One document matched: draft-ietf-softwire-ds-lite-tunnel-option-10.xml
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<rfc ipr="trust200902" category="std"
docName="draft-ietf-softwire-ds-lite-tunnel-option-10">
<front>
<title abbrev="DS-Lite DHCPv6 Option">Dynamic Host Configuration Protocol
for IPv6 (DHCPv6) Option for Dual-Stack Lite</title>
<author initials="D." surname="Hankins" fullname="David W. Hankins">
<organization abbrev="Google">Google, Inc.</organization>
<address>
<postal>
<street>1600 Amphitheatre Parkway</street>
<city>Mountain View</city>
<code>94043</code>
<region>CA</region>
<country>USA</country>
</postal>
<email>dhankins@google.com</email>
</address>
</author>
<author fullname="Tomasz Mrugalski" initials="T.M." surname="Mrugalski">
<organization>Gdansk University of Technology</organization>
<address>
<postal>
<street>ul. Storczykowa 22B/12</street>
<!-- Reorder these if your country does things differently -->
<code>80-177</code>
<city>Gdansk</city>
<country>Poland</country>
</postal>
<phone>+48 698 088 272</phone>
<email>tomasz.mrugalski@eti.pg.gda.pl</email>
<!-- uri and facsimile elements may also be added -->
</address>
</author>
<date day="7" month="March" year="2011"/>
<area>Internet</area>
<workgroup>Softwire</workgroup>
<keyword>DHCPv6</keyword>
<keyword>Softwire</keyword>
<keyword>DS-Lite</keyword>
<abstract>
<t>This document specifies a DHCPv6 option which is meant
to be used by a Dual-Stack Lite Basic Bridging Broadband (B4)
element to discover the IPv6 address of its corresponding Address
Family Transition Router (AFTR).</t>
</abstract>
</front>
<middle>
<section title="Requirements Language">
<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">RFC 2119</xref>.</t>
</section>
<section title="Introduction">
<t><xref target="I-D.softwire-ds-lite">Dual-Stack Lite</xref> is a
solution to offer both IPv4 and IPv6 connectivity to customers which
are addressed only with an IPv6 prefix (no IPv4 address is assigned to
the attachment device). One of its key components is an IPv4-over-IPv6
tunnel, commonly referred to as a Softwire. A DS-Lite "Basic
Bridging BroadBand" (B4) device will not know if the network it
is attached to offers Dual-Stack Lite service, and if it did would not
know the remote endpoint of the tunnel to establish a softwire.</t>
<t>To inform the B4 of the Address Family Transition Router's (AFTR)
location, a <xref target="RFC1035">DNS</xref> hostname may be used.
Once this information is conveyed, the presence of the configuration
indicating the AFTR's location also informs a host to initiate
Dual-Stack Lite (DS-Lite) service and become a Softwire Initiator.</t>
<t>To provide the conveyance of the configuration information, a single
<xref target="RFC3315">DHCPv6</xref> option is used, expressing the
AFTR's Fully Qualified Domain Name (FQDN) to the B4 element.</t>
<t>The details of how the B4 establishes an IPv4-in-IPv6 softwire
to the AFTR are out of scope for this document.</t>
</section>
<section title='The AFTR-Name DHCPv6 Option' anchor='option-name'>
<t>The AFTR-Name option consists of option-code and option-len fields
(as all DHCPv6 options have), and a variable length
tunnel-endpoint-name field containing a fully qualified domain name
that refers to the AFTR which the client MAY connect to.</t>
<t>The AFTR-Name option SHOULD NOT appear in any other than the
following DHCPv6 messages: Solicit, Advertise, Request, Renew, Rebind,
Information-Request and Reply.</t>
<t>The format of the AFTR-Name option is shown in the following
figure:</t>
<figure align="center" anchor="option-format-name"
title="AFTR-Name DHCPv6 Option Format">
<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_AFTR_NAME: (TBD) | option-len |
+-------------------------------+-------------------------------+
| |
| tunnel-endpoint-name (FQDN) |
| |
+---------------------------------------------------------------+
OPTION_AFTR_NAME: (TBD)
option-len: Length of the tunnel-endpoint-name field in
octets.
tunnel-endpoint-name: A fully qualified domain name of the AFTR
tunnel endpoint.
