Internet DRAFT - draft-hong-mobileip-acar
draft-hong-mobileip-acar
Mobile-IP Working Group Yong-Geun Hong
Internet Draft Myung-Ki Shin
Draft-hong-mobileip-acar-01.txt Jung-Soo Park
Expires: April 2004 Hyoung-Jun Kim
ETRI
October 2003
Access Router Based Movement Detection and CoA Configuration
draft-hong-mobileip-acar-01.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
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The list of current Internet-Drafts can be accessed at
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Abstract
This document proposes Access Router (AR) based movement detection
and Care-of Address (CoA) configuration for fast handover in Mobile
IPv6 using layer 2 hints (for example, Link Up in 802.11). After
receiving these layer 2 hints, an Active Access Router (AcAR) which
will serve a Mobile Node (MN) performs movement detection, formulates
a new CoA of the MN and does Duplicate Address Detection (DAD) on
behalf of the MN. After confirming the uniqueness of the new CoA, the
AcAR sends it through a RA message. Since an AcAR can quickly
determine the L3 movement by the comparison between neighbor caches
and L2 information of a MN, the movement detection delay is reduced.
Since DAD is performed by an AcAR in advance, a MN does not have to
do normal DAD and it can use a new CoA for its interface directly.
And it may reduce another handover delay which is added because of
the characteristics of an application layer.
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Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. Protocol Overview..............................................3
3.1 Movement Detection.........................................3
3.2 CoA configuration and Duplicate Address Detection..........4
3.3 Delivering new CoA to MN...................................4
4. Modification to IPv6 Neighbor Discovery........................5
4.1 Modified Router Solicitation Message Format................5
4.2 Modified Router Advertisement Message Format...............5
4.3 Modified Prefix Information Option Format..................6
Security Considerations...........................................7
References........................................................7
Acknowledgments...................................................8
Author's Addresses................................................8
1. Introduction
In Mobility Support in IPv6 (MIPv6) [1], a MN can determine its
network layer movement by using Router Discovery and Neighbor
Unreachability Detection. After a MN makes a new CoA, it must check
its uniqueness by DAD. The delay of movement detection, new CoA
configuration and DAD are inevitable in MIPv6 because of its basic
operations. But the combined delay could be appreciable for real-time
applications and throughput-sensitive applications [2]. Until now,
there are many efforts to reduce the handover latency, especially in
movement detection phase and in new CoA configuration phase. For fast
movement detection, there are many drafts such as IPv6 Fast Router
Advertisement [3], Fast Router Discovery with RA Caching in AP [4],
and Router Advertisement Link Identification for Mobile IPv6 Movement
Detection [5]. Also, there are many drafts such as Enhanced
Forwarding from Previous Care-of Address for Fast Mobile IPv6
Handover (eFWD) [6], Optimistic Duplicate Address Detection [7], and
Advance Duplicate Address Detection [8] for fast new CoA
configuration and DAD.
This document proposes Access Router (AR) based movement detection
and CoA configuration for fast handover in Mobile IPv6 using layer 2
hints (for example, Link Up in 802.11). After receiving these layer 2
hints, an Active Access Router (AcAR) which will serve a MN performs
movement detection, formulates a new CoA of the MN and does DAD on
behalf of the MN immediately after L2 handoff. Since an AcAR can
quickly determine the L3 movement by the comparison between neighbor
caches and L2 information of a MN, the movement detection delay is
reduced. After confirming the uniqueness of the new CoA, the AcAR
sends it through a RA message. Since DAD is performed by an AcAR in
advance, a MN does not have to do normal DAD and it can use the new
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CoA for its interface. And it may reduce another handover delay which
is added because of the characteristics of an application layer.
2. Terminology
CoA Care-of Address
DAD Duplicate Address Detection
MN Mobile Node
AcAR Active Access Router
It performs movement detection, CoA configuration and DAD on
behalf of a MN.
3. Protocol Overview
The goal of this draft is that it explicitly uses layer 2 hints for
fast handover. Although the increased rate of unsolicited Router
Advertisement (RA) messages may provide timely movement detection,
this scheme of modified interval time is not an ultimate solution :
it increases considerable overhead and makes it difficult to connect
another common networks. Another goal of this draft is that it
considers movement detection as well as new CoA configuration, and
DAD simultaneously at AR. Until now, most only focus on one of them.
And only a MN does any necessary operations to detect L3 movement
such as soliciting a Router Solicitation (RS), checking the
reachability of an old AR, checking the validation of an old CoA and
waiting RA messages from any ARs. If a MN and an AR have the same
information to detect L3 movement, the AR may take the role of
movement detection. It is same to CoA configuration and DAD. If an AR
generates a new CoA for a MN, it can do DAD instead of a MN.
