeda, H. and T. Schmidt, "IGMP and MLD Protocol Extensions
for Mobility",
draft-asaeda-multimob-igmp-mld-mobility-extensions-04.txt (work
in progress), March 2010.
[11] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[12] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet
Group Management Protocol (IGMP) / Multicast Listener Discovery
(MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")",
Asaeda & Uchida Expires April 28, 2011 [Page 14]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
RFC 4605, August 2006.
[13] Gundavelli, S, Ed., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
Asaeda & Uchida Expires April 28, 2011 [Page 15]
Internet-Draft Tuning the Behavior of IGMP and MLD October 2010
Authors' Addresses
Hitoshi Asaeda
Keio University
Graduate School of Media and Governance
5322 Endo
Fujisawa, Kanagawa 252-0882
Japan
Email: asaeda@wide.ad.jp
URI: http://www.sfc.wide.ad.jp/~asaeda/
Yogo Uchida
Keio University
Graduate School of Media and Governance
5322 Endo
Fujisawa, Kanagawa 252-0882
Japan
Email: uchida@sfc.wide.ad.jp
Asaeda & Uchida Expires April 28, 2011 [Page 16]