One document matched: draft-williams-exp-tcp-host-id-opt-04.xml
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<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
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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, indicating that a solution using
a TCP <xref target="RFC0793"></xref> option for this purpose is among
the possible approaches that could be applied with limited performance
impact and a high success ratio. The purpose of this document is to
define such a TCP option in order to factilitate further validation of
the mechanism.</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 that supersedes 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
intended 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 could 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>
<t>In addition, continued experimentation on the open internet
following publication of this memo is expected to allow further
refinement of requirements related to the values used to populate
the option and how those values can be interpretted by the receiver.
There is a tradeoff between providing the expected functionality to
the receiver and protecting the privacy of the sender, and
additional work is necessary in order to find the right balance.</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 uses
the experiment identification mechanism described in
<xref target="RFC6994"></xref> and 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 necessary (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 included, cases where only a single
identifier is included are more common and thus it is beneficial to
optimize for those cases.</t>
</section>
<section anchor="use" title="Option Use">
<t>This section describes requirements associated with the use of the
option, including: which hosts are allowed to include the option,
expected option values, and segments that include the option.</t>
<section anchor="host_reqs" title="Sending Host Requirements">
<t>The HOST_ID option MUST only be added by the sending 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>
</section>
<section anchor="value_reqs" title="Option Value Requirements">
<t>The information conveyed in the HOST_ID option is intended to
uniquely identify the sending host to the best capability of the
machine that adds the option to the segment, while at the same time
avoiding inclusion of information that does not assist this purpose.
In addition, the option is not intended to be used to expose
information about the sending host that could not be discovered by
observing segments in transit on some portion of the internet path
between the sender and the receiver. As noted in
<xref target="experiment_goals"></xref>, identifying the optimal set
of values to use for this purpose is one of the experiment goals for
this document. For this reason, the document attempts to provide a
high degree of flexibility for the machine that adds the option to TCP
segments.</t>
<t>The HOST_ID option value MUST correlate to IP addresses and/or TCP
port numbers that were changed by the inserting host/device (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>The device MUST be configured with the behavior to follow when a
HOST_ID TCP option is already present in the segment:
<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 segment.</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 segment 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 segments, 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
TCP option space. In particular, the local HOST_ID TCP option MUST
appear as the last occurrence of the HOST_ID TCP option in the
segment.
<list style="empty">
<t>Note: Because the order of appearance of TCP options could
be modified by some middleboxes, deployments MUST NOT rely on
option order to provide additional meaning to the individual
options. Instead, as indicated above, the full set of option
values, with their lengths, MUST be treated as a single
unified identifier.</t>
</list></t>
</list></t>
</section>
<section anchor="segment_reqs" title="Segment Inclusion Requirements">
<t>A sending host or intermediary device that is configured to include
the HOST_ID option MUST include the option in SYN segments.</t>
<t>The sending host or intermediary device cannot determine whether
the option value is used in a stateful manner by the receiver, nor can
it determine whether SYN cookies are in use by the receiver. For this
reason, the option MUST be included in all segments until return
segments from the receiver positively indicate that the TCP connection
is fully established on the receiver (e.g. the return segment either
includes or acknowledges data).</t>
<section anchor="alt_cookie_support" title="Alternative SYN Cookie Support">
<t>The authors have also considered an alternative approach to SYN
cookie support in which the receiving host (i.e. the host that
accepts the TCP connection) to echo the option back to the sender in
the SYN/ACK segment when a SYN cookie is being sent. This would
allow the sending host to determine whether further inclusion of the
option is necessary. This approach would have the benefit of not
requiring inclusion of the option in non-SYN packets if SYN cookies
had not been used. Unfortunately, this approach fails if the sending
host itself does not support the option, since an intermediate node
would have no way to determine that SYN cookies had been used.</t>
</section>
<section anchor="frag_reqs" title="Packet Fragmentation">
<t>The option SHOULD NOT be included in packets if the resulting
packet would require local fragmentation.</t>
</section>
</section>
</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 because the TCP options are
not included in the MAC calculation.</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>.</t>
<t>The content of the HOST_ID option MUST NOT be used for purposes that
require a trust relationship between the sender and the receiver (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.</t>
<t>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 is OPTIONAL.</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>The HOST_ID option MUST 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 MUST 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 MUST 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 MUST be stripped from IP packets traversing middle
boxes that provide network-based anonymity services.</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="03-to-04" title="Changes from version 03 to 04">
<t>Improve discussion of RFC6967.</t>
<t>Don't use "message" to describe TCP segments.</t>
<t>Add reference to RFC6994 to section 3.</t>
<t>Clarify that this draft superseeds earlier drafts.</t>
<t>Improve discussion of SYN cookie handling.</t>
<t>Remove lower case uses of keywords (e.g. must, should, etc.)
throughout the document.</t>
<t>Some stronger privacy guidance, replacing SHOULD with MUST.</t>
<t>Add an experiment goal related to optimal option value.</t>
<t>Add text related to the identification goals of the option
value (still needs more work).</t>
</section>
<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>
<section anchor="open_issues" title="Open Issues">
<t>[Note to RFC Editor: Please remove this section prior to
publication.]</t>
<t>Add discussion of non-local fragmentation.</t>
<t>Evaluate the reliability of attempts to exclude the option when
local fragmentation would be required.</t>
<t>Clarify exactly what the identifier is identifying.</t>
<t>Improve discussion on interpretation of multiple instances of the
option, including order of interpretation and set interpretation.</t>
<t>Evaluate whether use of multiple identifiers should be constrained.</t>
<t>Discuss the possibility of the option value changing over the
life of the connection.</t>
<t>Clarify use cases related to stripping and replacing the option.</t>
<t>Make this draft self-contained, rather than referring readers to
use-cases and requirements contained in other I.D.s that were never
published as RFCs.</t>
<t>Add discussion of TCP Fast Open.</t>
<t>Add experiment goal related to identifying methods for
receiver-side use of data conveyed in the option.</t>
<t>Re-evaluate all use of MUST, MAY, SHOULD thoughout the document.</t>
<t>Clarify use of SHOULD rather than MUST where possible, or perhaps
generally.</t>
<t>Correct some discussion of TCP-AO and TCP-AO-NAT.</t>
<t>Clarify the security requirements re: trust relationship.</t>
<t>Clarify privacy considerations regarding NATs that separate private
and public networks.</t>
<t>Remove restatement of requirements from other documents.</t>
</section>
</back>
</rfc>
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