DiffServ interconnection classes and practice
draft-geib-tsvwg-diffserv-intercon-07

TSVWG                                                       R. Geib, Ed.
Internet-Draft                                          Deutsche Telekom
Intended status: Informational                                  D. Black
Expires: April 27, 2015                                  EMC Corporation
                                                        October 24, 2014

             DiffServ interconnection classes and practice
                 draft-geib-tsvwg-diffserv-intercon-07

Abstract

   This document proposes a limited and well defined set of DiffServ
   PHBs and codepoints to be applied at (inter)connections of two
   separately administered and operated networks.  Many network
   providers operate MPLS using Treatment Aggregates for traffic marked
   with different DiffServ PHBs, and use MPLS for interconnection with
   other networks.  This document offers a simple interconnection
   approach that may simplify operation of DiffServ for network
   interconnection among providers.

Status of this Memo

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   This Internet-Draft will expire on April 27, 2015.

Copyright Notice

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   carefully, as they describe your rights and restrictions with respect

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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Related work . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  MPLS and the Short Pipe tunnel model . . . . . . . . . . . . .  5
   3.  An Interconnection class and codepoint scheme  . . . . . . . .  6
     3.1.  End-to-end QoS: PHB and DS CodePoint Transparency  . . . . 11
     3.2.  Treatment of Network Control traffic at carrier
           interconnection interfaces . . . . . . . . . . . . . . . . 12
   4.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Appendix A.  Change log  . . . . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16

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1.  Introduction

   DiffServ has been deployed in many networks.  As described by section
   2.3.4.2 of RFC 2475, remarking of packets at domain boundaries is a
   DiffServ feature [RFC2475].  This draft proposes a set of standard
   QoS classes and code points at interconnection points to which and
   from which locally used classes and code points should be mapped.

   RFC2474 specifies the DiffServ Codepoint Field [RFC2474].
   Differentiated treatment is based on the specific DSCP.  Once set, it
   may change.  If traffic marked with unknown or unexpected DSCPs is
   received, RFC2474 recommends forwarding that traffic with default
   (best effort) treatment without changing the DSCP markings.  Many
   networks do not follow this recommendation, and instead remark
   unknown or unexpected DSCPs to the zero DSCP for consistency with
   default (best effort) forwarding.

   Many providers operate MPLS-based backbones that employ backbone
   traffic engineering to ensure that if a major link, switch, or router
   fails, the result will be a routed network that continues to meet its
   Service Level Agreements (SLAs).  Based on that foundation,
   foundation, [RFC5127] introduces the concept of DiffServ Treatment
   Aggregates, which enable traffic marked with multiple DSCPs to be
   forwarded in a single MPLS Traffic Class (TC).  Like RFC 5127, this
   document assumes robust provider backbone traffic engineering.

   RFC5127 recommends transmission of DSCPs as they are received.  This
   is not possible, if the receiving and the transmitting domains at a
   network interconnection use different DSCPs for the PHBs involved.

   This document is motivated by requirements for IP network
   interconnection with DiffServ support among providers that operate
   MPLS in their backbones, but is applicable to other technologies.
   The operational simplifications and methods in this document help
   align IP DiffServ functionality with MPLS limitations, particularly
   when MPLS penultimate hop popping is used.  That is an important
   reason why this document specifies 4 interconnection Treatment
   Aggregates.  Limiting DiffServ to a small number Treatment Aggregates
   can help ensure that network traffic leaves a network with the same
   DSCPs that it was received with.  The approach proposed here may be
   extended by operators or future specifications.

   In isolation, use of standard interconnection PHBs and DSCPs may
   appear to be additional effort for a network operator.  The primary
   offsetting benefit is that the mapping from or to the interconnection
   PHBs and DSCPs is specified once for all of the interconnections to
   other networks that can use this approach.  Otherwise, the PHBs and
   DSCPs have to be negotiated and configured independently for each

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   network interconnection, which has poor scaling properties.  Further,
   end-to-end QoS treatment is more likely to result when an
   interconnection code point scheme is used because traffic is remarked
   to the same PHBs at all network interconnections.  This document
   supports one-to-one DSCP remarking at network interconnections (not n
   DSCP to one DSCP remarking).

