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   Query Interval)) plus (one Query Response Interval).

7.5.  Other Querier Present Interval

   The Other Querier Present Interval is the length of time that must
   pass before a router decides that there is no longer another router
   which should be the querier on a link.  This value MUST be ((the
   Robustness Variable) times (the Query Interval)) plus (one half of
   one Query Response Interval).

7.6.  Startup Query Interval

   The Startup Query Interval is the interval between General Queries
   sent by a Querier on startup.  Default: 1/4 the Query Interval.

7.7.  Startup Query Count

   The Startup Query Count is the number of Queries sent out on startup,
   separated by the Startup Query Interval.  Default: the Robustness
   Variable.






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7.8.  Last Listener Query Interval

   The Last Listener Query Interval is the Maximum Response Delay
   inserted into Multicast-Address-Specific Queries sent in response to
   Done messages, and is also the amount of time between Multicast-
   Address-Specific Query messages.  Default: 1000 (1 second)

   This value may be tuned to modify the "leave latency" of the link.  A
   reduced value results in reduced time to detect the departure of the
   last listener for an address.

7.9.  Last Listener Query Count

   The Last Listener Query Count is the number of Multicast-Address-
   Specific Queries sent before the router assumes there are no
   remaining listeners for an address on a link.  Default: the
   Robustness Variable.

7.10.  Unsolicited Report Interval

   The Unsolicited Report Interval is the time between repetitions of a
   node's initial report of interest in a multicast address.  Default:
   10 seconds.

8.  Message Destinations

   This information is provided elsewhere in the document, but is
   summarized here for convenience.

Message Type                       IPv6 Destination Address
------------                       ------------------------
General Query                      link-scope all-nodes (FF02::1)
Multicast-Address-Specific Query   the multicast address being queried
Report                             the multicast address being reported
Done                               link-scope all-routers (FF02::2)

9.  Security Considerations

   We consider the ramifications of a forged message of each type.  Note
   that the requirement that nodes verify that the IPv6 Source Address
   of all received MLD messages is a link-local address defends them
   from acting on forged MLD messages originated off-link, so we discuss
   only the effects of on-link forgery.








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   Query message:

        A forged Query message from a machine with a lower IP address
        than the current Querier will cause Querier duties to be
        assigned to the forger.  If the forger then sends no more Query
        messages, other routers' Other Querier Present timer will time
        out and one will resume the role of Querier.  During this time,
        if the forger ignores Done messages, traffic might flow to
        addresses with no listeners for up to [Multicast Listener
        Interval].

        A forged Query message sent to an address with listeners will
        cause one or more nodes that are listeners to that address to
        send a Report.  This causes a small amount of extra traffic on
        the link, but causes no protocol problems.

   Report message:

        A forged Report message may cause routers to think there are
        listeners for an address present on a link when there are not.
        However, since listening to a multicast address is generally an
        unprivileged operation, a local user may trivially gain the same
        result without forging any messages.

   Done message:

        A forged Done message will cause the Querier to send out
        Multicast-Address-Specific Queries for the address in question.
        This causes extra processing on each router and on each of the
        address's listeners, and extra packets on the link, but cannot
        cause loss of desired traffic.

10.  Acknowledgments

   MLD was derived from IGMPv2 [IGMPv2], which was designed by Rosen
   Sharma and Steve Deering and documented by Bill Fenner.















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11.  References

   [ADDR-ARCH]  Hinden, R. and S. Deering, "IP Version 6 Addressing
                Architecture", RFC 2373, July 1998.

   [ICMPv6]     Conta, A. and S. Deering, "Internet Control Message
                Protocol (ICMPv6) for the Internet Protocol Version 6
                (IPv6) Specification", RFC 2463, December 1998.

   [IGMPv2]     Fenner, W., "Internet Group Management Protocol, Version
                2", RFC 2236, November 1997.

   [IPv6]       Deering, S. and R. Hinden, "Internet Protocol, Version 6
                (IPv6) Specification", RFC 2460, December 1998.

   [IPv6-ETHER] Crawford, M., "Transmission of IPv6 Packets over
                Ethernet Networks", RFC 2464, December, 1998.

   [KEYWORDS]   Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RTR-ALERT]  Partridge, C. and A. Jackson, "IPv6 Router Alert
                Option", RFC 2711, October 1999.

   [STD-PROC]   Bradner, S., "The Internet Standards Process -- Revision
                3", BCP 9, RFC 2026, October 1996.

























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12.  Authors' Addresses

   Stephen E. Deering
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA 95134-1706
   USA

   Phone: [phone]
   EMail: [e-mail]


   William C. Fenner
   AT&T Research
   75 Willow Road
   Menlo Park, CA 94025
   USA

   Phone: [phone]
   EMail: [e-mail]


   Brian Haberman
   IBM Corporation
   800 Park Office Drive
   Research Triangle Park, NC  27709
   USA

   Phone: [phone]
   EMail: [e-mail]





















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13.  Full Copyright Statement

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.



















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