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Versions: (draft-geib-tsvwg-diffserv-intercon)
00 01 02 03 04 05 06 07 08 09 10 11
12 13 14 RFC 8100
TSVWG R. Geib, Ed.
Internet-Draft Deutsche Telekom
Intended status: Informational D. Black
Expires: February 26, 2017 EMC Corporation
August 25, 2016
Diffserv-Interconnection classes and practice
draft-ietf-tsvwg-diffserv-intercon-08
Abstract
This document defines a limited common set of Diffserv PHBs and
codepoints (DSCPs) to be applied at (inter)connections of two
separately administered and operated networks, and explains how this
approach can simplify network configuration and operation. 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 that use MPLS and apply the Short-
Pipe tunnel mode.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 26, 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
(http://trustee.ietf.org/license-info) in effect on the date of
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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 Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Related work . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Applicability Statement . . . . . . . . . . . . . . . . . 4
1.3. Document Organization . . . . . . . . . . . . . . . . . . 5
2. MPLS and the Short Pipe tunnel model . . . . . . . . . . . . 5
3. Relationship to RFC 5127 . . . . . . . . . . . . . . . . . . 6
3.1. RFC 5127 Background . . . . . . . . . . . . . . . . . . . 6
3.2. Differences from RFC 5127 . . . . . . . . . . . . . . . . 7
4. The Diffserv-Intercon Interconnection Classes . . . . . . . . 8
4.1. Diffserv-Intercon Example . . . . . . . . . . . . . . . . 9
4.2. End-to-end QoS: PHB and DS CodePoint Transparency . . . . 12
4.3. Treatment of Network Control traffic at carrier
interconnection interfaces . . . . . . . . . . . . . . . 13
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 15
Appendix A. Appendix A The MPLS Short Pipe Model and IP traffic 16
Appendix B. Change log (to be removed by the RFC editor) . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
Diffserv has been deployed in many networks; it provides
differentiated traffic forwarding based on the Diffserv Codepoint
(DSCP) field [RFC2474]. This document defines a set of common
Diffserv QoS classes (Per Hop Behaviors, PHBs)and code points at
interconnection points to which and from which locally used classes
and code points should be mapped.
As described by section 2.3.4.2 of RFC 2475, remarking of packets at
domain boundaries is a Diffserv feature [RFC2475]. 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
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do not follow this recommendation, and instead remark unknown or
unexpected DSCPs to zero upon receipt for default (best effort)
forwarding in accordance with the guidance in RFC 2475 [RFC2475] to
ensure that appropriate DSCPs are used within a Diffserv domain.
This draft assumes that latter approach by defining additional DSCPs
that are known and expected at network interconnection interfaces.
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 resulting from
the widely deployed Short Pipe tunnel model for 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 QoS
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,
consistent 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.
The interconnection approach described in this document (referred to
as Diffserv-Intercon) uses a set of PHBs and 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 benefitting
from a defined interconnection QoS interface.
The basic idea is that traffic sent with a Diffserv-Interconnect PHB
and DSCP is restored to that PHB and DSCP at each network
interconnection, even though a different PHB and DSCP may be used by
each network involved. 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. Traffic sent with other DSCPs can be remarked to an
interconnect DSCP or dealt with via additional agreement(s) among the
operators of the interconnected networks; remarking in the absence of
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additional agreement(s) when the MPLS Short Pipe model is used for
reasons explained 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. RFC 5160 suggests Meta-QoS-
Classes to enable deployment of standardized end to end QoS classes
[RFC5160]. The Diffserv-Intercon class- and codepoint scheme is
intended to complement that work (e.g. by enabling a defined set of
end-to-end QoS service classes).
BGP signaling Class of Service at interconnection interfaces by BGP
[I-D.knoll-idr-cos-interconnect], [ID.ietf-idr-sla] is complementary
to Diffserv-Intercon. 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 (e.g., via use
of the Diffserv-Intercon DSCPs) prior to BGP signaling of QoS.
