[Search] [txt|html|xml|pdf|bibtex] [Tracker] [Email] [Nits]

Versions: 00 01                                                         
Network Working Group                                            H. Chen
Internet-Draft                                                M. McBride
Intended status: Standards Track                               Futurewei
Expires: 25 April 2022                                           A. Wang
                                                           China Telecom
                                                               G. Mishra
                                                            Verizon Inc.
                                                                  L. Liu
                                                                 Fujitsu
                                                                  X. Liu
                                                          Volta Networks
                                                         22 October 2021


                       BIER-TE for Broadcast Link
                       draft-chen-bier-te-lan-00

Abstract

   This document describes extensions to "Bit Index Explicit Replication
   Traffic Engineering" (BIER-TE) for supporting LANs (i.e., broadcast
   links).  For a multicast packet with an explicit point-to-multipoint
   (P2MP) path traversing LANs, the packet is replicated and forwarded
   statelessly along the path.

Requirements Language

   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 [RFC2119] [RFC8174]
   when, and only when, they appear in all capitals, as shown here.

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 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
   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 25 April 2022.



Chen, et al.              Expires 25 April 2022                 [Page 1]


Internet-Draft               BIER-TE for LAN                October 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
   Provisions Relating to IETF Documents (https://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
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Example Application of Current BIER-TE with LAN . . . . . . .   4
     2.1.  Example BIER-TE Topology with LAN . . . . . . . . . . . .   4
     2.2.  BIER-TE BIFT on BFR . . . . . . . . . . . . . . . . . . .   5
     2.3.  Example P2MP Path with LAN  . . . . . . . . . . . . . . .  10
   3.  Improved BIER-TE with LAN . . . . . . . . . . . . . . . . . .  11
     3.1.  New BP Assignments for LAN  . . . . . . . . . . . . . . .  11
     3.2.  Improved BIER-TE BIFT on BFR  . . . . . . . . . . . . . .  12
     3.3.  Updated Forwarding Procedure  . . . . . . . . . . . . . .  16
   4.  Example Application of Improved BIER-TE . . . . . . . . . . .  17
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   [I-D.ietf-bier-te-arch] introduces Bit Index Explicit Replication
   (BIER) Traffic/Tree Engineering (BIER-TE).  It is an architecture for
   per-packet stateless explicit point to multipoint (P2MP) multicast
   path/tree.  A Bit-Forwarding Router (BFR) in a BIER-TE domain has a
   BIER-TE Bit Index Forwarding Table (BIFT).  A BIER-TE BIFT on a BFR
   comprises a forwarding entry for a BitPosition (BP) assigned to each
   of the adjacencies of the BFR.  If the BP represents a forward
   connected adjacency, the forwarding entry for the BP forwards the
   multicast packet with the BP to the directly connected BFR neighbor
   of the adjacency.  If the BP represents a BFER (i.e., egress node) or
   say a local decap adjacency, the forwarding entry for the BP



Chen, et al.              Expires 25 April 2022                 [Page 2]


Internet-Draft               BIER-TE for LAN                October 2021


   decapsulates the multicast packet with the BP and passes a copy of
   the payload of the packet to the packet's NextProto within the BFR.

   In [I-D.ietf-bier-te-arch], for a LAN, the adjacency to each
   neighboring BFR on the LAN is given a unique BitPosition.  The
   adjacency of this BitPosition is a forward connected adjacency
   towards the BFR and this BitPosition is populated into the BIFT of
   all the other BFRs on that LAN.  This solution for a LAN does not
   work in some cases.

   For a packet with an explicit point-to-multipoint (P2MP) path, if the
   path traverses some BFRs/nodes on a LAN, each of these BFRs/nodes on
   the LAN may receive duplicated packets.  Thus some of the egress
   nodes will receive duplicated packets.

   This document proposes a solution for LANs to resolve this issue.
   For a packet with an explicit P2MP path traversing LANs (i.e.,
   broadcast links), the packet is replicated and forwarded statelessly
   along the path.  Each of the egress nodes of the path will not
   receive any duplicated packet.

1.1.  Terminology

   BIER:  Bit Index Explicit Replication.

   BIER-TE:  BIER Traffic Engineering.

   BFR:  Bit-Forwarding Router.

   BFIR:  Bit-Forwarding Ingress Router.

   BFER:  Bit-Forwarding Egress Router.

   BFR-id:  BFR Identifier.  It is a number in the range [1,65535].

   BFR-NBR:  BFR Neighbor.

   BFR-prefix:  An IP address (either IPv4 or IPv6) of a BFR.

