One document matched: draft-jinchoi-mobileip-frd-00.txt

INTERNET DRAFT                                            JinHyeock Choi
Expires: August 2003                                        DongYun Shin
                                                             Samsung AIT
                                                           February 2003


              Fast Router Discovery with RA Caching in AP
                  <draft-jinchoi-mobileip-frd-00.txt>


Status of this Memo

     This document is an Internet-Draft and is in full conformance with
     all provisions of Section 10 of RFC2026.

     Internet Drafts are working documents of the Internet Engineering
     Task Force (IETF), its areas, and working groups. Note that other
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     Internet-Drafts are draft documents valid for a maximum of six
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     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt.

     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.


Abstract

     This document presents RA Caching in AP for Fast Router Discovery.
     For seamless handoff, a mobile node MUST quickly discover its new
     access router. In our proposal AP caches Router Advertisement
     message and sends it to a new mobile node as soon as L2 association
     is made.  We present a way for AP to cache necessary RA. By putting
     'RA Caching' and 'AP Notification' functionality on AP, we get the
     optimized result without IPv6 standard change.



Table of Contents:

     1. Introduction
     2. Terminology
     3. Proposal Overview
     4. Operation Description
       4.1 RA Caching
       4.2 AP Notification
     5. L2 trigger




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     6. Security Considerations
     References



1. Introduction

     The primary movement detection mechanism for Mobile IPv6 defined in
     [2] uses the facilities of IPv6 Neighbor Discovery [1], including
     Router Discovery and Neighbor Unreachability Detection. A mobile
     node MUST quickly detect when it moves to a link served by a new
     access router, so that it can acquire a new care-of address and
     send Binding Updates quickly. A mobile node MUST receive Router
     Advertisement from a new access router as soon as possible.

     There are several hindrances for sufficiently fast Router
     Discovery. First, Neighbor Discovery protocol [1] limits routers to
     a minimum interval of 3 seconds between sending unsolicited
     multicast Router Advertisement messages. Second, it SHOULD delay
     the transmission for a random amount of time before a mobile node
     sends an initial Router Solicitation. Third, a router MUST delay a
     response to a Router Solicitation by a random time too. Though
     solutions are proposed by [2],[3], they require IPv6 standard [1]
     change.

     In our proposal AP (Access Point) caches RA (Router Advertisement)
     message and sends it to a new mobile node as soon as L2 association
     is made.  We present a way for AP to cache necessary RA. By putting
     'RA Caching' and 'AP Notification' functionality on an Access
     Point, we get the optimized result without IPv6 standard change. In
     our scheme, mobile node receives Router Advertisement just after L2
     association is made which is the earliest possible time under
     current standard.



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.

          Access Router (AR)
            An Access Network Router residing on the edge of an Access
            Network and offers IP connectivity to mobile nodes

          Access Point (AP)
            An L2 entity that has station functionality and provides
            access to the distribution services, via the wireless
            medium for associated stations.






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INTERNET DRAFTFast Router Discovery with RA Caching in AP  February 2003


3. Proposal Overview

     In 802.11 b Wireless LAN technology, when a MN (mobile node)
     arrives at a new link, it should associate with its new AP.

     In our proposal, AP caches RA message beforehand and sends it to a
     mobile node as soon as L2 association is made.

     We can cache RA in AP manually or use the following scheme.  AR
     (Access Router) periodically multicasts unsolicited RA, which go
     through AP. So AP can scan incoming L2 frames and cache necessary
     RA. AP scans L2 frame either continuously or periodically to update
     stored RA. Moreover if AR and AP are under same network
     administration, they can be configured such that AP caches RA
     efficiently.



4. Operation Description

     Our proposal consists of 'RA Caching' and 'AP Notification', RA
     Caching periodically scans incoming L2 frame for unsolicited RA and
     stores it. AP Notification sends stored RA to new MN as soon as L2
     association is made.



4.1. RA Caching

     AP scans incoming L2 frame for unsolicited RA.

     First it scans L2 frame header to see whether it is a multicast
     frame. If not, AP sends that frame down link and scans next L2
     frame. If so, AP looks IP header to check whether it contains
     unsolicited RA. If incoming L2 frame doesn't contain unsolicited
     RA, AP sends that frame down link and scans next L2 frame.  When AP
     finds unsolicited RA, it stores it and sends a copy down link.

     AP can scan continuously, updating old RA with new RA. Or if it
     costs too much for AP to scan every incoming L2 frame, we can
     control the scanning rate. For example, we can set timer and
     execute scanning every T seconds. Or we can make AP to be able to
     send Router Solicitation message. Periodically AP sends Router
     Solicitation.  Then AR will send RA and AP caches it. It is noted
     that AP doesn't need to have IP address since it can use
     unspecified address as its source address.



4.2. AP Notification






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     When a new MN arrives at AP, it sends Association Request Message
     with its MAC address. Then AP grants association by sending
     Association Response Message. As soon as association is made, AP
     sends stored RA to a new MN with MAC address in Association Request
     message. MN receives RA just after association is made which is the
     earliest possible time in current standard.



5. L2 trigger

     L2 trigger is a notification from L2 that a certain event has
     happened or is about to happen. We formulate our poposal as a
     trigger like below.


             L2           Event        Recipient      Parameters
           Trigger
       +-------------+---------------+------------+-----------------+
       |    Fast     |  When new L2  |     MN     |     Router      |
       |   Router    |  association  |            |  Advertisement  |
       |  Discovery  |    is made.   |            |                 |


     In other way, the above trigger may be incorporated with Link Up
     trigger. We can add Router Advertisement message as a new parameter
     for Link Up Trigger.



6. Security Considerations

     Since our proposal is based on Neighbor Discovery, its trust models
     and threats are similar to the ones presented in [5]. There are
     also Movement Detection specific threats described in 8.0 of [4].


     If higher layer notification of connectivity is not available, and
     eager handoff strategies are in place, any node or router which
     advertises an RA with a false prefix will cause mobile nodes to
     perform spurious handover signalling and DAD operations.


     But above threats are inherent to all schemes which depends
     exclusively on Router Discovery for movement detection. Our
     proposal doesn't incur any additional threats. We will incorporate
     the solutions developed in IETF SEND Working Group when available.



References





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INTERNET DRAFTFast Router Discovery with RA Caching in AP  February 2003


[1]  T. Narten, E. Nordmark and W. Simpson, Neighbor Discovery for IP
     Version 6 (IPv6), RFC 2461, December, 1998.

[2]  D. Johnson, C. Perkins and J. Arkko, Mobility Support in IPv6,
     Internet-Draft (work in progress), January 2003

[3]  J. Kempf, M. M Khalil and B. Pentland, IPv6 Fast Router Advertise-
     ment, Internet-Draft (work in progress), October 2002

[4]  G. Daley and JinHyeock Choi, Movement Detection Optimization in
     Mobile IPv6, Internet-Draft (work in progress), February 2003

[5]  P. Nikander, J. Kempf and E. Nordmark, IPv6 Neighbor Discovery
     trust models and threats, Internet-Draft (work in progress), Jan-
     uary 2003



Author's Addresses

   JinHyeock Choi
   i-Networking Lab, Samsung AIT (SAIT)
   Phone: +82-31-280-9233
   Email: athene@sait.samgung.co.kr

   DongYun Shin
   i-Networking Lab, Samsung AIT (SAIT)
   Phone: +82-31-280-9552
   Email: yun7521@samgung.co.kr



























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