Using Entropy Label for Network Slice Identification in MPLS networks.
draft-decraene-mpls-slid-encoded-entropy-label-id-01

Document Type Active Internet-Draft (individual)
Authors Bruno Decraene  , Clarence Filsfils  , Wim Henderickx  , Tarek Saad  , Vishnu Beeram  , Luay Jalil 
Last updated 2021-02-22
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MPLS                                                    B. Decraene, Ed.
Internet-Draft                                                    Orange
Updates: 6790 (if approved)                                  C. Filsfils
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: August 26, 2021                                   W. Henderickx
                                                                   Nokia
                                                                 T. Saad
                                                               V. Beeram
                                                        Juniper Networks
                                                                L. Jalil
                                                                 Verizon
                                                       February 22, 2021

 Using Entropy Label for Network Slice Identification in MPLS networks.
          draft-decraene-mpls-slid-encoded-entropy-label-id-01

Abstract

   This document defines a solution to encode a slice identifier in MPLS
   in order to distinguish packets that belong to different slices, to
   allow enforcing per network slice policies (.e.g, Qos).

   The slice identification is independent of the topology.  It allows
   for QoS/DiffServ policy on a per slice basis in addition to the per
   packet QoS/DiffServ policy provided by the MPLS Traffic Class field.

   In order to minimize the size of the MPLS stack and to ease
   incremental deployment the slice identifier is encoded as part of the
   Entropy Label.

   This document also extends the use of the TTL field of the Entropy
   Label in order to provide a flexible set of flags called the Entropy
   Label Control field.

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
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   Drafts is at https://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

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   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 August 26, 2021.

Copyright Notice

   Copyright (c) 2021 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Entropy Label Control field . . . . . . . . . . . . . . . . .   3
   3.  Slice Identifier  . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Ingress LSR . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Transit LSR . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Bandwidth-Allocation Slice  . . . . . . . . . . . . . . .   4
     3.4.  Backward Compatibility  . . . . . . . . . . . . . . . . .   5
     3.5.  Benefits  . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  End to end absolute loss measurements . . . . . . . . . . . .   6
   5.  Programmed sampling of packets  . . . . . . . . . . . . . . .   6
   6.  Changes / Authors Notes . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Segment Routing (SR) [RFC8402] leverages the source-routing paradigm.
   A node steers a packet through a controlled set of instructions,
   called segments, by prepending the packet with an SR header.  In the
   SR-MPLS data plane [RFC8660], the SR header is instantiated through a
   label stack.

   This document defines a solution to encode a slice identifier in MPLS
   in order to provide QoS on a per slice basis.  It allows for QoS/

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   DiffServ policy on a per slice basis in addition to the per packet
   QoS/DiffServ policy provided by the MPLS Traffic Class field.  The
   slice identification is independent of the topology and the QoS of
   the network, thus enabling scalable network slicing.

   This document encodes the slice identifier in a portion of the MPLS
   Entropy Label (EL) defined in [RFC6790].  This has advantages in SR-
   MPLS networks as it avoids the use of additional label which would
   increase the size of the label stack.  This also reuses the data
   plane processing of the Entropy Label on the egress LSR, the
   signaling of the Entropy Label capability from the egress to the
   ingress [I-D.ietf-isis-mpls-elc] [I-D.ietf-ospf-mpls-elc], and the
   signaling capability of transit routers to read this label [RFC8491]
   which allows for an easier and faster incremental deployment.

2.  Entropy Label Control field

   [RFC6790] defines the MPLS Entropy Label.  [RFC6790] section 4.2
   defines the use of the Entropy Label Indicator (ELI) followed by the
   Entropy Label (EL) and the MPLS header fields (Label, TC, S, TTL) in
   each.  [RFC6790] also specifies that the TTL field of the EL must be
   set to zero by the ingress LSR.

   Following the procedures of [RFC6790] EL is never used for forwarding
   and its TTL is never looked at nor decremented:

   o  An EL capable Egress LSR performs a lookup on the ELI and as a
      result pop two labels: ELI and EL.

   o  An EL non-capable Egress LSR performs a lookup on the ELI and as a
      result must drop the packet as specified in [RFC3031] for the
      handling of an invalid incoming label.

   Hence essentially the TTL field of the EL behaves as a reserved field
   which must be set to zero when sent and ignored when received.

   This documents extends the TTL field of the EL and calls it the
   Entropy Label Control (ELC) field.  The ELC is a set of eight flags:
   ELC0 for bit 0, ELC1 for bit 1,..., ELC7 for bit 7.

   Given that the MPLS header is very compact (32 bits) with no reserved
   bits and that MPLS is used within a trusted administrative domain,
   the semantic of these bits is not standardized but defined on a per
   administrative domain basis.  This allows for increased re-use and
   flexibility of this scarce resource.  As a consequence, an
   application using one of those buts MUST allow the choice of the bit
   by configuration by the network operator.

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3.  Slice Identifier

   Each network slice in an MPLS domain is uniquely identified by a
   Slice Identifier (SLID).  This section proposes to encode the SLID in
   a portion of the MPLS Entropy Label defined in [RFC6790].

   The number of bits to be used for encoding the SLID in the EL is
   governed by a local policy and uniform within a network slice policy
   domain.

3.1.  Ingress LSR

   When an ingress LSR classifies that a packet belongs to the slice and
   that the egress has indicated via signaling that it can process EL
   for the tunnel, the ingress LSR pushes an Entropy Label with the:

   o  SLID encoded in the most significant bits of the Entropy Label.

   o  the entropy information encoded in the remaining lower bits of the
      Entropy Label as described in section 4.2 of [RFC6790].

   o  SPI bit (SLID Presence Indicator) set in one bit of the ELC field.

