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Versions: 00 01 02 draft-ietf-bier-mpls-encapsulation

Internet Engineering Task Force                        IJ. Wijnands, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                           E. Rosen, Ed.
Expires: June 7, 2015                             Juniper Networks, Inc.
                                                             A. Dolganow
                                                          Alcatel-Lucent
                                                             J. Tantsura
                                                                Ericsson
                                                               S. Aldrin
                                                     Huawei Technologies
                                                        December 4, 2014


   Encapsulation for Bit Index Explicit Replication in MPLS Networks
               draft-wijnands-mpls-bier-encapsulation-02

Abstract

   Bit Index Explicit Replication (BIER) is an architecture that
   provides optimal multicast forwarding through a "multicast domain",
   without requiring intermediate routers to maintain any per-flow state
   or to engage in an explicit tree-building protocol.  When a multicast
   data packet enters the domain, the ingress router determines the set
   of egress routers to which the packet needs to be sent.  The ingress
   router then encapsulates the packet in a BIER header.  The BIER
   header contains a bitstring in which each bit represents exactly one
   egress router in the domain; to forward the packet to a given set of
   egress routers, the bits corresponding to those routers are set in
   the BIER header.  The details of the encapsulation depend on the type
   of network used to realize the multicast domain.  This document
   specifies the BIER encapsulation to be used in an MPLS network.

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 June 7, 2015.



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Copyright Notice

   Copyright (c) 2014 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
   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.  The BIER-MPLS Label . . . . . . . . . . . . . . . . . . . . .   3
   3.  BIER Header . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Imposing and Processing the BIER Encapsulation  . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   8.  Contributor Addresses . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   [BIER_ARCH] describes a new architecture for the forwarding of
   multicast data packets.  That architecture provides optimal
   forwarding of multicast data packets through a "multicast domain".
   However, it does not require any explicit tree-building protocol, and
   does not require intermediate nodes to maintain any per-flow state.
   That architecture is known as "Bit Index Explicit Replication"
   (BIER).

   This document will use terminology defined in [BIER_ARCH].

   A router that supports BIER is known as a "Bit-Forwarding Router"
   (BFR).  A "BIER domain" is a connected set of Bit-Forwarding Routers
   (BFRs), each of which has been assigned a BFR-prefix.  A BFR-prefix
   is a routable IP address of a BFR, and is used by BIER to identify a
   BFR.  A packet enters a BIER domain at an ingress BFR (BFIR), and
   leaves the BIER domain at one or more egress BFRs (BFERs).  As



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   specified in [BIER_ARCH], each BFR of a given BIER domain is
   provisioned to be in one or more "sub-domains".  In the context of a
   given sub-domain, each BFIR and BFER must have a BFR-id that is
   unique within that sub-domain.  A BFR-id is just a number in the
   range [1,65535] that, relative to a BIER sub-domain, identifies a BFR
   uniquely.

   As described in [BIER_ARCH], BIER requires that multicast data
   packets be encapsulated with a header that provides the information
   needed to support the BIER forwarding procedures.  This information
   includes the sub-domain to which the packet has been assigned, a Set-
   Id (SI), a BitString, and a BitStringLength.  Together these values
   identify the set of BFERs to which the packet must be delivered.

   This document is applicable when a given BIER domain is both an IGP
   domain and an MPLS network.  In this environment, the BIER
   encapsulation consists of two components:

   o  an MPLS label (which we will call the "BIER-MPLS label"); this
      label appears at the bottom of a packet's MPLS label stack.

   o  a BIER header, as specified in Section 3.

   Following the BIER header is the "payload".  The payload may be an
   IPv4 packet, an IPv6 packet, an ethernet frame, or an MPLS packet.
   If it is an MPLS packet, then an MPLS label stack immediately follows
   the BIER header.  The top label of this MPLS label stack may be
   either a downstream-assigned label ([RFC3032]) or an upstream-
   assigned label ([RFC5331].  The BIER header contains information
   identifying the type of the payload.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  The BIER-MPLS Label

   As stated in [BIER_ARCH], when a BIER domain is also an IGP domain,
   IGP extensions can be used by each BFR to advertise the BFR-id and
   BFR-prefix.  The extensions for OSPF are given in
   [OSPF_BIER_EXTENSIONS].  The extensions for ISIS are given in
   [ISIS_BIER_EXTENSIONS].

   When a particular BIER domain is both an IGP domain and an MPLS
   network, we assume that each BFR will also use IGP extensions to
   advertise a set of one or more "BIER-MPLS" labels.  When the domain
   contains a single sub-domain, a given BFR needs to advertise one such
   label for each combination of SI and BitStringLength.  If the domain



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   contains multiple sub-domains, a BFR needs to advertise one such
   label per SI per BitStringLength for each sub-domain.

