One document matched: draft-williams-exp-tcp-host-id-opt-00.xml
<?xml version="1.0"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
<!ENTITY rfc0793 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.0793.xml">
<!ENTITY rfc2119 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml">
<!ENTITY rfc5925 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.5925.xml">
<!ENTITY rfc6269 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.6269.xml">
<!ENTITY rfc6824 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.6824.xml">
<!ENTITY rfc6967 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.6967.xml">
<!ENTITY rfc6994 SYSTEM
"http://xml.resource.org/public/rfc/bibxml/reference.RFC.6994.xml">
<!ENTITY I-D.boucadair-intarea-host-identifier-scenarios SYSTEM
"http://xml.resource.org/public/rfc/bibxml3/reference.I-D.boucadair-intarea-host-identifier-scenarios">
<!ENTITY I-D.wing-nat-reveal-option SYSTEM
"http://xml.resource.org/public/rfc/bibxml3/reference.I-D.wing-nat-reveal-option">
<!ENTITY I-D.abdo-hostid-tcpopt-implementation SYSTEM
"http://xml.resource.org/public/rfc/bibxml3/reference.I-D.abdo-hostid-tcpopt-implementation">
<!ENTITY I-D.williams-overlaypath-ip-tcp-rfc SYSTEM
"http://xml.resource.org/public/rfc/bibxml3/reference.I-D.williams-overlaypath-ip-tcp-rfc">
]>
<?rfc toc='no'?>
<?rfc rfcprocack="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc iprnotified="no" ?>
<?rfc strict="yes" ?>
<?rfc compact="yes" ?>
<?rfc subcompact="no" ?>
<?rfc sortrefs="yes" ?>
<?rfc colonspace='yes' ?>
<?rfc tocindent='yes' ?>
<rfc ipr="trust200902" category="exp">
<front>
<title abbrev="Experimental TCP Host ID Option">Experimental Option for TCP Host Identification</title>
<author initials="B." surname="Williams" fullname="Brandon Williams">
<organization>Akamai, Inc.</organization>
<address>
<postal>
<street>8 Cambridge Center</street>
<city>Cambridge</city>
<region>MA</region>
<code>02142</code>
<country>USA</country>
</postal>
<email>brandon.williams@akamai.com</email>
</address>
</author>
<author initials="M." surname="Boucadair" fullname="Mohamed Boucadair">
<organization>France Telecom</organization>
<address>
<postal>
<street></street>
<city>Rennes</city>
<region>35000</region>
<code></code>
<country>Fance</country>
</postal>
<email>mohamed.boucadair@orange.com</email>
</address>
</author>
<author initials="D." surname="Wing" fullname="Dan Wing">
<organization>Cisco Systems, Inc.</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<city>San Jose</city>
<region>CA</region>
<code>95134</code>
<country>USA</country>
</postal>
<email>dwing@cisco.com</email>
</address>
</author>
<date year="2014" />
<abstract>
<t>Recent IETF proposals have identified benefits to more distinctly
identifying the hosts that are hidden behind a shared address/prefix
sharing device or application-layer proxy. Analysis indicates that
the use of a TCP option for this purpose can be successfully applied
to a broad range of use cases. This document describes a common
experimental TCP option format for host identification.</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>A broad range of issues associated with address sharing have been
well documented in <xref target="RFC6269" /> and
<xref target="I-D.boucadair-intarea-host-identifier-scenarios" />. In
addition, <xref target="RFC6967" /> provides analysis of various
solutions to the problem of revealing the sending hosts's identifier
(HOST_ID) information to the receiver, which indicates that a solution
using a TCP <xref target="RFC0793" /> option for this purpose can be
successfully applied to a broad range of use cases with limited
performance impact.</t>
<t>Multiple recent Internet Drafts define TCP options for the purpose of host
identification: <xref target="I-D.wing-nat-reveal-option" />,
<xref target="I-D.abdo-hostid-tcpopt-implementation" />, and
<xref target="I-D.williams-overlaypath-ip-tcp-rfc" />. This document
defines a common TCP option format to meet the needs of all three of
the above proposals. The option defined in this document uses the TCP
experimental option codepoint sharing mechanism defined in
<xref target="RFC6994" /> and is intended to allow validation of this
common option format in order to conduct more experimental work that
will complement the experiment results already documented in
<xref target="I-D.abdo-hostid-tcpopt-implementation" />.</t>
<t><xref target="interaction">Section 5</xref> of this document
discusses compatibility between this new TCP option and existing
commonly deployed TCP options.</t>
</section>
<section title="Terminology">
<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 anchor="format" title="Option Format">
<t>When used for host identification, the TCP experimental option has
the following format and content.</t>
<figure>
<artwork>
0 1 2 3
01234567 89012345 67890123 45678901
+--------+--------+--------+--------+
| Kind | Length | ExID |
+--------+--------+--------+--------+
| Host ID ...
