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Versions: (draft-wu-multimob-igmp-mld-tuning) 00 01 02 03 04 05 06 RFC 6636

MULTIMOB Working Group                                         H. Asaeda
Internet-Draft                                           Keio University
Intended status: Informational                                    H. Liu
Expires: August 30, 2012                                           Q. Wu
                                                                  Huawei
                                                       February 27, 2012


 Tuning the Behavior of IGMP and MLD for Routers in Mobile and Wireless
                                Networks
                 draft-ietf-multimob-igmp-mld-tuning-04

Abstract

   IGMP and MLD are the protocols used by hosts and multicast routers to
   exchange their IP multicast group memberships with each other.  This
   document describes the ways of IGMPv3 and MLDv2 protocol optimization
   for mobility, and aims to become a guideline for tuning of IGMPv3/
   MLDv2 Queries and timer and counter values.

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
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   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 August 30, 2012.

Copyright Notice

   Copyright (c) 2012 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
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   (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



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   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Explicit Tracking of Membership Status . . . . . . . . . . . .  4
   4.  Tuning IGMP/MLD Timers and Values  . . . . . . . . . . . . . .  4
     4.1.  Tuning IGMP/MLD General Query Interval . . . . . . . . . .  5
     4.2.  Tuning IGMP/MLD Query Response Interval  . . . . . . . . .  6
     4.3.  Tuning Last Member Query Timer (LMQT) and Last
           Listener Query Timer (LLQT)  . . . . . . . . . . . . . . .  6
     4.4.  Tuning Startup Query Interval  . . . . . . . . . . . . . .  7
     4.5.  Tuning Robustness Variable . . . . . . . . . . . . . . . .  7
     4.6.  Tuning Scenarios for Various Mobile IP Networks  . . . . .  8
   5.  Destination Address of Specific Query  . . . . . . . . . . . .  9
   6.  Interoperability . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Unicasting General Query  . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12























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1.  Introduction

   The Internet Group Management Protocol (IGMP) [1] for IPv4 and the
   Multicast Listener Discovery Protocol (MLD) [2] for IPv6 are the
   standard protocols for hosts to initiate joining or leaving of
   multicast sessions.  These protocols must be also supported by
   multicast routers or IGMP/MLD proxies [6] that maintain multicast
   membership information on their downstream interfaces.  Conceptually,
   IGMP and MLD work on both wireless and mobile networks.  However,
   wireless access technologies operate on a shared medium or a point-
   to-point link with limited spectrum 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.  The motion
   of a host may cause disruption of a multicast service initiation and
   termination in the new or previous network upon its movement.  Slow
   multicast service activation following a join may incur additional
   delay in receiving multicast packets and degrade reception quality.
   Slow service termination triggered by a rapid departure of the mobile
   host without leaving the group in the previous network may waste
   network resources.

   When IGMP and MLD are used with mobile IP protocols, the proximity of
   network entities should be considered.  For example, when bi-
   directional tunnel is used with the mobility entities described in
   [7][8], the mobile host experiences additional latency, because the
   round-trip time using bi-directional tunnel between mobility entities
   is larger comparing to the case that a host and an upstream router
   attach to a LAN.

   This document describes the ways of tuning the IGMPv3 and MLDv2
   protocol behavior on multicast router and proxy side for wireless and
   mobile networks, including query and related 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.  The proposed behavior interoperates with
   the IGMPv3 and MLDv2 protocols.


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 [3].

   In this document, "router" means both multicast router and IGMP/MLD
   proxy.



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3.  Explicit Tracking of Membership Status

   Mobile hosts use IGMP and MLD to request to join or leave multicast
   sessions.  When an adjacent upstream router receives the IGMP/MLD
   Report messages, it recognizes the membership status on the link.  To
   update the membership status reliably, the router sends IGMP/MLD
   Query messages periodically, and sends Group-Specific and/or Group-
   and-Source Specific Queries when a member host reports its leave.
   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
   the efficiency of mobile communications.  It enables the router to
   keep track of the membership status of the downstream IGMPv3 or MLDv2
   member hosts.  That is, if a router enables the explicit tracking
   function, it does not always need to ask Current-State Report
   message's transmission from the receiver hosts since the router
   implicitly recognizes the (potential) last member host when it
   receives the State-Change Report reporting a leave.  The router can
   therefore send IGMP/MLD Group-Specific and Group-and-Source Specific
   Queries LMQC/LLQC times (see Section 4.3 for LMQC/LLQC) only when it
   recognizes the last member has left from the network.  This reduces
   the transmitted number of Current-State Report messages.

