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Internet Engineering Task Force (IETF)                      R. Geib, Ed.Request for Comments: 8100                              Deutsche TelekomCategory: Informational                                         D. BlackISSN: 2070-1721                                                 Dell EMC                                                              March 2017Diffserv-Interconnection Classes and PracticeAbstract   This document defines a limited common set of Diffserv Per-Hop   Behaviors (PHBs) and Diffserv Codepoints (DSCPs) to be applied at   (inter)connections of two separately administered and operated   networks, and it explains how this approach can simplify network   configuration and operation.  Many network providers operate   Multiprotocol Label Switching (MPLS) using Treatment Aggregates for   traffic marked with different Diffserv Per-Hop Behaviors 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 that use MPLS   and apply the Short Pipe Model.  While motivated by the requirements   of MPLS network operators that use Short Pipe Model tunnels, this   document is applicable to other networks, both MPLS and non-MPLS.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 Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Not all documents   approved by the IESG are a candidate for any level of Internet   Standard; seeSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc8100.Geib & Black                  Informational                     [Page 1]

RFC 8100                    Diffserv-Intercon                 March 2017Copyright Notice   Copyright (c) 2017 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://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.  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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .31.1.  Related Work  . . . . . . . . . . . . . . . . . . . . . .41.2.  Applicability Statement . . . . . . . . . . . . . . . . .51.3.  Document Organization . . . . . . . . . . . . . . . . . .52.  MPLS and Short Pipe Model Tunnels . . . . . . . . . . . . . .63.  Relationship toRFC 5127  . . . . . . . . . . . . . . . . . .73.1.  Background ofRFC 5127  . . . . . . . . . . . . . . . . .73.2.  Differences fromRFC 5127 . . . . . . . . . . . . . . . .74.  The Diffserv-Intercon Interconnection Classes . . . . . . . .84.1.  Diffserv-Intercon Example . . . . . . . . . . . . . . . .114.2.  End-to-End PHB and DSCP Transparency  . . . . . . . . . .13     4.3.  Treatment of Network Control Traffic at Carrier           Interconnection Interfaces  . . . . . . . . . . . . . . .135.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .156.  Security Considerations . . . . . . . . . . . . . . . . . . .157.  References  . . . . . . . . . . . . . . . . . . . . . . . . .167.1.  Normative References  . . . . . . . . . . . . . . . . . .167.2.  Informative References  . . . . . . . . . . . . . . . . .16Appendix A.  The MPLS Short Pipe Model and IP Traffic . . . . . .18   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .21   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .21Geib & Black                  Informational                     [Page 2]

RFC 8100                    Diffserv-Intercon                 March 20171.  Introduction   Diffserv has been deployed in many networks; it provides   differentiated traffic forwarding based on the Diffserv Codepoint   (DSCP) field, which is part of the IP header [RFC2474].  This   document defines a set of common Diffserv classes (Per-Hop Behaviors   (PHBs)) and codepoints for use at interconnection points to which and   from which locally used classes and codepoints should be mapped.   As described bySection 2.3.4.2 of [RFC2475], the re-marking of   packets at domain boundaries is a Diffserv feature.  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 to better support   incremental Diffserv deployment in existing networks as well as with   routers that do not support Diffserv or are not configured to support   it.  Many networks do not follow this recommendation and instead   re-mark unknown or unexpected DSCPs to zero upon receipt for default   (best-effort) forwarding in accordance with the guidance in [RFC2475]   to ensure that appropriate DSCPs are used within a Diffserv domain.   This document is based on the latter approach and defines additional   DSCPs that are known and expected at network interconnection   interfaces in order to reduce the amount of traffic whose DSCPs are   re-marked to zero.   This document is motivated by requirements for IP network   interconnection with Diffserv support among providers that operate   Multiprotocol Label Switching (MPLS) in their backbones, but it is   also applicable to other technologies.  The operational   simplifications and methods in this document help align IP Diffserv   functionality with MPLS limitations resulting from the widely   deployed Short Pipe Model for MPLS tunnel operation [RFC3270].   Further, limiting Diffserv to a small number of Treatment Aggregates   can enable network traffic to leave a network with the DSCP value   with which it was received, even if a different DSCP is used within   the network, thus providing an opportunity to extend consistent   Diffserv treatment across network boundaries.   In isolation, use of a defined set of interconnection PHBs and DSCPs   may appear to be additional effort for a network operator.  The   primary offsetting benefit is that 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.   Absent this approach, the PHBs and DSCPs have to be negotiated and   configured independently for each network interconnection, which has   poor administrative and operational scaling properties.  Further,Geib & Black                  Informational                     [Page 3]

