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Versions: 00 01 02                                          Experimental
Transport WG                                                  A. Knutsen
Internet-Draft                                         Blue Coat Systems
Intended status: Experimental                                 A. Ramaiah
Expires: July 25, 2013                                       NTT MCL Inc
                                                             A. Ramasamy
                                                        January 21, 2013

            TCP option for transparent Middlebox negotiation


   This document describes a TCP option for use by middleboxes to
   facilitate transparent detection of other middleboxes along the path
   of the TCP connection during the connection initiation phase.  The
   option has no effect if an appropriate middlebox is not present on
   the path.

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 July 25, 2013.

Copyright Notice

   Copyright (c) 2013 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
   to this document.  Code Components extracted from this document must

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   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.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Requirements of the TCP-MNO  . . . . . . . . . . . . . . . . .  6
   4.  Description  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  TCP-MNO option format  . . . . . . . . . . . . . . . . . . . .  8
   6.  TCP option interoperability  . . . . . . . . . . . . . . . . .  9
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   9.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 13
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     11.1.  Normative References  . . . . . . . . . . . . . . . . . . 15
     11.2.  Informative References  . . . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16

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1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119]


      "Middleboxes: Taxonomy and Issues" [RFC3234] defines a middlebox
      as follows:

      "A middlebox is defined as any intermediary device performing
      functions other than the normal, standard functions of an IP
      router on the datagram path between a source host and destination


      HTTP1.1 [RFC2616] defines a proxy as follows: "An intermediary
      program which acts as both a server and a client for the purpose
      of making requests on behalf of other clients."  Proxies exist for
      many protocols, such as HTTP, CIFS, MAPI and streaming.  Since
      they act as both server and client, they have separate TCP
      connections to the original client and the actual server (also
      referred to as the "Original Content Server").  Proxies are often
      implemented on middleboxes.  Proxies fall into two general
      categories: "Explicit" and "Transparent".  The client must be
      configured to connect to an explicit proxy; it then passes the
      server address to it using an application protocol, such as HTTP.
      Transparent proxies require no client configuration; they
      intercept the client connection to the server, speaking to the
      client on its behalf, and make a separate connection to the server
      without the knowledge of the client.  This memo deals exclusively
      with cooperating transparent proxies.


      Two or more middleboxes with an effective association or
      relationship are peers.  For example, one middlebox might compress
      data while another middlebox decompresses; neither middlebox can
      correctly manipulate traffic unless they both establish the
      existence of the other and coordinate their actions.  The most
      common peering relationships are two-way (like the compression
      example) in which one middlebox performs a transformation that the
      other middlebox inverts.  However, two-way peering that does not
      involve an invertible transformation is also found, as are n-way
      peering relationships where the "intermediate" peers are simply
      operating in a pass-through or failover mode.

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2.  Introduction

   For middleboxes that operate on TCP-based application protocols, it
   is highly desirable for negotiation information to be carried within
   packets containing valid TCP protocol data.  One significant kind of
   service offered by such middleboxes is application acceleration, in
   which there is an intrinsic requirement to be efficient and avoid
   network round trips.  A middlebox-negotiation mechanism that imposes
   additional round trips could defeat the purpose of such middleboxes.
   Middlebox negotiation on a per-connection basis allows for
   significant advantages in scale and flexibility.  Middlebox-based
   services can be invoked dynamically, using the appropriate peers,
   without any need for statically identifying middleboxes to end hosts
   or identifying middleboxes to each other.  Dynamic negotiation means
   that there is no overlay routing required for middlebox-based
   services, where such overlay routing could potentially clash with the
   underlying IP routing.  For all of these reasons, multiple vendors
   have implemented TCP-option-based negotiation mechanisms; and for
   similar reasons, this memo requests a TCP option for middle box

   The TCP middlebox negotiation option (TCP-MNO) allows a source node
   (initiating middlebox) on the initiating path of a TCP connection to
   request a response from other middleboxes with a matching capability
   closer to the destination host.  In addition, it allows the
   initiating middlebox to provide information to the other middleboxes
   which they may need to decide whether to respond to this request.  A
   middlebox MAY examine TCP packets with the SYN bit set to determine
   if the associated TCP connection qualifies for the middlebox-provided
   service.  If so, the middlebox MAY insert the TCP-MNO into the packet
   header before sending it on.  A middlebox MAY examine packets
   containing the TCP-MNO to determine if the associated TCP connection
   qualifies for the middlebox-provided service.  If so, the middlebox
   MAY take additional actions to coordinate with the initiating
   middlebox.  Such actions MAY include acknowledging the SYN packet to
   intercept the connection; originating a separate connection to the
   client; or perhaps notifying a management station.