   BIRT:  Bit Index Routing Table.  It is a table that maps from the
         BFR-id (in a particular sub-domain) of a BFER to the BFR-prefix
         of that BFER, and to the BFR-NBR on the path to that BFER.

   BIFT:  Bit Index Forwarding Table.

   IGP:  Interior Gateway Protocol.

   LSDB:  Link State DataBase.



Chen, et al.              Expires 25 April 2022                 [Page 3]


Internet-Draft               BIER-TE for LAN                October 2021


   OSPF:  Open Shortest Path First.

   IS-IS:  Intermediate System to Intermediate System.

2.  Example Application of Current BIER-TE with LAN

   This section illustrates an example application of the current BIER-
   TE defined in [I-D.ietf-bier-te-arch] to the BIER-TE topology with
   LAN in Figure 1.

2.1.  Example BIER-TE Topology with LAN

   An example BIER-TE topology with a LAN for a BIER-TE domain is shown
   in Figure 1.  It has 8 nodes/BFRs A, B, C, D, E, F, G and H.  Nodes/
   BFRs D, F, E, H and A are BFERs and have local decap adjacency
   BitPositions (BPs for short) 1, 2, 3, 4, and 5 respectively.  For
   simplicity, these BPs are represented by (SI:BitString), where SI = 0
   and BitString is of 8 bits.  BPs 1, 2, 3, 4, and 5 are represented by
   1 (0:00000001), 2 (0:00000010), 3 (0:00000100), 4 (0:00001000) and 5
   (0:00010000) respectively.


                                      4'              |         4
                             /-----------( G )--------+       ( H )
                            /                  14'    |________/
                           /                          |       15'
                          /3'                _________|
          1'        2'   /            6'    /13'      |     16'
     ( A )------------( B )--------------( C )        +--------( D )
       5              7'\    5'            \11'       |          1
                         \                  \        LAN
                          \                  \
                           \8'          10'   \12'
                          ( E )--------------( F )
                            3     9'           2

          Figure 1: Example BIER-TE Topology with BP to BFR on LAN

   The BitPositions for the forward connected adjacencies are
   represented by i', where i is from 1 to 16.  In one option, they are
   encoded as (n+i), where n is a power of 2 such as 32768.  For
   simplicity, these BitPositions are represented by (SI:BitString),
   where SI = (6 + (i-1)/8) and BitString is of 8 bits.  BitPositions i'
   (i from 1 to 16) are represented by 1'(6:00000001), 2'(6:00000010),
   3'(6:00000100), 4'(6:00001000), 5'(6:00010000), 6'(6:00100000),
   7'(6:01000000), 8'(6:10000000), 9'(7:00000001), 10'(7:00000010), . .
   . , 16'(7:10000000).




Chen, et al.              Expires 25 April 2022                 [Page 4]


Internet-Draft               BIER-TE for LAN                October 2021


   For a link between two nodes X and Y, there are two BitPositions for
   two forward connected adjacencies.  These two forward connected
   adjacency BitPositions are assigned on nodes X and Y respectively.
   The BitPosition assigned on X is the forward connected adjacency of
   Y.  The BitPosition assigned on Y is the forward connected adjacency
   of X.

   For example, for the link between nodes B and C in the figure, two
   forward connected adjacency BitPositions 5' and 6' are assigned to
   two ends of the link.  BitPosition 5' is assigned on node B to B's
   end of the link.  It is the forward connected adjacency of node C.
   BitPosition 6' is assigned on node C to C's end of the link.  It is
   the forward connected adjacency of node B.

   For a LAN (i.e., broadcast link) connecting nodes X1, X2, ..., Xm,
   there are m BitPositions for m forward connected adjacencies.  These
   m forward connected adjacency BitPositions are assigned on nodes X1,
   X2, ..., Xm respectively.

   For the LAN connecting 4 nodes C, G, H and D in the figure, 4 forward
   connected adjacency BitPositions 13', 14', 15' and 16' are assigned
   to C, G, H and D respectively.

2.2.  BIER-TE BIFT on BFR

   Every BFR in a BIER-TE domain/topology has a BIER-TE BIFT.  This
   section shows the BIER-TE BIFT on every BFR/node of the BIER-TE
   topology with LAN in Figure 1.

   For the BIER-TE topology in Figure 1, each of 8 nodes/BFRs A, B, C,
   D, E, F, G and H has its BIER-TE BIFT for the topology.  The BIFT on
   a BFR comprises a forwarding entry for each of the adjacencies of the
   BFR.