RFC 8100                    Diffserv-Intercon                 March 2017   consistent end-to-end Diffserv treatment is more likely to result   when an interconnection codepoint scheme is used because traffic is   re-marked to the same DSCPs at all network interconnections.   The interconnection approach described in this document (referred to   as "Diffserv-Intercon") uses a set of PHBs (mapped to four   corresponding MPLS Treatment Aggregates) along with a set of   interconnection DSCPs allowing straightforward rewriting to domain-   internal DSCPs and defined DSCP markings for traffic forwarded to   interconnected domains.  The solution described here can be used in   other contexts benefiting from a defined Diffserv interconnection   interface.   The basic idea is that traffic sent with a Diffserv-Intercon PHB and   DSCP is restored to that PHB and DSCP at each network   interconnection, even though a different PHB and DSCP may be used   within each network involved.  The key requirement is that the   network ingress interconnect DSCP be restored at the network egress,   and a key observation is that this is only feasible in general for a   small number of DSCPs.  Traffic sent with other DSCPs can be   re-marked to an interconnect DSCP or dealt with via an additional   agreement(s) among the operators of the interconnected networks; use   of the MPLS Short Pipe Model favors re-marking unexpected DSCPs to   zero in the absence of an additional agreement(s), as explained   further in this document.   In addition to the common interconnecting PHBs and DSCPs,   interconnecting operators need to further agree on the tunneling   technology used for interconnection (e.g., MPLS, if used) and control   or mitigate the impacts of tunneling on reliability and MTU.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.  [RFC5160] suggests   Meta-QoS-Classes to help enable deployment of standardized end-to-end   QoS classes.  The Diffserv-Intercon class and codepoint scheme is   intended to complement that work (e.g., by enabling a defined set of   interconnection DSCPs and PHBs).   Border Gateway Protocol (BGP) support for signaling Class of Service   at interconnection interfaces [BGP-INTERCONNECTION] [SLA-EXCHANGE] is   complementary to Diffserv-Intercon.  These two BGP documents focus on   exchanging Service Level Agreement (SLA) and traffic conditioning   parameters and assume that common PHBs identified by the signaled   DSCPs have been established (e.g., via use of the Diffserv-Intercon   DSCPs) prior to BGP signaling of PHB id codes.Geib & Black                  Informational                     [Page 4]

RFC 8100                    Diffserv-Intercon                 March 20171.2.  Applicability Statement   This document is applicable to the use of Differentiated Services for   interconnection traffic between networks and is particularly suited   to interconnection of MPLS-based networks that use MPLS Short Pipe   Model tunnels.  This document is also applicable to other network   technologies, but it is not intended for use within an individual   network, where the approach specified in [RFC5127] is among the   possible alternatives; seeSection 3 for further discussion.   The Diffserv-Intercon approach described in this document simplifies   IP-based interconnection to domains operating the MPLS Short Pipe   Model for IP traffic, both terminating within the domain and   transiting onward to another domain.  Transiting traffic is received   and sent with the same PHB and DSCP.  Terminating traffic maintains   the PHB with which it was received; however, the DSCP may change.   Diffserv-Intercon is also applicable to Pipe Model tunneling   [RFC2983] [RFC3270], but it is not applicable to Uniform Model   tunneling [RFC2983] [RFC3270].   The Diffserv-Intercon approach defines a set of four PHBs for support   at interconnections (or network boundaries in general).   Corresponding DSCPs for use at an interconnection interface are also   defined.  Diffserv-Intercon allows for a simple mapping of PHBs and   DSCPs to MPLS Treatment Aggregates.  It is extensible by IETF   standardization, and this allows additional PHBs and DSCPs to be   specified for the Diffserv-Intercon scheme.  Coding space for private   interconnection agreements or provider internal services is   available, as only a single digit number of standard DSCPs are   applied by the Diffserv-Intercon approach.1.3.  Document Organization   This document is organized as follows:Section 2 reviews the MPLS   Short Pipe Model for Diffserv Tunnels [RFC3270], because effective   support for that model is a crucial goal of Diffserv-Intercon.Section 3 provides background on the approach described inRFC 5127   to Traffic Class (TC) aggregation within a Diffserv network domain   and contrasts it with the Diffserv-Intercon approach.Section 4   introduces Diffserv-Intercon Treatment Aggregates, along with the   PHBs and DSCPs that they use, and explains how other PHBs (and   associated DSCPs) may be mapped to these Treatment Aggregates.Section 4 also discusses treatment of IP traffic, MPLS VPN Diffserv   considerations, and the handling of high-priority network management   traffic.Appendix A describes how the MPLS Short Pipe Model   (Penultimate Hop Popping (PHP)) impacts DSCP marking for IP   interconnections.Geib & Black                  Informational                     [Page 5]

