One document matched: draft-xia-16ng-end-00.txt
Network Working Group F. Xia
Internet-Draft B. Sarikaya
Expires: December 7, 2006 Huawei USA
June 5, 2006
Duplicate Address Detection Optimization Using Enhanced Neighbor
Discovery
draft-xia-16ng-end-00
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This draft describes a possible optimization to Duplicate Address
Detection (DAD) which can be used to successfully terminate DAD
early. The method is based on a positive RA message sent by an
access router that knows all the IPv6 addresses of the nodes
currently attached to it.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Existing Alternatives . . . . . . . . . . . . . . . . . . . . 5
3.1. A-DAD . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Optimistic DAD . . . . . . . . . . . . . . . . . . . . . . 5
3.3. MLD-DAD . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Scenario of Enhanced Neighbor Discovery . . . . . . . . . . . 6
4.1. Address cache . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Relay DAD procedure . . . . . . . . . . . . . . . . . . . 6
4.3. Modifications to RFC-Mandated behavior . . . . . . . . . . 6
4.3.1. Neighbor Solicitation Message Format . . . . . . . . . 7
4.3.2. Router Advertisement Message Format . . . . . . . . . 7
4.4. Host (MS) Behavior . . . . . . . . . . . . . . . . . . . . 8
4.5. Access Router Behavior . . . . . . . . . . . . . . . . . . 9
4.6. Stateful Address Configuration . . . . . . . . . . . . . . 9
4.7. Timing Analysis . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Normative References . . . . . . . . . . . . . . . . . . . 11
6.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
IPv6 nodes can statelessly auto configure their own IP addresses on a
network, based on the information sent by the IPv6 router of that
network. When a node wishes to create a new address on an interface,
it combines the network prefix obtained from the router with a suffix
generated from its 64-bit Interface Identifier. This new untested
address is referred to as a Tentative Address (TA). The node joins
the appropriate solicited-node multicast group for this address, then
sends a Neighbor Solicitation (NS) message containing the TA. If the
TA is already in use by another node, that node will reply with a
Neighbor Advertisement (NA) defending the TA.
Once it has sent the NS, the node waits for RetransTimer [DISCOVERY]
milliseconds to see if a defending NA is forthcoming, and this
solicit-and-wait process is repeated DupAddrDetectTransmits
[DISCOVERY] times. The default value of RetransTimer is 1000ms and
by default the process is only done once, resulting a delay of 1000ms
or 1s.
This procedure provides a reasonable approach to checking address
uniqueness in situations such as fixed installation, or even mobile
web-browsing where 1s is not a significant delay. However, it is not
tolerable for some time-critical mobile applications like Voice Over
IP (VoIP).
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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 BCP 14 [STANDARDS].
node - a device that implements IPv6.
host - a node that is not a router.
router - a node that forwards IPv6 packets not explicitly addressed
to itself
MS - mobile station
BRAS - Broadband Remote Access Server
ASN-GW - Access Service Network Gateway, defined in WiMAX System
Architecture
access router - a router knowing all access hosts information about
IP address, accounting, QoS and so on, e.g. BRAS, or ASN-GW
END - Enhanced Neighbor Discovery
MLD - Multicast Listener Discovery
A-DAD - Advanced Duplicate Address Detection
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3. Existing Alternatives
3.1. A-DAD
An A-DAD capable router as per [draft-han-mobileip-adad-01] supplies
address to a node from a pool of addresses which are known to be
unique on the link. A host can safely configure this address without
performing DAD, as the router has ensured that the address is unique.
In order to provide the addresses for this pool, the router must
create addresses based on random suffixes as per [PESAA] and
undertake standard DAD on them. In essence, DAD is done in advance
by the router.
3.2. Optimistic DAD
The standard DAD strategy can be described as pessimistic, since the
node delays all communication until it is confident that a new
address is not a duplicate. [DISCOVERY] introduces the concept of
Tentative (in Section 5.4) and Deprecated (in Section 5.5.4)
addresses. Addresses that are neither are said to be Preferred.
Tentative addresses may not be used for communication, and Deprecated
addresses should not be used for new communications. [OPTDAD]
introduces a new address state, 'Optimistic', that is used to mark an
address that is available for use but that has not completed DAD.
Unless noted otherwise, components of the IPv6 protocol stack should
treat addresses in the Optimistic state equivalently to those in the
Deprecated state, indicating that the address is available for use
but should not be used if another suitable address is available. In
essence, DAD is done in parallel.