   The BIER-TE BIFT on BFR A (i.e., node A) is shown in Figure 2.  There
   are two adjacencies of A.  One is the forward connected adjacency
   from A to B (represented by BP 2'); the other is the local decap
   adjacency (represented by BP 5) for BFER (i.e., egress) A.  The BIFT
   on A has two forwarding entries.












Chen, et al.              Expires 25 April 2022                 [Page 5]


Internet-Draft               BIER-TE for LAN                October 2021


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              | 2'(6:00000010)  | fw-connected |     B      |
              +-----------------+--------------+------------+
              | 5 (0:00010000)  | local-decap  |            |
              +-----------------+--------------+------------+

                      Figure 2: BIER-TE BIFT on BFR A

   The 1st forwarding entry in the BIFT is for BitPosition 2', which is
   the forward connected adjacency from A to B.  For a multicast packet
   with BitPosition 2', which indicates that the P2MP path in the packet
   traverses the adjacency from A to B, the forwarding entry forwards
   the packet to B along the link from A to B.

   The 2nd forwarding entry in the BIFT locally decapsulates a multicast
   packet with BitPosition 5 and passes a copy of the payload of the
   packet to the packet's NextProto.  It is for BitPosition 5, which is
   the local decap adjacency for BFER (i.e., egress) A.  For a multicast
   packet with BitPosition 5, which indicates that the P2MP path in the
   packet has node A as one of its destinations (i.e., egress nodes),
   the forwarding entry decapsulates the packet and passes a copy of the
   payload of the packet to the packet's NextProto within node A.

   The BIER-TE BIFT on BFR B (i.e., node B) is shown in Figure 3.  There
   are four forward connected adjacencies of B.  They are the forward
   connected adjacencies from B to A (represented by BP 1'), B to G
   (represented by BP 4'), B to C (represented by BP 6') and B to E
   (represented by BP 8') respectively.  The BIFT on B has four
   forwarding entries for these adjacencies.


              +----------------+--------------+------------+
              |  Adjacency BP  |    Action    |  BFR-NBR   |
              | (SI:BitString) |              | (Next Hop) |
              +================+==============+============+
              | 1'(6:00000001) | fw-connected |     A      |
              +----------------+--------------+------------+
              | 4'(6:00001000) | fw-connected |     G      |
              +----------------+--------------+------------+
              | 6'(6:00100000) | fw-connected |     C      |
              +----------------+--------------+------------+
              | 8'(6:10000000) | fw-connected |     E      |
              +----------------+--------------+------------+

                      Figure 3: BIER-TE BIFT on BFR B



Chen, et al.              Expires 25 April 2022                 [Page 6]


Internet-Draft               BIER-TE for LAN                October 2021


   The 1st forwarding entry in the BIFT is for BitPosition 1', which is
   the forward connected adjacency from B to A.  For a multicast packet
   with BitPosition 1', which indicates that the P2MP path in the packet
   traverses the adjacency from B to A, the forwarding entry forwards
   the packet to A along the link from B to A.

   The 2nd forwarding entry in the BIFT is for BitPosition 4', which is
   the forward connected adjacency from B to G.  For a multicast packet
   with BitPosition 4', which indicates that the P2MP path in the packet
   traverses the adjacency from B to G, the forwarding entry forwards
   the packet to G along the link from B to G.

   The 3rd forwarding entry in the BIFT is for BitPosition 6', which is
   the forward connected adjacency from B to C.  For a multicast packet
   with BitPosition 6', which indicates that the P2MP path in the packet
   traverses the adjacency from B to C, the forwarding entry forwards
   the packet to C along the link from B to C.

   The 4-th forwarding entry in the BIFT is for BitPosition 8', which is
   the forward connected adjacency from B to E.  For a multicast packet
   with BitPosition 8', which indicates that the P2MP path in the packet
   traverses the adjacency from B to E, the forwarding entry forwards
   the packet to E along the link from B to E.

   The BIER-TE BIFT on BFR C (i.e., node C) is shown in Figure 4.  There
   are five forward connected adjacencies of C.  They are the forward
   connected adjacencies from C to B (represented by BP 5'), C to F
   (represented by BP 12'), C to G (represented by BP 14'), C to H
   (represented by BP 15') and C to D (represented by BP 16')
   respectively.  The BIFT on C has five forwarding entries for these
   adjacencies.