+--------+---
</artwork>
</figure>
<t><list style="hanging">
<t hangText="Kind:">The option kind value is 253</t>
<t hangText="Length:">The length of the option is variable, based on
the required size of the host identifier (e.g. a 2 octet host ID
will require a length of 6, while a 4 octet host ID will require a
length of 8).</t>
<t hangText="ExID:">The experiment ID value is 0x0348 (840).</t>
<t hangText="Host ID:">The host identifier is an application
dependent value with an interpretation agreed upon by the sender
and the receiver.</t>
</list></t>
<t>When multiple host identifiers are required (e.g.
<xref target="I-D.williams-overlaypath-ip-tcp-rfc" /> defines an
option that provides multiple IPv4 addresses, and
<xref target="I-D.abdo-hostid-tcpopt-implementation" /> defines an
option that may provide both an address and a port), the HOST_ID
option is included multiple times within the packet, once for each
identifier. While this approach significantly increases option space
utilization when multiple identifiers are required, cases where only a
single identifier is required are more common and thus it is
beneficial to optimize for those cases.</t>
</section>
<section anchor="use" title="Option Use">
<t>Intermediary devices (e.g. address sharing device) SHOULD be
configurable to enable including the HOST_ID TCP option. These devices
MUST be configured with the type of information to populate the
HOST_ID TCP option (e.g. certain bits of the source IPv6 address, the
full source IPv6 address, certain bits of the source IPv4 address, the
full source IPv4 address, the source port number, etc.).</t>
<t>The device may be configured to include multiple identifiers (e.g.
both a source IP address and a source port number). In such case, the
device MUST insert two instances of the HOST_ID option, each of which
contains the appropriate information. Note, there is no need to signal
the semantic of the included data as this specification assumes the
service is aware of that information by out of band means (e.g. both
the service and the address sharing device are managed by the same
administrative entity).</t>
<t>When an intermediary device is configured to include the HOST_ID
option, it MUST include the HOST_ID TCP option in SYN messages. In
addition, an intermediary device and a receiving end device MAY be
configurable to allow inclusion of the HOST_ID TCP option in
additional messages in order to support the use of SYN cookies. For
example:
<list style="symbols">
<t>The HOST_ID option from the initial SYN might be included in the
SYN/ACK message when a SYN cookie is being sent in order to echo
the HOST_ID value back to the intermediary device.</t>
<t>The HOST_ID option might be included in ACK messages that contain
no data.</t>
<t>The HOST_ID option might be included in all ACK messages until
return messages from the receiver positively indicate that an ACK
has been received (e.g. the return messages either includes or
acknowledges data).</t>
</list>
</t>
<t>The option SHOULD NOT be included in packets if the resulting packet
would require local fragmentation. The option MUST NOT be include in
packets when there is not enough space for at least one valid
identifier of the configured type.</t>
<t>The device MUST be configured with the behavior to follow when a
HOST_ID TCP option is already present in the message:
<list style="symbols">
<t>If the device is configured to strip any existing HOST_ID TCP
option, it MUST remove any occurrence of the HOST_ID in a received
TCP message.</t>
<t>If the device is configured to strip any existing HOST_ID TCP
option and insert a local HOST_ID TCP Option, it MUST remove any
occurrence of the HOST_ID in a received TCP message and then
MUST include a local HOST_ID TCP option.</t>
<t>The device may be configured to maintain any existing HOST_ID TCP
option(s) in the received message, the device MUST NOT remove
those instances of the option. Furthermore, it MUST add a new
HOST_ID TCP option while preserving the order of appearance in the
message. In particular, the local HOST_ID TCP option MUST appear
as the last occurrence of the HOST_ID TCP option in the
message.</t>
</list>
</t>
</section>
<section anchor="interaction" title="Interaction with Other TCP Options">
<t>This section details how the HOST_ID option functions in conjunction
with other TCP options.</t>
<section title="Option Space">
<t>TCP provides for a maximum of 40 octets for TCP options. As
discussed in Appendix A of Multipath TCP (MPTCP)
<xref target="RFC6824" />, a typical SYN from modern, popular
operating systems contain several TCP options (MSS, window scale,
SACK permitted, and timestamp) which consume 19-24 octets depending
on word alignment of the options. The initial SYN from a multipath