   The example given in RFC 5127 on aggregation of DiffServ service
   classes uses 4 Treatment Aggregates, and this document does likewise
   because:

   o  The available coding space for carrying QoS information (e.g.,
      DiffServ PHB) in MPLS and Ethernet is only 3 bits in size, and is
      intended for more than just QoS purposes (see e.g.  [RFC5129]).

   o  There should be unused codes for interconnection purposes.  This
      leaves space for future standards, for private bilateral
      agreements and for local use PHBs and DSCPs.

   o  Migrations from one code point scheme to another may require spare
      QoS code points.

   RFC5127 provides recommendations on aggregation of DSCP-marked
   traffic into MPLS Treatment Aggregates and offers a deployment
   example [RFC5127] that does not work for the MPLS Short Pipe model
   when that model is used for ordinary network traffic.  This document
   supports the MPLS Short Pipe model for ordinary network traffic and
   hence differs from the RFC5127 approach as follows:

   o  remarking of received DSCPs to domain internal DSCPs is to be
      expected for ordinary IP traffic at provider edges (and for outer
      headers of tunneled IP traffic).

   o  document follows RFC4594 in the proposed marking of provider
      Network Control traffic and expands RFC4594 on treatment of CS6
      marked traffic at interconnection points (see section 3.2).

   This document is organized as follows: section 2 reviews the MPLS
   Short Pipe tunnel model for DiffServ Tunnels [RFC3270]; effective
   support for that model is a crucial goal of this document.  Section 3
   introduces DiffServ interconnection Treatment Aggregates, plus the
   PHBs and DSCPs that are mapped to these Treatment Aggregates.
   Further, section 3 discusses treatment of non-tunneled and tunneled
   IP traffic and MPLS VPN QoS aspects.  Finally Network Management PHB
   treatment is described.  Annex A discusses how domain internal IP
   layer QoS schemes impact interconnection.  Annex B describes the
   impact of the MPLS Short Pipe model (pen ultimate hop popping) on QoS
   related IP interconnections.

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1.1.  Related work

   In addition to the activities that triggered this work, there are
   additional RFCs and Internet-drafts that may benefit from an
   interconnection PHB and DSCP scheme.  RFC 5160 suggests Meta-QoS-
   Classes to enable deployment of standardized end to end QoS classes
   [RFC5160].  In private discussion, the authors of that RFC agree that
   the proposed interconnection class- and codepoint scheme and its
   enablement of standardised end to end classes would complement their
   own work.

   Work on signaling Class of Service at interconnection interfaces by
   BGP [I-D.knoll-idr-cos-interconnect], [ID.idr-sla] is beyond the
   scope of this draft.  When the basic DiffServ elements for network
   interconnection are used as described in this document, signaled
   access to QoS classes may be of interest.  These two BGP documents
   focus on exchanging SLA and traffic conditioning parameters and
   assume that common PHBs identified by the signaled DSCPs have been
   established prior to BGP signaling of QoS.

2.  MPLS and the Short Pipe tunnel model

   The Pipe and Uniform models for Differentiated Services and Tunnels
   are defined in [RFC2983].  RFC3270 adds the MPLS Short Pipe model in
   order to support penultimate hop popping (PHP) of MPLS Labels,
   primarily for IP tunnels and VPNs.  The Short Pipe model and PHP have
   become popular with many network providers that operate MPLS networks
   and are now widely used for ordinary network traffic, not just
   traffic encapsulated in IP tunnels and VPNs.  This has important
   implications for DiffServ functionality in MPLS networks.

   RFC 2474's recommendation to forward traffic with unrecognized DSCPs
   with Default (best effort) service without rewriting the DSCP has
   proven to be a poor operational practice.  Network operation and
   management are simplified when there is a 1-1 match between the DSCP
   marked on the packet and the forwarding treatment (PHB) applied by
   network nodes.  When this is done, CS0 (the all-zero DSCP) is the
   only DSCP used for Default forwarding of best effort traffic, so a
   common practice is to use CS0 to remark traffic received with
   unrecognized or unsupported DSCPs at network edges.

   MPLS networks are more subtle in this regard, as it is possible to
   encode the provider's DSCP in the MPLS TC field and allow that to
   differ from the PHB indicated by the DSCP in the MPLS-encapsulated IP
   packet.  That would allow an unrecognized DSCP to be carried edge-to-
   edge over an MPLS network, because the effective DSCP used by the
   MPLS network would be encoded in the MPLS label TC field (and also

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   carried edge-to-edge); this approach assumes that a provider MPLS
   label with the provider's TC field being present at all hops within
   the provider's network.

