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Network Working Group                                     A. Yourtchenko
Internet-Draft                                                     cisco
Intended status:  Standards Track                          March 5, 2012
Expires:  September 6, 2012


     Revealing hosts sharing an IP address using ICMP Echo Request
                  draft-yourtchenko-nat-reveal-ping-00

Abstract

   When an IP address is shared among several subscribers -- with a NAT
   or with an application-level proxy -- it is impossible for the server
   to differentiate between different clients.  Such differentiation is
   valuable in several scenarios.  This memo describes a technique to
   differentiate TCP and UDP clients sharing an IP address.  The
   proposed method uses an ICMP Echo Request packet, which allows for
   more information about the user mapping to be transmitted than in the
   case of using the TCP option - and allows the use with UDP and other
   protocols.

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
   working documents as Internet-Drafts.  The list of current Internet-
   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 September 6, 2012.

Copyright Notice

   Copyright (c) 2012 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   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.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Description . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     3.1.  Operation of Address Sharing Device . . . . . . . . . . . . 4
     3.2.  Encoding the information into the ICMP Echo Request . . . . 4
     3.3.  Operation of the TCP Server . . . . . . . . . . . . . . . . 4
   4.  Interaction with the transport layer protocols  . . . . . . . . 5
     4.1.  Upstream NATs and Load Balancers  . . . . . . . . . . . . . 5
   5.  Interaction with TCP SYN Cookies  . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Change History . . . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7


























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1.  Introduction

   The transport-layer proposal mentioned in
   [I-D.wing-nat-reveal-option] has one drawback:  a relatively small
   amount of information that can be transmitted.  This is caused by the
   fact that the TCP option space is very scarce.

   Another potential problem is blocking of the new TCP option by the
   middleboxes, which, as [I-D.abdo-hostid-tcpopt-implementation] shows
   a noticeable failure rate of 2.6%

   This document describes a mechanism where the address sharing device
   encapsulates the necessary differentiating information into an ICMP
   Echo Request packet that it sends in parallel with the initial
   session creation.  The information included in the ICMP Request Data
   portion describes the five-tuples as seen on both of the sides of the
   translating device.  This allows the server to differentiate
   different internal addresses.  At the same time, since the data
   travels in ICMP packets, even if they are blocked on the way, the
   user connection does not have to block.

   An analysis of other techniques is available in
   [I-D.boucadair-intarea-nat-reveal-analysis].


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 [RFC2119].

   subscriber:  the client accessing an address sharing device, who is
   responsible for the actions of their device(s).  This might be an
   individual handset (with mobile devices), a home Internet connection,
   a small-medium business Internet connection, a University dormitory
   room, an individual employee of a company, or the company itself.


3.  Description

   This proposal suggests to initiate the ICMP Echo Request / Echo
   Response exchange with the target for each of the new sessions that
   are being created.  The data portion of the ICMP Echo Request packet
   will contain the necessary information about the connection -
   internal and external five-tuples, as well as any other information
   that the translation device considers useful to share.

   The transactional nature of the ICMP Echo/Echo Reply sequence allows



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   to assert the fact of the remote server (or ICMP proxy thereof)
   receiving the information - thus, this approach allows reliable
   transfer of translation information to the target.

3.1.  Operation of Address Sharing Device

   Upon the creation of the new address mapping, the address sharing
   device initiates the new ICMP exchange with the target.  This
   exchange happens in parallel with the main connection establishment.
   In case of not receiving the ICMP Echo Reply, the address sharing
   device MUST retransmit the echo requests several (exact value TBD)
   times with exponential backoff.

   The source of the ICMP Echo Reply MAY be a separate address on the
   address-sharing device, dedicated to these ICMP exchanges.


     TCP client           address sharing device      TCP server
          |                         |                     |
          |---TCP SYN-------------->|                     |
          |                         |----TCP SYN--------->|
          |                         |--ICMP Echo Request->|
          |                         |<---TCP SYNACK-------|
          |<--TCP SYNACK------------|                     |
          |                         |<-ICMP Echo Response-|
          |---TCP ACK-------------->|                     |
          |                         |--TCP ACK----------->|
          |                         |                     |



3.2.  Encoding the information into the ICMP Echo Request

   A strawman proposal is to use the payload within the Echo Request
   similar in format to the one described in
   [I-D.shen-traceroute-ping-ext], with a different magic number.  This
   has the advantage of reusing the code and allowing for some forms of
   authentication of the NAT devices.