</artwork>
</figure>
<t>The tunnel-endpoint-name field is formatted as
required in <xref target="RFC3315">DHCPv6</xref> Section 8
("Representation and Use of Domain Names"). Briefly, the
format described is using a single octet noting the length of one
DNS label (limited to at most 63 octets), followed by the label
contents. This repeats until all labels in the FQDN are exhausted,
including a terminating zero-length label. Any updates to Section 8
of <xref target="RFC3315">DHCPv6</xref> also apply to encoding of this
field. An example format for this option is shown in
<xref target="fqdn-example"/>, which conveys the FQDN
"aftr.example.com.".</t>
<figure align="center" anchor="fqdn-example"
title="Example tunnel-endpoint-name.">
<artwork>
+------+------+------+------+------+------+------+------+------+
| 0x04 | a | f | t | r | 0x07 | e | x | a |
+------+------+------+------+------+------+------+------+------+
| m | p | l | e | 0x03 | c | o | m | 0x00 |
+------+------+------+------+------+------+------+------+------+
</artwork>
</figure>
<t>Note that in the specific case of the
<xref target="fqdn-example">example tunnel-endpoint-name</xref>,
the length of the tunnel-endpoint-name is 18 octets, and so an
option-len field value of 18 would be used.</t>
<!--<t>The option is validated by confirming that the option-len is greater
than 3, that the option data can be contained by the option length
(that the option length does not run off the end of the packet), that
individual label lengths do not exceed the option length, and
that the tunnel-endpoint-name is of valid format as described in
<xref target="RFC3315">DHCPv6 Section 8</xref>; there are no
compression tags, there is at least one label of nonzero
length.</t>-->
<t>The option is validated by confirming that all of the
following conditions are met:
<list style="numbers">
<t>the option-len is greater than 3;</t>
<t>the option data can be contained by the option length
(that the option length does not run off the end of the
packet);</t>
<t>the individual label lengths do not exceed the option length;</t>
<t>the tunnel-endpoint-name is of valid format as described in
DHCPv6 Section 8 <xref target="RFC3315"/>;</t>
<t>there are no compression tags;</t>
<t>there is at least one label of nonzero length.</t>
</list>
</t>
</section>
<section title="DHCPv6 Server Behavior">
<t>A DHCPv6 server SHOULD NOT send more than one AFTR-Name
option. It SHOULD NOT permit the configuration of multiple names
within one AFTR-Name option. Both of these conditions are handled
exceptionally by the client, so an operator using software that does
not perform these validations should be careful not to configure
multiple domain names.</t>
<t><xref target="RFC3315">RFC 3315 Section 17.2.2</xref>
describes how a DHCPv6 client and server negotiate configuration
values using the Option Request Option (OPTION_ORO). As a convenience
to the reader, we mention here that a server will not reply with a
AFTR-Name option if the client has not explicitly enumerated it on
its Option Request Option.</t>
</section>
<section title="DHCPv6 Client Behavior">
<t>A client that supports the B4 functionality of DS-Lite (defined
in <xref target="I-D.softwire-ds-lite"/>) and conforms to
this specification MUST include OPTION_AFTR_NAME on its OPTION_ORO.</t>
<t>Because it requires DNS name to address resolution, the client MAY
also wish to include the
<xref target="RFC3646">OPTION_DNS_SERVERS</xref> option on its
OPTION_ORO.</t>
<t>If the client receives the AFTR-Name option, it MUST verify the
option contents as described in <xref target="option-name"/>.</t>
<t>Note that in different environments, the B4 element and DHCPv6 client
may be integrated, joined, or separated by a third pieces of software.
For the purpose of this specification, we refer to the "B4 system" when
specifying implementation steps that may be processed at any stage of
integration between the DHCPv6 client software and the B4 element it is
configuring.</t>
<t>If the B4 system receives more than one AFTR-Name option, it
MUST use only the first instance of that option.</t>
<t>If the AFTR-Name option contains more than one FQDN,
as distinguished by the presence of multiple root labels, the B4
system MUST use only the first FQDN listed in configuration.</t>
<t>The B4 system performs standard DNS resolution using the provided FQDN
to resolve a AAAA Resource Record, as defined in
<xref target="RFC3596"/> and STD 13 <xref target="RFC1034"/>
<xref target="RFC1035"/>.</t>
<t>If any DNS response contains more than one IPv6 address, the B4 system
picks only one IPv6 address and uses it as a remote tunnel endpoint for
the interface being configured in the current message exchange.
The B4 system MUST NOT establish more than one DS-Lite tunnel at the
same time per interface. For a redundancy and high availability
discussion, see Section 12.3 "High availability" of
<xref target="I-D.softwire-ds-lite"/>.</t>
<t>Note that a B4 system may have multiple network interfaces, and these
interfaces may be configured differently; some may be connected to
networks that call for DS-Lite, and some may be connected to networks
that are using normal dual stack or other means. The B4 system should
approach this specification on an interface-by-interface basis. For
example, if the B4 system is attached to multiple networks that provide
the AFTR Name option, then the B4 system MUST configure a tunnel for
each interface separately as each DS-Lite tunnel provides IPv4
connectivity for each distinct interface. Means to bind a
AFTR Name and DS-Lite tunnel configuration to a given interface in a
multiple interfaces device are out of scope of this document.
</t>
</section>
<section title="Security Considerations">
<t>This document does not present any new security issues, but as with
all DHCPv6-derived configuration state, it is completely possible that
the configuration is being delivered by a third party (Man In The
Middle). As such, there is no basis to trust that the access the
DS-Lite Softwire connection represents can be trusted, and it should
not therefore bypass any security mechanisms such as IP firewalls.</t>
<t><xref target="RFC3315">RFC 3315</xref> discusses DHCPv6-related
security issues.</t>
<t><xref target="I-D.softwire-ds-lite"></xref> discusses DS-Lite
related security issues.</t>
</section>
<section title="IANA Considerations">
<t>IANA is requested to allocate single DHCPv6 option code referencing
this document, delineating OPTION_AFTR_NAME.</t>
</section>
<section title="Acknowledgements">
<t>Authors would like to thank Alain Durand, Rob Austein, Dave
Thaler, Paul Selkirk, Ralph Droms, Mohamed Boucadair, Roberta
Maglione and Shawn Routhier for their valuable feedback and
suggestions.</t>
<t>This work has been partially supported by the Polish Ministry
of Science and Higher Education under the European Regional Development
Fund, Grant No. POIG.01.01.02-00-045/09-00 (Future Internet Engineering
Project).</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc1034;
&rfc1035;
&rfc2119;
&rfc3315;
&rfc3596;
&rfc3646;
<reference anchor="I-D.softwire-ds-lite">
<front>
<title>Dual-stack lite broadband deployments post IPv4
exhaustion</title>
<author initials='A.' surname='Durand' fullname='Alain
Durand' role="editor">
<organization abbrev='CMCST'>Comcast</organization>
</author>
<!-- <date day="11" month="August" year='2010'/> -->
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-softwire-dual-stack-lite"/>
</reference>
</references>
</back>
</rfc>
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