One document matched: draft-ietf-6man-addr-select-opt-07.xml
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
<!ENTITY rfc2119 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml'>
<!ENTITY rfc2460 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.2460.xml'>
<!ENTITY rfc4291 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4291.xml'>
<!ENTITY rfc4861 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4861.xml'>
<!ENTITY rfc4941 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.4941.xml'>
<!ENTITY rfc3315 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3315.xml'>
<!ENTITY rfc3493 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3493.xml'>
<!ENTITY rfc3484 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.3484.xml'>
<!ENTITY rfc6724 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.6724.xml'>
<!ENTITY rfc5220 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5220.xml'>
<!ENTITY rfc5221 PUBLIC ''
'http://xml.resource.org/public/rfc/bibxml/reference.RFC.5221.xml'>
<!ENTITY SELECTSOL PUBLIC 'SELECTSOL'
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-6man-addr-select-sol.xml'>
<!ENTITY DTCONS PUBLIC 'DTCONS'
'http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-6man-addr-select-considerations.xml'>
]>
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<?rfc autobreaks="yes" ?>
<?rfc toc="no" ?>
<?rfc compact="yes" ?>
<?rfc sortrefs="yes"?>
<?rfc iprnotified="no" ?>
<?rfc strict="yes" ?>
<?rfc symrefs="yes" ?>
<rfc category="std" ipr="pre5378Trust200902" docName="draft-ietf-6man-addr-select-opt-07.txt">
<front>
<title abbrev='DHCPv6 Address Selection Policy Opt'>
Distributing Address Selection Policy using DHCPv6
</title>
<author initials='A.M.' surname="Matsumoto" fullname='Arifumi Matsumoto'>
<organization abbrev='NTT'>NTT NT 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='T.F.' surname="Fujisaki" fullname='Tomohiro Fujisaki'>
<organization abbrev='NTT'>NTT NT 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='T.C.' surname="Chown" fullname='Tim Chown'>
<organization abbrev='University of Southampton'>University of Southampton</organization>
<address>
<postal>
<street>Southampton, Hampshire SO17 1BJ</street>
<country>United Kingdom</country>
</postal>
<email>tjc@ecs.soton.ac.uk</email>
</address>
</author>
<date month="November" year="2012"/>
<area>Internet</area>
<workgroup>6man Working Group</workgroup>
<keyword>Internet-Draft</keyword>
<abstract>
<t>
RFC 6724 defines default address selection mechanisms for IPv6 that
allow nodes to select appropriate address when faced with multiple
source and/or destination addresses to choose between. The RFC 6724
allowed for the future definition of methods to administratively
configure the address selection policy information. This document
defines a new DHCPv6 option for such configuration, allowing a site
administrator to distribute address selection policy overriding the
default address selection parameters and policy table, and thus
control the address selection behavior of nodes in their site.
</t>
</abstract>
</front>
<middle>
<section title="Introduction"> <!-- 1 -->
<t>
RFC 3484 <xref target="RFC3484"/> describes default algorithms
for selecting an address when a node has multiple destination and/or
source addresses to choose from by using an address selection policy.
In Section 2 of RFC 6724, it is suggested that the default policy table
may be administratively configured to suit the specific needs of a site.
This specification defines a new DHCPv6 option for such configuration.
</t>
<t>
Some problems have been identified with the default RFC 3484 address
selection policy <xref target="RFC5220"/>.
It is unlikely that any default policy will suit all scenarios, and thus
mechanisms to control the source address selection policy will be
necessary. Requirements for those mechanisms are described in <xref
target="RFC5221"/>, while solutions are discussed
in <xref target="I-D.ietf-6man-addr-select-sol"/> and
<xref target="I-D.ietf-6man-addr-select-considerations"/>. Those
documents have helped shape the improvements in
the default address selection algorithm
<xref target="RFC6724"/> as well as the DHCPv6
option defined in this specification.
</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 <xref target="RFC2119"/>.
</t>
</section>
<section title="Terminology">
<t>
This document uses the terminology defined in <xref
target="RFC2460"/> and the DHCPv6 specification defined in
<xref target="RFC3315"/>
</t>
</section>
</section>
<section title="Address Selection options"> <!-- 2 -->
<t>The Address Selection option provides
the address selection policy table, and some other configuration
parameters.
</t>
<t>
An Address Selection option contains zero or more policy table options.