   The BIER-MPLS labels are locally significant (i.e., unique only to
   the BFR that advertises them) downstream-assigned MPLS labels.  For
   example, suppose that there is a single sub-domain (the default sub-
   domain), that the network is using a BitStringLength of 256, and that
   all BFERs in the sub-domain have BFR-ids in the range [1,512].  Since
   each BIER BitString is 256 bits long, this requires the use of two
   SIs: SI=0 and SI=1.  So each BFR will advertise, via IGP extensions,
   two MPLS labels for BIER: one corresponding to SI=0 and one
   corresponding to SI=1.  The advertisements of these labels will also
   bind each label to the default sub-domain and to the BitStringLength
   256.

   As another example, suppose a particular BIER domain contains 2 sub-
   domains (sub-domain 0 and sub-domain 1), supports 2 BitStringLengths
   (256 and 512), and contains 1024 BFRs.  A BFR that is provisioned for
   both sub-domains, and that supports both BitStringLengths, would have
   to advertise the following set of BIER-MPLS labels:

      L1:   corresponding to sub-domain 0, BitStringLength 256, SI 0.

      L2:   corresponding to sub-domain 0, BitStringLength 256, SI 1.

      L3:   corresponding to sub-domain 0, BitStringLength 256, SI 2.

      L4:   corresponding to sub-domain 0, BitStringLength 256, SI 3.

      L5:   corresponding to sub-domain 0, BitStringLength 512, SI 0.

      L6:   corresponding to sub-domain 0, BitStringLength 512, SI 1.

      L7:   corresponding to sub-domain 1, BitStringLength 256, SI 0.

      L8:   corresponding to sub-domain 1, BitStringLength 256, SI 1.

      L9:   corresponding to sub-domain 1, BitStringLength 256, SI 2.

      L10:  corresponding to sub-domain 1, BitStringLength 256, SI 3.

      L11:  corresponding to sub-domain 1, BitStringLength 512, SI 0.

      L12:  corresponding to sub-domain 1, BitStringLength 512, SI 1.

   The above example should not be taken as implying that the BFRs need
   to advertise 12 individual labels.  For instance, instead of
   advertising a label for <sub-domain 1, BitStringLength 512, SI 0> and



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   a label for <sub-domain 1, BitStringLength 512, SI 1>, a BFR could
   advertise a contiguous range of labels (in this case, a range
   containing exactly two labels) corresponding to <sub-domain 1,
   BitStringLength 512>.  The first label in the range could correspond
   to SI 0, and the second to SI 1.  The precise mechanism for
   generating and forming the advertisements is outside the scope of
   this document.  See [OSPF_BIER_EXTENSIONS] and
   [ISIS_BIER_EXTENSIONS].

   Note that, in practice, labels only have to be assigned if they are
   going to be used.  If a particular BIER domain supports
   BitStringLengths 256 and 512, but some sub-domain, say sub-domain 1,
   only uses BitStringLength 256, then it is not necessary to assign
   labels that correspond to the combination of sub-domain 1 and
   BitStringLength 512.

   When a BFR receives an MPLS packet, and the next label to be
   processed is one of its BIER-MPLS labels, it will assume that a BIER
   header (see Section 3) immediately follows the stack.  It will also
   infer the packet's sub-domain, SI, and BitStringLength from the
   label.  The packet's "incoming TTL" (see below) is taken from the TTL
   field of the label stack entry that contains the BIER-MPLS label.

   The BFR MUST perform the MPLS TTL processing correctly.  If the
   packet is forwarded to one or more BFR adjacencies, the BIER-MPLS
   label carried by the forwarded packet MUST have a TTL field whose
   value is one less than that of the incoming TTL.  (Of course, if the
   incoming TTL is 1, the packet will not be forwarded at all, but will
   be discarded as an MPLS packet whose TTL has been exceeded.)

3.  BIER Header

   The BIER header is shown in Figure 1.  This header appears after the
   end of the MPLS label stack, immediately after the MPLS-BIER label.

















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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |0 0 0 0| Proto |  Len  |              Entropy                  |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                BitString  (first 32 bits)                     ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                                                               ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                BitString  (last 32 bits)                      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   Reserved                    |            BFIR-id            |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 1: BIER Header

   Ver:

      The first 4 bits of the header are all set to zero; this ensures
      that the BIER header will not be confused with an IP header.  This
      field can also be used as a version number if there are future
      revisions of the BIER header.  However, the values 4 and 6 MUST
      NOT be used, as that may make the packets appear to some hardware
      forwarder to be IP packets.

   Proto:

      This 4-bit field identifies the type of the payload.  (The
      "payload" is the packet or frame immediately following the BIER
      header.)  The protocol field may take any of the following values:

      1: MPLS packet with downstream-assigned label at top of stack.

