Aggregated Option for SYN Option Space Extension
draft-nishida-tcpm-agg-syn-ext-00

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Network Working Group                                         Y. Nishida
Internet-Draft                                       Amazon Web Services
Intended status: Standards Track                        February 2, 2021
Expires: August 6, 2021

            Aggregated Option for SYN Option Space Extension
                   draft-nishida-tcpm-agg-syn-ext-00

Abstract

   TCP option space is scarce resource as its max length is limited to
   40 bytes.  This limitation becomes more significant in SYN segments
   as all options used in a connection should be exchanged during SYN
   negotiations.  This document proposes a new SYN option negotiation
   scheme that provide a feature to compress TCP options in SYN segments
   and provide more option space.  The proposed scheme does not update
   the format of TCP header nor transmit any additional SYN or SYN-like
   segments so that it has lower risks for middlebox interventions.  In
   addition, by combining another proposal for option space extension,
   it is possible to provide further option space.

Status of This Memo

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   This Internet-Draft will expire on August 6, 2021.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents

Nishida                  Expires August 6, 2021                 [Page 1]
Internet-Draft              Aggregated Option              February 2021

   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions and Terminology . . . . . . . . . . . . . . . . .   4
   3.  Basic Design  . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Aggregated Option . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Additional Information Exchange Using 3rd ACK Segments  .   6
     3.3.  Examples of Option Exchanges with Aggregated Options  . .   7
   4.  Option Bits Registration  . . . . . . . . . . . . . . . . . .   9
   5.  Discussions . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  Incremental Deployments for Aggregated Option . . . . . .  10
     5.2.  Middlebox Considerations  . . . . . . . . . . . . . . . .  10
     5.3.  Which Options are Aggregatable  . . . . . . . . . . . . .  10
     5.4.  Further Extensions  . . . . . . . . . . . . . . . . . . .  11
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     7.1.  Aggregated Option . . . . . . . . . . . . . . . . . . . .  11
     7.2.  Option Bits Registry for Aggregated Option  . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   TCP option space is scarce resource as its max length is limited to
   40 bytes.  This limitation is a nominal issue especially for SYN
   segment.  This is because although a TCP endpoint can send only one
   SYN segment to the peer, SYN segments need to contain all options
   expected to be used for the connection.  As a result, the current SYN
   option space tends to be congested.  Many TCP connections use MSS
   [RFC0793], Timestamp and Window Scale [RFC7323], SACK Permitted
   options [RFC2018] which already consume 19 bytes (10 + 4 + 3 + 2).
   In addition to them, if a connection wants to use Multipath TCP
   [RFC8684], it requires additional 4-12 bytes for MP_CAPABLE or 12-16
   bytes for MP_JOIN option.  Similarly, TCP Fast Open [RFC7413] and TCP
   AO [RFC5925] require additional 6-18 bytes and 16 bytes respectively.
   Moreover, Experimental Option Format defined in [RFC6994] consumes