Transport Protocol Path Signals
RFC 8558

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Internet Architecture Board (IAB)                         T. Hardie, Ed.
Request for Comments: 8558                                    April 2019
Category: Informational
ISSN: 2070-1721

                    Transport Protocol Path Signals

Abstract

   This document discusses the nature of signals seen by on-path
   elements examining transport protocols, contrasting implicit and
   explicit signals.  For example, TCP's state machine uses a series of
   well-known messages that are exchanged in the clear.  Because these
   are visible to network elements on the path between the two nodes
   setting up the transport connection, they are often used as signals
   by those network elements.  In transports that do not exchange these
   messages in the clear, on-path network elements lack those signals.
   Often, the removal of those signals is intended by those moving the
   messages to confidential channels.  Where the endpoints desire that
   network elements along the path receive these signals, this document
   recommends explicit signals be used.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Architecture Board (IAB)
   and represents information that the IAB has deemed valuable to
   provide for permanent record.  It represents the consensus of the
   Internet Architecture Board (IAB).  Documents approved for
   publication by the IAB are not candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8558.

Hardie                        Informational                     [Page 1]
RFC 8558             Transport Protocol Path Signals          April 2019

Copyright Notice

   Copyright (c) 2019 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
   (https://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.

Table of Contents

   1. Introduction ....................................................3
   2. Signal Types Inferred ...........................................4
      2.1. Session Establishment ......................................4
           2.1.1. Session Identity ....................................4
           2.1.2. Routability and Intent ..............................4
           2.1.3. Flow Stability ......................................5
           2.1.4. Resource Requirements ...............................5
      2.2. Network Measurement ........................................5
           2.2.1. Path Latency ........................................5
           2.2.2. Path Reliability and Consistency ....................5
   3. Options .........................................................5
      3.1. Do Not Restore These Signals ...............................6
      3.2. Replace These with Network-Layer Signals ...................6
      3.3. Replace These with Per-Transport Signals ...................6
      3.4. Create a Set of Signals Common to Multiple Transports ......6
   4. Recommendation ..................................................7
   5. IANA Considerations .............................................8
   6. Security Considerations .........................................8
   7. Informative References ..........................................9
   IAB Members at the Time of Approval ...............................10
   Acknowledgements ..................................................10
   Author's Address ..................................................10

Hardie                        Informational                     [Page 2]
RFC 8558             Transport Protocol Path Signals          April 2019

1.  Introduction

   This document discusses the nature of signals seen by on-path
   elements examining transport protocols, contrasting implicit and
   explicit signals.  For example, TCP's state machine uses a series of
   well-known messages that are exchanged in the clear.  Because these
   are visible to network elements on the path between the two nodes
   setting up the transport connection, they are often used as signals
   by those network elements.  While the architecture of the Internet
   may be best realized by end-to-end protocols [RFC1958], there are
   cases such as the use of Network Address Translators [RFC3234] where
   some functions are commonly provided by on-path network elements.  In
   transports that do not exchange these messages in the clear, on-path
   network elements lack those signals.  Often, the removal of those