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              |  5'(6:00010000) | fw-connected |     B      |
              +-----------------+--------------+------------+
              | 12'(7:00001000) | fw-connected |     F      |
              +-----------------+--------------+------------+
              | 14'(7:00100000) | fw-connected |     G      |
              +-----------------+--------------+------------+
              | 15'(7:01000000) | fw-connected |     H      |
              +-----------------+--------------+------------+
              | 16'(7:10000000) | fw-connected |     D      |
              +-----------------+--------------+------------+




Chen, et al.              Expires 25 April 2022                 [Page 7]


Internet-Draft               BIER-TE for LAN                October 2021


                      Figure 4: BIER-TE BIFT on BFR C

   The BIER-TE BIFT on BFR D (i.e., node D) is shown in Figure 5.  There
   are four adjacencies of D.  Three of them are the forward connected
   adjacencies from D to C (represented by BP 13'), D to G (represented
   by BP 14') and D to H (represented by BP 15') respectively; the other
   is the local decap adjacency (represented by BP 1) for BFER (i.e.,
   egress) D.  The BIFT on D has four forwarding entries for these
   adjacencies.


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              | 13'(7:00010000) | fw-connected |     C      |
              +-----------------+--------------+------------+
              | 14'(7:00100000) | fw-connected |     G      |
              +-----------------+--------------+------------+
              | 15'(7:01000000) | fw-connected |     H      |
              +-----------------+--------------+------------+
              |  1 (0:00000001) | local-decap  |            |
              +-----------------+--------------+------------+

                      Figure 5: BIER-TE BIFT on BFR D

   The BIER-TE BIFT on BFR E (i.e., node E) is shown in Figure 6.  There
   are three adjacencies of E.  Two of them are the forward connected
   adjacencies from E to B (represented by BP 7') and E to F
   (represented by BP 10') respectively; the other is the local decap
   adjacency (represented by BP 3) for BFER (i.e., egress) E.  The BIFT
   on E has three forwarding entries for these adjacencies.


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              |  7'(6:01000000) | fw-connected |     B      |
              +-----------------+--------------+------------+
              | 10'(7:00000010) | fw-connected |     F      |
              +-----------------+--------------+------------+
              |  3 (0:00000100) | local-decap  |            |
              +-----------------+--------------+------------+

                      Figure 6: BIER-TE BIFT on BFR E





Chen, et al.              Expires 25 April 2022                 [Page 8]


Internet-Draft               BIER-TE for LAN                October 2021


   The BIER-TE BIFT on BFR F (i.e., node F) is shown in Figure 7.  There
   are three adjacencies of F.  Two of them are the forward connected
   adjacencies from F to E (represented by BP 9') and F to C
   (represented by BP 11') respectively; the other is the local decap
   adjacency (represented by BP 2) for BFER (i.e., egress) F.  The BIFT
   on F has three forwarding entries for these adjacencies.


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              |  9'(7:00000001) | fw-connected |     E      |
              +-----------------+--------------+------------+
              | 11'(7:00000100) | fw-connected |     C      |
              +-----------------+--------------+------------+
              |  2 (0:00000010) | local-decap  |            |
              +-----------------+--------------+------------+

                      Figure 7: BIER-TE BIFT on BFR F

   The BIER-TE BIFT on BFR G (i.e., node G) is shown in Figure 8.  There
   are four forward connected adjacencies of G.  They are the
   adjacencies from G to B (represented by BP 3'), G to C (represented
   by BP 13'), G to H (represented by BP 15') and G to D (represented by
   BP 16') respectively.  The BIFT on G has four forwarding entries for
   these adjacencies.


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              |  3'(6:00000100) | fw-connected |     B      |
              +-----------------+--------------+------------+
              | 13'(7:00010000) | fw-connected |     C      |
              +-----------------+--------------+------------+
              | 15'(7:01000000) | fw-connected |     H      |
              +-----------------+--------------+------------+
              | 16'(7:10000000) | fw-connected |     D      |
              +-----------------+--------------+------------+

                      Figure 8: BIER-TE BIFT on BFR G

   The BIER-TE BIFT on BFR H (i.e., node H) is shown in Figure 9.  There
   are four adjacencies of H.  Three of them are the forward connected
   adjacencies from H to C (represented by BP 13'), H to G (represented
   by BP 14') and H to D (represented by BP 16') respectively; the other



Chen, et al.              Expires 25 April 2022                 [Page 9]


Internet-Draft               BIER-TE for LAN                October 2021


   is the local decap adjacency (represented by BP 4) for BFER (i.e.,
   egress) H.  The BIFT on H has four forwarding entries for these
   adjacencies.