3.3.  Operation of the TCP Server

   The TCP server identifies the ICMP Echo Request as a special one by
   inspecting the payload and matching the included outside five-tuple
   with one of its active connections.  After the processing of the Echo
   Request packet the server sends back the Echo Reply packet with
   identical contents.

   Note that the out-of-band nature of the proposed signaling allowes



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   multiple scenarios of implementing the server-side handling.  An
   early prototype implementation is in progress using libipq on Linux,
   which would delay the inbound SYN segments for a configurable
   interval, in the hope that the ICMP Echo Request with the translation
   details arrives shortly.

   Another implementation could employ some more sophisticated
   processing - e.g. intercept the SYN segments only from hosts who
   according to certain heuristics are misbehaving - thus, avoiding any
   delay for the well-behaving hosts.


4.  Interaction with the transport layer protocols

   This section discusses the pros and cons of using a separate channel
   to discriminate the internal 5-tuples.

4.1.  Upstream NATs and Load Balancers

   The upstream translators may not understand the contents of the
   packet, and might simply translate it as another ping packet
   exchange.  TBD:  the data format needs to provision for detection of
   this.  This item needs further consideration, specifically how to
   cascade the multiple translators in a chain.

   However, the extra address translator north of CGN-style one is
   rather unlikely.


5.  Interaction with TCP SYN Cookies

   TCP SYN cookies [RFC4987] are commonly deployed to mitigate TCP SYN
   attacks, which have some side effects - the ICMP Echo packet
   containing the 5-tuple mapping information may not match an existing
   TCP connection on the server.  However, in this case the flow of
   operation of neither TCP SYN Cookies nor ICMP Echo Request is
   disturbed - the host can simply respond as normal.  TBD:  one way is
   for the server to defer sending Echo Reply if there is no matching
   connection - this will cause the Address Sharing Device to keep
   retransmitting the Echo Request, and if the connection is legitimate,
   then eventually the Echo Request will match a newly established
   connection.


6.  Security Considerations

   An attacker might use this functionality to appear as if IP address
   sharing is occurring, in the hopes that a naive server will allow



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   additional attack traffic.  TCP servers and applications SHOULD NOT
   assume the mere presence of the functionality described in this paper
   indicates there are other (benign) users sharing the same IP address.


7.  Acknowledgements

   Thanks to Dan Wing for the discussions, the reviews of early versions
   of the draft, very helpful suggestions on the text and the nice ASCII
   art.


8.  IANA Considerations

   None.


9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, June 2010.

9.2.  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-02 (work in
              progress), January 2012.

   [I-D.boucadair-intarea-nat-reveal-analysis]
              Boucadair, M., Touch, J., Levis, P., and R. Penno,
              "Analysis of Solution Candidates to Reveal a Host
              Identifier in Shared Address Deployments",
              draft-boucadair-intarea-nat-reveal-analysis-04 (work in
              progress), September 2011.

   [I-D.despres-intarea-4rd]
              Despres, R., Matsushima, S., Murakami, T., and O. Troan,
              "IPv4 Residual Deployment across IPv6-Service networks
              (4rd) ISP-NAT's made optional",
              draft-despres-intarea-4rd-01 (work in progress),
              March 2011.



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   [I-D.ietf-intarea-shared-addressing-issues]
              Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
              Roberts, "Issues with IP Address Sharing",
              draft-ietf-intarea-shared-addressing-issues-05 (work in
              progress), March 2011.

   [I-D.ietf-mptcp-multiaddressed]
              Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", draft-ietf-mptcp-multiaddressed-04 (work in
              progress), July 2011.

   [I-D.shen-traceroute-ping-ext]
              Shen, N., Pignataro, C., Asati, R., Chen, E., and A.
              Atlas, "Traceroute and Ping Message Extension",
              draft-shen-traceroute-ping-ext-04 (work in progress),
              February 2012.

   [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-02 (work in progress),
              June 2011.

   [I-D.ymbk-aplusp]
              Bush, R., "The A+P Approach to the IPv4 Address Shortage",
              draft-ymbk-aplusp-10 (work in progress), May 2011.

   [RFC4987]  Eddy, W., "TCP SYN Flooding Attacks and Common
              Mitigations", RFC 4987, August 2007.


Appendix A.  Change History

   [Note to RFC Editor:  Please remove this section prior to
   publication.]















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Author's Address

   Andrew Yourtchenko
   Cisco Systems, Inc.
   6a de Kleetlaan
   Diegem  1831
   BE

   Phone:  +32 2 704 5494
   Email:  ayourtch@cisco.com









































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