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Versions: (draft-malis-mpls-sfc-encapsulation) 00 01 02 03

MPLS Working Group                                              A. Malis
Internet-Draft                                                 S. Bryant
Intended status: Informational                       Huawei Technologies
Expires: June 7, 2019                                         J. Halpern
                                                           W. Henderickx
                                                       December 04, 2018

                     MPLS Encapsulation for SFC NSH


   This document describes how to use a Service Function Forwarder (SFF)
   Label (similar to a pseudowire label or VPN label) to indicate the
   presence of a Service Function Chaining (SFC) Network Service Header
   (NSH) between an MPLS label stack and the packet payload.  This
   allows SFC packets using the NSH to be forwarded between SFFs over an
   MPLS network, and the selection between multiple SFFs in the
   destination MPLS node.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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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 June 7, 2019.

Copyright Notice

   Copyright (c) 2018 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
   (https://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
   2.  MPLS Encapsulation Using an SFF Label . . . . . . . . . . . .   3
     2.1.  MPLS Label Stack Construction at the Sending Node . . . .   3
     2.2.  SFF Label Processing at the Destination Node  . . . . . .   4
   3.  Equal Cost Multipath (ECMP) Considerations  . . . . . . . . .   4
   4.  Operations, Administration, and Maintenance (OAM)
       Considerations  . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   As discussed in [RFC8300], a number of transport encapsulations for
   the Service Function Chaining (SFC) Network Service Header (NSH)
   already exist, such as Ethernet, UDP, GRE, and others.

   This document describes an MPLS transport encapsulation for the NSH,
   and also describes how to use a Service Function Forwarder (SFF)
   [RFC7665] Label to indicate the presence of the NSH in the MPLS
   packet payload.  This allows SFC packets using the NSH to be
   forwarded between SFFs in an MPLS transport network, where MPLS is
   used to interconnect the network nodes that contain one or more SFFs.
   The label is also used to select between multiple SFFs in the
   destination MPLS node.

   SFF Labels are similar to other service labels at the bottom of an
   MPLS label stack that denote the contents of the MPLS payload being
   other than IP, such as a layer 2 pseudowire, an IP packet that is
   routed in a VPN context with a private address, or an Ethernet
   virtual private wire service.

   This informational document follows well-established MPLS procedures
   and does not require any actions by IANA or any new protocol

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2.  MPLS Encapsulation Using an SFF Label

   The encapsulation is a standard MPLS label stack [RFC3032] with an
   SFF Label at the bottom of the stack, followed by a NSH as defined by
   [RFC8300] and the NSH payload.

   Much like a pseudowire label, an SFF Label is allocated by the
   downstream receiver of the NSH from its per-platform label space.

   If a receiving node supports more than one SFF (i.e, more than one
   SFC forwarding instance), then the SFF Label can be used to select
   the proper SFF, by having the receiving node advertise more than one
   SFF Label to its upstream sending nodes as appropriate.

   The method used by the downstream receiving node to advertise SFF
   Labels to the upstream sending node is out of scope of this document.
   That said, a number of methods are possible, such as via a protocol
   exchange, or via a controller that manages both the sender and the
   receiver using NETCONF/YANG, BGP, PCEP, etc.  These are meant as
   possible examples and not to constrain the future definition of such
   advertisement methods.

   While the SFF label will usually be at the bottom of the label stack,
   there may be cases where there are additional label stack entries
   beneath it.  For example, when an ACH is carried that applies to the
   SFF, a GAL [RFC5586] will be in the label stack below the SFF.
   Similarly, an ELI/EL [RFC6790] may be carried below the SFF in the
   label stack.  This is identical to the situation with VPN labels.

2.1.  MPLS Label Stack Construction at the Sending Node

   When one SFF wishes to send an SFC packet with the NSH to another SFF
   over an MPLS transport network, a label stack needs to be constructed
   by the MPLS node that contains the sending SFF in order to transport
   the packet to the destination MPLS node that contains the receiving
   SFF.  The label can be constructed as follows:

   1.  Push on zero or more labels that are interpreted by the
       destination MPLS node, such as the Generic Associated Channel
       [RFC5586] label (see OAM Considerations below).

   2.  Push on the SFF Label to identify the desired SFF in the
       receiving MPLS node.

   3.  Push on zero or more additional labels such that (a) the
       resulting label stack will cause the packet to be transported to
       the destination MPLS node, and (b) when the packet arrives at the
       destination node, either:

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       *  the SFF Label will be at the top of the label stack, or

       *  the SFF Label will rise to the top of the label stack before
          the packet is forwarded to another node and before the packet
          is dispatched to a higher layer.

2.2.  SFF Label Processing at the Destination Node

   The destination MPLS node performs a lookup on the SFF label to
   retrieve the next-hop context between the SFF and SF, e.g. to
   retrieve the destination MAC address in the case where native
   Ethernet encapsulation is used between SFF and SF.  How the next-hop
   context is populated is out of the scope of this document.