3.3. MLD-DAD
The Multicast Listener Discovery (MLD) [MLD] requires a node to send
an MLD report before listening to the solicited-node multicast
address. This process requires informing the router on a link about
the presence of listeners for the address, so that a multicast group
can be managed.
The optimization described in [draft-daley-ipv6-mcast-dad-02]
document allows a node to ask the router to tell it if it is the
first node to enter this multicast group. If it is the first to
enter the group, then it follows that no one else is currently
performing DAD defense against the required unicast address. In
essence, DAD is done in a positive way.
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4. Scenario of Enhanced Neighbor Discovery
In WiMAX architecture, an access router (ASN-GW) is the first IP
attachment point for an MS. The ASN-GW knows all the IPv6 addresses
of the nodes currently attached to it. The ASN-GW maintains an
Address Cache containing all addresses on the IP link. The ASN-GW
can receive all the packets sent by MSs irrespective of the
destination address type (unicast/multicast).
4.1. Address cache
Address Cache is a conceptual data structure managed by an ASN-GW
that contains a list of addresses that are being used by the MSs.
The entries can be created from information received in DAD Neighbor
Solicitations or other way. The entries in the address cache can be
deleted when there is an explicit deregistration message from the
corresponding MS or another entity that is authorized to deregister
on behalf of the MS
4.2. Relay DAD procedure
Relay DAD is the procedure to perform when address collision occurs
in architectures like WiMAX Network Architecture.
To check an address, an MS sends Neighbor Solicitations as per
[DISCOVERY] and [ADDRCONF]. Upon receiving the NS, the ASN-GW
compares the tentative address in the NS against the entries in its
Address Cache. If there is no match, the ASN-GW makes an entry for
the (tentative) address in its Address Cache and sends a special
Router Advertisement to the MS indicating the address's uniqueness,
as will be descripted later.
If there exists a match which indicates that the address is
duplicate, the ASN-GW relays the NS to the address owner without any
modification. Upon receiving the NS, the address owner replies with
an NA to defend its address. The NA's Target Address is copied from
the Target Address of the NS, the IP Source Address is also set to
the Target Address of the NS and the IP Destination Address is set to
the all-node multicast address. The ASN-GW relays the NA to the
soliciting MS without any modification. Upon receiving the defending
NA, the soliciting MS perceives the address conflict and refrains
from assigning the tentative address to the interface.
4.3. Modifications to RFC-Mandated behavior
1. A "P" indication bit is added to the reserved section of NS.
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2. A "P" indication bit is added to the reserved section of RA.
3. Some procedures change to deal with these bits.
4.3.1. Neighbor Solicitation Message Format
The new NS message format is shown in Figure 1 where the extension
proposed in this document is P bit.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Target Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 1: Neighbor Solicitation Format
The fields are as defined in [DISCOVERY]. P is one bit, SHOULD be
set if an MS wants to get a positive reply.
4.3.2. Router Advertisement Message Format
The new RA message format is shown in Figure 2 where the extension
proposed in this document is P bit.
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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|P|Reserved | Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Information Option |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Other Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 2: Router Advertisement Format
The fields are as defined in [DISCOVERY], one bit (P bit) is added to
the Reserved field. When an access router (ASN-GW) receives a NS
with P bit set for DAD, it checks the Target Address in it's address
cache, and finds that the address is unique, the access router SHOULD
send a solicited RA. In this message, the P bit MUST be set, and a
prefix information option MUST be included. The prefix information
option is as defined in [DISCOVERY]. The prefix length MUST be set
to 128. The prefix field MUST be filled with the Target Address of
the NS used for DAD. When the MS(host) performing DAD receives this
message, it SHOULD stop DAD process, and configure the address on
it's interface.
4.4. Host (MS) Behavior
With the P bit in NS and RA, a host(MS) can work in a very active
way. That is, the host SHOULD send NS with P bit set, wait for a
reply which could be an NA or RA, and set a timer. It SHOULD resend
the NS if an NA or RA is not received in a given time interval,
RetransTimer. This process SHOULD repeat a configurable number of
times, DupAddrDetectTransmits. After retrying configured times, if
there is still no reply, the host SHOULD stop retrying and abandon
the address.
In the WiMAX environment, END is an improvement to the normal DAD
[ADDRCONF] and optimistic DAD defined in [OPTDAD]. Both of them are
working in a passive mode, that is, if no defending NA is received,
the detected address is considered unique. In fact, there are some
other possibilities why a defending NA is not received, such as the
solicited NS is lost, or the defending NA is lost.
