One document matched: draft-carpenter-6man-ext-transmit-01.xml

<?xml version="1.0" encoding="UTF-8"?>

<!-- This is built from a template for a generic Internet Draft. Suggestions for
     improvement welcome - write to Brian Carpenter, brian.e.carpenter @ gmail.com -->

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<!ENTITY DRAFT-fragdrop SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.taylor-v6ops-fragdrop.xml"> 


]>


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<!-- This defines the specific filename and version number of your draft (and inserts the appropriate IETF boilerplate -->
<rfc ipr="trust200902" docName="draft-carpenter-6man-ext-transmit-01" category="std" updates="2460, 2780" >


<front>
<title abbrev="IPv6 Extension Header Transmission">Transmission of IPv6 Extension Headers</title>


<author initials="B. E." surname="Carpenter" fullname="Brian Carpenter">
    <organization abbrev="Univ. of Auckland"></organization>
    <address>
      <postal>
        <street>Department of Computer Science</street>
        <street>University of Auckland</street>
        <street>PB 92019</street>
        <city>Auckland</city>
        <region></region>
        <code>1142</code>
        <country>New Zealand</country>
      </postal>
      
      <email>brian.e.carpenter@gmail.com</email>
    </address>
</author>




   <author fullname="Sheng Jiang" initials="S." surname="Jiang">
      <organization>Huawei Technologies Co., Ltd</organization>
      <address>
        <postal>
          <street>Q14, Huawei Campus</street>
          <street>No.156 Beiqing Road</street>
          <city>Hai-Dian District, Beijing</city>
          <code>100095</code>
          <country>P.R. China</country>
        </postal>
        <email>jiangsheng@huawei.com</email>
      </address>
    </author>


 


 <date day="13" month="November" year="2012" />

<area>Internet</area>
<workgroup>6man</workgroup>

 


<abstract>

<t>Various IPv6 extension headers have been defined since the IPv6 standard was first published. This document
updates RFC 2460 to clarify how intermediate nodes should deal with such extension headers and with any that
are defined in future. It also specifies how extension headers should be registered by IANA,
with a corresponding minor update to RFC 2780.
</t>
    
</abstract>
</front>

<middle>
<section anchor="intro" title="Introduction">

<t>An initial set of IPv6 extension headers was defined by <xref target="RFC2460"/>,
which also described how they should be handled by intermediate nodes,
with the exception of the hop-by-hop options header:</t>

<figure><artwork>
"...extension headers are not examined or processed
by any node along a packet's delivery path, until the packet reaches
the node (or each of the set of nodes, in the case of multicast)
identified in the Destination Address field of the IPv6 header."
</artwork></figure>

<t>This provision allowed for the addition of new extension headers, since it
means that forwarding nodes should be completely transparent to them. Thus, new
extension headers could be introduced progressively, used only by hosts that
have been updated to create and interpret them. Several such extension headers
have been defined since RFC 2460. </t>

<t>Unfortunately, experience has showed that the network is not transparent to 
these headers. The main reason for this is that some firewalls attempt to inspect
the transport header or payload. This means that they need to traverse the chain of extension
headers, if present, until they find the transport header (or an encrypted payload). 
Unfortunately, because some IPv6 extension headers do not follow a uniform TLV format, 
this process is clumsy and requires knowledge of each extension header's format. </t>

<t>The process is slow as well as clumsy, precluding its use in nodes attempting
to process packets at line speed. The present document does not intend to solve this
problem, which is caused by the fundamental architecture of IPv6 extension headers. 
This document focuses on clarifying how the header chain should be traversed
in the current IPv6 architecture. </t>