   The Short Pipe tunnel model and PHP violate that assumption because
   PHP pops and discards the MPLS provider label carrying the provider's
   TC field.  That discard occurs one hop upstream of the MPLS tunnel
   endpoint, resulting in no provider TC info being available at tunnel
   egress.  Therefore the DSCP field in the MPLS-encapsulated IP header
   has to contain a DSCP that is valid for the provider's network;
   propagating another DSCP edge-to-edge requires an IP tunnel of some
   form.  In the absence of IP tunneling (a common case for MPLS
   networks), it is not possible to pass all 64 possible DSCP values
   edge-to-edge across an MPLS network.  See Annex B for a more detailed
   discussion.

   If transport of a large number (much greater than 4) DSCPs is
   required across a network that supports this DiffServ interconnection
   scheme, a tunnel or VPN can be provisioned for this purpose, so that
   the inner IP header carries the DSCP that is to be preserved not to
   be changed.  From a network operations perspective, the customer
   equipment (CE) is the preferred location for tunnel termination,
   although a receiving domains Provider Edge router is another viable
   option.

3.  An Interconnection class and codepoint scheme

   At an interconnection, the networks involved need to agree on the
   PHBs used for interconnection and the specific DSCP for each PHB.
   This may involve remarking for the interconnection; such remarking is
   part of the DiffServ Architecture [RFC2475], at least for the network
   edge nodes involved in interconnection.  See Annex A for a more
   detailed discussion.  This draft proposes a standard interconnection
   set of 4 Treatment Aggregates with well-defined DSCPs to be
   aggregated by them.  A sending party remarks DSCPs from internal
   schemes to the interconnection code points.  The receiving party
   remarks DSCPs to her internal scheme.  The set of DSCPs and PHBs
   supported across the two interconnected domains and the treatment of
   PHBs and DSCPs not recognized by the receiving domain should be part
   of the interconnect SLA.

   RFC 5127's four treatment aggregates include a Network Control
   aggregate for routing protocols and OAM traffic that is essential for
   network operation administration, control and management.  Using this
   aggregate as one of the four in RFC 5127 implicitly assumes that
   network control traffic is forwarded in potential competition with
   all other network traffic, and hence DiffServ must favor such traffic

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   (e.g., via use of the CS6 codepoint) for network stability.  That is
   a reasonable assumption for IP-based networks where routing and OAM
   protocols are mixed with all other types of network traffic;
   corporate networks are an example.

   In contrast, mixing of all traffic is not a reasonable assumption for
   MPLS-based provider or carrier networks, where customer traffic is
   usually segregated from network control (routing and OAM) traffic via
   other means, e.g., network control traffic use of separate LSPs that
   can be prioritized over customer LSPs (e.g., for VPN service) via
   other means.  This sort of of network control traffic from customer
   traffic is also used for MPLS-based network interconnections.  In
   addition, many customers of a network provider do not exchange
   Network Control traffic (e.g., routing) with the network provider.
   For these reasons, a separate Network Control traffic aggregate is
   not important for MPLS-based carrier or provider networks; when such
   traffic is not segregated from other traffic, it may reasonably share
   the Assured Elastic treatment aggregate (as RFC 5127 suggests for a
   situation in which only three treatment aggregates are supported).

   In contrast, VoIP is emerging as a valuable and important class of
   network traffic for which network-provided QoS is crucial, as even
   minor glitches are immediately apparent to the humans involved in the
   conversation.

   For these reasons, the Diffserv Interconnect scheme in this document
   departs from the approach in RFC 5127 by not providing a Network
   Control traffic aggregate, and instead dedicating the fourth traffic
   aggregate for VoIP traffic.  Network Control traffic may still be
   exchanged across network interconnections, see Section 3.2 for
   further discussion.

   Similar approaches to use of a small number of traffic aggregates
   (including recognition of the importance of VoIP traffic) have been
   taken in related standards and recommendations from outside the IETF,
   e.g., Y.1566 [Y.1566], GSMA IR.34 [IR.34] andMEF23.1 [MEF23.1].

   The list of the four DiffServ Interconnect traffic aggregates
   follows, highlighting differences from RFC 5127 and the specific
   traffic classes from RFC 4594 that each class aggregates.