      2: MPLS packet with upstream-assigned label at top of stack (see
         [RFC5331]).  If this value of the Proto field is used, the I
         bit MUST be set, and the BFR-id of the BFIR must be placed in
         the BFIR-id field.  The BFIR-id provides the "context" in which
         the upstream-assigned label is interpreted.

      3: Ethernet frame.

      4: IPv4 packet.

      6: IPv6 packet.

   Len:





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      This 4-bit field encodes the length in bits of the BitString.  If
      k is the length of the BitString, the value of this field is
      log2(k)-5.  However, only certain values are supported:

         1: 64 bits

         2: 128 bits

         3: 256 bits

         4: 512 bits

         5: 1024 bits

         6: 2048 bits

         7: 4096 bits

      All other values of this field are illegal.

   Entropy:

      This 20-bit field specifies an "entropy" value that can be used
      for load balancing purposes.  The BIER forwarding process may do
      equal cost load balancing, but the load balancing procedure MUST
      choose the same path for any two packets have the same entropy
      value.

      If a BFIR is encapsulating (as the payload) MPLS packets that have
      entropy labels, the BFIR MUST ensure that if two such packets have
      the same MPLS entropy label, they also have the same value of the
      BIER entropy field.

   BitString:

      The BitString that, together with the packet's SI, identifies the
      destination BFERs for this packet.  Note that the SI for the
      packet is inferred from the BIER-MPLS label that precedes the BIER
      header.

   BFIR-id

      By default, this is the BFR-id of the BFIR, in the sub-domain to
      which the packet has been assigned.  The BFR-id is encoded in the
      16-bit field as an unsigned integer in the range [1,65535].






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      Certain applications may require that the BFIR-id field contain
      the BFR-id of a BFR other than the BFIR.  However, that usage of
      the BFIR-id field is outside the scope of the current document.

4.  Imposing and Processing the BIER Encapsulation

   When a BFIR receives a multicast packet from outside the BIER domain,
   the BFIR carries out the following procedure:

   1.  By consulting the "multicast flow layer" ([BIER_ARCH]), it
       determines the value of the "Proto" field.

   2.  By consulting the "multicast flow layer", it determines the set
       of BFERs that must receive the packet.

   3.  If more than one sub-domain is supported, the BFIR assigns the
       packet to a particular sub-domain.  Procedures for determining
       the sub-domain to which a particular packet should be assigned
       are outside the scope of this document.

   4.  The BFIR looks up the BFR-id, in the given sub-domain, of each of
       those BFERs.

   5.  The BFIR converts each such BFR-id into (SI, BitString) format,
       as described in [BIER_ARCH].

   6.  All such BFR-ids that have the same SI can be encoded into the
       same BitString.  Details of this encoding can be found in
       [BIER_ARCH].  For each distinct SI that occurs in the list of the
       packet's destination BFERs:

       a.   The BFIR makes a copy of the multicast data packet, and
            encapsulates the copy in a BIER header (see Section 3).  The
            BIER header contains the BitString that represents all the
            destination BFERs whose BFR-ids (in the given sub-domain)
            correspond to the given SI.  It also contains the BFIR's
            BFIR-id in the sub-domain to which the packet has been
            assigned.

            N.B.: For certain applications, it may be necessary for the
            BFIR-id field to contain the BFR-id of a BFR other than the
            BFIR that is creating the header.  Such uses are outside the
            scope of this document, but may be discussed in future
            revisions.

       b.   The BFIR then applies to that copy the forwarding procedure
            of [BIER_ARCH].  This may result in one or more copies of




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            the packet (possibly with a modified BitString) being
            transmitted to a neighboring BFR.

       c.   Before transmitting a copy of the packet to a neighboring
            BFR, the BFIR finds the BIER-MPLS label that was advertised
            by the neighbor as corresponding to the given SI, sub-
            domain, and BitStringLength.  An MPLS label stack is then
            preprended to the packet.  This label stack [RFC3032] will
            contain one label, the aforementioned BIER-MPLS label.  The
            "S" bit MUST be set, indicating the end of the MPLS label
            stack.  The TTL field of this label stack entry is set
            according to policy.  The packet may then be transmitted to
            the neighboring BFR.  (This may result in additional MPLS
            labels being pushed on the stack.  For example, if an RSVP-
            TE tunnel is used to transmit packets to the neighbor, a
            label representing that tunnel would be pushed onto the
            stack.)

   When an intermediate BFR is processing a received MPLS packet, and
   one of the BFR's own BIER-MPLS labels rises to the top of the label
   stack, the BFR infers the sub-domain, SI, and BitStringLength from
   the label.  The BFR then follows the forwarding procedures of
   [BIER_ARCH].  If it forwards a copy of the packet to a neighboring
   BFR, it first swaps the label at the top of the label stack with the
   BIER-MPLS label, advertised by that neighbor, that corresponds to the
   same SI, sub-domain, and BitStringLength.  Note that when this swap
   operation is done, the TTL field of the BIER-MPLS label of the
   outgoing packet MUST be one less than the "incoming TTL" of the
   packet, as defined in Section 2.