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              | 13'(7:00010000) | fw-connected |     C      |
              +-----------------+--------------+------------+
              | 14'(7:00100000) | fw-connected |     G      |
              +-----------------+--------------+------------+
              | 16'(7:10000000) | fw-connected |     D      |
              +-----------------+--------------+------------+
              |  4 (0:00001000) | local-decap  |            |
              +-----------------+--------------+------------+

                      Figure 9: BIER-TE BIFT on BFR H

2.3.  Example P2MP Path with LAN

   This section presents the forwarding behaviors along an explicit P2MP
   path in Figure 1 going through the LAN in the figure.

   The explicit P2MP path traverses the link/adjacency from A to B
   (indicated by BP 2'), the link/adjacency from B to G (indicated by BP
   4') and the link/adjacency from B to C (indicated by BP 6'), the
   link/adjacency from G to H (indicated by BP 15'), and the link/
   adjacency from C to F (indicated by BP 12').  This path is
   represented by {2', 4', 6', 12', 15', 2, 4}.  The packet at A has
   this path.

   For the packet with the P2MP path, A forwards the packet to B
   according to the forwarding entry for BP 2' in its BIFT.

   After receiving the packet from A, B forwards the packet to G and C
   according to the forwarding entries for BPs 4' and 6' in B's BIFT
   respectively.  The packet received by G has path {12', 15', 2, 4}.
   The packet received by C has path {12', 15', 2, 4}.

   After receiving the packet from B, G sends the packet to H according
   to the forwarding entry for BP 15' in G's BIFT.

   After receiving the packet from B, C copies and sends the packet to H
   and F according to the forwarding entries for BPs 15' and 12' in C's
   BIFT respectively.




Chen, et al.              Expires 25 April 2022                [Page 10]


Internet-Draft               BIER-TE for LAN                October 2021


   Egress node H of the P2MP path receives the duplicated packets.  One
   packet is from G, and the same copy is from C.

   The solution proposed for LANs in this document resolve this issue.
   For a packet with an explicit P2MP path traversing LANs (i.e.,
   broadcast links), the packet is replicated and forwarded statelessly
   along the path.  Each of the egress nodes of the path will not
   receive any duplicated packet.

3.  Improved BIER-TE with LAN

3.1.  New BP Assignments for LAN

   For all the nodes/BFRs attached to a LAN (i.e., broadcast link), it
   is assumed that they are connected a pseudo node.  In one
   implementation, the pseudo node is the Designated Router (DR) of the
   LAN in OSPF or the Designated Intermediate System (DIS) of the LAN in
   IS-IS.

   For the connection between the pseudo node and each of the nodes/BFRs
   attached to a LAN, two BPs are assigned to it.  One is for the
   adjacency from the BFR to the pseudo node, the other is for the
   adjacency from the pseudo node to the BFR.

   The adjacency from a BFR to the pseudo node is called a LAN
   adjacency.  The adjacency from the pseudo node to a BFR is a forward
   connected adjacency.

   For example, suppose that the pseudo node for the LAN in Figure 1 is
   Px.  The BP assignments for the LAN (i.e., connections between Px and
   BFRs C, G, H and D) are illustrated in Figure 10.


                                      4'                           4
                             /-----------( G )---------+         ( H )
                            /                 15'      |  ________/
                           /                        16'| /18'    17'
                          /3'                _________ Px
          1'        2'   /            6'    /13'   14' |20'   19'
     ( A )------------( B )--------------( C )         +---------( D )
       5              7'\    5'            \11'                    1
                         \                  \
                          \                  \
                           \8'          10'   \12'
                          ( E )--------------( F )
                            3     9'           2

            Figure 10: Example BIER-TE Topology with BPs for LAN



Chen, et al.              Expires 25 April 2022                [Page 11]


Internet-Draft               BIER-TE for LAN                October 2021


   The connection/adjacency from Px to C is assigned BP 13', and the
   connection/adjacency from C to Px is assigned BP 14'.

   The connection/adjacency from Px to G is assigned BP 15', and the
   connection/adjacency from G to Px is assigned BP 16'.

   The connection/adjacency from Px to H is assigned BP 17', and the
   connection/adjacency from H to Px is assigned BP 18'.

   The connection/adjacency from Px to D is assigned BP 19', and the
   connection/adjacency from D to Px is assigned BP 20'.

   In an alternative, all the nodes/BFRs attached to a LAN are assumed
   fully connected each other (i.e., they are fully meshed).  For a
   connection between any two BFRs on the LAN, two forward connected
   adjacencies are assigned to the two ends of the connection.

   For example, there are four BFRs C, G, H and D attached to the LAN in
   Figure 1.  There are six connections among these four BFRs.  They are
   connections between C and G, C and H, C and D, G and H, G and D, H
   and D.  Twelve BPs are needed for these six connections.

