Internet Engineering Task Force                                 R. Bless
Internet-Draft                   Karlsruhe Institute of Technology (KIT)
Updates: 3662,4594 (if approved)                       November 14, 2016
Intended status: Standards Track
Expires: May 18, 2017

                A Lower Effort Per-Hop Behavior (LE PHB)


   This document specifies properties and characteristics of a Lower
   Effort (LE) per-hop behavior (PHB).  The primary objective of this LE
   PHB is to protect best-effort (BE) traffic (packets forwarded with
   the default PHB) from LE traffic in congestion situations, i.e., when
   resources become scarce, best-effort traffic has precedence over LE
   traffic and may preempt it.  There are numerous uses for this PHB,
   e.g., for background traffic of low precedence, such as bulk data
   transfers with low priority in time, non time-critical backups,
   larger software updates, web search engines while gathering
   information from web servers and so on.  This document recommends a
   standard DSCP value for the LE PHB.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on May 18, 2017.

Copyright Notice

   Copyright (c) 2016 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

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   ( in effect on the date of
   publication of this document.  Please review these documents
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Applicability . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Deployment Considerations . . . . . . . . . . . . . . . .   4
     1.3.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  PHB Description . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Traffic Conditioning Actions  . . . . . . . . . . . . . . . .   5
   4.  Recommended DS Codepoint  . . . . . . . . . . . . . . . . . .   5
   5.  Remarking to other DSCPs/PHBs . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Appendix A.  History of the LE PHB  . . . . . . . . . . . . . . .   7
   Appendix B.  Acknowledgments  . . . . . . . . . . . . . . . . . .   7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   This document defines a Differentiated Services per-hop behavior
   RFC 2474 [RFC2474] called "Lower Effort" (LE) which is intended for
   traffic of sufficiently low urgency, in which all other traffic takes
   precedence over LE traffic in consumption of network link bandwidth.
   Low urgency traffic has got a low priority in time, which does not
   necessarily imply that it is generally of minor importance.  From
   this viewpoint, it can be considered as a network equivalent to a
   background priority for processes in an operating system.  There may
   or may not be memory (buffer) resources allocated for this type of

   Some networks carry traffic for which delivery is considered
   optional; that is, packets of this type of traffic ought to consume
   network resources only when no other traffic is present.
   Alternatively, the effect of this type of traffic on all other
   network traffic is strictly limited.  This is distinct from "best-
   effort" (BE) traffic since the network makes no commitment to deliver
   LE packets.  In contrast, BE traffic receives an implied "good faith"
   commitment of at least some available network resources.  This

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   document proposes a Lower Effort Differentiated Services per-hop
   behavior (LE PHB) for handling this "optional" traffic in a
   differentiated services node.

1.1.  Applicability

   A Lower Effort PHB is for sending extremely non-critical traffic
   across a Differentiated Services (DS) domain or DS region.  There
   should be an expectation that packets of the LE PHB may be delayed or
   dropped when any other traffic is present.  Use of the LE PHB might
   assist a network operator in moving certain kinds of traffic or users
   to off-peak times.  Alternatively, or in addition, packets can be
   designated for the LE PHB when the goal is to protect all other
   packet traffic from competition with the LE aggregate while not
   completely banning LE traffic from the network.  An LE PHB should not
   be used for a customer's "normal internet" traffic nor should packets
   be "downgraded" to the LE PHB used as a substitute for dropping
   packets that ought simply to be dropped as unauthorized.  The LE PHB
   is expected to have applicability in networks that have at least some
   unused capacity at some times of day.

   This is a PHB that allows networks to protect themselves from
   selected types of traffic rather than giving a selected traffic
   aggregate preferential treatment.  Moreover, it may also exploit all
   unused resources from other PHBs.

   There is no intrinsic reason to limit the applicability of the LE PHB
   to any particular application or type of traffic.  It is intended as
   an additional tool for administrators in engineering networks.  For
   instance, it can be used for filling up protection capacity of
   transmission links which is otherwise unused.  Some network providers
   keep link utilization below 50% in order to being able carrying all
   traffic without loss in case of rerouting due to a link failure.  LE
   marked traffic can utilize the normally unused capacity and will be
   preempted automatically in case of link failure when 100% of the link
   capacity is required for all other traffic.  Ideally, applications
   mark their packets as LE traffic, since they know the urgency of

   Example uses for the LE PHB comprise:

   o  For traffic caused by world-wide web search engines while they
      gather information from web servers.

   o  For software updates or dissemination of new releases of operating

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   o  For backup traffic or non-time critical sychronization or
      mirroring traffic.

   o  For content distribution transfers between caches.

   o  For Netnews and other "bulk mail" of the Internet.

   o  For "downgraded" traffic from some other PHB when this does not
      violate the operational objectives of the other PHB or the overall
      network.  LE should not be used for the general case of downgraded
      traffic, but may be used by design, e.g., to protect an internal
      network from untrusted external traffic sources.  In this case
      there is no way for attackers to preempt internal (non LE) traffic
      by flooding.  Another use case is mentioned in [RFC3754]: non-
      admitted multicast traffic.