   The receiving MPLS node then pops the SFF Label (and any labels
   beneath it) so that the destination SFF receives the SFC packet with
   the NSH is at the top of the packet.

3.  Equal Cost Multipath (ECMP) Considerations

   As discussed in [RFC4928] and [RFC7325], there are ECMP
   considerations for payloads carried by MPLS.

   Many existing routers use deep packet inspection to examine the
   payload of an MPLS packet, and if the first nibble of the payload is
   equal to 0x4 or 0x6, these routers (sometimes incorrectly, as
   discussed in [RFC4928]) assume that the payload is IPv4 or IPv6
   respectively, and as a result, perform ECMP load balancing based on
   (presumed) information present in IP/TCP/UDP payload headers or in a
   combination of MPLS label stack and (presumed) IP/TCP/UDP payload
   headers in the packet.

   For SFC, ECMP may or may not be desirable.  To prevent unintended
   ECMP when it is not desired, the NSH Base Header was carefully
   constructed so that the NSH could not look like IPv4 or IPv6 based on
   its first nibble.  See Section 2.2 of [RFC8300] for further details.

   If ECMP is desired when SFC is used with an MPLS transport network,
   there are two possible options, Entropy [RFC6790] and Flow-Aware
   Transport [RFC6391] labels.  A recommendation between these options,
   and their proper placement in the label stack, is for future study.

4.  Operations, Administration, and Maintenance (OAM) Considerations

   OAM at the SFC Layer is handled by SFC-defined mechanisms [RFC8300].
   However, OAM may be required at the MPLS transport layer.  If so,
   then standard MPLS-layer OAM mechanisms such as the Generic
   Associated Channel [RFC5586] label may be used.

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5.  IANA Considerations

   This document does not request any actions from IANA.

   Editorial note to RFC Editor: This section may be removed at your

6.  Security Considerations

   This document describes a method for transporting SFC packets using
   the NSH over an MPLS transport network.  It follows well-established
   MPLS procedures in widespread operational use and does not define any
   new protocol elements or allocate any new code points, and is no more
   or less secure than carrying any other protocol over MPLS.  To the
   MPLS network, the NSH and its contents is simply an opaque payload.

   Discussion of the security properties of SFC networks can be found in
   [RFC7665].  Further security discussion regarding the NSH is
   contained in [RFC8300].

   [RFC8300] references a number of transport encapsulations of the NSH,
   including Ethernet, GRE, UDP, and others.  This document simply
   defines one additional transport encapsulation.  The NSH was
   specially constructed to be agnostic to its transport encapsulation.
   As as result, in general this additional encapsulation is no more or
   less secure than carrying the NSH in any other encapsulation.

   However, it can be argued that carrying the NSH over MPLS is more
   secure than using other encapsulations, as it is extremely difficult,
   due to the MPLS architecture, for an attempted attacker to inject
   unexpected MPLS packets into a network, as MPLS networks do not by
   design accept MPLS packets from external interfaces, and an attacker
   would need knowledge of the specific labels allocated by control and/
   or management plane protocols.  Thus, an attacker attempting to spoof
   MPLS-encapsulated NSH packets would require insider knowledge of the
   network's control and management planes and a way to inject packets
   into internal interfaces.  This is compared to, for example, NSH over
   UDP over IP, which could be injected into any external interface in a
   network that was not properly configured to filter out such packets
   at the ingress.

7.  Acknowledgements

   The authors would like to thank Jim Guichard, Eric Rosen, Med
   Boucadair, Sasha Vainshtein, and Jeff Tantsura for their reviews and

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8.  References

8.1.  Normative References

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,

8.2.  Informative References

   [RFC4928]  Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
              Cost Multipath Treatment in MPLS Networks", BCP 128,
              RFC 4928, DOI 10.17487/RFC4928, June 2007,

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,

   [RFC6391]  Bryant, S., Ed., Filsfils, C., Drafz, U., Kompella, V.,
              Regan, J., and S. Amante, "Flow-Aware Transport of
              Pseudowires over an MPLS Packet Switched Network",
              RFC 6391, DOI 10.17487/RFC6391, November 2011,

   [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,

   [RFC7325]  Villamizar, C., Ed., Kompella, K., Amante, S., Malis, A.,
              and C. Pignataro, "MPLS Forwarding Compliance and
              Performance Requirements", RFC 7325, DOI 10.17487/RFC7325,
              August 2014, <https://www.rfc-editor.org/info/rfc7325>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,

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Authors' Addresses

   Andrew G. Malis
   Huawei Technologies

   Email: agmalis@gmail.com

   Stewart Bryant
   Huawei Technologies

   Email: stewart.bryant@gmail.com

   Joel M. Halpern

   Email: joel.halpern@ericsson.com

   Wim Henderickx

   Email: wim.henderickx@nokia.com

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