DHC Working Group T. Fujisaki
Internet-Draft A. Matsumoto
Intended status: Standards Track S. Niinobe
Expires: September 10, 2009 NTT
R. Hiromi
Intec Netcore
K. Kanayama
Intec
March 9, 2009
Distributing Address Selection Policy using DHCPv6
draft-fujisaki-dhc-addr-select-opt-07.txt
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Internet-Draft DHCPv6 Address Selection Policy Opt March 2009
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Abstract
This document describes a new DHCPv6 option for distributing 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.
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
described in [RFC5220], and mechanisms to control a proper source
address selection will be necessary. Requiremets for those
mechanisms are described in [RFC5221], and solutions are discussed in
[I-D.ietf-6man-addr-select-sol] This document describes an option for
distributing address selection policy information using DHCPv6, which
is refered as `most proactive approach' in the solution document.
1.1. Conventions Used in This Document
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 RFC2119 [RFC2119].
1.2. Terminology
This document uses the terminology defined in [RFC2460] and the DHCP
specification defined in [RFC3315]
2. Address Selection Policy Option
The 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.
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Each end node is expected to configure its policy table, as described
in RFC 3484, using the Address Selection Policy option information as
an reference.
The format of the Address Selection Policy option is given below:
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 |z|n| reserved | prefix-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| zone-index (if present (z = 1)) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Prefix (Variable Length) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| label | precedence |z|n| reserved | prefix-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| zone-index (if present (z = 1)) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Prefix (Variable Length) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| label | precedence |z|n| reserved | prefix-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| zone-index (if present (z = 1)) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Prefix (Variable Length) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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[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.
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.
z bit 'zone-index' bit. If z bit is set to 1, 32 bit zone-index
value is included right after the "prefix-len" field, and
"Prefix" value continues after the "zone-index" field. If z bit
is 0, "Prefix" value contitunes right after the "prefix-len"
value.
n bit 'no privacy iid' bit. If n bit is set to 1, RFC 4941
[RFC4941] privacy extensions MUST NOT be used for this prefix.
If n bit is 0, interface ID may use RFC4941.
reserved 6-bit reservied field. Initialized to zero by sender, and
ignored by receiver.
zone-index: If z-bit is set to 1, this field is inserted between
"prefix-len" field and "Prefix" field. Zone-index field is an
32-bit unsigned integer and used to specify zones for scoped
addresses. This bit length is defined in RFC3493 [RFC3493] as
'scope ID'.
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.
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3. Appearance of this Option
The Address Selection Policy option MUST NOT appear in any messages
other than the following ones : Solicit, Advertise, Request, Renew,
Rebind, Information-Request, and Reply.
4. 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 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
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.
o If a ndoe has multiple interfaces, the node may have multiple
address selection policies. Since RFC3484 policy table is one and
global for a node, multiple polices should be merged in one. In a
case that node's interfaces belong to different management domain
(e.g. each interfaces are connected different site), it would have
conflict policies. In that case, it would be possible to merge
them by using other information such as routing information or
preference for each interfaces, however, such automatic policy
merge lead to potential security problems such as using unintended
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source addresses.
5. 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, in general case,
it is hard to use this value.
o Since we got a comment that some implementations use 32-bit
integers for zone index value, we extended the bit lenght of the
'zone index' field. However, as described above, there might be
few cases to specify 'zone index' in policy distribution, we
defined this field as optional, controled by a flag.
o There may be some demands to control the use of special address
types such as the temporary addresses described in RFC4941
[RFC4941], address assigned by DHCPv6 and so on. (e.g., informing
not to use a temporary address when it communicate within the an
organization's network). It is possible to indicate the type of
addresses using reserved field value.
o We also proposed a policy distribution option using a Router
Advertisement message defined in RFC4861 [RFC4861]. 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.
6. Security Considerations
A rogue DHCPv6 server could issue bogus address selection policies to
a client. This might lead to incorrect address selection 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."
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7. 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
07:
Added the n bit and its description.
06:
Added the reason to extend zone index field in discussions
section.
References updated.
Authors' e-mail addresses corrected.
Some editorial changes.
05:
Extended bit length of the zone-index field to 32-bits (thank you
Jinmei-sanfor your comment), and changed packet format to reflect
the extension.
Refrect Yoshifuji-san's comment to use this option information as
an reference.
Modified the text controling special address types.
04:
Added description about policy merge.
Modified the text controling special address types.
03:
Discussion about DHCPv6 packetsize and number of rules added.
Authors' e-mail addresses corrected.
Some editorial changes.
8. References
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8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
8.2. Informative References
[I-D.ietf-6man-addr-select-sol]
Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
"Solution approaches for address-selection problems",
draft-ietf-6man-addr-select-sol-01 (work in progress),
June 2008.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, February 2003.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC5220] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
"Problem Statement for Default Address Selection in Multi-
Prefix Environments: Operational Issues of RFC 3484
Default Rules", RFC 5220, July 2008.
[RFC5221] Matsumoto, A., Fujisaki, T., Hiromi, R., and K. Kanayama,
"Requirements for Address Selection Mechanisms", RFC 5221,
July 2008.
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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@nttv6.net
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
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
Ruri Hiromi
Intec Netcore, Inc.
Shinsuna 1-3-3
Koto-ku, Tokyo 136-0075
Japan
Phone: +81 3 5665 5069
Email: hiromi@inetcore.com
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Ken-ichi Kanayama
INTEC Systems Institute, Inc.
Shimoshin-machi 5-33
Toyama-shi, Toyama 930-0804
Japan
Phone: +81 76 444 8088
Email: kanayama_kenichi@intec-si.co.jp
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