One document matched: draft-williams-exp-tcp-host-id-opt-03.xml
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<rfc category="exp" ipr="trust200902">
<front>
<title abbrev="Experimental TCP Host ID Option">Experimental Option for
TCP Host Identification</title>
<author fullname="Brandon Williams" initials="B." surname="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 fullname="Mohamed Boucadair" initials="M." surname="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 fullname="Dan Wing" initials="D." surname="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"></xref> and <xref
target="I-D.boucadair-intarea-host-identifier-scenarios"></xref>. In
addition, <xref target="RFC6967"></xref> provides analysis of various
solutions to the problem of revealing the sending host's identifier
(HOST_ID) information to the receiver, which indicates that a solution
using a TCP <xref target="RFC0793"></xref> option for this purpose could
be applied with limited performance impact and a high success ratio.</t>
<t>Multiple recent Internet Drafts define TCP options for the purpose of
host identification: <xref target="I-D.wing-nat-reveal-option"></xref>,
<xref target="I-D.abdo-hostid-tcpopt-implementation"></xref>, and <xref
target="I-D.williams-overlaypath-ip-tcp-rfc"></xref>. Specification of
multiple option formats to serve the purpose of host identification
increases the burden for potential implementers and presents
interoperability challenges as well. This document defines a common TCP
option format to meet the needs of all three of the above proposals.</t>
<t>The option defined in this document uses the TCP experimental option
codepoint sharing mechanism defined in <xref target="RFC6994"></xref>
and is intended to allow broad deployment of the mechanism on the public
Internet in order to validate the utility of this option format for the
required use cases.</t>
<t><xref target="interaction"></xref> of this document discusses
compatibility between this new TCP option and existing commonly deployed
TCP options.</t>
<section anchor="use_cases" title="Important Use Cases">
<t>This memo focuses primarily on the carrier grade NAT (CGN),
application proxy, and overlay network use cases described in <xref
target="I-D.boucadair-intarea-host-identifier-scenarios"></xref>.
This means that the option could either be applied to an individual
TCP packet at the connection endpoint (e.g. an application proxy or
a transport layer overlay network) or at an address-sharing middle
box (e.g. a CGN or a network layer overlay network). See <xref
target="use"></xref> below for additional details about the types of
devices that may add the option to a TCP packet, as well as
limitations on use of the option when it is to be inserted by an
address-sharing middlebox, including issues related to packet
fragmentation.</t>
<t>The receiver-side use cases considered by this memo include the
following:
<list style="symbols">
<t>Differentiating between attack and non-attack traffic when the
source of the attack is sharing an address with non-attack
traffic.</t>
<t>Application of per-client policies for resource utilization,
etc. when multiple clients are sharing a common address.</t>
<t>Improving server-side load-balancing decisions by allowing the
load for multiple clients behind a shared address to be assigned
to different servers, even when session-affinity is required at
the application layer.</t>
</list></t>
<t>In all of the above cases, differentiation between address-sharing
clients commonly needs to be performed by a network function that
does not process the application layer protocol (e.g. HTTP) or the
sercurity protocol (e.g. TLS), because the action needs to be
performed prior to decryption or parsing the application layer. Due
to this, a solution implemented within the application layer or
security protocol cannot fully meet the receiver-side requirements.
At the same time, as noted in <xref target="RFC6967"></xref>, use of
an IP option for this purpose has a low success rate. For these
reasons, using a TCP option to deliver the host identifier has been
selected as the most effective way to satisfy these specific use
cases.</t>
</section>
<section anchor="experiment_goals" title="Experiment Goals">
<t>The extensive testing effort documented in <xref
target="I-D.abdo-hostid-tcpopt-implementation"></xref> confirmed that
a TCP option could be used for host identification purposes without
significant disruption of TCP connectivity to legacy servers that do
no support the option. It also showed how mechanisms available in
existing TCP implementations could make use of such a TCP option for
improved diagnostics and/or packet filtering.</t>
<t>Specification of the TCP option described in this memo will allow
further experiments to be conducted in order to assess the viability
of the option for the receiver-side use cases discussed above:
<list style="symbols">
<t>Differentiate between attack and non-attack traffic.</t>
<t>Enforce per-client policies.</t>
<t>Assist load-balancing decision-making.</t>
</list>
In particular, real-world deployment of the option is expected to
provide opportunities for engagement with a broader range of both
application and middleware implementations in order to develop a
more complete picture of how well the option meets the use-case
requirements.</t>
</section>
</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"></xref>.</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><![CDATA[
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. a list of IP
addresses, an IP address and a port number), 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>The HOST_ID option should only be added by the origin host or any
device involved in the forwarding path that changes IP addresses and/or
TCP port numbers (e.g., NAT44 <xref target="RFC3022"></xref>, Layer-2
Aware NAT, DS-Lite AFTR <xref target="RFC6333"></xref>, NPTv6 <xref
target="RFC6296"></xref>, NAT64 <xref target="RFC6146"></xref>,
Dual-Stack Extra Lite <xref target="RFC6619"></xref>, TCP Proxy, etc.).