    Telephony Service Treatment Aggregate:  PHB EF, DSCP 101 110 and
           VOICE-ADMIT, DSCP 101100, see [RFC3246] , [RFC4594][RFC5865].
           This Treatment Aggregate corresponds to RFC 5127s real time
           Treatment Aggregate definition regarding the queuing, but it
           is restricted to transport Telephony Service Class traffic in
           the sense of RFC 4594.

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   Bulk Real-Time Treatment Aggregate:  This Treatment Aggregate is
           designed to transport PHB AF41, DSCP 100 010 (the other AF4
           PHB group PHBs and DSCPs may be used for future extension of
           the set of DSCPs carried by this Treatment Aggregate).  This
           Treatment Aggregate is designed to transport the portions of
           RFC 5127's Real Time Treatment Aggregate, which consume large
           amounts of bandwidth, namely Broadcast Video, Real-Time
           Interactive and Multimedia Conferencing.  The treatment
           aggregate should be configured with a rate queue (which is in
           line with RFC 4594 for the mentioned traffic classes).  As
           compared to RFC 5127, the number of DSCPs has been reduced to
           one (initially) and the proposed queuing mechanism.  The
           latter is however in line with RFC4594.

   Assured Elastic Treatment Aggregate  This Treatment Aggregate
           consists of the entire AF3 PHB group AF3, i.e., DSCPs 011
           010, 011 100 and 011 110.  As compared to RFC5127, just the
           number of DSCPs, which has been reduced.  This document
           suggests to transport signaling marked by AF31.  RFC5127
           suggests to map Network Management traffic into this
           Treatment Aggregate, if no separate Network Control Treatment
           Aggregate is supported (for a more detailed discussion of
           Network Control PHB treatment see section 3.2).  GSMA IR.34
           proposes to transport signaling traffic by AF31 too.

   Default / Elastic Treatment Aggregate:   transports the default PHB,
           CS0 with DSCP 000 000.  RFC 5127 example refers to this
           Treatment Aggregate as Aggregate Elastic.  An important
           difference as compared to RFC5127 is that any traffic with
           unrecognized or unsupported DSCPs may be remarked to this
           DSCP.

   RFC 4594's Multimedia Streaming class has not been mapped to the
   above scheme.  By the time of writing, the most popular streaming
   applications use TCP transport and adapt picture quality in the case
   of congestion.  These applications are proprietary and still change
   behaviour frequently.  At this state, the Bulk Real-Time Treatment
   Aggregate or the Bulk Real-Time Treatment Aggregate may be a
   reasonable match.

   The overall approach to DSCP marking at network interconnections is
   illustrated by the following example.  Provider O and provider W are
   peered with provider T. They have agreed upon a QoS interconnection
   SLA.

   Traffic of provider O terminates within provider Ts network, while
   provider W's traffic transits through the network of provider T to
   provider F. Assume all providers to run their own internal codepoint

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   schemes for a PHB groupwith properties of the DiffServ Intercon
   Assured Treatment Aggregate.

           Provider-O             Provider-W
           RFC5127                GSMA 34.1
               |                      |
          +----------+           +----------+
          |AF21, AF22|           | CS3, CS2 |
          +----------+           +----------+
               |                      |
               V                      V
           +++++++++              +++++++++
           |Rtr PrO|              |Rtr PrW|  Rtr Pr:
           +++++++++              +++++++++  Router Peering
               |        DiffServ      |
          +----------+           +----------+
          |AF31, AF32|           |AF31, AF32|
          +----------+           +----------+
               |        Intercon      |
               V                      V
           +++++++++                  |
           |RtrPrTI|------------------+
           +++++++++
               |     Provider-T domain
          +-----------+
          | MPLS TC 2 |
          | DSCP rew. |
          | AF21, AF22|
          +-----------+
             |      |  Local DSCPs Provider-T
             |      |  +----------+   +++++++++
             V      +->|AF21, AF22|->-|RtrDstH|
             |         +----------+   +++++++++
         +----------+                 RtrDst:
         |AF21, AF22|                 Router Destination
         +----------+
             |
          +++++++++
          |RtrPrTE|
          +++++++++
             |        DiffServ
         +----------+
         |AF31, AF32|
         +----------+
             |        Intercon