RFC 8100                    Diffserv-Intercon                 March 20172.  MPLS and Short Pipe Model Tunnels   This section provides a summary of the implications of MPLS Short   Pipe Model tunnels and, in particular, their use of PHP (seeRFC3270) on the Diffserv tunnel framework described inRFC 2983.  The   Pipe and Uniform Models for Differentiated Services and Tunnels are   defined in [RFC2983].RFC 3270 adds the Short Pipe Model to reflect   the impact of MPLS PHP, primarily for MPLS-based IP tunnels and VPNs.   The Short Pipe Model and PHP have subsequently become popular with   network providers that operate MPLS networks and are now widely used   to transport unencapsulated IP traffic.  This has important   implications for Diffserv functionality in MPLS networks.   PerRFC 2474, the recommendation to forward traffic with unrecognized   DSCPs with default (best-effort) service without rewriting the DSCP   has not been widely deployed in 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, and a   common practice is to re-mark to CS0 any 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.  If the MPLS label with the provider's TC field is present at   all hops within the provider network, this approach would allow an   unrecognized DSCP to be carried edge-to-edge over an MPLS network,   because the effective DSCP used by the provider's MPLS network would   be encoded in the MPLS label TC field (and also carried   edge-to-edge).  Unfortunately, this is only true for Pipe Model   tunnels.   Short Pipe Model tunnels and PHP behave differently because PHP   removes and discards the MPLS provider label carrying the provider's   TC field before the traffic exits the provider's network.  That   discard occurs one hop upstream of the MPLS tunnel endpoint (which is   usually at the network edge), resulting in no provider TC information   being available at the tunnel egress.  To ensure consistent handling   of traffic at the tunnel egress, the DSCP field in the MPLS-   encapsulated IP header has to contain a DSCP that is valid for the   provider's network, so that the IP header cannot be used to carry a   different DSCP edge-to-edge.  SeeAppendix A for a more detailed   discussion.Geib & Black                  Informational                     [Page 6]

RFC 8100                    Diffserv-Intercon                 March 20173.  Relationship toRFC 5127   This document draws heavily upon the approach to aggregation of   Diffserv TCs for use within a network as described inRFC 5127, but   there are important differences caused by characteristics of network   interconnects that differ from links within a network.3.1.  Background ofRFC 5127   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   function.  Based on that foundation, [RFC5127] introduced the concept   of Diffserv Treatment Aggregates, which enable traffic marked with   multiple DSCPs to be forwarded in a single MPLS TC based on robust   provider backbone traffic engineering.  This enables differentiated   forwarding behaviors within a domain in a fashion that does not   consume a large number of MPLS TCs.RFC 5127 provides an example aggregation of Diffserv service classes   into four Treatment Aggregates.  A small number of aggregates are   used because:   o  The available coding space for carrying TC information (e.g.,      Diffserv PHB) in MPLS (and Ethernet) is only 3 bits in size and is      intended for more than just Diffserv purposes (see, e.g.,      [RFC5129]).   o  The common interconnection DSCPs ought not to use all 8 possible      values.  This leaves space for future standards, private bilateral      agreements, and local use PHBs and DSCPs.   o  Migrations from one DSCP scheme to a different one is another      possible application of otherwise unused DSCPs.3.2.  Differences fromRFC 5127   LikeRFC 5127, this document also uses four Treatment Aggregates, but   it differs fromRFC 5127 in some important ways:   o  It followsRFC 2475 in allowing the DSCPs used within a network to      differ from those used to exchange traffic with other networks (at      network edges), but it provides support to restore ingress DSCP      values if one of the recommended interconnect DSCPs in this      document is used.  This results in DSCP re-marking at both network      ingress and network egress, and this document assumes that such      re-marking at network edges is possible for all interface types.Geib & Black                  Informational                     [Page 7]

RFC 8100                    Diffserv-Intercon                 March 2017   o  Diffserv-Intercon suggests limiting the number of interconnection      PHBs per Treatment Aggregate to the minimum required.  As further      discussed below, the number of PHBs per Treatment Aggregate is no      more than two.  When two PHBs are specified for a Diffserv-      Intercon Treatment Aggregate, the expectation is that the provider      network supports DSCPs for both PHBs but uses a single MPLS TC for      the Treatment Aggregate that contains the two PHBs.   o  Diffserv-Intercon suggests mapping other PHBs and DSCPs into the      interconnection Treatment Aggregates as further discussed below.   o  Diffserv-Intercon treats network control (NC) traffic as a special      case.  Within a provider's network, the CS6 DSCP is used for local      network control traffic (routing protocols and Operations,      Administration, and Maintenance (OAM) traffic that is essential to      network operation administration, control, and management) that      may be destined for any node within the network.  In contrast,      network control traffic exchanged between networks (e.g., BGP)      usually terminates at or close to a network edge and is not      forwarded through the network because it is not part of internal      routing or OAM for the receiving network.  In addition, such      traffic is unlikely to be covered by standard interconnection      agreements; rather, it is more likely to be specifically      configured (e.g., most networks impose restrictions on use of BGP      with other networks for obvious reasons).  SeeSection 4.2 for      further discussion.   o  BecauseRFC 5127 used a Treatment Aggregate for network control      traffic, Diffserv-Intercon can instead define a fourth Treatment      Aggregate for use at network interconnections instead of the      Network Control Treatment Aggregate inRFC 5127.  Network control      traffic may still be exchanged across network interconnections as      further discussed inSection 4.2.  Diffserv-Intercon uses this      fourth Treatment Aggregate for Voice over IP (VoIP) traffic, where      network-provided service differentiation is crucial, as even minor      glitches are immediately apparent to the humans involved in the      conversation.4.  The Diffserv-Intercon Interconnection Classes   At an interconnection, the networks involved need to agree on the   PHBs used for interconnection and the specific DSCP for each PHB.   This document defines a set of four interconnection Treatment   Aggregates with well-defined DSCPs to be aggregated by them.  A   sending party re-marks DSCPs from internal usage to the   interconnection codepoints.  The receiving party re-marks DSCPs to   their internal usage.  The interconnect SLA defines the set of DSCPs   and PHBs supported across the two interconnected domains and theGeib & Black                  Informational                     [Page 8]