1.2. Applicability Statement
This document is applicable to use of Differentiated Services for
interconnection traffic between networks, and in particular to
interconnection of MPLS-based networks. This document is not
intended for use within an individual network, where the approach
specified in RFC 5127 [RFC5127] is among the possible alternatives;
see Section 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 may also be applied to the Pipe tunneling model
[RFC2983], [RFC3270], but is not applicable to the Uniform tunneling
model [RFC2983], [RFC3270].
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1.3. Document Organization
This document is organized as follows: section 2 reviews the MPLS
Short Pipe tunnel model for Diffserv Tunnels [RFC3270], because
effective support for that model is a crucial goal of Diffserv-
Intercon. Section 3 provides background on RFC 5127's approach to
traffic class aggregation within a Diffserv network domain and
contrasts it with the Diffserv-Intercon approach. Section 4
introduces Diffserv-Interconnection 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 non-tunneled and tunneled IP
traffic and MPLS VPN QoS considerations and handling of high-priority
Network Management traffic is described. Appendix A describes how
the MPLS Short Pipe model (penultimate hop popping) impacts QoS and
DSCP marking for IP interconnections.
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 Short Pipe model in order
to support MPLS penultimate hop popping (PHP) of Labels, 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 non-tunneled IP
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, and a
common practice is to remark 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 Traffic Class (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
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(and also carried edge-to-edge). Unfortunately this is only true for
the Pipe tunnel model.
The Short Pipe tunnel model 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 info being
available at 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 IP header cannot be used to carry a different DSCP
edge-to-edge. See Appendix A for a more detailed discussion.
3. Relationship to RFC 5127
This document draws heavily upon RFC 5127's approach to aggregation
of Diffserv traffic classes for use within a network, but there are
important differences caused by characteristics of network
interconnects that differ from links within a network.
3.1. RFC 5127 Background
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 Traffic Class (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 Traffic Classes.
RFC 5127 provides an example aggregation of Diffserv service classes
into 4 Treatment Aggregates. A small number of aggregates are used
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 The common interconnection DSCPs ought not to use all 8 possible
values. This leaves space for future standards, for private
bilateral agreements and for local use PHBs and DSCPs.
o Migrations from one Diffserv code point scheme to a different one
is another possible application of otherwise unused QoS code
points.
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3.2. Differences from RFC 5127
Like RFC 5127, this document also uses four traffic aggregates, but
differs from RFC 5127 in some important ways:
o It follows RFC 2475 in allowing the DSCPs used within a network to
differ from those to exchange traffic with other networks (at
network edges), but provides support to restore ingress DSCP
values if one of the recommended interconnect DSCPs in this draft
is used. This results in DSCP remarking at both network ingress
and network egress, and this draft assumes that such remarking at
network edges is possible for all interface types.
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 Aggreagate 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 traffic as a special
case. Within a provider's network, the CS6 DSCP is used for local
network control traffic (routing protocols and 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). See Section 4.2 for
further discussion.
o Because RFC 5127 used a Treatment Aggregate for network control
traffic, Diffserv-Intercon can instead define a fourth traffic
aggregate to be defined for use at network interconnections
instead of the Network Control aggregate in RFC 5127. Network
Control traffic may still be exchanged across network
interconnections as further discussed in Section 4.2. Diffserv-
Intercon uses this fourth traffic aggregate for VoIP traffic,
where network-provided QoS is crucial, as even minor glitches are
immediately apparent to the humans involved in the conversation.
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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 4 interconnection 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 their internal scheme.
The interconnect SLA defines the set of DSCPs and PHBs supported
across the two interconnected domains and the treatment of PHBs and
DSCPs that are not recognized by the receiving domain.
Similar approaches that 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]and MEF23.1 [MEF23.1].