   Enabling the explicit tracking function is advantageous for mobile
   multicast, but the function requires additional processing capability
   and possibly a large memory for routers to keep all membership
   status.  Especially when a router needs to maintain a large number of
   receiver hosts, this resource requirement is potentially impacted.
   Therefore, in this document it is RECOMMENDED that adjacent upstream
   multicast routers enable the explicit tracking function for IP
   multicast communications on wireless and mobile networks, if they
   have enough resources.  If operators think that their routers do not
   have enough resources, they MAY disable this function on their
   routers.  Note that whether routers enable the explicit tracking
   function or not, they need to maintain downstream membership status
   by sending IGMPv3/MLDv2 General Query messages as some IGMPv3/MLDv2
   messages MAY be lost during transmission.


4.  Tuning IGMP/MLD Timers and Values







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4.1.  Tuning IGMP/MLD General Query Interval

   IGMP and MLD are non-reliable protocols; to cover the possibility of
   a State-Change Report being missed by one or more multicast routers,
   "hosts retransmit the same State-Change Report messages [Robustness
   Variable] - 1 more times", at intervals chosen at random from the
   range (0, [Unsolicited Report Interval]) [1][2].  Although this
   behavior increases the protocol robustness, it does not guarantee
   that the State-Change Report reaches the routers.  Therefore, routers
   still need to refresh the downstream membership information by
   receiving Current-State Report periodically solicited by IGMP/MLD
   General Query sent in the [Query Interval] period, in order to
   enhance robustness of the host in case of link failures and packet
   loss.  It also supports the situation that mobile hosts turn off or
   move from a network to other network managed by a different router
   without any notification (e.g., leave request).

   The [Query Interval] is the interval between General Queries sent by
   the regular IGMPv3/MLDv2 querier, and the default value is 125
   seconds [1][2].  By varying the [Query Interval], multicast routers
   can tune the number of IGMP/MLD messages on the network; larger
   values cause IGMP/MLD Queries to be sent less often.

   This document proposes 150 seconds for the [Query Interval] value by
   changing the Querier's Query Interval Code (QQIC) field specified in
   the IGMP/MLD Query message, for the case that a router enabling the
   explicit tracking function sends General Query and potentially
   operates a large number of member hosts such as more than 200 hosts
   on the wireless link.  This longer interval value contributes to
   minimizing traffic of Report messages and battery power consumption
   for mobile hosts.

   On the other hand, this document also proposes 60 to 90 seconds for
   the [Query Interval] value for the case that a router enabling the
   explicit tracking function attaches to a wireless link having higher
   capacity of the resource.  This shorter interval contributes to quick
   synchronization of the membership information tracked by the router
   but MAY consume battery power of mobile hosts.

   If a router does not enable the explicit tracking function, the
   [Query Interval] value would be its default value, 125 seconds.

   In situations where Mobile IPv6 [8] is used, when the home agent
   implements multicast router functionality and multicast data packets
   are tunneled to and from the home agent, the home agent MAY want to
   slow down Query periodicity, especially when network congestion is
   detected.  This can be done by the home agent starting forwarding
   queries with the default [Query Interval] value and increasing it in



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   a gradual manner until it exceeds the mobile host's lifetime.

4.2.  Tuning IGMP/MLD Query Response Interval

   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 "Max Resp Code=100" for IGMPv3 [1] and "Maximum Response
   Code=10000" for MLDv2 [2].  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's
   responses are spread out over a larger interval, but will increase
   join latency when State-Change Report (i.e., join request) is
   missing.

   According to our experimental analysis, this document proposes two
   tuning scenarios for tuning the [Query Response Interval] value in
   different wireless link conditions; one scenario is for a wireless
   link with a lower capacity of network resource or a lossy link, and
   the other scenario is for a wireless link with enough capacity or
   reliable condition for IGMP/MLD message transmission.

   Regarding the first scenario, for instance, when a multicast router
   attaches to a bursty IEEE 802.11b link, the router configures the
   longer [Query Response Interval] value, such as 10 to 20 (sec).  This
   configuration will reduce congestion of the Current-State Report
   messages on a link but MAY increase join latency and leave latency
   when the unsolicited messages (State-Change Record) are lost on the
   router.

   The second scenario MAY happen for a multicast router attaching to a
   wireless link having higher capacity of the resource or a point-to-
   (multi-)point link such as an IEEE 802.16e link, because IGMP/MLD
   messages do not seriously affect the link condition.  The router can
   seek Current-State Report messages with the shorter [Query Response
   Interval] value, such as 5 to 10 (sec).  This configuration will
   contribute to quickly (at some level) discovering non-tracked member
   hosts and synchronizing the membership information.

4.3.  Tuning Last Member Query Timer (LMQT) and Last Listener Query
      Timer (LLQT)

   Shortening the Last Member Query Timer (LMQT) for IGMPv3 and the Last
   Listener Query Timer (LLQT) for MLDv2 contributes to minimizing leave
   latency.  LMQT is represented by the Last Member Query Interval
   (LMQI), multiplied by the Last Member Query Count (LMQC), and LLQT is
   represented by the Last Listener Query Interval (LLQI), multiplied by
   the Last Listener Query Count (LLQC).