RFC 8100                    Diffserv-Intercon                 March 2017   treatment of PHBs and DSCPs that are not recognized by the receiving   domain.   Similar approaches that use a small number of Treatment 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], Global System for Mobile Communications   Association (GSMA) IR.34 [IR.34], and MEF23.1 [MEF23.1].   The list of the four Diffserv-Intercon Treatment Aggregates follows,   highlighting differences fromRFC 5127 and suggesting mappings for   allRFC 4594 TCs to Diffserv-Intercon Treatment Aggregates:   Telephony Service Treatment Aggregate:  PHB Expedited Forwarding           (EF), DSCP 101 110 and PHB VOICE-ADMIT, DSCP 101 100 (see           [RFC3246], [RFC4594], and [RFC5865]).  This Treatment           Aggregate corresponds to the Real-Time Treatment Aggregate           definition regarding the queuing (both delay and jitter           should be minimized) perRFC 5127, but this aggregate is           restricted to transport Telephony service class traffic in           the sense of [RFC4594].   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 intended to provide Diffserv-Intercon           network interconnection of a subset of the Real-Time           Treatment Aggregate defined inRFC 5127, specifically the           portions that consume significant bandwidth.  This traffic is           expected to consist of the following classes defined inRFC4594: Broadcast Video, Real-Time Interactive, and Multimedia           Conferencing.  This Treatment Aggregate should be configured           with a rate-based queue (consistent with the recommendation           for the transported TCs inRFC 4594).  By comparison toRFC5127, the number of DSCPs has been reduced to one           (initially).  The AF42 and AF43 PHBs could be added if there           is a need for three-color marked Multimedia Conferencing           traffic.   Assured Elastic Treatment Aggregate:  This Treatment Aggregate           consists of PHBs AF31 and AF32 (i.e., DSCPs 011 010 and 011           100).  By comparison toRFC 5127, the number of DSCPs has           been reduced to two.  This document suggests to transport           signaling marked by AF31 (e.g., as recommended by GSMA IR.34           [IR.34]).  AF33 is reserved for the extension of PHBs to be           aggregated by this Treatment Aggregate.  For Diffserv-           Intercon network interconnection, the following serviceGeib & Black                  Informational                     [Page 9]

RFC 8100                    Diffserv-Intercon                 March 2017           classes (perRFC 4594) should be mapped to the Assured           Elastic Treatment Aggregate: the Signaling service class           (being marked for lowest loss probability), the Multimedia           Streaming service class, the Low-Latency Data service class,           and the High-Throughput Data service class.   Default / Elastic Treatment Aggregate:   Transports the Default PHB,           CS0 with DSCP 000 000.  An example inRFC 5127 refers to this           Treatment Aggregate as "Elastic Treatment Aggregate".  An           important difference fromRFC 5127 is that any traffic with           unrecognized or unsupported DSCPs may be re-marked to this           DSCP.  For Diffserv-Intercon network interconnection, the           Standard service class and Low-Priority Data service class           defined inRFC 4594 should be mapped to this Treatment           Aggregate.  This document does not specify an interconnection           class for Low-Priority Data (also definedRFC 4594).  This           traffic may be forwarded with a Lower Effort PHB in one           domain (e.g., the PHB proposed by Informational [RFC3662]),           but the methods specified in this document re-mark this           traffic with DSCP CS0 at a Diffserv-Intercon network           interconnection.  This has the effect that Low-Priority Data           is treated the same as data sent using the Standard service           class.  (Note: In a network that implementsRFC 2474, Low-           Priority traffic marked as CS1 would otherwise receive better           treatment than Standard traffic using the default PHB.)RFC 2475 states that ingress nodes must condition all inbound traffic   to ensure that the DS codepoints are acceptable; packets found to   have unacceptable codepoints must either be discarded or 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 CS0.  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; re-marking to CS0 is a widely   deployed behavior.   During the process of setting up a Diffserv interconnection, both   networks should define the set of acceptable and unacceptable DSCPs   and specify the treatment of traffic marked with each DSCP.   While Diffserv-Intercon allows modification of unacceptable DSCPs, if   traffic using one or more of the PHBs in a PHB group (e.g., AF3x,   consisting of AF31, AF32, and AF33) is accepted as part of a   supported Diffserv-Intercon Treatment Aggregate, then traffic using   other PHBs from the same PHB group should not be modified to use PHBs   outside of that PHB group and, in particular, should not be re-markedGeib & Black                  Informational                    [Page 10]