The list of the four Diffserv-Interconnect traffic aggregates
follows, highlighting differences from RFC 5127 and suggesting
mappings for all RFC 4594 traffic classes to Diffserv-Intercon
Treatment Aggregates:
Telephony Service Treatment Aggregate: PHB EF, DSCP 101 110 and PHB
VOICE-ADMIT, DSCP 101100, see [RFC3246],[RFC4594]and
[RFC5865]. This Treatment Aggregate corresponds to RFC 5127s
real time Treatment Aggregate definition regarding the
queuing (both delay and jitter should be minimized), but this
aggregate is restricted to transport Telephony Service Class
traffic in the sense of RFC 4594 [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 for Diffserv-Intercon network
interconnection of the portions of RFC 5127's Real Time
Treatment Aggregate, that consume significant bandwidth.
This traffic is expected to consist of the RFC4594 classes
Broadcast Video, Real-Time Interactive and Multimedia
Conferencing. This treatment aggregate should be configured
with a rate queue (consistent with RFC 4594's recommendation
for the transported traffic classes). By comparison to RFC
5127, 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.
Assured Elastic Treatment Aggregate This Treatment Aggregate
consists of PHBs AF31 and AF32 ( i.e., DSCPs 011 010 and 011
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100). By comparison to RFC 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 extension of PHBs to be
aggregated by this TA. For Diffserv-Intercon network
interconnection, the following RFC 4594 service classes
should be mapped to the Assured Elastic Treatment Aggregate:
the Signaling Service Class (being marked for lowest loss
probability), 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. RFC 5127 example refers to this
Treatment Aggregate as Aggregate Elastic. An important
difference from RFC 5127 is that any traffic with
unrecognized or unsupported DSCPs may be remarked to this
DSCP. For Diffserv-Intercon network interconnection, the RFC
4594 standard service class and Low-priority Data service
class should be mapped to this Treatment Aggregate. This
document does not specify an interconnection class for RFC
4594 Low-priority data. This data may be forwarded by a
Lower Effort PHB in one domain (like the PHB proposed by
Informational [RFC3662]), but using the methods specified in
this document will be remarked 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
default class. (Note: In a network that implements RFC 2474,
Low-priority traffic marked as CS1 would otherwise receive
better treatment than traffic using the default class.)
RFC2575 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 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 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; remarking to CS0 is a
widely deployed behavior.
4.1. Diffserv-Intercon Example
The overall approach to DSCP marking at network interconnections is
illustrated by the following example. Provider O and provider W are
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peered with provider T. They have agreed upon a QoS 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 and
CS2 are used in the example).
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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
+----------+
Diffserv-Intercon example
Figure 1
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Providers only need to deploy mappings of internal DSCPs to/from
Diffserv-Intercon DSCPs in order to 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 remarks AF21 traffic to AF31. The domain
internal PHB of provider T meeting the requirement of Diffserv-
Intercon Assured Elastic Treatment Aggregate are from AF2x PHB group.
Hence AF31 traffic received at the interconnection with provider T is
remarked to AF21 by the peering router of domain T, and domain T has
chosen to use MPLS Traffic Class 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 which 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 remarked 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 Diffserv-Intercon's 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 be transported by QoS within Provider-T domain. Then
Provider-O will remark 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 remarked to CS0 by Provider-T.
4.2. End-to-end QoS: PHB and DS CodePoint Transparency
This section briefly discusses end-to-end QoS approaches related to
the Uniform, Pipe and Short Pipe tunnel models ([RFC2983],
[RFC3270]), when used edge-to-edge in a network.
o With the Uniform model, neither the DCSP nor the PHB change. This
implies that a network management packet received with a CS6 DSCP
would be forwarded with an MPLS Traffic Class corresponding to
CS6. The uniform model is outside the scope of this document.
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o With the Pipe model, the inner tunnel DCSP remains unchanged, but
an outer tunnel DSCP and the PHB could changed. For example a
packet received with a (network specific) CS1 DSCP would be
transported by default PHB and if MPLS is applicable, forwarded
with an MPLS Traffic Class corresponding to Default PHB. The CS1
DSCP is not rewritten. Transport of a large variety (much greater
than 4) DSCPs may be required across an interconnected network
operating MPLS Short pipe 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 DCSP likely changes and the PHB
might change. This document describes a method to simplify QoS
for network interconnection when a DSCP rewrite can't be avoided.
