Requirements for the design of a Substrate Protocol for User Datagrams (SPUD)

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Network Working Group                                   B. Trammell, Ed.
Internet-Draft                                        M. Kuehlewind, Ed.
Intended status: Informational                                ETH Zurich
Expires: January 7, 2016                                   July 06, 2015

 Requirements for the design of a Substrate Protocol for User Datagrams


   The Substrate Protocol for User Datagrams (SPUD) BoF session at the
   IETF 92 meeting in Dallas in March 2015 identified the potential need
   for a UDP-based encapsulation protocol to allow explicit cooperation
   with middleboxes while using new, encrypted transport protocols.
   This document proposes an initial set of requirements for such a
   protocol, and discusses tradeoffs to be made in further refining
   these requirements.

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1.  Motivation

   A number of efforts to create new transport protocols or experiment
   with new network behaviors have been built on top of UDP, as it
   traverses firewalls and other middleboxes more readily than new
   protocols do.  Each such effort must, however, either manage its
   flows within common middlebox assumptions for UDP or train the
   middleboxes on the new protocol (thus losing the benefit of using
   UDP).  A common Substrate Protocol for User Datagrams (SPUD) would
   allow each effort to re-use a set of shared methods for notifying
   middleboxes of the flows' semantics, thus avoiding both the
   limitations of current flow semantics and the need to re-invent the
   mechanism for notifying the middlebox of the new semantics.

   As a concrete example, it is common for some middleboxes to tear down
   required state (such as NAT bindings) very rapidly for UDP flows.  By
   notifying the path that a particular transport using UDP maintains
   session state and explicitly signals session start and stop using the
   substrate, the using protocol may reduce or avoid the need for
   heartbeat traffic.

   This document defines a specific set of requirements for a SPUD
   facility, based on analysis on a target set of applications to be
   developed on SPUD developing experience with a prototype described in
   [I-D.hildebrand-spud-prototype].  It is intended as the basis for
   determining the next steps to make progress in this space, including
   eventually chartering an working group for specific protocol
   engineering work.

2.  History

   An outcome of the IAB workshop on Stack Evolution in a Middlebox
   Internet (SEMI) [I-D.iab-semi-report], held in Zurich in January
   2015, was a discussion on the creation of a substrate protocol to
   support the deployment of new transport protocols in the Internet.
   Assuming that a way forward for transport evolution in user space
   would involve encapsulation in UDP datagrams, the workshop noted that
   it may be useful to have a facility built atop UDP to provide minimal
   signaling of the semantics of a flow that would otherwise be
   available in TCP.  At the very least, indications of first and last
   packets in a flow may assist firewalls and NATs in policy decision
   and state maintenance.  Further transport semantics would be used by
   the protocol running atop this facility, but would only be visible to
   the endpoints, as the transport protocol headers themselves would be

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