   In general, for n BFRs attached to a LAN, there are n*(n-1)/2
   connections among these n BFRs and n*(n-1) BPs are needed for these
   connections.  This may not be scalable.  But for this alternative,
   the BIER-TE BIFT on a BFR needs not to be changed except for
   considering the full mesh connections among the BFRs attached to a
   LAN.

3.2.  Improved BIER-TE BIFT on BFR

   Each BFR in a BIER-TE domain has a BIER-TE BIFT.  For a BFR not
   attached to any LAN, the BIER-TE BIFT on the BFR is the same as
   before.  For a BFR attached to a LAN, its BIER-TE BIFT is changed for
   considering the LAN.

   For example, BFRs C, G, H and D are attached to a LAN in Figure 1.
   The BIER-TE BIFT on each of these four BFRs is changed for the new BP
   assignments for the LAN in Figure 10.

   For a BFR attached to a LAN, suppose that the pseudo node for the LAN
   is Px.  The improved BIER-TE BIFT on the BFR comprises a forwarding
   entry for the LAN adjacency from the BFR to Px and a secondary BIFT
   for Px.  The secondary BIFT for Px on the BFR contains a forwarding
   entry for each of the forward connected adjacencies from Px to the
   BFRs attached to the LAN except for the adjacency from Px to the BFR.





Chen, et al.              Expires 25 April 2022                [Page 12]


Internet-Draft               BIER-TE for LAN                October 2021


   For example, the improved BIER-TE BIFT on BFR C is illustrated in
   Figure 11.  It comprises the forwarding entry for the LAN adjacency
   from C to Px (indicated by BP 14') and the secondary BIFT for Px on
   BFR C.  The secondary BIFT contains three forwarding entries for
   three forward connected adjacencies from Px to G (indicated by 15'),
   Px to H (indicated by 17') and Px to D (indicated by 19')
   respectively.


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              | 15'(7:01000000) | fw-connected |     G      |
              +-----------------+--------------+------------+
              | 17'(8:00000001) | fw-connected |     H      |
              +-----------------+--------------+------------+
              | 19'(8:00000100) | fw-connected |     D      |
              +-----------------+--------------+------------+
                        Secondary BIFT for Px on BFR C

              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              |  5'(6:00010000) | fw-connected |     B      |
              +-----------------+--------------+------------+
              | 12'(7:00001000) | fw-connected |     F      |
              +-----------------+--------------+------------+
              | 14'(7:00100000) |lan-connected |     Px     |
              +-----------------+--------------+------------+

                 Figure 11: Improved BIER-TE BIFT on BFR C

   The improved BIER-TE BIFT on BFR G is illustrated in Figure 12.  It
   comprises the forwarding entry for the LAN adjacency from G to Px
   (indicated by BP 16') and the secondary BIFT for Px on BFR G.  The
   secondary BIFT contains three forwarding entries for three forward
   connected adjacencies from Px to C (indicated by 13'), Px to H
   (indicated by 17') and Px to D (indicated by 19') respectively.











Chen, et al.              Expires 25 April 2022                [Page 13]


Internet-Draft               BIER-TE for LAN                October 2021


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              | 13'(7:00010000) | fw-connected |     C      |
              +-----------------+--------------+------------+
              | 17'(8:00000001) | fw-connected |     H      |
              +-----------------+--------------+------------+
              | 19'(8:00000100) | fw-connected |     D      |
              +-----------------+--------------+------------+
                        Secondary BIFT for Px on BFR G

              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              |  3'(6:00000100) | fw-connected |     B      |
              +-----------------+--------------+------------+
              | 16'(7:00100000) |lan-connected |     Px     |
              +-----------------+--------------+------------+

                 Figure 12: Improved BIER-TE BIFT on BFR G

   The improved BIER-TE BIFT on BFR H is illustrated in Figure 13.  It
   comprises the forwarding entry for the LAN adjacency from H to Px
   (indicated by BP 18') and the secondary BIFT for Px on BFR H.  The
   secondary BIFT contains three forwarding entries for three forward
   connected adjacencies from Px to C (indicated by 13'), Px to G
   (indicated by 15') and Px to D (indicated by 19') respectively.






