4.3. Treatment of Network Control traffic at carrier interconnection
interfaces
As specified by RFC4594, section 3.2, Network Control (NC) traffic
marked by CS6 is expected at some interconnection interfaces. This
document does not change 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. 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 QoS discussion in the previous section (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,
Pipe model for Diffserv tunneling is used.
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.
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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 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 the NC service class [RFC4594], 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 remarked or dropped.
5. Acknowledgements
Bob Briscoe and Gorry Fairhurst reviewed the draft and provided rich
feedback. Fred Baker, Brian Carpenter, Al Morton and Sebastien
Jobert discussed the draft and helped improving it. Mohamed
Boucadair and Thomas Knoll helped adding awareness of related work.
James Polk's discussion during IETF 89 helped to improve the text on
the relation of this draft to RFC 4594 and RFC 5127.
6. IANA Considerations
This memo includes no request to IANA.
7. Security Considerations
This document does not introduce new features; it describes how to
use existing ones. The Diffserv security considerations in RFC 2475
[RFC2475] and RFC 4594 [RFC4594] apply.
8. References
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8.1. 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>.
[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>.
8.2. Informative References
[I-D.knoll-idr-cos-interconnect]
Knoll, T., "BGP Class of Service Interconnection", draft-
knoll-idr-cos-interconnect-16 (work in progress), May
2016.
[ID.ietf-idr-sla]
IETF, "Inter-domain SLA Exchange", IETF,
http://datatracker.ietf.org/doc/
draft-ietf-idr-sla-exchange/, 2013.
[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.
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Internet-Draft Diffserv-Intercon August 2016
[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.
[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>.
[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.
Appendix A. Appendix 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 non-tunneled IPv4 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
(below) for an example.
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For tunneled IPv4 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.
Non-tunneled IPv6 traffic as well as 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 QoS PHBs and DSCP 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 non-
tunneled IP traffic, even if the PHB is suitably mapped by the
carriers involved.
Although RFC3270 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.
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|
\|/ IPv4, DSCP_send
V
|
Peering Router
|
\|/ IPv4, DSCP_send
V
|
MPLS Edge Router
| Mark MPLS Label, TC_internal
\|/ Remark 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 QoS 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
| Remark DSCP to
\|/ IPv4, DSCP_send
V
|
Short-Pipe / penultimate hop popping example
Figure 2
The packets 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 QoS 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 remarked into the first network's Diffserv
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scheme at the ingress MPLS Edge Router, to DSCP_d in the example.
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.
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Internal Router
|
| Outer Header
\|/ IPv4, DSCP_send
V
|
Peering Router
| Remark DSCP to
\|/ IPv4, DSCP_ds-int Diffserv-Intercon DSCP and PHB
V
|
MPLS Edge Router
|
| Mark MPLS Label, TC_internal
\|/ Remark 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--------------------+
| |
\|/ Remark DSCP to \|/ IPv4, DSCP_d
V IPv4, DSCP_ds-int V
| |
| |
Peer Router Domain internal Broadband
| Access Router
\|/ Remark DSCP to \|/
V IPv4, DSCP_send V IPv4, DSCP_d
| |
Short-Pipe example with Diffserv-Intercon
Figure 3
Appendix B. Change log (to be removed by the RFC editor)
00 to 01 Added an Applicability Statement. Put the main part of the
RFC5127 related discussion into a separate chapter.
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01 to 02 More emphasis on the Short-Pipe tunel model as compared to
Pipe and Uniform tunnel models. Further editorial
improvements.
02 to 03 Suggestions how to remark all RFC4594 classes to Diffserv-
Intercon classes at interconnection.
03 to 04 Minor clarifications and editorial review, preparation for
WGLC.
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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