   The choice of the ELC field used for SPI, and the number of bits to
   be used for encoding the SLID MUST be configurable by the network
   operator.

   The slice classification method is outside the scope of this
   document.

3.2.  Transit LSR

   Any router within the SR domain that forwards a packet with the SPI
   bit set MUST use the SLID to select a slice and apply per-slice
   policies.

   There are many different policies that could define a slice for a
   particular application or service.  The most basic of these is
   bandwidth-allocation, an implementation complying with this
   specification SHOULD support the bandwidth-allocation slice as
   defined in the next section.

3.3.  Bandwidth-Allocation Slice

   A per-slice policy is configured at each interface of each router in
   the SR domain, with one traffic shaper per SLID.  The bit rate of
   each shaper is configured to reflect the bandwidth allocation of the
   per-slice policy.

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   If shapers are not available, or desirable, an implementation MAY
   configure one scheduling queue per SLID with a guaranteed bandwidth
   equal to the bandwidth-allocation for the slice.  This option allows
   a slice to consume more bandwidth than its allocation when available.

   Per-slice shapers or queues effectively provides a virtual port per
   slice.  This solution MAY be complemented with a per-virtual-port
   hierarchical DiffServ policy.  Within the context of one specific
   slice, packets are further classified into children DiffServ queues
   which hang from the virtual port.  The Traffic Class value in the
   MPLS header SHOULD be used for queue selection.

3.4.  Backward Compatibility

   The Entropy Label usage described in this document is consistent with
   [RFC6790] as ingress LSRs freely chooses the EL of a given flow, and
   transit LSRs treat the EL as an opaque set of bits.

   As per [RFC6790] an ingress LSR that does not support this extension
   has the SPI bit cleared, and thus does not enable the SLID semantic
   of the Entropy bits.  Hence, SLID-aware transit LSRs will not
   classify these packets into a slice.

3.5.  Benefits

   From a Segment Routing architecture perspective, this network slice
   identifier for SR-MPLS is inline with the network slice identifier
   for SRv6 proposed in [I-D.filsfils-spring-srv6-stateless-slice-id].

   From an SR-MPLS perspective, using the EL to carry the network slice
   identifier has multiple benefits:

   o  This limits the number of labels pushed on the MPLS stack compared
      to using a pair of labels (ELI+EL) for flow entropy plus two or
      three labels for the slice indicator and the slice identifier.
      This is beneficial for the ingress LSR which may have limitations
      with regards to the number of labels pushed, for the transit LSR
      which may have limitations with regards to the label stack depth
      to be examined during transit in order to read both the entropy
      and the SLID.  This presents additional benefit to network
      operators by reducing the packet overhead for traffic carried
      through the network;

   o  This avoids defining new extensions for the signaling of the
      egress capability to support the slice indicator and the slice
      identifier;

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   o  This improves incremental deployment as all egress LSRs supporting
      EL can be sent the slice identifier from day one, allowing slice
      classification on transit LSRs.

4.  End to end absolute loss measurements

   This section describes the usage of a ELC flag to enable packet loss
   measurements, as described in section 3.1 of [RFC8321], for SR-MPLS
   networks.

   TBD

5.  Programmed sampling of packets

   This section describes the usage of a ELC flag to detect end to end
   packet loss.

   TBD

6.  Changes / Authors Notes

   [RFC Editor: Please remove this section before publication]

   00: Initial version.

   01: New co-author

7.  References

7.1.  Normative References

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, DOI 10.17487/RFC6790, November 2012,
              <https://www.rfc-editor.org/info/rfc6790>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [RFC8660]  Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing with the MPLS Data Plane", RFC 8660,
              DOI 10.17487/RFC8660, December 2019,
              <https://www.rfc-editor.org/info/rfc8660>.

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7.2.  Informative References

   [I-D.filsfils-spring-srv6-stateless-slice-id]
              Filsfils, C., Clad, F., Camarillo, P., and K. Raza,
              "Stateless and Scalable Network Slice Identification for
              SRv6", draft-filsfils-spring-srv6-stateless-slice-id-02
              (work in progress), January 2021.

   [I-D.ietf-isis-mpls-elc]
              Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
              and M. Bocci, "Signaling Entropy Label Capability and
              Entropy Readable Label Depth Using IS-IS", draft-ietf-
              isis-mpls-elc-13 (work in progress), May 2020.

   [I-D.ietf-ospf-mpls-elc]
              Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
              and M. Bocci, "Signaling Entropy Label Capability and
              Entropy Readable Label Depth Using OSPF", draft-ietf-ospf-
              mpls-elc-15 (work in progress), June 2020.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC8321]  Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
              L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
              "Alternate-Marking Method for Passive and Hybrid
              Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
              January 2018, <https://www.rfc-editor.org/info/rfc8321>.

   [RFC8491]  Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
              DOI 10.17487/RFC8491, November 2018,
              <https://www.rfc-editor.org/info/rfc8491>.

Authors' Addresses

   Bruno Decraene (editor)
   Orange

   Email: bruno.decraene@orange.com

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   Clarence Filsfils
   Cisco Systems, Inc.
   Belgium

   Email: cf@cisco.com

   Wim Henderickx
   Nokia
   Copernicuslaan 50
   Antwerp 2018, CA  95134
   Belgium

   Email: wim.henderickx@nokia.com

   Tarek Saad
   Juniper Networks

   Email: tsaad@juniper.net

   Vishnu Pavan Beeram
   Juniper Networks

   Email: vbeeram@juniper.net

   Luay Jalil
   Verizon

   Email: luay.jalil@verizon.com

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