Experimental Option for TCP Host Identification
draft-williams-exp-tcp-host-id-opt-01
The information below is for an old version of the document.
draft-williams-exp-tcp-host-id-opt-01
Network Working Group B. Williams
Internet-Draft Akamai, Inc.
Intended status: Experimental M. Boucadair
Expires: August 15, 2014 France Telecom
D. Wing
Cisco Systems, Inc.
February 11, 2014
Experimental Option for TCP Host Identification
draft-williams-exp-tcp-host-id-opt-01
Abstract
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 15, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
1. Introduction
A broad range of issues associated with address sharing have been
well documented in [RFC6269] and
[I-D.boucadair-intarea-host-identifier-scenarios]. In addition,
[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 [RFC0793]
option for this purpose can be successfully applied to a broad range
of use cases with limited performance impact.
Multiple recent Internet Drafts define TCP options for the purpose of
host identification: [I-D.wing-nat-reveal-option],
[I-D.abdo-hostid-tcpopt-implementation], and
[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. This document is self-contained; required information to
implement the proposed TCP option is specified in this memo.
The option defined in this document uses the TCP experimental option
codepoint sharing mechanism defined in [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 [I-D.abdo-hostid-tcpopt-implementation].
In addition to the extensive testing effort documented in
[I-D.abdo-hostid-tcpopt-implementation], further experiments will be
conducted to assess the validity of the following points:
o Differentiate between attack and non-attack traffic when the
source of the attack is hidden behind a NAT (including CGN
(Carrier Grade NAT) in the Service Provider's network or a NAT in
a CDN overlay infrastructure).
o Enforce per-client policies in the presence of address sharing
devices.
o Help load-balancing decision-making process at the receiver side
(e.g. to maintain session affinity in a load-balancing system).
Section 5 of this document discusses compatibility between this new
TCP option and existing commonly deployed TCP options.
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2. Terminology
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 [RFC2119].
3. Option Format
When used for host identification, the TCP experimental option has
the following format and content.
0 1 2 3
01234567 89012345 67890123 45678901
+--------+--------+--------+--------+
| Kind | Length | ExID |
+--------+--------+--------+--------+
| Host ID ...
+--------+---
Kind: The option kind value is 253
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).
ExID: The experiment ID value is 0x0348 (840).
Host ID: The host identifier is an application dependent value with
an interpretation agreed upon by the sender and the receiver.
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.
4. Option Use
The HOST_ID option should only be added by the origin host or any
device involved in the forwarding path that changes the IP and/or TCP
headers (e.g., NAT44 [RFC3022], Layer-2 Aware NAT, DS-Lite AFTR
[RFC6333], NPTv6 [RFC6296], NAT64 [RFC6146], Dual-Stack Extra Lite
[RFC6619], TCP Proxy, etc.). The HOST_ID option MUST NOT be added or
modified en-route by any device that does not modify the IP header or
the transport header.
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The information conveyed in the HOST_ID option SHOULD correlate to
the IP and/or transport headers change(s) (i.e., some of the IP
address and /or port number bits are used to generate the HOST_ID.
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.).
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).
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:
o 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.
o The HOST_ID option might be included in ACK messages that contain
no data.
o 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).
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.
The device MUST be configured with the behavior to follow when a
HOST_ID TCP option is already present in the message:
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o 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.
o 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.
o 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.
5. Interaction with Other TCP Options
This section details how the HOST_ID option functions in conjunction
with other TCP options.
5.1. Option Space
TCP provides for a maximum of 40 octets for TCP options. As
discussed in Appendix A of Multipath TCP (MPTCP) [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
16 octets.
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.
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5.2. Authentication Option (TCP-AO)
The TCP-AO option [RFC5925] supports a "TCP option flag" to indicate
whether TCP options other than TCP-AO are included in the MAC
calculation (Section 3.1 of [RFC5925]). 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.
Because TCP-AO is incompatible with address sharing, an experimental
extension to TCP-AO (called TCP-AO-NAT) is introduced in [RFC6978].
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.
As specified in [RFC5925], TCP-AO must be the first TCP option
processed on incoming segments.
6. Security Considerations
Security (including privacy) considerations common to all HOST_ID
solutions are discussed in [RFC6967]. These considerations should be
taken into account.
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.
7. Privacy Considerations
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
[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
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anonymity, in which case use of the HOST_ID TCP option would be
incompatible with the purpose of the device.
Use of the HOST_ID TCP option described here should follow the
recommendations laid out in [RFC6967]. In particular:
o 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.
o 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.
o The HOST_ID option SHOULD be stripped from IP packets traversing
middle boxes that provide network-based anonymity services.
8. IANA Considerations
This document specifies a new TCP option that uses the shared
experimental options format [RFC6994], with ExID=0x0348 (840) in
network-standard byte order. This ExID has already been registered
with IANA.
9. Acknowledgements
Many thanks to J. Touch, M. Scharf, W. Eddy, T. Reddy, and Y. Nishida
for their comments.
10. References
10.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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10.2. Informative References
[I-D.abdo-hostid-tcpopt-implementation]
Abdo, E., Boucadair, M., and J. Queiroz, "HOST_ID TCP
Options: Implementation & Preliminary Test Results",
draft-abdo-hostid-tcpopt-implementation-03 (work in
progress), July 2012.
[I-D.boucadair-intarea-host-identifier-scenarios]
Boucadair, M., Binet, D., Durel, S., Chatras, B., Reddy,
T., and B. Williams, "Host Identification: Use Cases",
draft-boucadair-intarea-host-identifier-scenarios-03 (work
in progress), March 2013.
[I-D.williams-overlaypath-ip-tcp-rfc]
Williams, B., "Overlay Path Option for IP and TCP", draft-
williams-overlaypath-ip-tcp-rfc-04 (work in progress),
June 2013.
[I-D.wing-nat-reveal-option]
Yourtchenko, A. and D. Wing, "Revealing hosts sharing an
IP address using TCP option", draft-wing-nat-reveal-
option-03 (work in progress), December 2011.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022, January
2001.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, June 2010.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269, June
2011.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, June 2011.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
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[RFC6619] Arkko, J., Eggert, L., and M. Townsley, "Scalable
Operation of Address Translators with Per-Interface
Bindings", RFC 6619, June 2012.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, January 2013.
[RFC6967] Boucadair, M., Touch, J., Levis, P., and R. Penno,
"Analysis of Potential Solutions for Revealing a Host
Identifier (HOST_ID) in Shared Address Deployments", RFC
6967, June 2013.
[RFC6978] Touch, J., "A TCP Authentication Option Extension for NAT
Traversal", RFC 6978, July 2013.
[RFC6994] Touch, J., "Shared Use of Experimental TCP Options", RFC
6994, August 2013.
Authors' Addresses
Brandon Williams
Akamai, Inc.
8 Cambridge Center
Cambridge, MA 02142
USA
Email: brandon.williams@akamai.com
Mohamed Boucadair
France Telecom
Rennes, 35000
Fance
Email: mohamed.boucadair@orange.com
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
Email: dwing@cisco.com
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