Internet DRAFT - draft-harris-estab-wscale

draft-harris-estab-wscale







TCP Maintenance & Minor Extensions (tcpm)             J. Harris, Ed.
Internet-Draft                                                      None
Updates: 1323 (if approved)                             October 31, 2016
Intended status: Experimental
Expires: May 4, 2017


             WSCALE options in established TCP connections
                      draft-harris-estab-wscale-00

Abstract

   The TCP Window Scale option modifies the interpretation of packets in
   a flow but is transmitted only at the start of the connection.  As
   such there is a problem for observability and fault-finding, since a
   packet capture by a third party may miss the start of a relevant
   connection.  This document describes the use of TCP options to
   provide the scale values during a connection.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on May 4, 2017.

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   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  TCP WINDOW SCALE OPTION . . . . . . . . . . . . . . . . . . .   2
     2.1.  Format  . . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.2.  Sender  . . . . . . . . . . . . . . . . . . . . . . . . .   2
     2.3.  Receiver  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   3
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   3

1.  Introduction

   The TCP WSCALE option [RFC1323] provides a means for scaling the
   effective value of window size value in the TCP header.  This is
   needed for high bandwidth-delay product connections for adequate
   performance as large window sizes must be used.  Use of the facility
   is negotiated by the presence in both SYN-bearing packets at the
   start of the connection of WSCALE options, and is valid with the
   shift values presented there for the remainder of the connection.
   When debugging network problems it is common to take a packet capture
   and heuristically interpret it.  If a TCP connection is captured
   without the initiating SYN packets the window scale information will
   not be available.  The TCP extension usage defined here makes it
   available for such debugging purposes.

1.1.  Requirements Language

   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 RFC 2119 [RFC2119].

2.  TCP WINDOW SCALE OPTION

2.1.  Format

   The wire format of the option is as defined in [RFC1323].

2.2.  Sender

   A TCP endpoint which has both sent and received WSCALE options in
   SYN-bearing packet MAY send a WSCALE option in a subsequent non-SYN-




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   bearing packet for that connection.  Any such option MUST carry the
   same content as the original sent by the endpoint.

   [Discussion: I'd like to see these advisory WSCALE options at about
   the rate of one in a thousand packets.  Deferring for other use of
   option-space, eg SACK, might be wise; the absolute rate is
   unimportant.]

   A sender which supports this facility MUST provide a means for
   disabling it.  This means MAY act on a per-connection basis.

   [Discussion: The usual one about middleboxes failing on non-
   understood protocol features.]

2.3.  Receiver

   A TCP endpoint MUST ignore any WSCALE option received on a non-SYN-
   bearing packet.

3.  IANA Considerations

   This memo includes no request to IANA.

4.  Security Considerations

   This facility does not introduce any new security issues.

5.  Normative References

   [RFC1323]  Jacobson, V., Braden, R., and D. Borman, "TCP Extensions
              for High Performance", RFC 1323, DOI 10.17487/RFC1323, May
              1992, <http://www.rfc-editor.org/info/rfc1323>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

Author's Address

   Jeremy Harris (editor)
   None
   20 Lodge Lane
   Chalfont St.Gile, Bucks
   UK

   Email: j16759@wizmail.org




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