<t>If they encounter an unknown
extension header type, some firewalls treat the packet as suspect and
drop it. It is an established fact that several widely used firewalls do not
recognise some or all of the extension headers defined since RFC 2460. It has also
been observed that certain firewalls do not even handle all the extension headers
in RFC 2460, including the fragment header <xref target="I-D.taylor-v6ops-fragdrop"/>,
causing fundamental problems of connectivity. This applies in particular to firewalls
that attempt to inspect packets statelessly at very high speed, since they cannot
take the time to reassemble fragmented packets, especially when under a denial
of service attack. </t>

<t>Other types of middlebox, such as load balancers or packet
classifiers, might also fail in the presence of extension headers that
they do not recognise. </t> 

<t>A contributory factor to this problem is that, because extension headers
are numbered out of the existing IP Protocol Number space, there is no collected
list of them. For this reason, it is hard for an implementor to quickly identify
the full set of defined extension headers. An implementor who consults only RFC 2460
will miss all extension headers defined subsequently.  </t>

<t>The uniform TLV format now defined for extension headers <xref target="RFC6564"/> 
will improve the situation, but only for future extensions.
Some tricky cases would be avoided by forbidding very long chains of extension headers
that might otherwise be fragmented <xref target="I-D.ietf-6man-oversized-header-chain"/>. </t>

<t>However, these changes are insufficient to correct the underlying problem. 
The present document clarifies that the above requirement from
RFC 2460 applies to all types of node that forward IPv6 packets and to
all extension headers defined now and in the future. It also requests IANA to
create a subsidiary registry that clearly identifies extension header types,
and updates RFC 2780 accordingly. However, fundamental changes to the IPv6
extension header architecture are out of scope for this document. </t>

<t>Also, Hop-by-Hop options are not handled by many high speed routers, or are
processed only on a slow path. This document also updates the requirements for
processing the Hop-by-Hop options header to make them more realistic. </t>

<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> <!-- intro -->

<section anchor="reqt" title="Requirement to Transmit Extension Headers">

<t>The IPv6 Hop-by-Hop Options header SHOULD be processed by intermediate nodes
as described in <xref target="RFC2460"/>.
However, it is to be expected that high performance routers will either
ignore it, or assign packets containing it to a slow processing path. Designers
planning to use a Hop-by-Hop option should be aware of this likely behaviour. </t>

<t>As a reminder, in RFC 2460, it is stated that the Hop-by-Hop Options header, if present,
must be first. </t>

<t>Apart from that, any node along an IPv6 packet's path, which forwards it for any reason,
SHOULD do so regardless of any extension headers that are present, as described in RFC 2460.
Exceptionally, if this node is designed to examine extension headers for any reason,
such as firewalling, it MUST recognise and deal appropriately with all IPv6 extension header
types. The list of currently defined extension header types is maintained by IANA (see <xref target="iana"/>). </t>

<t>RFC 2460 requires destination hosts to discard packets containing unrecognised extension headers.
However, intermediate forwarding nodes MUST NOT do this by default, since that might cause them to
inadvertently discard traffic using a recently defined extension header, not yet recognised by
the intermediate node. </t>

<t>As mentioned above, firewalls that violate RFC 2460 by discarding packets containing
extension headers are known to cause connectivity failures. Therefore, it is
important that firewalls are capable of parsing all defined IPv6 extension headers
and behave according to the above requirements. If a firewall
chooses to discard a packet containing a defined IPv6 extension header, it MUST be
the result of an explicitly configured firewall policy, and not just the result of a failure to
recognise such a header. To be clear, this means that the default configuration
of a firewall MUST NOT cause defined extension headers to be discarded. Explicit configuration
of a discard policy is needed to change this. </t>

<t>The IPv6 Routing Header Types 0 and 1 have been deprecated and SHOULD NOT be used.
However, as specified in <xref target="RFC5095"/>, this does not mean that the
IPv6 Routing Header can be unconditionally dropped by forwarding nodes.
Packets containing undeprecated Routing Headers MUST be forwarded by default. 
At the time of writing, these include Type 2 <xref target="RFC6275"/>, Type 3 <xref target="RFC6554"/>,
and Types 253 and 254 <xref target="RFC4727"/>. Others may be defined in future. </t>