Multiple Policy Table options in an Address Selection option
constitute a single policy table.
</t>
<t>The format of the Address Selection 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_ADDRSEL | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |A|P| |
+-+-+-+-+-+-+-+-+ POLICY TABLE OPTIONS |
| (variable length) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Address Selection option format
</artwork></figure>
<t>
<list style='hanging' hangIndent='5'>
<t hangText="option-code:"> OPTION_ADDRSEL (TBD).
<vspace blankLines='1' />
</t>
<t hangText="option-len:">
The total length of the Reserved field, A, P flags,
and POLICY TABLE OPITONS in octets.
<vspace blankLines='1' />
</t>
<t hangText="Reserved:">
Reserved field. Server MUST set this value to zero and
client MUST ignore its content.
<vspace blankLines='1' />
</t>
<t hangText="A:">
Automatic Row Addition flag.
This flag toggles the Automatic Row Addition flag
at client hosts, which is described in the section 2.1
in RFC 6724 <xref target="RFC6724"></xref>.
If this flag is set to 1, it does not change client
host behavior, that is, a client MAY automatically
add additional site-specific rows to the policy table.
If set to 0, the Automatic Row Addition flag is disabled,
and a client SHOULD NOT automatically add rows to the
policy table.
<vspace blankLines='1' />
</t>
<t hangText="P:">
Privacy Preference flag.
This flag toggles the Privacy Preference flag
at client hosts, which is described in the section 5
in RFC 6724
<xref target="RFC6724"></xref>.
If this flag is set to 1, it does not change client
host behavior, that is, a client will prefer
temporary addresses.
If set to 0, the Privacy Preference flag is disabled,
and a client will prefer public addresses.
<vspace blankLines='1' />
</t>
<t hangText="POLICY TABLE OPTIONS:">
Zero or more Address Selection Policy Table options
described below.
<vspace blankLines='1' />
</t>
</list>
</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_ADDRSEL_TABLE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| label | precedence | prefix-len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| prefix (variable length) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Address Selection Policy Table option format
</artwork></figure>
<t>
<list style='hanging' hangIndent='5'>
<t hangText="option-code:"> OPTION_ADDRSEL_TABLE (TBD).
<vspace blankLines='1' />
</t>
<t hangText="option-len:">
The total length of the label field, precedence field,
prefix-len field, and prefix field.
<vspace blankLines='1' />
</t>
<t hangText="label:">
An 8-bit unsigned integer; this value is for correlation 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="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.
<vspace blankLines='1' />
</t>
<t hangText="prefix:">
A variable-length field containing an IP address or the
prefix of an IP address. An IPv4-mapped address <xref target="RFC4291"/>
must be used
to represent an IPv4 address as a prefix value.
The prefix should be left aligned, big-endian, and zero padded on the right up to the next octet boundary.
So the length of this field should be between 0 and 16 bytes.
<vspace blankLines='1' />
</t>
</list>
</t>
</section>
<section title="Appearance of the Address Selection options"> <!-- 3 -->
<t>The Address Selection options MUST NOT appear in
any DHCPv6 messages other than the following ones: Solicit, Advertise,
Request, Renew, Rebind, Reconfigure, Information-Request, and Reply.</t>
</section>
<section title="Processing the Policy Table option"> <!-- 4 -->
<t>
This section describes how to process received
Policy Table option at the DHCPv6 client.
</t>
<t>
This option's concept is to serve as a hint for
a node about how to behave in the network.
So, basically, it should be up to the node's administrator
how to deal with the received policy information in the way described below.
</t>
<section title="Handling of the local policy table">
<t>
RFC 6724 defines the default policy table.
Also, users are usually able to configure the policy table
to satisfy their own requirements.
</t>
<t>
The client implementation SHOULD provide the following choices
to the user:
</t>
<t>
<list style="hanging">
<t hangText="a)">
replace the existing active policy table with the DHCPv6 distributed policy table.
</t>
<t hangText="b)">
preserve the existing active policy table, whether this be the default policy table, or user configured policy.
</t>
</list>
</t>
</section>
<section title="Handling of the stale policy table">
<t>
When the information from the DHCP server goes stale,
the policy received form the DHCP server should be
deprecated.
</t>
<t>
The received information can be considered stale in
several cases, such as, when the interface goes down,
the DHCP server does not respond for a certain amount
of time, and the Information Refresh Time is expired.