Chen, et al.              Expires 25 April 2022                [Page 14]


Internet-Draft               BIER-TE for LAN                October 2021


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              | 13'(7:00010000) | fw-connected |     C      |
              +-----------------+--------------+------------+
              | 15'(7:01000000) | fw-connected |     G      |
              +-----------------+--------------+------------+
              | 19'(8:00000100) | fw-connected |     D      |
              +-----------------+--------------+------------+
                        Secondary BIFT for Px on BFR H

              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              |  4 (0:00001000) | local-decap  |            |
              +-----------------+--------------+------------+
              | 18'(8:00000010) |lan-connected |     Px     |
              +-----------------+--------------+------------+

                 Figure 13: Improved BIER-TE BIFT on BFR H

   The improved BIER-TE BIFT on BFR D is illustrated in Figure 14.  It
   comprises the forwarding entry for the LAN adjacency from D to Px
   (indicated by BP 20') and the secondary BIFT for Px on BFR D.  The
   secondary BIFT contains three forwarding entries for three forward
   connected adjacencies from Px to C (indicated by 13'), Px to G
   (indicated by 15') and Px to H (indicated by 17') respectively.






















Chen, et al.              Expires 25 April 2022                [Page 15]


Internet-Draft               BIER-TE for LAN                October 2021


              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              | 13'(7:00010000) | fw-connected |     C      |
              +-----------------+--------------+------------+
              | 15'(7:01000000) | fw-connected |     G      |
              +-----------------+--------------+------------+
              | 17'(8:00000001) | fw-connected |     H      |
              +-----------------+--------------+------------+
                        Secondary BIFT for Px on BFR D

              +-----------------+--------------+------------+
              |  Adjacency BP   |    Action    |  BFR-NBR   |
              | (SI:BitString)  |              | (Next Hop) |
              +=================+==============+============+
              |  1 (0:00000001) | local-decap  |            |
              +-----------------+--------------+------------+
              | 20'(8:00000001) |lan-connected |     Px     |
              +-----------------+--------------+------------+

                 Figure 14: Improved BIER-TE BIFT on BFR D

3.3.  Updated Forwarding Procedure

   The forwarding procedure defined in [I-D.ietf-bier-te-arch] is
   updated/enhanced for using an improved BIER-TE BIFT to support BIER-
   TE with LAN.

   The updated procedure is described in Figure 15.  For a multicast
   packet containing the BitString encoding an explicit P2MP path, if
   the BP in the BitString is for a LAN adjacency to pseudo node Px for
   the LAN, the updated forwarding procedure on a BFR sends the packet
   towards Px's next hop nodes on the P2MP path encoded in the packet.

   The procedure on a BFR "sends" (i.e., works as sending) the packet
   with the BP for the LAN adjacency to Px according to the forwarding
   entry for the BP in the improved BIER-TE BIFT on the BFR.  And then
   it acts on Px to "send" (i.e., works as sending) the packet to each
   of the Px's next hop nodes that are on the P2MP path using the
   secondary BIFT for Px.

   It obtains the secondary BIFT for Px on the BFR, clears all the BPs
   for the adjacencies of the BFR including the adjacency from the BFR
   to Px, copies and sends the packet to each of the Px's next hop nodes
   on the P2MP path using the secondary BIFT for Px.





Chen, et al.              Expires 25 April 2022                [Page 16]


Internet-Draft               BIER-TE for LAN                October 2021


   For each Px's next hop node on the P2MP path, which is represented by
   BP j in the packet's BitString, it gets the forwarding entry for BP j
   from the secondary BIFT for Px, copies the packet, updates the copy's
   BitString by clearing all the BPs for Px's adjacencies, and sends the
   updated copy to the next hop node according to the forwarding entry.


     Packet = the packet received by BFR;
     FOR each BP k (from the rightmost in Packet's BitString) {
        IF BP k is local decap adjacency (or say BP of BFER) {
           Copies Packet, sends the copy to the multicast
           flow overlay and clears bit k in Packet's BitString
        } ELSE IF BP k is forward connected adjacency of the BFR {
           Finds the forwarding entry in the BIER-TE BIFT using BP k,
           Copies Packet, updates the copy's BitString by
           clearing all the BPs for the adjacencies of the BFR,
           and sends the updated copy to BFR-NBR
        } ELSE IF BP k is LAN adjacency to Px {
           Obtains the secondary BIFT for Px,
           Clears all the BPs for the adjacencies of the BFR,
           FOR each BP j (from the rightmost in Packet's BitString) {
               IF BP j is Px's forward connected adjacency {
                   Gets the forwarding entry for BP j in the
                   secondary BIFT for Px,
                   Copies Packet, updates the copy's BitString by
                   clearing all the BPs for Px's adjacencies,
                   and sends the updated copy to BFR-NBR
               }
           }
        }
     }

                  Figure 15: Updated Forwarding Procedure

4.  Example Application of Improved BIER-TE

   This section illustrates an example application of improved BIER-TE
   to Figure 1.  It shows the forwarding behaviors along an explicit
   P2MP path in Figure 10 going through the LAN in the figure.

