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
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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
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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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