RFC 8100                    Diffserv-Intercon                 March 2017   to CS0 unless the entire PHB group is re-marked to CS0.  This avoids   unexpected forwarding behavior (and potential reordering; see also   [RFC7657]) when using Assured Forwarding (AF) PHBs [RFC2597].4.1.  Diffserv-Intercon Example   The overall approach to DSCP marking at network interconnections is   illustrated by the following example.  Provider O, provider W, and   provider F are peered with provider T.  They have agreed upon a   Diffserv interconnection SLA.   Traffic of provider O terminates within provider T's network, while   provider W's traffic transits through the network of provider T to   provider F.  This example assumes that all providers use their own   internal PHB and codepoint (DSCP) that correspond to the AF31 PHB in   the Diffserv-Intercon Assured Elastic Treatment Aggregate (AF21, CS2,   and AF11 are used in the example).Geib & Black                  Informational                    [Page 11]

RFC 8100                    Diffserv-Intercon                 March 2017    Provider O            Provider W          |                      |     +----------+           +----------+     |   AF21   |           |   CS2    |     +----------+           +----------+          V                      V      +~~~~~~~+              +~~~~~~~+      |Rtr PrO|              |Rtr PrW|               Rtr:   Router      +~~~~~~~+              +~~~~~~~+             Pr[L]:   Provider[L]          |        Diffserv      |     +----------+           +----------+     |   AF31   |           |   AF31   |     +----------+           +----------+          V        Intercon      V      +~~~~~~~+                  |      |RtrPrTI|------------------+            Router Provider T Ingress      +~~~~~~~+          |            Provider T Domain     +------------------+     | MPLS TC 2, AF21  |     +------------------+        |      |    +----------+   +~~~~~~~+        V      `--->|   AF21   |->-|RtrDstH|    Router Destination Host    +----------+    +----------+   +~~~~~~~+    |   AF21   |       Local DSCPs Provider T    +----------+        |     +~~~~~~~+     |RtrPrTE|                                Router Provider T Egress     +~~~~~~~+        |          Diffserv    +----------+    |   AF31   |    +----------+        |          Intercon     +~~~~~~~+     |RtrPrF |                                Router Provider F     +~~~~~~~+        |    +----------+    |   AF11   |   Provider F    +----------+                    Figure 1: Diffserv-Intercon ExampleGeib & Black                  Informational                    [Page 12]

RFC 8100                    Diffserv-Intercon                 March 2017   Providers only need to deploy mappings of internal DSCPs to/from   Diffserv-Intercon DSCPs, so that they can exchange traffic using the   desired PHBs.  In the example, provider O has decided that the   properties of his internal class AF21 are best met by the Diffserv-   Intercon Assured Elastic Treatment Aggregate, PHB AF31.  At the   outgoing peering interface connecting provider O with provider T, the   former's peering router re-marks AF21 traffic to AF31.  The domain   internal PHB of provider T that meets the requirement of the   Diffserv-Intercon Assured Elastic Treatment Aggregate is from the   AF2x PHB group.  Hence, AF31 traffic received at the interconnection   with provider T is re-marked to AF21 by the peering router of domain   T, and domain T has chosen to use MPLS TC value 2 for this aggregate.   At the penultimate MPLS node, the top MPLS label is removed and   exposes the IP header marked by the DSCP that has been set at the   network ingress.  The peering router connecting domain T with domain   F classifies the packet by its domain-T-internal DSCP AF21.  As the   packet leaves domain T on the interface to domain F, this causes the   packet's DSCP to be re-marked to AF31.  The peering router of domain   F classifies the packet for domain-F-internal PHB AF11, as this is   the PHB with properties matching the Diffserv-Intercon Assured   Elastic Treatment Aggregate.   This example can be extended.  The figure shows provider W using CS2   for traffic that corresponds to Diffserv-Intercon Assured Elastic   Treatment Aggregate PHB AF31; that traffic is mapped to AF31 at the   Diffserv-Intercon interconnection to provider T.  In addition,   suppose that provider O supports a PHB marked by AF22, and this PHB   is supposed to obtain Diffserv transport within provider T's domain.   Then provider O will re-mark it with DSCP AF32 for interconnection to   provider T.   Finally, suppose that provider W supports CS3 for internal use only.   Then no Diffserv-Intercon DSCP mapping needs to be configured at the   peering router.  Traffic, sent by provider W to provider T marked by   CS3 due to a misconfiguration may be re-marked to CS0 by provider T.4.2.  End-to-End PHB and DSCP Transparency   This section briefly discusses end-to-end Diffserv approaches related   to the Uniform, Pipe, and Short Pipe Model tunnels [RFC2983]   [RFC3270] when used edge-to-edge in a network.   o  With the Uniform Model, neither the DSCP nor the PHB change.  This      implies that a network management packet received with a CS6 DSCP      would be forwarded with an MPLS TC corresponding to CS6.  The      Uniform Model is outside the scope of this document.Geib & Black                  Informational                    [Page 13]