3.1 Movement Detection
When mobile IPv6 networks have a possibility to connect another
public networks and the frequency of unsolicited RAs have problems
for traffic loads, the proposed mechanism provides a reasonable
solution for receiving Router Advertisement more quickly.
After the completion of L2 handoff, a MN and an AR may know it by
some general L2 event. Especially in 802.11 networks, the LU trigger
may be used after reassociation.request and reassociation.reply
messages sharing.
In our proposed scheme, L3 movement detection is processed by an AR.
We call this AR as an Active Access Router (AcAR). The initiation of
movement detection is enabled by L2 triggers at a MN immediately
after the completion of L2 handoff and delivered to the network layer
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of a MN. When L2 triggers are delivered to a network layer, the MN
sends a unicast RS message before any general operations. This
operation should be happened before any general operations and
processed independently of an application layer.
Note that in general operations, sending unicast Neighbor
Solicitation of an old AR and multicasting RS are happen after the
failure of application layer operation trial or other layer operation
trial. In some test, we found it takes a few seconds.
After an AcAR receive this RS message, it can do movement detection
operation. The AcAR compare the L2 identifier of a MN (MAC address in
case of 802.11) with the values in neighbor caches. The comparison
results in two cases.
- The L2 identifier is not found in neighbor cache. It means that
the MN is a new comer of the subnet area of the AcAR. So the AcAR
prepare CoA generation and DAD operation. This situation is that
the MN is moved between each AR which has a different subnet
prefix.
- The L2 identifier is found in neighbor caches. It means that the
MN is already served by the AcAR. So the AcAR does not have to do
CoA generation and DAD operation. The only thing needed is that
the AcAR must immediately inform it to the MN and enables the MN
to continuously use the existing CoA. This situation is that the
MN is not moved between each AR which has a different subnet
prefix. For example, in 802.11 networks, the MN is moved between
different AP but each AP is connected to the same AR. In this case,
L2 handoff is happened, but L3 handover is not happened. So other
CoA configuration and DAD operation for the MN is unnecessary.
3.2 CoA configuration and Duplicate Address Detection
If an AcAR decides to generate a CoA for a MN, it uses its prefix
information and L2 information of the MN which is included in Source
link-layer address options of RS. As described in IPv6 Stateless
Address Autoconfiguration [12], a CoA is generated using normal IPv6
mechanism. An AcAR already has a prefix as one router and L2
information is provided by a modified RS messages.
After configuration of a new CoA, an AcAR does DAD operation on
behalf of a MN. If DAD is succeeded, an AcAR can deliver the CoA to a
MN. If DAD is failed, it follows normal IPv6 mechanism.
3.3 Delivering new CoA to MN
When a MN requests a CoA through a modified RS message, an AcAR
responds to the MN with a modified RA message which includes a new
CoA. When L3 movement is not happened even thought L2 handoff is
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happened, an AcAR informs it to an MN and enables the MN to
continuously use the existing CoA immediately after movement
detection.
4. Modification to IPv6 Neighbor Discovery
4.1 Modified Router Solicitation Message Format
Host sends Router Solicitations in order to prompt routers to
generate Router Advertisements quickly [13]. Like this, a MN can send
modified RS messages to AcARs to obtain a new CoA. To do this, we
modify the basic RS message by the addition of a single flag bit (C)
to indicate that the MN sending the RS message wants to get a new CoA
from AcARs.
0 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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|C| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source link-layer address options
+-+-+-+-+-+-+-+-+-+-+-+-
This format represents the following changes over that originally
specified for Neighbor Discovery [13].
CoA Generate (C)
1-bit CoA generate flag. When set, indicates that this RS message
is to request AcARs to generate a new CoA and respond
Reserved
Reduced from a 32-bit field to a 31-bit field to account for the
addition of the above bit
Options
Use Source link-layer address options. This options is used to
check the proper node for assigning new CoA by AcAR
4.2 Modified Router Advertisement Message Format
Routers send out Router Advertisement messages periodically, or in
response to a router Solicitation [13]. Like this, an AcAR responds
to the above RS message. We modify the basic RA message by the
addition of a single flag bit (C) to indicate that the modified
prefix information option includes the new generated CoA for the MN.
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0 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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O|H|C|Res... | Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Information options
+-+-+-+-+-+-+-+-+-+-+-+-
This format represents the following changes over that originally
specified for MIPv6 [1].
CoA Generate (C)
1-bit CoA generate flag. When set, indicates that this RA message
is advertised by an AcAR and the prefix information option in
this RA message includes the new generated CoA for the MN.