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          +++++++++
          |RtrPrF|
          +++++++++
             |
         +----------+
         | CS4, CS3 |
         +----------+
             |
         Provider-F
         GSM IR.34

   DiffServ Intercon example

                                 Figure 1

   It is easily visible that all providers only need to deploy internal
   DSCP to DiffServ Intercon DSCP mappings to exchange traffic in the
   desired classes.  Provider W has decided that the properties of his
   internal classes CS3 and CS2 are best met by the Diffserv Intercon
   Assured Elastic Treatment Aggregate, PHBs AF31 and AF32 respectively.
   At the outgoing peering interface connecting provider W with provider
   T remarks CS3 traffic to AF31 and CS 2 traffic to CS32.  The domain
   internal PHBs of provider T meeting the Diffserv Intercon Assured
   Elastic Treatment Aggregate requirements is AF2.  Hence AF31 traffic
   received at the interconnection with provider T is remarked to AF21
   by the peering router of domain T. As domain T deploys MPLS, further
   the MPLS TC ist set to 2.  Traffic received with AF32 is remarked to
   AF22.  The MPLS TC of the Treatment Aggregate is the same, TC 2.  At
   the pen-ultimate MPLS node, the top MPLS label is removed.  The
   packet should be forwarded as determined by the incoming MPLS TC.
   The peering router connecting domain T with domain F classifies the
   packet by it's domain T internal DSCP AF21 for the Diffserv Intercon
   Assured Elastic Treatment Aggregate.  As it leaves domain T on the
   interface to domain F, it is remarked to AF31.  The peering router of
   domain F classifies the packet for domain F internal PHB CS4, as this
   is the PHB with properties matching DiffServ Intercon's Assured
   Elastic Treatment Aggregate.  Likewise, AF21 traffic is remarked to
   AF32 by the peering router od domain T when leaving it and from AF32
   to CS3 by domain F's peering router when receiving it.

   This example can be extended.  Suppose Provider-O also supports a PHB
   marked by CS2 and this PHB is supposed to be transported by QoS
   within Provider-T domain.  Then Provider-O will remark it with a DSCP
   other than AF31 DSCP in order to preserve the differentiation from
   CS2; AF11 is one possibility that might be private to the
   interconnection between Provider-O and Provider-T; there's no

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   assumption that Provider-W can also use AF11, as it may not be in the
   SLA with Provider-W.

   Now suppose Provider-W supports CS2 for internal use only.  Then no
   DiffServ intercon DSCP mapping may be configured at the peering
   router.  Traffic, sent by Provider-W to Provider-T marked by CS2 due
   to a misconfiguration may be remarked to CS0 by Provider-T.

   See section 3.1 for further discussion of this and DSCP transparency
   in general.

   RFC5127 specifies a separate Treatment Aggregate for network control
   traffic.  It may be present at interconnection interfaces too, but
   depending on the agreement between providers, Network Control traffic
   may also be classified into a different interconnection class.  See
   section 3.2 for a detailed discussion on the treatment of Network
   Control traffic.

   RFC2575 states that Ingress nodes must condition all other inbound
   traffic to ensure that the DS codepoints are acceptable; packets
   found to have unacceptable codepoints must either be discarded or
   must have their DS codepoints modified to acceptable values before
   being forwarded.  For example, an ingress node receiving traffic from
   a domain with which no enhanced service agreement exists may reset
   the DS codepoint to the Default PHB codepoint.  As a consequence, an
   interconnect SLA needs to specify not only the treatment of traffic
   that arrives with a supported interconnect DSCP, but also the
   treatment of traffic that arrives with unsupported or unexpected
   DSCPs.

   The proposed interconnect class and code point scheme is designed for
   point to point IP layer interconnections among MPLS networks.  Other
   types of interconnections are out of scope of this document.  The
   basic class and code point scheme is applicable on Ethernet layer
   too, if a provider e.g. supports Ethernet pririties like specified by
   IEEE 802.1p.

3.1.  End-to-end QoS: PHB and DS CodePoint Transparency

   This section describes how the use of a common PHB and DSCP scheme
   for interconnection can lead to end-to-end DiffServ-based QoS across
   networks that do not have common policies or practices for PHB and
   DSCP usage.  This will initially be possible for PHBs and DSCPs
   corresponding to at most 3 or 4 Treatment Aggregates due to the MPLS
   considerations discussed previously.

