One document matched: draft-fujisaki-dhc-addr-select-opt-03.txt
Differences from draft-fujisaki-dhc-addr-select-opt-02.txt
DHC Working Group T. Fujisaki
Internet-Draft A. Matsumoto
Intended status: Standards Track J. Kato
Expires: July 5, 2007 S. Niinobe
NTT
Jan 2007
Distributing Default Address Selection Policy using DHCPv6
draft-fujisaki-dhc-addr-select-opt-03.txt
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Copyright Notice
Copyright (C) The Internet Society (2007).
Abstract
This document describes a new DHCPv6 option for distributing default
address selection policy information defined in RFC3484 to a client.
With this option, site administrators can distribute address
selection policy to control the node's address selection behavior.
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1. Introduction
RFC3484 [RFC3484] describes algorithms for selecting a default
address when a node has multiple destination and/or source addresses
by using an address selection policy. However, there are some
problems with the default address selection policy in RFC3484
[I-D.ietf-v6ops-addr-select-ps], and administrators can change the
node's address selection behavior by distributing the policy.
Practical usages are described in [I-D.arifumi-ipv6-policy-dist].
This document describes an option for distributing default address
selection policy information using DHCPv6.
2. Terminology
This document uses the terminology defined in [RFC2460] and the DHCP
specification defined in [RFC3315]
3. Default Address Selection Policy Option
The Default Address Selection Policy Option provides policy
information for address selection rules. Specifically, it transmits
a set of IPv6 source and destination address prefixes and some
parameters that are used to control address selection as described in
RFC 3484.
Each end node is expected to configure its policy table, as described
in RFC 3484, in a manner consistent with the Default Address
Selection Policy option information.
The format of the Default Address Selection Policy option is given
below:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_DASP | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| label | precedence | zone-index | prefix-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Prefix (Variable Length) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| label | precedence | zone-index | prefix-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Prefix (Variable Length) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| label | precedence | zone-index | prefix-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Prefix (Variable Length) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[Fig. 1]
Fields:
option-code: OPTION_DASP (TBD)
option-len: The total length of the label fields, precedence fields,
zone-index fields, prefix-len fields, and prefix fields in
octets.
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label: An 8-bit unsigned integer; this value is used to make a
combination of source address prefixes and destination address
prefixes.
precedence: An 8-bit unsigned integer; this value is used for
sorting destination addresses.
zone-index: An 8-bit unsigned integer; this value is used to specify
zones for scoped addresses.
prefix-len: An 8-bit unsigned integer; the number of leading bits in
the prefix that are valid. The value ranges from 0 to 128. The
Prefix field is 0, 4, 8, 12, or 16 octets, depending on the
length.
Prefix: A variable-length field containing an IP address or the
prefix of an IP address. IPv4-mapped address [mapped] must be
used to represent an IPv4 address as a prefix value.
4. Appearance of this Option
The Default Address Selection Policy option MUST NOT appear in any
messages other than the following ones : Solicit, Advertise, Request,
Renew, Rebind, Information-Request, and Reply.
5. Implementation Considerations
o The value 'label' is passed as an unsigned integer, but there is
no special meaning for the value, that is whether it is a large or
small number. It is used to select a preferred source address
prefix corresponding to a destination address prefix by matching
the same label value within this DHCP message. DHCPv6 clients
need to convert this label to a representation specified by each
implementation (e.g., string).
o Currently, the value label, precedence, and zone indices are
defined as 8-bit unsigned integers. In almost all cases, this
value will be enough.
o The 'precedence' is used to sort destination addresses. There
might be some cases where precedence values will conflict when a
client already has a selection policy configured or a client
receives multiple policies from multiple DHCP servers (e.g., when
a home gateway in a user network is connected to multiple upstream
ISPs). In such cases, manual configuration of the policy will be
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necessary.
o The maximum number of address selection rules in one DHCPv6
message depend on the prefix length of each rules and maximum
DHCPv6 message size defined in RFC3315. It is possible to carry
over 3,000 rules (e.g. default policy table defined in RFC3484
contains 5 rules) in one DHCPv6 message (maximum UDP message
size).
o Since the number of selection rules would be large, policy
distributer should be care about the DHCPv6 message size.
6. Discussion
o The 'zone index' value is used to specify a particular zone for
scoped addresses. This can be used effectively to control address
selection in the site scope (e.g., to tell a node to use a
specified source address corresponding to a site-scoped multicast
address). However, in some cases such as a link-local scope
address, the value specifying one zone is only meaningful locally
within that node. There might be some cases where the
administrator knows which clients are on the network and wants
specific interfaces to be used though. However, it is hard to use
this value in general case.
o We also proposed a policy distribution option using a Router
Advertisement message defined in RFC2461 [RFC2461]. There was a
discussion that using DHCPv6 was more suitable to distribute a
selection policy, because such policy should be distributed under
the site administrator's centralized control.
o There may be some demands to control the use of temporary
addresses described in RFC3041 [RFC3041] (e.g., informing not to
use a temporary address when it communicate within the an
organization's network). Since a temporary address cannot
represent as an IPv6 address and its prefix, some semantics to
specify the temporary address will be necessary to control it
(such as a flag to indicate a temporary address or a special
representation for temporary address in prefix field).
7. Security Considerations
A rogue DHCPv6 server could issue bogus default address selection
policies to a client. This might lead to incorrect address selection
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by the client, and the affected packets might be blocked at an
outgoing ISP because of ingress filtering.
To guard against such attacks, both DCHP clients and servers SHOULD
use DHCP authentication, as described in section 21 of RFC 3315,
"Authentication of DHCP messages."
8. IANA Considerations
IANA is requested to assign option codes to OPTION_DASP from the
option-code space as defined in section "DHCPv6 Options" of RFC 3315.
Appendix A. RFC3484 implementation status
Today, many operating systems implement address selection mechanism
defined in RFC3484. Many of them, however, implement the
specification partially. We summarize current implementation status
of RFC 3484 at http://www.nttv6.net/dass/.
Appendix B. Revision History
03:
Discussion about DHCPv6 packetsize and number of rules added.
Authors' e-mail addresses corrected.
Some editorial changes.
9. References
9.1. Normative References
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
9.2. Informative References
[I-D.arifumi-ipv6-policy-dist]
Matsumoto, A., "Practical Usages of Address Selection
Policy Distribution", draft-arifumi-ipv6-policy-dist-01
(work in progress), June 2006.
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[I-D.ietf-v6ops-addr-select-ps]
Matsumoto, A., "Problem Statement of Default Address
Selection in Multi-prefix Environment: Operational Issues
of RFC3484 Default Rules",
draft-ietf-v6ops-addr-select-ps-00 (work in progress),
November 2006.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2461] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461,
December 1998.
[RFC3041] Narten, T. and R. Draves, "Privacy Extensions for
Stateless Address Autoconfiguration in IPv6", RFC 3041,
January 2001.
Authors' Addresses
Tomohiro Fujisaki
NTT PF Lab
3-9-11 Midori-Cho
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81 422 59 7351
Email: fujisaki.tomohiro@lab.ntt.co.jp
Arifumi Matsumoto
NTT PF Lab
3-9-11 Midori-Cho
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81 422 59 3334
Email: arifumi@nttv6.net
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Jun-ya Kato
NTT PF Lab
3-9-11 Midori-Cho
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81 422 59 2939
Email: kato@syce.net
Shirou Niinobe
NTT PF Lab
3-9-11 Midori-Cho
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81 422 59 4949
Email: nin@syce.net
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