</t>
</section>
<section title="Multi-interface situation">
<t>
The policy table, and other parameters specified in this document
are node-global information by their nature.
One reason being that the outbound interface is usually chosen after
destination address selection.
So, a host cannot make use of multiple address selection policies even
if they are stored per interface.
</t>
<t>
Even if the received policy from one source is
merged with one from another source, the effect of both policy
are more or less changed.
The policy table is defined as a whole, so the slightest
addition/deletion from the policy table brings a change in
semantics of the policy.
</t>
<t>
It also should be noted that absence of the distributed policy from a certain
network interface should not be treated as absence of policy itself, because
it may mean preference for the default address selection policy.
</t>
<t>
Under the above assumptions, how to handle received policy is specified below.
</t>
<t>
A node MAY use Address Selection options by default in any of the following
two cases:
</t>
<t>
<list style="hanging">
<t hangText="1:">
The host is single-homed, where the host belongs to one administrative
network domain exclusively usually through one active network interface.
</t>
<t hangText="2:">
The host implements some advanced heuristics to deal with multiple received
policy, which is outside the scope of this document.
</t>
</list>
</t>
<t>
The above restrictions do not preclude implementations from providing
configuration options to enable this option on a certain network interface.
</t>
<t>
Nor, they do not preclude implementations from storing distributed
address selection policies per interface.
They can be used effectively on such implementations that adopt
per-application interface selection.
</t>
</section>
</section>
<section title="Implementation Considerations"> <!-- 5 -->
<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 the DHCP message. DHCPv6 clients SHOULD convert this
label to a representation appropriate for the local implementation (e.g.,
string).
<vspace blankLines='1' />
</t>
<t>
Currently, the label and precedence values 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 that may be conveyed
in one DHCPv6 message depends
on the prefix length of each rule and the maximum DHCPv6 message
size defined in RFC 3315. It is possible to carry over 3,000 rules
in one DHCPv6 message (maximum UDP message size).
However, it should not be expected that DHCP clients, servers and
relay agents can handle UDP fragmentation.
Network adiministrators SHOULD consider local limitations to the maximum
DHCPv6 message size that can be reliably transported via their specific
local infrastructure to end nodes; and therefore they SHOULD consider
the number of options, the total size of the options, and the resulting
DHCPv6 message size, when defining their Policy Table.
<vspace blankLines='1' />
</t>
<t>
Since the number of selection rules could be large, an administrator
configuring the policy to be distributed should consider the resulting
DHCPv6 message size.
<vspace blankLines='1' />
</t>
</list>
</t>
</section>
<section title="Security Considerations"> <!-- 6 -->
<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, incur additional network charges,
or be misdirected to an attacker's machine.
Alternatively, an IPv6 transition mechanism might be preferred over native
IPv6, even if it is available.
To guard against such attacks, a legitimate DHCPv6 server should
communicate through a secure, trusted channel, such as a channel
protected by IPsec, SEND and DHCP authentication, as described in
section 21 of RFC 3315,
</t>
<t>
Another threat is about privacy concern.
As in the security consideration section of RFC 6724, at least
a part of, the address selection policy stored in a host
can be leaked by a packet from a remote host.
This issue will not be modified by the introduction
of this option, regardless of whether the host is multihomed or not.
</t>
</section>
<section title="IANA Considerations"> <!-- 7 -->
<t>
IANA is requested to assign option codes to OPTION_ADDRSEL and
OPTION_ADDRSEL_TABLE 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;
&rfc6724;
</references>
<references title="Informative References">
&DTCONS;
&rfc2460;
&rfc3493;
&rfc4291;
&rfc4941;
&rfc5220;
&rfc5221;
&SELECTSOL;
</references>
<section title="Acknowledgements">
<t>
Authors would like to thank to Dave Thaler, Pekka Savola, Remi Denis-
Courmont, Francois-Xavier Le Bail, Ole Troan, Bob Hinden, Dmitry Anipko,
Ray Hunter, Rui Paulo, Brian E Carpenter, Tom Petch,
and the members of 6man's address selection design team for their invaluable
contributions to this document.
</t>
</section>
<section title="Past 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 really rare case, and the field was removed.
<vspace blankLines='1' />
</t>
</list></t>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 13:38:59 |