Reserved
Reduced from a 5-bit field to a 4-bit field to account for the
addition of the above bit
Options
Use the modified prefix information option. This option is used
to deliver the generated CoA to the MN by AcAR.
4.3 Modified Prefix Information Option Format
MIPv6 extends Neighbor Discovery to allow a router to advertise its
global address, by the addition a single flag bit in the format of a
prefix information for use in a RA message [1]. Like this, we modify
the prefix information option by the addition a single flag (C) bit
to indicate that the prefix field in this option contains the CoA for
the MN.
0 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 | Length | Prefix Length |L|A|R|C|Res.. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This format represents the following changes over that originally
specified for MIPv6 [1].
CoA Generate (C)
1-bit CoA generate flag. When set, indicates that the prefix
field contains a complete IP address that will be assigned to the
MN as a CoA.
Reserved
Reduced from a 5-bit field to a 4-bit field to account for the
addition of the above bit
Prefix
The complete IP address which is generated by an AcAR for a CoA of
the MN. If the IP address is the same to the existing CoA of MN,
it indicated that the MN can use the existing CoA even though L2
handoff.
Security Considerations
In our proposed scheme, a delivering of L2 triggers to a network
layer of a MN may not be security issues because it operates in a
system. Security issues of using a modified RS, RA message and
modified Prefix Information Option is not beyond the scope of
Neighbor Discovery and MIPv6.
References
[1] D. Johnson, C. Perkins, J. Arkko, "Mobility Support in IPv6",
draft-ietf-mobileip-ipv6-24.txt (work in progress), June 2003
[2] Koodli, R., "Fast Handovers for Mobile IPv6", draft-ietf-mipshop-
fast-mipv6-00.txt (work in progress), October 2003.
[3] J. Kempf, M. Khalil, B. Pentland. "IPv6 Fast Router
Advertisement", draft-mkhalil-ipv6-fastra-03.txt, March 2002.
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[4] JinHyoeck Choi, DongYun Shin. "Fast Router Discovery with RA",
draft-jinchoi-mobileip-frd-00.txt (work in progress), Feb 2003.
[5] B. Pentland, G. Daley, "Router Advertisement Link Identification
for Mobile IPv6 Movement Detection", draft-pentland-mobileip-
linkid-00.txt (work in progress), May 2003.
[6] Youngjune Gwon, A. Yegin, "Enhanced Forwarding from Previous
Care-of Address for Fast Mobile IPv6 Handovers (eFWD)",
draft-gwon-mobileip-efwd-fmipv6-01.txt, June 2002.
[7] N. Moore, "Optimistic Duplicated Address Detection", draft-moore-
ipv6-optimistic-dad-01.txt (work in progress), Feb 2003.
[8] Y. Han, Y. Choi, S. Park, "Advance Duplicate Address Detection",
draft-han-mobileip-adad-00.txt (work in progress), June 2003.
[9] A. Yegin, et al, "Supporting Optimized Handover for IP Mobility-
Requirements for Underlying Systems", draft-manyfolks-l2-
mobilereq-02.txt, June 2002.
[10]"Recommended Practice for Multi-Vendor Access Point
Interoperability via an Inter-Access Point Protocol Across
Distribution Systems Supporting IEEE 802.11 Operation," IEEE Std
802.11f/D1, DRAFT.
[11] A. Yegin, "Link-layer Triggers Protocol", draft-yegin-l2-
triggers-00.txt, June 2002.
[12] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[13] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
IP Version 6 (IPv6)", RFC 2461, December 1998.
Acknowledgments
Thanks to Hee Young Jung, Seok Joo Koh and Kyeong Jin Lee for
providing valuable feedback and contributing to this draft.
Author's Addresses
Yong-Guen Hong
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
Tel : +82 42 860 6447
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AR-Based MD and CoA Configuration June 2003
Fax : +82 42 861 5404
E-mail : yghong@etri.re.kr
Myung-Ki Shin
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
Tel : +82 42 860 4847
Fax : +82 42 861 5404
E-mail : mkshin@etri.re.kr
Jung-Soo Park
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
Tel : +82 42 860 6514
Fax : +82 42 861 5404
E-mail : pjs@etri.re.kr
Hyoung-Jun Kim
ETRI PEC
161 Gajeong-Dong, Yuseong-Gu, Daejeon 305-350, Korea
Tel : +82 42 860 6576
Fax : +82 42 861 5404
E-mail : khj@etri.re.kr
Hong, Shin, Park, Kim Expires: April 2004 [Page 9]
