One document matched: draft-fujisaki-6man-addr-select-opt-00.xml
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<rfc category="std" ipr="trust200902" docName="draft-fujisaki-6man-addr-select-opt-00.txt">
<front>
<title abbrev='DHCPv6 Address Selection Policy Opt'>
Distributing Address Selection Policy using DHCPv6
</title>
<author initials='T.F.' surname="Fujisaki" fullname='Tomohiro Fujisaki'>
<organization abbrev='NTT'>NTT PF Lab</organization>
<address>
<postal>
<street>3-9-11 Midori-Cho</street>
<city>Musashino-shi</city>
<region>Tokyo</region>
<code>180-8585</code>
<country>Japan</country>
</postal>
<phone>+81 422 59 7351</phone>
<email>fujisaki@nttv6.net</email>
</address>
</author>
<author initials='A.M.' surname="Matsumoto" fullname='Arifumi Matsumoto'>
<organization abbrev='NTT'>NTT PF Lab</organization>
<address>
<postal>
<street>3-9-11 Midori-Cho</street>
<city>Musashino-shi</city>
<region>Tokyo</region>
<code>180-8585</code>
<country>Japan</country>
</postal>
<phone>+81 422 59 3334</phone>
<email>arifumi@nttv6.net</email>
</address>
</author>
<author initials='R.H.' surname="Hiromi" fullname='Ruri Hiromi'>
<organization abbrev='Intec Netcore'>Intec Netcore, Inc.</organization>
<address>
<postal>
<street>Shinsuna 1-3-3</street>
<city>Koto-ku</city>
<region>Tokyo</region>
<code>136-0075</code>
<country>Japan</country>
</postal>
<phone>+81 3 5665 5069</phone>
<email>hiromi@inetcore.com</email>
</address>
</author>
<date month="July" year="2010"> </date>
<area>Internet</area>
<workgroup>6man Working Group</workgroup>
<keyword>Internet-Draft</keyword>
<abstract>
<t>
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.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
RFC3484 <xref target="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
<xref target="RFC5220"/>, and mechanisms to
control a proper source address selection will be necessary.
Requiremets for those mechanisms are described in <xref target="RFC5221"/>.
Solutions are discussed
in <xref target="I-D.ietf-6man-addr-select-sol"/> and
<xref target="I-D.ietf-6man-addr-select-considerations"/>.
This document describes an
option for distributing address selection policy information
using DHCPv6, which is refered as `most proactive approach' in the
solution document, and `perferable protocol to deliver RFC3848 policies'
in consideration document.
</t>
<section title="Conventions Used in This Document">
<t>
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 <xref target="RFC2119"/>.
</t>
</section>
<section title="Terminology">
<t>This document uses the terminology defined in <xref
target="RFC2460"/> and the DHCP specification defined in
<xref target="RFC3315"/></t>
</section>
</section>
<section title="Address Selection Policy Option">
<t>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. </t>
<t>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.</t>
<t>The format of the Address Selection Policy option is
given below:</t>
<figure><artwork>
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) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[Fig. 1]
</artwork></figure>
<t>
<list style='hanging' hangIndent='5'>
<t hangText="Fields:"> <vspace blankLines='1' /> </t>
<t hangText="option-code:"> OPTION_DASP (TBD)
<vspace blankLines='1' />
</t>
<t hangText="option-len:">
The total length of the label fields, precedence fields,
zone-index fields, prefix-len fields, and prefix fields
in octets.
<vspace blankLines='1' />
</t>
<t hangText="label:">
An 8-bit unsigned integer; this value is used to make a combination of
source address prefixes and destination address prefixes.
<vspace blankLines='1' />
</t>
<t hangText="precedence:">
An 8-bit unsigned integer; this value is used for sorting destination
addresses.
<vspace blankLines='1' />
</t>
<t hangText="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.
<vspace blankLines='1' />
</t>
<t hangText="n bit:">
'no privacy iid' bit. If n bit is set to 1,
RFC 4941 <xref target="RFC4941"/> privacy extensions MUST NOT be
used for this prefix. If n bit is 0, interface ID may use RFC4941.
<vspace blankLines='1' />
</t>
<t hangText="reserved:">
6-bit reservied field. Initialized to zero by sender, and ignored
by receiver.
<vspace blankLines='1' />
</t>
<t hangText="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 <xref target="RFC3493"/> as 'scope ID'.
<vspace blankLines='1' />
</t>
<t hangText="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.
<vspace blankLines='1' />
</t>
<t hangText="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.
<vspace blankLines='1' />
</t>
</list></t>
</section>
<section title="Appearance of this Option ">
<t>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.</t>
</section>
<section title="Implementation Considerations">
<t>
<list style='symbols'>
<t>
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).
<vspace blankLines='1' />
</t>
<t>
Currently, the value label, precedence are defined
as 8-bit unsigned integers. In almost all cases, this value will be
enough.
<vspace blankLines='1' />
</t>
<t>
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).
<vspace blankLines='1' />
</t>
<t>
Since the number of selection rules would be large, policy distributer
should be care about the DHCPv6 message size.
<vspace blankLines='1' />
</t>
<t>
If there are multiple DHCPv6 servers (e.g. a node with multiple
interface), a node may have multiple address selection policies.
Since RFC3484 policy table is one and global for a node, the node have
to decide how to process multiple policies. This policy conflict is
discussed in
<xref target="I-D.ietf-6man-addr-select-considerations"/>.
<vspace blankLines='1' />
</t>
</list></t>
</section>
<section title="Discussion">
<t>
<list style='symbols'>
<t>
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.
<vspace blankLines='1' />
</t>
<t>
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.
<vspace blankLines='1' />
</t>
<t>
There may be some demands to control the use of special address types
such as the temporary addresses described in RFC4941 <xref
target="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.
<vspace blankLines='1' />
</t>
</list></t>
</section>
<section title="Security Considerations">
<t>
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.
</t>
<t>
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."
</t>
</section>
<section title="IANA Considerations">
<t>
IANA is requested to assign option codes to OPTION_DASP from the
option-code space as defined in section "DHCPv6 Options" of RFC 3315.
</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2119;
&rfc3315;
&rfc3484;
</references>
<references title="Informative References">
&rfc2460;
&rfc3493;
&rfc4941;
&rfc5220;
&rfc5221;
&SELECTSOL;
&CONSIDER;
</references>
</back>
</rfc>
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