RFC 8100                    Diffserv-Intercon                 March 2017   o  With the Pipe Model, the inner tunnel DSCP remains unchanged, but      an outer tunnel DSCP and the PHB could change.  For example, a      packet received with a (network-specific) CS1 DSCP would be      transported by a Default PHB and, if MPLS is applicable, forwarded      with an MPLS TC corresponding to the Default PHB.  The CS1 DSCP is      not rewritten.  Transport of a large variety (much greater than      four) DSCPs may be required across an interconnected network      operating MPLS Short Pipe Model transport for IP traffic.  In that      case, a tunnel based on the Pipe Model is among the possible      approaches.  The Pipe Model is outside the scope of this document.   o  With the Short Pipe Model, the DSCP likely changes, and the PHB      might change.  This document describes a method to simplify      Diffserv network interconnection when a DSCP rewrite can't be      avoided.4.3.  Treatment of Network Control Traffic at Carrier Interconnection      Interfaces   As specified inSection 3.2 of RFC 4594, NC traffic marked by CS6 is   expected at some interconnection interfaces.  This document does not   changeRFC 4594 but observes that network control traffic received at   a network ingress is generally different from network control traffic   within a network that is the primary use of CS6 envisioned byRFC4594.  A specific example is that some CS6 traffic exchanged across   carrier interconnections is terminated at the network ingress node,   e.g., when BGP is used between the two routers on opposite ends of an   interconnection link; in this case, the operators would enter into a   bilateral agreement to use CS6 for that BGP traffic.   The end-to-end discussion inSection 4.2 is generally inapplicable to   network control traffic -- network control traffic is generally   intended to control a network, not be transported between networks.   One exception is that network control traffic makes sense for a   purchased transit agreement, and preservation of the CS6 DSCP marking   for network control traffic that is transited is reasonable in some   cases, although it is generally inappropriate to use CS6 for   forwarding that traffic within the network that provides transit.   Use of an IP tunnel is suggested in order to conceal the CS6 markings   on transiting network control traffic from the network that provides   the transit.  In this case, the Pipe Model for Diffserv tunneling is   used.   If the MPLS Short Pipe Model is deployed for unencapsulated 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.Geib & Black                  Informational                    [Page 14]

RFC 8100                    Diffserv-Intercon                 March 2017   Interconnecting carriers should specify treatment of CS6-marked   traffic received at a carrier interconnection that 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 and that traffic's destination is beyond the   interconnected ingress node:   o  classification of traffic that is network control traffic for both      domains.  This traffic should be classified and marked for the CS6      DSCP.   o  classification of traffic that is network control traffic for the      sending domain only.  This traffic should be forwarded with a PHB      that is appropriate for transiting NC service class traffic      [RFC4594] in the receiving domain, e.g., AF31 as specified by this      document.  As an example, GSMA IR.34 recommends an Interactive      class / AF31 to carry SIP and DIAMETER traffic.  While this is      service control traffic of high importance to interconnected      Mobile Network Operators, it is certainly not network control      traffic for a fixed network providing transit among such operators      and hence should not receive CS6 treatment in such a transit      network.   o  any other CS6-marked traffic should be re-marked or dropped.5.  IANA Considerations   This document does not require any IANA actions.6.  Security Considerations   The DSCP field in the IP header can expose additional traffic   classification information at network interconnections by comparison   to the use of a zero DSCP for all interconnect traffic.  If traffic   classification information is sensitive, the DSCP field could be   re-marked to zero to hide the classification as a countermeasure, at   the cost of loss of Diffserv information and differentiated traffic   handling on the interconnect and subsequent networks.  When AF PHBs   are used, any such re-marking should respect AF PHB group boundaries   as further discussed at the end ofSection 4.   This document does not introduce new features; it describes how to   use existing ones.  The Diffserv security considerations in [RFC2475]   and [RFC4594] apply.Geib & Black                  Informational                    [Page 15]