TCP client would consume an additional 12 octets.</t>
<t>To save option space, the intermediate device adding the HOST_ID
Option can break word-alignment of the TCP options, ensuring
40-19=21 octets (without MPTCP) or 40-19-12=9 octets (with MPTCP)
are available for the HOST_ID option and its value. If, however,
the intermediate device preserves word alignment (perhaps for
compatibility with TCP servers that need word alignment), the
intermediate device is left with less space: 40-24=16 octets
(without MPTCP) or 40-24-12=4 octets (with MPTCP).</t>
<t>HOST_ID needs at least 6 octets to be useful, so 9-21 octets are
sufficient for many scenarios that benefit from HOST_ID. However, 4
octets are not enough space for the HOST_ID option. Thus, a TCP SYN
containing all the typical TCP options (MSS, window Scale, SACK
permitted, timestamp), and also containing multipath capable or
multipath join), and also being word aligned, has insufficient space
to also accommodate HOST_ID. This means something has to give. The
choices are to avoid word alignment in that case (freeing 5 octets),
remove a TCP option from the original TCP SYN, or avoid adding the
HOST_ID option. We expect to learn from deployment experience
during the experiment which of these options, or a combination of
these options, is best.</t>
</section>
<section title="Authentication Option (TCP-AO)">
<t>The TCP-AO option <xref target="RFC5925" /> is incompatible with an
intermediate device adding the HOST_ID option because TCP-AO
provides integrity protection of the TCP SYN, including TCP options.
However, TCP-AO is already incompatible with address sharing,
because TCP-AO provides integrity protection of the source IP
address. So the incompatibility with TCP-AO is not a problem in
practice.</t>
</section>
</section>
<section anchor="security" title="Security Considerations">
<t>Security (including privacy) considerations common to all HOST_ID
solutions are discussed in <xref target="RFC6967" />. These
considerations should be taken into account.</t>
</section>
<section anchor="privacy" title="Privacy Considerations">
<t>Sending a TCP SYN across the public internet necessarily discloses
the public IP address of the sending host. When an intermediate
address sharing device is deployed on the public internet (see
<xref target="I-D.boucadair-intarea-host-identifier-scenarios" /> for
examples), anonymity of the hosts using the device will be increased,
with hosts represented by multiple source IP addresses on the ingress
side of the device using a single source IP address on the egress
side. The HOST_ID TCP option removes that increased anonymity, taking
information that was already visible in TCP packets on the public
internet on the ingress side of the address sharing device and making
it available on the egress side of the device as well. In some cases,
an explicit purpose of the address sharing device is anonymity, in
which case use of the HOST_ID TCP option would be incompatible with
the purpose of the device.</t>
<t>Use of the HOST_ID TCP option described here should follow the
recommendations laid out in <xref target="RFC6967" />. In particular:
<list style="symbols">
<t>The HOST_ID option SHOULD NOT be used to provide client
geographic or network location information that was not publicly
visible in IP packets for the TCP flows processed by the
inserting host. For example, the client's IP address MAY be used
as the HOST_ID option value, but any geographic or network
location information derived from the client's IP address SHOULD
NOT be used as the HOST_ID value.</t>
<t>The HOST_ID option MAY provide differentiating information that
is locally unique such that individual TCP flows processed by
the inserting host can be reliably identified. The HOST_ID option
SHOULD NOT provide client identification information that was not
publicly visible in IP packets for the TCP flows processed by
the inserting host.</t>
<t>The HOST_ID option SHOULD be stripped from IP packets traversing
middle boxes that provide network-based anonymity services.</t>
</list>
</t>
</section>
<section anchor="iana" title="IANA Considerations">
<t>This document specifies a new TCP option that uses the shared
experimental options format
<xref target="RFC6994" />, with ExID=0x0348 (840) in network-standard
byte order. This ExID has already been registered with IANA.</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc0793;
&rfc2119;
</references>
<references title="Informative References">
&rfc5925;
&rfc6269;
&rfc6824;
&rfc6967;
&rfc6994;
&I-D.boucadair-intarea-host-identifier-scenarios;
&I-D.wing-nat-reveal-option;
&I-D.abdo-hostid-tcpopt-implementation;
&I-D.williams-overlaypath-ip-tcp-rfc;
</references>
</back>
</rfc>
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