The HOST_ID option MUST NOT be added or modified en-route by any device
that does not modify IP addresses and/or TCP port numbers.</t>
<t>The information conveyed in the HOST_ID option SHOULD correlate to IP
addresses and/or TCP port numbers change(s) (i.e., some of the IP
address and /or port number bits are used to generate the HOST_ID).</t>
<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 option in SYN messages. In addition,
an intermediary device and a receiving end device MAY be configurable to
allow inclusion of the HOST_ID 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 included 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 all occurrences of the HOST_ID in a received
TCP message.</t>
<t>If the device is configured to strip existing HOST_ID TCP
options and insert a local HOST_ID TCP Option, it MUST remove all
occurrences of the HOST_ID in a received TCP message and then MUST
include a local HOST_ID TCP option. The device MAY be configured to
use existing HOST_ID TCP options as differentiators when selecting
the value to use in the 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.
<list style="empty">
<t>Note: Because the order of appearance of TCP options may be
modified by some middleboxes, deployments relying on
manipulating multiple occurrences of the HOST_ID option may
experience some complications. These complications can be soften
if the devices adding HOST_ID options belong the same
administrative domain. The administrative entity managing that
domain should ensure involved middleboxes do not alter the order
of TCP options. </t>
</list></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"></xref>, 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 16 octets.</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"></xref> supports a "TCP
option flag" to indicate whether TCP options other than TCP-AO are
included in the MAC calculation (Section 3.1 of <xref
target="RFC5925"></xref>). When the options are not included in the
MAC calculation, the use of HOST_ID option does not interfere with
TCP-AO option. However, because TCP-AO provides integrity protection
of the source IP address, TCP-AO is broken in the presence of NAT.</t>
<t>Because TCP-AO is incompatible with address sharing, an
experimental extension to TCP-AO (called TCP-AO-NAT) is introduced in
<xref target="RFC6978"></xref>. Injecting a HOST_ID TCP option does
not interfere with the use of TCP-AO-NAT if the TCP options are not
included in the MAC calculation.</t>
<t>As specified in <xref target="RFC5925"></xref>, TCP-AO must be the
first TCP option processed on incoming segments.</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"></xref>. These
considerations should be taken into account.</t>
<t>The content of the HOST_ID option SHOULD NOT be used for purposes
that require a trust relationship between the host and the server (e.g.
billing and/or intrusion prevention) unless a mechanism outside the
scope of this specification is used to ensure the necessary level of
trust. When the receiving network uses the values provided by the option
in a way that does not require trust (e.g. maintaining session affinity
in a load-balancing system), then use of a mechanism to enforce the
trust relationship might not be required.</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"></xref> 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"></xref>. 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"></xref>, with
ExID=0x0348 (840) in network-standard byte order. This ExID has already
been registered with IANA.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>Many thanks to J. Touch, M. Scharf, W. Eddy, T. Reddy, and Y. Nishida
for their comments.</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc0793;
&rfc2119;
</references>
<references title="Informative References">
&rfc3022;
&rfc5925;
&rfc6146;
&rfc6269;
&rfc6296;
&rfc6333;
&rfc6619;
&rfc6824;
&rfc6967;
&rfc6978;
&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>
<section anchor="change_history" title="Change History">
<t>[Note to RFC Editor: Please remove this section prior to
publication.]</t>
<section anchor="02-to-03" title="Changes from version 02 to 03">
<t>Clarification of arguments in favor of this approach.</t>
<t>Add discussion of important use cases.</t>
<t>Clarification of experiment goals and earlier test results.</t>
</section>
<section anchor="01-to-02" title="Changes from version 01 to 02">
<t>Add note re: order of appearance.</t>
</section>
<section anchor="00-to-01" title="Changes from version 00 to 01">
<t>Add discussion of experiment goals.</t>
<t>Limit external references to the earlier drafts.</t>
<t>Add guidance to limit the types of device that add the option.</t>
<t>Improve/correct discussion of TCP-AO and security.</t>
</section>
</section>
</back>
</rfc>
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