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A host which implements the enhanced neighbor discover (END) can
interoperate with other nodes implementing [ADDRCONF] or [OPTDAD].
In a host, END and [OPTDAD] modes of operation MAY be enabled
simultaneously.
4.5. Access Router Behavior
When an access router (ASN-GW) receives an NS with P bit set for DAD,
if it finds there is no such address in it's address cache, it SHOULD
send a positive RA message with "P" bit set, else it MUST relay the
message to the IP address owner.
When a access router receives a normal NS without P bit set, if it
finds that there is a such address in the address cache, it MUST
relay the message to the IP address owner using Relay DAD, else it
SHOULD ignore the message.
4.6. Stateful Address Configuration
If a host configures its address using stateful address configuration
and if DHCP server assures the uniqueness of the IPv6 address
assigned, then ND procedure is not necessary, so END is not
applicable. However if the address assigned may not be unique then
the host MUST follow the procedure defined in Section 4.4 above.
4.7. Timing Analysis
In normal DAD, the process defined in [DISCOVERY] and [ADDRCONF],
takes DupAddrDetectTransmits*RetransTimer before the host can start
using the address. In Optimistic DAD process [OPTDAD], as soon as an
address is configured on an interface, the address can be used. That
is, it takes 0 ms to use a tentative address with the risk of address
collision.
In case of END described in this memo, it takes a NS and RA round
trip time so that an address can be determined unique in most cases.
The round trip duration is much less than
DupAddrDetectTransmits*RetransTimer.
If END and [OPTDAD] are enabled, the host will benefit from both the
reliability and time advantages.
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5. Security Considerations
There are existing security concerns with Neighbor Discovery and
Stateless Address Auto configuration. Secure Neighbor Discovery
(SEND) [SEND] provides protection against the threats to Neighbor
Discovery described in [NDTM]. This memo does not introduce any
additional threats to Neighbor Discovery.
In Relay DAD, access routers relay NS and NA between MSs without
modifying any contents of messages. The target address in Neighbor
Advertisement and in solicited Router Advertisement is equal to the
source address of the packet.
MS can use CGAs for it's own address as defined [SEND]. MS can also
use Authorization Delegation Discovery [SEND] to find an authorized
access router (ASN-GW).
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6. References
6.1. Normative References
[ADDRCONF]
Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998,
<ftp://ftp.isi.edu/in-notes/rfc2462>.
[DISCOVERY]
Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998, <ftp://ftp.isi.edu/in-notes/rfc2461>.
[MLD] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery for IPv6", RFC 2710, October 1999,
<ftp://ftp.isi.edu/in-notes/rfc2710>.
[NDTM] Nikander, P., Kempf, J., and E. Nordmark, "IPv6 Neighbor
Discovery (ND) Trust Models and Threats", RFC 3756,
May 2004, <ftp://ftp.isi.edu/in-notes/rfc3756 >.
[OPTDAD] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, April 2006,
<ftp://ftp.isi.edu/in-notes/rfc4429>.
[PESAA] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001, <ftp://ftp.isi.edu/in-notes/rfc3041>.
[SEND] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "Secure
Neighbor Discovery (SEND)", RFC 3971, March 2005,
<ftp://ftp.isi.edu/in-notes/rfc3971>.
[STANDARDS]
Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997,
<ftp://ftp.isi.edu/in-notes/rfc2119>.
6.2. Informative References
[draft-daley-ipv6-mcast-dad-02]
Daley, G. and R. Nelson, "Duplicate Address Detection
Optimization using IPv6 Multicast Listener Discovery",
September 2003, <http://www.watersprings.org/pub/id/
draft-daley-ipv6-mcast-dad-02.txt>.
[draft-han-mobileip-adad-01]
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Han, Y., Choi, J., Jang, H., and S. Park, "Advance
Duplicate Address Detection", December 2003, <http://
www.watersprings.org/pub/id/
draft-han-mobileip-adad-01.txt>.
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Authors' Addresses
Frank Xia
Huawei USA
1700 Alma Dr. Suite 100
Plano, TX 75075
Phone: +1 972-509-5599
Email: xiayangsong@huawei.com
Behcet Sarikaya
Huawei USA
1700 Alma Dr. Suite 100
Plano, TX 75075
Phone: +1 972-509-5599
Email: sarikaya@ieee.org
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