   Thus a BIER-encapsulated packet in an MPLS network consists of a
   packet that has:

   o  An MPLS label stack with a BIER-MPLS label at the bottom of the
      stack.

   o  A BIER header, as described in Section 3.

   o  The payload.

   The payload may be an IPv4 packet, an IPv6 packet, an ethernet frame,
   or an MPLS packet.  If it is an MPLS packet, the BIER header is
   followed by a second MPLS label stack; this stack is separate from
   the stack that precedes the BIER header.  For an example of an
   application where it is useful to carry an MPLS packet as the BIER
   payload, see [BIER_MVPN].





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5.  IANA Considerations

   This document has no actions for IANA.

6.  Security Considerations

   As this document makes use of MPLS, it inherits any security
   considerations that apply to the use of the MPLS data plane.

   As this document makes use of IGP extensions, it inherits any
   security considerations that apply to the IGP.

   The security considerations of [BIER_ARCH] also apply.

7.  Acknowledgements

   The authors wish to thank Rajiv Asati, John Bettink, Nagendra Kumar,
   Christian Martin, Neale Ranns, Greg Shepherd, Ramji Vaithianathan,
   and Jeffrey Zhang for their ideas and contributions to this work.

8.  Contributor Addresses

   Below is a list of other contributing authors in alphabetical order:




























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   Mach (Guoyi) Chen
   Huawei

   Email: mach.chen@huawei.com

   Arkadiy Gulko
   Thomson Reuters
   195 Broadway
   New York  NY 10007
   US

   Email: arkadiy.gulko@thomsonreuters.com

   Wim Henderickx
   Alcatel-Lucent
   Copernicuslaan 50
   Antwerp 2018
   BE

   Email: wim.henderickx@alcatel-lucent.com

   Martin Horneffer
   Deutsche Telekom
   Hammer Str. 216-226
   Muenster 48153
   DE

   Email: Martin.Horneffer@telekom.de

   Uwe Joorde
   Deutsche Telekom
   Hammer Str. 216-226
   Muenster  D-48153
   DE

   Email: Uwe.Joorde@telekom.de

   Tony Przygienda
   Ericsson
   300 Holger Way
   San Jose, CA 95134
   US

   Email: antoni.przygienda@ericsson.com







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9.  References

9.1.  Normative References

   [BIER_ARCH]
              Wijnands, IJ., "Multicast using Bit Index Explicit
              Replication Architecture", internet-draft draft-wijnands-
              bier-architecture-02, December 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [RFC5331]  Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
              Label Assignment and Context-Specific Label Space", RFC
              5331, August 2008.

9.2.  Informative References

   [BIER_MVPN]
              Rosen, E., Ed., Sivakumar, M., Wijnands, IJ., Aldrin, S.,
              Dolganow, A., and T. Przygienda, "Multicast VPN Using
              Bier", internet-draft draft-rosen-l3vpn-mvpn-bier-02,
              December 2014.

   [ISIS_BIER_EXTENSIONS]
              Przygienda, T., Ginsberg, L., Aldrin, S., and J. Zhang,
              "OSPF Extensions for Bit Index Explicit Replication",
              internet-draft draft-przygienda-bier-isis-ranges-01.txt,
              October 2014.

   [OSPF_BIER_EXTENSIONS]
              Psenak, P., Kumar, N., Wijnands, IJ., Dolganow, A.,
              Przygienda, T., and J. Zhang, "OSPF Extensions for Bit
              Index Explicit Replication", internet-draft draft-psenak-
              ospf-bier-extensions-01.txt, October 2014.

Authors' Addresses










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   IJsbrand Wijnands (editor)
   Cisco Systems, Inc.
   De Kleetlaan 6a
   Diegem  1831
   BE

   Email: ice@cisco.com


   Eric C. Rosen (editor)
   Juniper Networks, Inc.
   10 Technology Park Drive
   Westford, Massachusetts  01886
   US

   Email: erosen@juniper.net


   Andrew Dolganow
   Alcatel-Lucent
   600 March Rd.
   Ottawa, Ontario  K2K 2E6
   CA

   Email: andrew.dolganow@alcatel-lucent.com


   Jeff Tantsura
   Ericsson
   300 Holger Way
   San Jose, California  95134
   US

   Email: jeff.tantsura@ericsson.com


   Sam K Aldrin
   Huawei Technologies
   2330 Central Express Way
   Santa Clara, California
   US

   Email: aldrin.ietf@gmail.com








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