RFC 8100                    Diffserv-Intercon                 March 20177.  References7.1.  Normative References   [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,              <http://www.rfc-editor.org/info/rfc2474>.   [RFC2597]  Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,              "Assured Forwarding PHB Group",RFC 2597,              DOI 10.17487/RFC2597, June 1999,              <http://www.rfc-editor.org/info/rfc2597>.   [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, DOI 10.17487/RFC3246, March 2002,              <http://www.rfc-editor.org/info/rfc3246>.   [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, DOI 10.17487/RFC3270, May 2002,              <http://www.rfc-editor.org/info/rfc3270>.   [RFC5129]  Davie, B., Briscoe, B., and J. Tay, "Explicit Congestion              Marking in MPLS",RFC 5129, DOI 10.17487/RFC5129, January              2008, <http://www.rfc-editor.org/info/rfc5129>.   [RFC5865]  Baker, F., Polk, J., and M. Dolly, "A Differentiated              Services Code Point (DSCP) for Capacity-Admitted Traffic",RFC 5865, DOI 10.17487/RFC5865, May 2010,              <http://www.rfc-editor.org/info/rfc5865>.7.2.  Informative References   [BGP-INTERCONNECTION]              Knoll, T.,"BGP Class of Service Interconnection", Work in              Progress,draft-knoll-idr-cos-interconnect-17, November              2016.   [IR.34]    GSMA, "Guidelines for IPX Provider networks (Previously              Inter-Service Provider IP Backbone Guidelines)", Official              Document IR.34, Version 11.0, November 2014,              <http://www.gsma.com/newsroom/wp-content/uploads/IR.34-v11.0.pdf>.Geib & Black                  Informational                    [Page 16]

RFC 8100                    Diffserv-Intercon                 March 2017   [MEF23.1]  MEF, "Implementation Agreement MEF 23.1: Carrier Ethernet              Class of Service - Phase 2", MEF 23.1, January 2012,              <http://metroethernetforum.org/PDF_Documents/technical-specifications/MEF_23.1.pdf>.   [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,              <http://www.rfc-editor.org/info/rfc2475>.   [RFC2983]  Black, D., "Differentiated Services and Tunnels",RFC 2983, DOI 10.17487/RFC2983, October 2000,              <http://www.rfc-editor.org/info/rfc2983>.   [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,              <http://www.rfc-editor.org/info/rfc3662>.   [RFC4594]  Babiarz, J., Chan, K., and F. Baker, "Configuration              Guidelines for DiffServ Service Classes",RFC 4594,              DOI 10.17487/RFC4594, August 2006,              <http://www.rfc-editor.org/info/rfc4594>.   [RFC5127]  Chan, K., Babiarz, J., and F. Baker, "Aggregation of              Diffserv Service Classes",RFC 5127, DOI 10.17487/RFC5127,              February 2008, <http://www.rfc-editor.org/info/rfc5127>.   [RFC5160]  Levis, P. and M. Boucadair, "Considerations of Provider-              to-Provider Agreements for Internet-Scale Quality of              Service (QoS)",RFC 5160, DOI 10.17487/RFC5160, March              2008, <http://www.rfc-editor.org/info/rfc5160>.   [RFC7657]  Black, D., Ed. and P. Jones, "Differentiated Services              (Diffserv) and Real-Time Communication",RFC 7657,              DOI 10.17487/RFC7657, November 2015,              <http://www.rfc-editor.org/info/rfc7657>.   [SLA-EXCHANGE]              Shah, S., Patel, K., Bajaj, S., Tomotaki, L., and M.              Boucadair, "Inter-domain SLA Exchange Attribute", Work in              Progress,draft-ietf-idr-sla-exchange-10, January 2017.   [Y.1566]   ITU-T, "Quality of service mapping and interconnection              between Ethernet, Internet protocol and multiprotocol              label switching networks", ITU-T Recommendation Y.1566,              July 2012,              <http://www.itu.int/rec/T-REC-Y.1566-201207-I/en>.Geib & Black                  Informational                    [Page 17]

RFC 8100                    Diffserv-Intercon                 March 2017Appendix A.  The MPLS Short Pipe Model and IP Traffic   The MPLS Short Pipe Model (or penultimate hop label popping) is   widely deployed in carrier networks.  If unencapsulated IP traffic is   transported using MPLS Short Pipe, IP headers appear inside the last   section of the MPLS domain.  This impacts the number of PHBs and   DSCPs that a network provider can reasonably support.  See Figure 2   for an example.   For encapsulated IP traffic, only the outer tunnel header is relevant   for forwarding.  If the tunnel does not terminate within the MPLS   network section, only the outer tunnel DSCP is involved, as the inner   DSCP does not affect forwarding behavior; in this case, all DSCPs   could be used in the inner IP header without affecting network   behavior based on the outer MPLS header.  Here, the Pipe Model   applies.   Layer 2 and Layer 3 VPN traffic all use an additional MPLS label; in   this case, the MPLS tunnel follows the Pipe Model.  Classification   and queuing within an MPLS network is always based on an MPLS label,   as opposed to the outer IP header.   Carriers often select PHBs and DSCPs without regard to   interconnection.  As a result, PHBs and DSCPs typically differ   between network carriers.  With the exception of best-effort traffic,   a DSCP change should be expected at an interconnection at least for   unencapsulated IP traffic, even if the PHB is suitably mapped by the   carriers involved.   AlthoughRFC 3270 suggests that the Short Pipe Model is only   applicable to VPNs, current networks also use it to transport   non-tunneled IPv4 traffic.  This is shown in Figure 2 where Diffserv-   Intercon is not used, resulting in exposure of the internal DSCPs of   the upstream network to the downstream network across the   interconnection.Geib & Black                  Informational                    [Page 18]