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   While LMQI and LLQI are changeable, it is reasonable to use the
   default values (i.e., 1 second) for LMQI and LLQI in a wireless
   network.  LMQC and LLQC, whose default value is the [Robustness
   Variable] value, are also tunable.  Therefore, LMQC and LLQC MAY be
   set to "1" for routers enabling the explicit tracking function, and
   then LMQT and LLQT are set to 1 second.  However, setting LMQC and
   LLQC to 1 increases the risk of missing the last member; LMQC and
   LLQC SHOULD be set to 1 only when network operators think that their
   wireless link is stable enough.

   On the other hand, if network operators think that their wireless
   link is lossy (e.g., due to a large number of attached hosts or
   limited resources), they MAY set LMQC and LLQC to "2" for their
   routers enabling the explicit tracking function.  Although bigger
   LMQC and LLQC values MAY cause longer leave latency, the risk of
   missing the last member will be reduced.

4.4.  Tuning Startup Query Interval

   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, in this document it is RECOMMENDED that the use
   of its shortened value such as 1 second since the shorter value would
   contribute to shortening handover delay for mobile hosts in, e.g.,
   the base solution with PMIPv6 [10].  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.

4.5.  Tuning Robustness Variable

   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 [1][2].  The QRV (Querier's Robustness Variable) field
   in IGMP/MLD Query contains the [Robustness Variable] value used by
   the querier.  The default [Robustness Variable] value defined in
   IGMPv3 [1] and MLDv2 [2] is "2".

   This document proposes "2" for the [Robustness Variable] value for
   mobility, when a router attaches to a wireless link having lower
   capacity of the resource or a large number of hosts.  For a router
   that attaches to a wireless link having higher capacity of the
   resource or reliable condition, it is not required to retransmit the
   same State-Change Report message; hence the router sets the
   [Robustness Variable] to "1".





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4.6.  Tuning Scenarios for Various Mobile IP Networks

   In mobile IP networks, IGMP and MLD are used either with three
   deployment scenarios; (1) running directly between host and access
   router on a wireless network, (2) running between host and home
   router through a tunnel link, and (3) running between home router and
   foreign router through a tunnel link.

   When a receiver host connects directly through a wireless link to a
   foreign access router or a home router, the tuning of the IGMP/MLD
   protocol parameters SHOULD be the same as suggested in the previous
   sections.  The example of this scenario occurs when route
   optimization is adopted in MIPv6 [8] or Mobile IP [11], or when in
   Proxy Mobile IPv6 (PMIPv6) [7], the mobile access gateway, whose role
   is similar to the one of a foreign router, acts as a multicast
   router.

   The second scenario occurs when bi-directional tunnel established
   between host and home router is used to exchange IGMP/MLD messages
   such as [8][11].  There are difficulties in tuning the parameters in
   this situation, because the tunnel link condition is diverse and
   changeable.  When a host is far away from the home router, the
   transmission delay between the two entities MAY be longer and the
   packet delivery MAY be more unreliable.  Thus the effects of the
   IGMP/MLD message transmission through a tunnel link SHOULD be
   considered during the parameter setting.  For example, the [Query
   Interval] and [Query Response Interval] could be set shorter to
   compensate the transmission delay, and the [Robustness Variable]
   could be increased for possible packet loss.

   The third scenario occurs in [10], in which the mobile access gateway
   (i.e., foreign router) acts as the IGMP/MLD Proxy [6] in PMIPv6 [7].
   Through the bi-directional tunnel established with the local mobility
   anchor (i.e., home router), the mobile access gateway sends summary
   reports of its downstream member hosts to the local mobility anchor.
   Apart from the distance factor that influences the parameter setting,
   the [Query Response Interval] on the local mobility anchor could be
   set to a smaller value because the number of the mobile access
   gateways is much smaller compared to that of the host and the chances
   of packet burst is low for the same reason.  And the power
   consumption due to a lower query interval is not an issue for the
   moble access gateways because the mobile access gateways are usually
   not battery-powered.

   Ideally, the IGMP/MLD querier router adjusts its parameter setting
   according to the actual mobile IP network conditions to benefit
   service performance and resource utilization.  It would be desirable
   that a home router determines aforementioned timers and values



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   according to the delay between the initiating IGMP/MLD Query and the
   responding IGMP/MLD Report, while describing such mechanism
   dynamically adjusting these timers and values is out of scope of this
   document.


5.  Destination Address of Specific Query

   IGMP/MLD Group-Specific and Group-and-Source Specific Queries defined
   in [1][2] 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 all desired hosts with specific 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 to these specific Queries, and only
   active member hosts that have been receiving multicast contents with
   the specified address reply IGMP/MLD reports.