</section> <!-- reqt -->



<section anchor="security" title="Security Considerations">

<t>Firewall devices MUST conform to the requirements in the previous section in order
to respect the IPv6 extension header architecture.
In particular, packets containing specific extension headers are only to be discarded
as a result of explicit policy, and never as a result of the default configuration. </t>

<t>When new extension headers are defined in the future, those implementing and configuring
firewalls will need to take account of them. It is to be expected that this process will
be slow. Until it is complete, the new extension will fail in some parts of the Internet.
This aspect needs to be considered when deciding to standardise a new extension. </t>

 
</section> <!-- security -->


<section anchor="iana" title="IANA Considerations">

<t>IANA is requested to clearly mark in the Assigned Internet Protocol Numbers registry
those values which are also IPv6 Extension Header types, for example by adding an extra
column to indicate this. This will also apply to any IPv6 Extension Header types 
defined in the future. </t>

<t>Additionally, IANA is requested to replace the existing empty IPv6 Next Header Types
registry by an IPv6 Extension Header Types registry. It will contain only those protocol
numbers which are also  marked as IPv6 Extension Header types in the Assigned 
Internet Protocol Numbers registry. The initial list will be
as follows: 

<list style="symbols">

<t>0, Hop-by-Hop Options, <xref target="RFC2460"/> </t>
<t>43, Routing, <xref target="RFC2460"/>, <xref target="RFC5095"/>  </t> 
<t>44, Fragment, <xref target="RFC2460"/> </t>
<t>50, Encapsulating Security Payload, <xref target="RFC4303"/> </t>
<t>51, Authentication, <xref target="RFC4302"/> </t>
<t>58, ICMPv6, <xref target="RFC2460"/> </t>
<t>59, No Next Header, <xref target="RFC2460"/> </t>
<t>60, Destination Options, <xref target="RFC2460"/> </t>
<t>135, MIPv6, <xref target="RFC6275"/> </t>
<t>139, HIP, <xref target="RFC5201"/> </t>
<t>140, shim6, <xref target="RFC5533"/> </t>

</list> 
</t>



<t>The references to the IPv6 Next Header field in <xref target="RFC2780"/> are to be 
interpreted as also applying to the IPv6 Extension Header field. </t>


</section> <!-- iana -->




<section anchor="ack" title="Acknowledgements">

<t>
This document was triggered by mailing list discussions including
John Leslie, Stefan Marksteiner and others.

Valuable comments and contributions were made by
Dominique Barthel,
Lorenzo Colitti, 
Fernando Gont,
Suresh Krishnan,
Michael Richardson,
Dave Thaler,
Joe Touch,
and others.
 </t>

<t>Brian Carpenter was a visitor at the Computer Laboratory, Cambridge University during part of this work. </t>

<t>This document was produced using the xml2rfc tool
<xref target="RFC2629"/>.</t>

</section> <!-- ack -->


<section anchor ="changes" title="Change log [RFC Editor: Please remove]">

<t>draft-carpenter-6man-ext-transmission-01: feedback at IETF85: clarify scope
and impact on firewalls, discuss line-speed processing and lack of uniform TLV format,
added references, restructured IANA considerations, 2012-11-13.</t>

<t>draft-carpenter-6man-ext-transmission-00: original version, 2012-08-14.</t>

</section> <!-- changes -->

</middle>

<back>

<references title="Normative References">

&RFC2119;
&RFC2460;
&RFC2780;
&RFC5533;
&RFC5095;
&RFC4302;
&RFC4303;
&RFC5201;
&RFC6275;
&RFC6564;
&RFC4727;



</references>

<references title="Informative References">

&RFC2629;
&RFC6554;
&DRAFT-chain;
&DRAFT-fragdrop;

</references>



</back>
</rfc>