1.2.  Deployment Considerations

   Internet-wide deployment of the LE PHB is eased by the following

   o  No harm to other traffic: since the LE PHB has got the lowest
      priority it does not take resources from other PHBs.  Deployment
      across different provider domains causes no trust issues or attack
      vectors to existing traffic.

   o  No parameters or configuration: the LE PHB requires no parameters
      and no configuration of traffic profiles and so on.

   o  No traffic conditioning mechanisms: the LE PHB requires only a
      queue and a scheduling mechanism, but no traffic meters, droppers
      or shapers.

   Since LE traffic may be starved completely for a longer period of
   time, transport protocols or applications should be able to detect
   such a situation and should resume the transfer as soon as possible.

1.3.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  PHB Description

   This PHB is defined in relation to the default PHB (best-effort).  A
   packet forwarded with this PHB SHOULD have lower precedence than
   packets forwarded with the default PHB.  Ideally, LE packets should

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   be forwarded only if no best-effort packet is waiting for its
   transmission.  A straightforward implementation could be a simple
   priority scheduler serving the default PHB queue with higher priority
   than the lower-effort PHB queue.  Alternative implementations may use
   scheduling algorithms that assign a very small weight to the LE
   class.  This, however, may sometimes cause better service for LE
   packets compared to BE packets in cases when the BE share is fully
   utilized and the LE share not.

3.  Traffic Conditioning Actions

   As for most other PHBs an initial classification and marking would
   usually be performed at the first DS boundary node.  In many cases,
   packets may also be pre-marked in DS aware end systems by
   applications due to their specific knowledge about the particular
   precedence of packets.  There is no incentive for DS domains to
   distrust this initial marking, because letting LE traffic enter a DS
   domain causes no harm.  In the worst case it evokes the same effect
   as it would have been marked with the default PHB, i.e., as best-
   effort traffic.  Thus, any policing such as limiting the traffic rate
   is not necessary at the DS boundary.

   Usually, the amount of LE traffic is implicitly limited by queueing
   mechanisms and related discard actions of the PHB.  Therefore, there
   is normally no need to meter and police LE traffic explicitly.

4.  Recommended DS Codepoint

   The recommended codepoint for the LE PHB is 000010.

   RFC 4594 [RFC4594] recommended to use CS1 as codepoint (as mentioned
   in [RFC3662].  This is problematic since it may cause a priority
   inversion resulting in treating LE packets with higher precedence
   than BE packets.  Existing implementations SHOULD therefore use the
   unambiguous LE codepoint 000010 whenever possible.

5.  Remarking to other DSCPs/PHBs

   "DSCP bleaching", i.e., setting the DSCP to 000000 (default PHB) is
   not recommended for this PHB.  This may cause effects that are in
   contrast to the original intent in protecting BE traffic from LE
   traffic.  In case DS domains do not support the LE PHB, they may
   treat LE marked packets with the default PHB instead, but they should
   do so without remarking to the DSCP 000000.  The reason for this is
   that later traversed DS domains may then have still the possibility
   to treat such packets according the LE PHB.

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6.  IANA Considerations

   This memo includes a request to assign a Differentiated Services
   Field Codepoint (DSCP) 000010 from the Differentiated Services Field
   Codepoints (DSCP) registry

7.  Security Considerations

   There are no specific security exposures for this PHB.  Since it
   defines a new class of low forwarding priority, other traffic may be
   downgraded to this LE PHB in case it is remarked as LE traffic.  See
   the general security considerations in RFC 2474 [RFC2474] and RFC
   2475 [RFC2475].

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
              and W. Weiss, "An Architecture for Differentiated
              Services", RFC 2475, DOI 10.17487/RFC2475, December 1998,

8.2.  Informative References

              Bless, R. and K. Wehrle, "A Lower Than Best-Effort Per-Hop
              Behavior", draft-bless-diffserv-lbe-phb-00 (work in
              progress), September 1999, <

   [RFC3662]  Bless, R., Nichols, K., and K. Wehrle, "A Lower Effort
              Per-Domain Behavior (PDB) for Differentiated Services",
              RFC 3662, DOI 10.17487/RFC3662, December 2003,

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   [RFC3754]  Bless, R. and K. Wehrle, "IP Multicast in Differentiated
              Services (DS) Networks", RFC 3754, DOI 10.17487/RFC3754,
              April 2004, <>.

   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration
              Guidelines for DiffServ Service Classes", RFC 4594,
              DOI 10.17487/RFC4594, August 2006,

Appendix A.  History of the LE PHB

   A first version of this PHB was suggested by Roland Bless and Klaus
   Wehrle in 1999 [draft-bless-diffserv-lbe-phb-00].  After some
   discussion in the DiffServ Working Group Brian Carpenter and Kathie
   Nichols proposed a bulk handling per-domain behavior and believed a
   PHB was not necessary.  Eventually, Lower Effort was specified as
   per-domain behavior and finally became [RFC3662].  More detailed
   information about its history can be found in Section 10 of

Appendix B.  Acknowledgments

   Since text is borrowed from earlier Internet-Drafts and RFCs the co-
   authors of previous specifications are acknowledged here: Kathie
   Nichols and Klaus Wehrle.

Author's Address

   Roland Bless
   Karlsruhe Institute of Technology (KIT)
   Kaiserstr. 12
   Karlsruhe  76131

   Phone: +49 721 608 46413

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