6.  Interoperability

   IGMPv3 [1] and MLDv2 [2] 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 is required to support
   Source-Specific Multicast (SSM) [4].

   Recently, the Lightweight-IGMPv3 (LW-IGMPv3) and Lightweight-MLDv2
   (LW-MLDv2) [5] protocols have been defined as the proposed standard
   protocols 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 that both multicast routers and mobile hosts
   MUST be IGMPv3/MLDv2 capable, regardless whether the protocols are
   the full or lightweight version.  And this document does not consider
   interoperability with older version protocols.  The main reason not
   being interoperable with older IGMP/MLD protocols is that the
   explicit tracking function does not work properly with older IGMP/MLD
   protocols.




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7.  IANA Considerations

   This document has no actions for IANA.


8.  Security Considerations

   This document neither provides new functions or modifies the standard
   functions defined in [1][2][5].  Therefore there is no additional
   security consideration provided.


9.  Acknowledgements

   Luis M. Contreras, Marshall Eubanks, Gorry Fairhurst, Dirk von Hugo,
   Imed Romdhani, Behcet Sarikaya, Stig Venaas, Jinwei Xia, and others
   provided many constructive and insightful comments.


10.  References

10.1.  Normative References

   [1]   Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
         Thyagarajan, "Internet Group Management Protocol, Version 3",
         RFC 3376, October 2002.

   [2]   Vida, R. and L. Costa, "Multicast Listener Discovery Version 2
         (MLDv2) for IPv6", RFC 3810, June 2004.

   [3]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", March 1997.

   [4]   Holbrook, H. and B. Cain, "Source-Specific Multicast for IP",
         RFC 4607, August 2006.

   [5]   Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet Group
         Management Protocol Version 3 (IGMPv3) and Multicast Listener
         Discovery Version 2 (MLDv2) Protocols", RFC 5790,
         February 2010.

10.2.  Informative References

   [6]   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.




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   [7]   Gundavelli, S, Ed., Leung, K., Devarapalli, V., Chowdhury, K.,
         and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.

   [8]   Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
         IPv6", RFC 6275, July 2011.

   [9]   Asaeda, H. and N. Leymann, "IGMP/MLD-Based Explicit Membership
         Tracking Function for Multicast Routers",
         draft-ietf-pim-explicit-tracking-00.txt (work in progress),
         October 2011.

   [10]  Schmidt, T., Waehlisch, M., and S. Krishnan, "Base Deployment
         for Multicast Listener Support in Proxy Mobile IPv6 (PMIPv6)
         Domains", RFC 6224, April 2011.

   [11]  Perkins, Ed., C., "IP Mobility Support for IPv4, Revised",
         RFC 5944, November 2010.


Appendix A.  Unicasting General Query

   IGMPv3 and MLDv2 specifications [1][2] 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.  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.  On the other hand, according to [1][2], a router MAY
   be able to unicast General Query to the tracked member hosts in
   [Query Interval], if the router keeps track of membership information
   (Section 3).

   Unicasting IGMP/MLD General Query would reduce the drain on battery
   power of mobile hosts as only the active hosts that have been
   receiving multicast contents respond the unicast IGMP/MLD General
   Query messages and non-active hosts do not need to pay attention to
   the IGMP/MLD Query messages.  This also allows the upstream router to
   proceed fast leaves (or shorten leave latency) by setting LMQC/LLQC
   smaller, because the router can immediately converge and update the
   membership information, ideally.

   However, there is a 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 retransmit the same join requests (i.e., unsolicited
   Report messages), they lose 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



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   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.  However, using two
   different timers for General Queries would require the protocol
   extension this document does not focus on.  If a router does not
   distinguish the multicast and unicast General Query Intervals, the
   router SHOULD only use and enable multicast General Query.

   Also, unicasting General Query does not remove multicasting General
   Query.  Multicast General Query is necessary to update membership
   information if it is not correctly synchronized due to missing
   Reports.  Therefore, enabling unicast General Query SHOULD NOT be
   used for the implementation that does not allow to configure
   different query interval timers as [Query Interval] and [Unicast
   Query Interval].  If a router does not distinguish these multicast
   and unicast General Query Intervals, the router SHOULD only use and
   enable multicast General Query.


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/


   Hui Liu
   Huawei Technologies Co., Ltd.
   Huawei Bld., No.3 Xinxi Rd.
   Shang-Di Information Industry Base
   Hai-Dian Distinct, Beijing  100085
   China

   Email: helen.liu@huawei.com











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Internet-Draft     Tuning the Behavior of IGMP and MLD     February 2012


   Qin Wu
   Huawei Technologies Co., Ltd.
   Site B, Floor 12F, Huihong Mansion
   No.91 Baixia Rd.
   Nanjing, Jiangsu  21001
   China

   Email: bill.wu@huawei.com











































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