   Networks can be expected to differ in the number of PHBs available at
   interconnections (for terminating or transit service) and the DSCP

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   values used within their domain.  At an interconnection, Treatment
   Aggregate and PHB properties are best described by SLAs and related
   explanatory material.  See annex A for a more detailed discussion
   about why PHB and g DSCP usage is likely to differ among networks.
   For the above reasons and the desire to support interconnection among
   networks with different DiffServ schemes, the DiffServ
   interconnection scheme supports a small number of PHBs and DSCPs;
   this scheme is expandable.

   The basic idea is that traffic sent with a DiffServ interconnect PHB
   and DSCP is restored to that PHB and DSCP (or a PHB and DSCP within
   the AF3 PHB group for the Assured Treatment Aggregate) at each
   network interconnection, even though a different PHB and DSCP may be
   used by each network involved.  So, Bulk Inelastic traffic could be
   sent with AF41, remarked to CS3 by the first network and back to AF41
   at the interconnection with the second network, which could mark it
   to CS5 and back to AF41 at the next interconnection, etc.  The result
   is end-to-end QoS treatment consistent with the Bulk Inelastic
   Traffic Aggregate, and that is signaled or requested by the AF41 DSCP
   at each network interconnection in a fashion that allows each network
   operator to use their own internal PHB and DSCP scheme.

   The key requirement is that the network ingress interconnect DSCP be
   restored at network egress, and a key observation is that this is
   only feasible in general for a small number of DSCPs.

3.2.  Treatment of Network Control traffic at carrier interconnection
      interfaces

   As specified by RFC4594, section 3.2, Network Control (NC) traffic
   marked by CS6 is to be expected at interconnection interfaces.  This
   document does not change NC specifications of RFC4594, but observes
   that network control traffic received at network ingress is generally
   different from network control traffic within a network that is the
   primary use of CS6 envisioned by RFC 4594.  A specific example is
   that some CS6 traffic exchanged across carrier interconnections is
   terminated at the network ingress node (e.g., if BGP is running
   between two routers on opposite ends of an interconnection link),
   which is consistent with RFC 4594's recommendation to not use CS6
   when forwarding CS6-marked traffic originating from user-controlled
   end points.

   The end-to-end QoS discussion in the previous section (3.1) is
   generally inapplicable to network control traffic - network control
   traffic is generally intended to control a network, not be
   transported across it.  One exception is that network control traffic
   makes sense for a purchased transit agreement, and preservation of
   CS6 for network control traffic that is transited is reasonable in

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   some cases.  Use of an IP tunnel is suggested in order to reduce the
   risk of CS6 markings on transiting network control traffic being
   interpreted by the network providing the transit.

   If the MPLS Short Pipe model is deployed for non tunneled IPv4
   traffic, an IP network provider should limit access to the CS6 and
   CS7 DSCPs so that they are only used for network control traffic for
   the provider's own network.

   Interconnecting carriers should specify treatment of CS6 marked
   traffic received at a carrier interconnection which is to be
   forwarded beyond the ingress node.  An SLA covering the following
   cases is recommended when a provider wishes to send CS6 marked
   traffic across an interconnection link which isn't terminating at the
   interconnected ingress node:

   o  classification of traffic which is network control traffic for
      both domains.  This traffic should be classified and marked for
      the NC PHB.

   o  classification of traffic which is network control traffic for the
      sending domain only.  This traffic should be classified for a PHB
      offering similar properties as the NC class (e.g.  AF31 as
      specified by this document).  As an example GSMA IR.34 proposes an
      Interactive class / AF31 to carry SIP and DIAMETER traffic.  While
      this is service control traffic of high importance to the
      interconnected Mobile Network Operators, it is certainly no
      Network Control traffic for a fixed network providing transit.
      The example may not be perfect.  It was picked nevertheless
      because it refers to an existing standard.

   o  any other CS6 marked traffic should be remarked or dropped.

4.  Acknowledgements

   Al Morton and Sebastien Jobert provided feedback on many aspects
   during private discussions.  Mohamed Boucadair and Thomas Knoll
   helped adding awareness of related work.  Fred Baker and Brian
   Carpenter provided intensive feedback and discussion.

5.  IANA Considerations

   This memo includes no request to IANA.