   TCP end hosts are unaware of TCP-MNO, and its usage is strictly for
   use by TCP middleboxes.  Note however that the middlebox may be
   running on the TCP end host itself in some form, and may use TCP-MNO.
   Multiple vendors of WAN optimization products have used similar (but
   incompatible and proprietary) mechanisms since at least 2004.  Those
   existing vendor systems use multiple TCP option code points, all of
   which are officially unassigned by IANA.  The goal of this memo is to
   standardize a single TCP option code point for this functionality.
   Note that TCP is inherently end-to-end, and the network
   infrastructure (including middleboxes) are not supposed to alter the

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   TCP headers, but the current deployment practice has resulted in the
   middleboxes violating this architectural principle to address a
   market need.  Goal of this memo is not to say this is good or bad but
   merely acknowledges the reality and encourages the use of a shared
   documented option number for such uses.

   This memo is the product of discussion among some of the vendors
   currently using incompatible proprietary TCP options for middlebox
   negotiation.  It is a non-goal of this memo to achieve
   interoperability of middlebox negotiation between multiple vendors.
   It needs to be noted that an earlier document
   [I-D.knutsen-tcpm-middlebox-discovery], is re-written as the current
   document after agreement from multiple vendors.

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3.  Requirements of the TCP-MNO

   The following are the requirements of TCP-MNO :

   1) The TCP-MNO MUST be variable length to accommodate multiple vendor
      option formats.

   2) The TCP-MNO MUST have a vendor ID which can identify the specific
      vendor as implied by 1)

   3) The TCP option space limitation puts a burden on how flexible the
      option can be.  Please refer section 6 below.

   4) TCP option numbers already in use by proprietary systems SHOULD
      NOT be reused for TCP-MNO since it would create confusion.  (These
      option numbers would get eventually retired when all vendors
      migrate to the newly allocated TCP-MNO option)

   5) The TCP-MNO SHOULD be used for middleboxes only.  The hosts are
      expected to silently ignore this option.

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4.  Description

   The TCP-MNO MAY be included in the TCP handshake (SYN and SYN+
   ACKpackets).  The TCP-MNO contained in the SYN packet is used to
   discover peer middleboxes along the path to the server.  The TCP-MNO
   option MAY be present in the TCP SYN+ACK and other TCP data packets
   as well.

   It should be noted that a common use of middleboxes is to set up
   cooperating peer proxies.  One example is to implement a feature
   which optimizes the WAN traffic, like a compression protocol.  In
   these cases, the option is used by the device nearer to the client to
   discover a possible device nearer to the server.  Thus the client and
   server application are not aware of the option.  Figure 1 illustrates
   the text above.

        CLIENT ----- Middlebox1 ================ Middlebox2 ------ SERVER
                                    WAN link

           ------SYN------->|---- SYN, TCP-MNO ----->|----SYN--->
              <---SYN+ACK---|<---SYN+ACK, TCP-MNO----|<---SYN+ACK----

          Figure 1: TCP-MNO option insertion during TCP handshake

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5.  TCP-MNO option format

   The following is the agreed-upon option format for TCP-MNO.

        0               1                 2               3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
        | Kind = xx   | Length         |   Vendor = YY  |   Vendor    |
        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+             |
        |      Payload data dependent on Vendor typecode              |
        |                                                             |
        |             (Variable Length)                               |
        |                                                             |

        (One tick mark represents one bit)
              Figure 2 : Format of TCP-MNO

   Even after 8 years of commercial development, there are only a
   handful of vendors with different option-based negotiation schemes.
   Accordingly, 8 bits is likely to be more than sufficient for vendor
   identification.  Ideally, future work would define a single
   interoperable middlebox negotiation scheme to replace the multiple
   vendor-specific schemes.

   The PEN (32 bit Private Enterprise numbers) is an existing mechanism
   which could be used to identify various vendors
   (http://www.iana.org/assignments/enterprise-numbers).  Because of the
   very limited amount of TCP option space, using 32 bits for an
   enterprise number is impractical.  The next section talks more about
   the TCP option space issue.

   Other formats for TCP-MNO have been previously considered, including
   an approach in which the option contains a Type code followed by
   Vendor ID.  That design had the advantage of supporting an extension
   into 32-bit enterprise numbers.  But no meaningful commonality could
   be identified among the different vendor schemes; at any level beyond
   the use of a TCP option, each functions quite differently and there
   was no clear basis for choosing a standardized type scheme.

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6.  TCP option interoperability

   This section touches upon the interoperability issues of TCP-MNO with
   other TCP options.