RFC 8100                    Diffserv-Intercon                 March 2017       |      \|/           IPv4, DSCP_send       V       |  Peering Router       |      \|/           IPv4, DSCP_send       V       |  MPLS Edge Router       |          Mark MPLS Label, TC_internal      \|/         Re-mark DSCP to       V            (Inner: IPv4, DSCP_d)       |  MPLS Core Router  (penultimate hop label popping)       |                        \       |            IPv4, DSCP_d |  The DSCP needs to be in network-       |                 ^^^^^^^^|  internal Diffserv context.  The Core      \|/                         > Router may require or enforce       V                         |  that.  The Edge Router may wrongly       |                         |  classify, if the DSCP is not in       |                        /   network-internal Diffserv context.  MPLS Edge Router       |                        \   Traffic leaves the network marked      \|/           IPv4, DSCP_d |  with the network-internal       V                          > DSCP_d that must be dealt with       |                         |  by the next network (downstream).       |                        /  Peer Router       |          Re-mark DSCP to      \|/           IPv4, DSCP_send       V       |       Figure 2: Short Pipe Model / Penultimate Hop Popping Example   The packet's IP DSCP must be in a well-understood Diffserv context   for schedulers and classifiers on the interfaces of the ultimate MPLS   link (last link traversed before leaving the network).  The necessary   Diffserv context is network-internal, and a network operating in this   mode enforces DSCP usage in order to obtain robust differentiated   forwarding behavior.   Without Diffserv-Intercon treatment, the traffic is likely to leave   each network marked with network-internal DSCP.  DSCP_send in the   figure above has to be re-marked into the first network's Diffserv   scheme at the ingress MPLS Edge Router, to DSCP_d in the example.Geib & Black                  Informational                    [Page 19]

RFC 8100                    Diffserv-Intercon                 March 2017   For that reason, the traffic leaves this domain marked by the   network-internal DSCP_d.  This structure requires that every carrier   deploys per-peer PHB and DSCP mapping schemes.   If Diffserv-Intercon is applied, DSCPs for traffic transiting the   domain can be mapped from and remapped to an original DSCP.  This is   shown in Figure 3.  Internal traffic may continue to use internal   DSCPs (e.g., DSCP_d), and they may also be used between a carrier and   its direct customers.   Internal Router        |        |   Outer Header       \|/    IPv4, DSCP_send        V        |   Peering Router        |  Re-mark DSCP to       \|/    IPv4, DSCP_ds-int    Diffserv-Intercon DSCP and PHB        V        |   MPLS Edge Router        |        |   Mark  MPLS Label, TC_internal       \|/  Re-mark DSCP to        V     (Inner: IPv4, DSCP_d)   Domain Internal DSCP for        |                             the PHB   MPLS Core Router  (penultimate hop label popping)        |        |     IPv4, DSCP_d        |           ^^^^^^       \|/        V        |        |   MPLS Edge Router--------------------+        |                              |       \|/  Re-mark DSCP to           \|/  IPv4, DSCP_d        V     IPv4, DSCP_ds-int        V        |                              |        |                              |   Peer Router              Domain Internal Broadband        |                        Access Router       \|/  Re-mark DSCP to           \|/        V     IPv4, DSCP_send          V  IPv4, DSCP_d        |                              |         Figure 3: Short Pipe Model Example with Diffserv-InterconGeib & Black                  Informational                    [Page 20]

RFC 8100                    Diffserv-Intercon                 March 2017Acknowledgements   Bob Briscoe and Gorry Fairhurst reviewed this specification and   provided rich feedback.  Brian Carpenter, Fred Baker, Al Morton, and   Sebastien Jobert discussed the specification and helped improve it.   Mohamed Boucadair and Thomas Knoll helped by adding awareness of   related work.  James Polk's discussion during IETF 89 helped to   improve the text on the relation of this specification to 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   Dell EMC   176 South Street   Hopkinton, MA   United States of America   Phone: +1 (508) 293-7953   Email: david.black@dell.comGeib & Black                  Informational                    [Page 21]