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6.  Security Considerations

   This document does not introduce new features, it describes how to
   use existing ones.  The security section of RFC 2475 [RFC2475] and
   RFC 4594 [RFC4594] apply.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, 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,
              December 1998.

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

   [RFC2597]  Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
              "Assured Forwarding PHB Group", RFC 2597, June 1999.

   [RFC3246]  Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,
              J., Courtney, W., Davari, S., Firoiu, V., and D.
              Stiliadis, "An Expedited Forwarding PHB (Per-Hop
              Behavior)", RFC 3246, March 2002.

   [RFC3260]  Grossman, D., "New Terminology and Clarifications for
              Diffserv", RFC 3260, April 2002.

   [RFC3270]  Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
              P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
              Protocol Label Switching (MPLS) Support of Differentiated
              Services", RFC 3270, May 2002.

   [RFC5129]  Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion
              Marking in MPLS", RFC 5129, January 2008.

   [RFC5462]  Andersson, L. and R. Asati, "Multiprotocol Label Switching
              (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
              Class" Field", RFC 5462, February 2009.

   [RFC5865]  Baker, F., Polk, J., and M. Dolly, "A Differentiated
              Services Code Point (DSCP) for Capacity-Admitted Traffic",

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              RFC 5865, May 2010.

   [min_ref]  authSurName, authInitials., "Minimal Reference", 2006.

7.2.  Informative References

   [I-D.knoll-idr-cos-interconnect]
              Knoll, T., "BGP Class of Service Interconnection",
              draft-knoll-idr-cos-interconnect-12 (work in progress),
              May 2014.

   [ID.idr-sla]
              IETF, "Inter-domain SLA Exchange", IETF,  http://
              datatracker.ietf.org/doc/draft-ietf-idr-sla-exchange/,
              2013.

   [IEEE802.1Q]
              IEEE, "IEEE Standard for Local and Metropolitan Area
              Networks - Virtual Bridged Local Area Networks", 2005.

   [IR.34]    GSMA Association, "IR.34 Inter-Service Provider IP
              Backbone Guidelines Version 7.0", GSMA,  GSMA IR.34 http:/
              /www.gsma.com/newsroom/wp-content/uploads/2012/03/
              ir.34.pdf, 2012.

   [MEF23.1]  MEF, "Implementation Agreement MEF 23.1 Carrier Ethernet
              Class of Service Phase 2", MEF,  MEF23.1 http://
              metroethernetforum.org/PDF_Documents/
              technical-specifications/MEF_23.1.pdf, 2012.

   [RFC2983]  Black, D., "Differentiated Services and Tunnels",
              RFC 2983, October 2000.

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

   [RFC5127]  Chan, K., Babiarz, J., and F. Baker, "Aggregation of
              Diffserv Service Classes", RFC 5127, February 2008.

   [RFC5160]  Levis, P. and M. Boucadair, "Considerations of Provider-
              to-Provider Agreements for Internet-Scale Quality of
              Service (QoS)", RFC 5160, March 2008.

   [Y.1566]   ITU-T, "Quality of service mapping and interconnection
              between Ethernet, IP and multiprotocol label switching
              networks", ITU,
               http://www.itu.int/rec/T-REC-Y.1566-201207-I/en, 2012.

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Appendix A.  Change log

   00 to 01  Added terminology and references.  Added details and
           information to interconnection class and codepoint scheme.
           Editorial changes.

   01 to 02  Added some references regarding related work.  Clarified
           class definitions.  Further editorial improvements.

   02 to 03  Consistent terminology.  Discussion of Network Management
           PHB at interconnection interfaces.  Editorial review.

   03 to 04  Again improved terminology.  Better wording of Network
           Control PHB at interconnection interfaces.

   04 to 05  Large rewrite and re-ordering of contents.

   05 to 06  Description of IP and MPLS related requirements and
           constraints on DSCP rewrites.

   06 to 07  Largely rewrite, improved match and comparison with RFCs
           4594 and 5127.

Authors' Addresses

   Ruediger Geib (editor)
   Deutsche Telekom
   Heinrich Hertz Str. 3-7
   Darmstadt,   64295
   Germany

   Phone: +49 6151 5812747
   Email: Ruediger.Geib@telekom.de

   David L. Black
   EMC Corporation
   176 South Street
   Hopkinton, MA
   USA

   Phone: +1 (508) 293-7953
   Email: david.black@emc.com

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