   It needs to be noted that the TCP-MNO can be inserted only if the TCP
   option space permits.  Given that there is a maximum of 40 bytes for
   TCP options, A SYN (with MSS, window scale, SACK permitted, and
   timestamp options) leaves 16 bytes spare (if the options are word-
   aligned) or 21 bytes spare (if the options are not word-aligned)
   which may just make it.  In particular, it is not typically possible
   to insert TCP-MNO if a vendor-proprietary option has already been
   inserted, nor vice-versa.  Strictly speaking, this conflict is not a
   new problem but the attempt at standardization may mean it occurs
   more often.  It is already true in most cases that it is not possible
   to insert vendor A's option if vendor B's option has previously been
   inserted.  This memo does not attempt to define rules on precedence
   or priority of such options, nor does it define circumstances in
   which a proprietary option may safely be replaced by TCP-MNO.

   Multipath TCP ([I-D.ietf-mptcp-multiaddressed]) would have more
   options sent in the SYN, therby restricting the TCP option space that
   can be used for TCP-MNO.

   The TCP-MNO option is incompatible with TCP options which aim to
   protect the integrity of the TCP SYN.  An example of such an option
   is the TCP MD5 signature option[RFC2385].  Such TCP options are not
   commonly seen by current WAN optimization systems, so the restriction
   should not pose any worries.

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7.  IANA Considerations

   This section is interpreted according to [RFC5226])

   This document needs a new TCP option to be allocated by IANA for the
   TCP-MNO option from the "TCP Option Kind Numbers" registry maintained
   at http://www.iana.org.

   This document also defines an 8 bit middle-box vendor id field, for
   which IANA is requested to create and maintain a new sub-registry
   entitled "Middle box vendor id" under the new middle box TCP option.
   The middle box vendor id will be used to differentiate multiple
   vendors.  Initial values for the middle box vendor id sub-registry
   are given below; future assignments are to be made on a "First Come
   First Served" basis.

               ID       Middle-box Vendor
               ----     -----------------
               0        Reserved
               1        Bluecoat
               2        Riverbed
               3        Cisco
               4-127    Unassigned
               128-255  Reserved

   It is envisioned that the reserved codes can be used in the following
   manner in future.  Exact definitions of them is not spelled out here
   and it is left to such a time when there is more clarity around
   requirements and usage model.

   1) Standard code: Standard code can be used in a such way that
      multiple vendors recognize the same and are interoperable for
      negotiation purposes

   2) Extended vendor id: Should the unassigned space run out in the
      future, either the reserved space can be opened up for assignment,
      or a speical id can be added to extend the vendor id space to more
      than one byte (say by including OUI after the 1 byte vendor id)

   It needs to be noted that at the time of writing this document, the
   following vendors have used the following TCP option numbers for TCP
   middlebox auto-discovery.

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       Vendor               TCP option number
       Bluecoat             253
       Cisco                33
       Riverbed             76 and 78

      Figure 3: Current TCP auto-discovery option numbers used by various vendors.

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8.  Security Considerations

   The TCP-MNO option is incompatible with any TCP option which aims to
   protect the integrity of the TCP SYN, such as the TCP MD5 signature
   option[RFC2385] and TCP-AO option[RFC5925].  In addition, this memo's
   approach to middlebox negotiation introduces two security issues.
   First, the option-based paradigm intrinsically involves modifying
   traffic.  Some traffic may be modified even though it cannot or
   should not receive the middlebox-based service.  Secondly, there is
   no authentication mechanism defined in this memo to ensure that
   middleboxes communicate only with well-behaved and trusted potential
   peers.  A rogue middlebox can potentially insert itself into a
   functioning community of middleboxes, disrupting the service

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9.  Contributors

   The following individuals contributed immensely to this document :

      Ron Fredrick, Blue Coat.

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10.  Acknowledgements

   Thanks to Lars Eggert for forming the middisc alias which was
   responsible for discussions leading to the current document.  Thanks
   to Wes Eddy and David Harrington for the constant encouragement in
   getting this document written.

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11.  References

11.1.  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.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

11.2.  Informative References

              Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", draft-ietf-mptcp-multiaddressed-12 (work in
              progress), October 2012.

              Knutsen, A., Frederick, R., Mahdavi, J., Li, Q., and W.
              Yeh, "TCP Option for Transparent Middlebox Discovery",
              draft-knutsen-tcpm-middlebox-discovery-04 (work in
              progress), May 2010.

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, August 1998.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC3234]  Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
              Issues", RFC 3234, February 2002.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

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

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Authors' Addresses

   Andrew Knutsen
   Blue Coat Systems
   420 North Mary Ave
   Sunnyvale, CA  94085-4121

   Phone: +1 (408) 220-2250
   Email: andrew.knutsen@bluecoat.com

   Anantha Ramaiah
   NTT MCL Inc
   101 S. Ellsworth Avenue, Suite 350
   San Mateo, CA  94401

   Email: ananth@nttmcl.com

   Arivu Ramasamy
   170 Tasman Drive
   San Jose, CA  95134

   Phone: +1 (408) 525-5962
   Email: mani@cisco.com

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