   The new BP assignments for the LAN in Figure 1 is shown in Figure 10.
   The improved BIER-TE BIFT on each of the BFRs attached to the LAN is
   given in Section 3.2.

   The explicit P2MP path traverses the link/adjacency from A to B
   (indicated by BP 2'), the link/adjacency from B to G (indicated by BP
   4') and the link/adjacency from B to C (indicated by BP 6'), the
   link/adjacency from G to Px (indicated by BP 16'), the link/adjacency



Chen, et al.              Expires 25 April 2022                [Page 17]


Internet-Draft               BIER-TE for LAN                October 2021


   from C to F (indicated by BP 12'), and the link/adjacency from Px to
   H (indicated by BP 17').  This path is represented by {2', 4', 6',
   12', 16', 17', 2, 4}.  The packet at A has this path.

   For the packet with the P2MP path, A forwards the packet to B
   according to the forwarding entry for BP 2' in its BIFT.

   After receiving the packet from A, B forwards the packet to G and C
   according to the forwarding entries for BPs 4' and 6' in B's BIFT
   respectively.  The packet received by G has path {12', 16', 17', 2,
   4}.  The packet received by C has path {12', 16', 17', 2, 4}.

   After receiving the packet from B, G "sends" the packet to Px
   according to the forwarding entry for BP 16' in G's improved BIER-TE
   BIFT.  After receiving the packet from G, which has path {12', 17',
   2, 4}, Px "sends" the packet to H according to the forwarding entry
   for BP 17' in the secondary BIFT for Px (a part of G's improved BIER-
   TE BIFT).

   After receiving the packet from G, which has path {12', 2, 4}, H
   decapsulates the packet and passes a copy of the payload of the
   packet to the packet's NextProto within node H according to the
   forwarding entry for BP 4 in H's improved BIER-TE BIFT.

   After receiving the packet from B, which has path {12', 16', 17', 2,
   4}, C sends the packet to F according to the forwarding entry for BP
   12' in C's improved BIER-TE BIFT.

   After receiving the packet from C, which has path {16', 17', 2, 4}, F
   decapsulates the packet and passes a copy of the payload of the
   packet to the packet's NextProto within node F according to the
   forwarding entry for BP 2 in F's BIER-TE BIFT.

   Egress node H of the P2MP path does not receive any duplicated
   packet.

5.  Security Considerations

   TBD.

6.  IANA Considerations

   No requirements for IANA.

7.  Acknowledgements

   The authors would like to thank people for their comments to this
   work.



Chen, et al.              Expires 25 April 2022                [Page 18]


Internet-Draft               BIER-TE for LAN                October 2021


8.  References

8.1.  Normative References

   [I-D.ietf-bier-te-arch]
              Eckert, T., Cauchie, G., and M. Menth, "Tree Engineering
              for Bit Index Explicit Replication (BIER-TE)", Work in
              Progress, Internet-Draft, draft-ietf-bier-te-arch-10, 9
              July 2021, <https://www.ietf.org/archive/id/draft-ietf-
              bier-te-arch-10.txt>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://www.rfc-editor.org/info/rfc5226>.

   [RFC5250]  Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
              OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
              July 2008, <https://www.rfc-editor.org/info/rfc5250>.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <https://www.rfc-editor.org/info/rfc5286>.

   [RFC5714]  Shand, M. and S. Bryant, "IP Fast Reroute Framework",
              RFC 5714, DOI 10.17487/RFC5714, January 2010,
              <https://www.rfc-editor.org/info/rfc5714>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC7356]  Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
              Scope Link State PDUs (LSPs)", RFC 7356,
              DOI 10.17487/RFC7356, September 2014,
              <https://www.rfc-editor.org/info/rfc7356>.

   [RFC7490]  Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
              So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
              RFC 7490, DOI 10.17487/RFC7490, April 2015,
              <https://www.rfc-editor.org/info/rfc7490>.




Chen, et al.              Expires 25 April 2022                [Page 19]


Internet-Draft               BIER-TE for LAN                October 2021


   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [RFC8556]  Rosen, E., Ed., Sivakumar, M., Przygienda, T., Aldrin, S.,
              and A. Dolganow, "Multicast VPN Using Bit Index Explicit
              Replication (BIER)", RFC 8556, DOI 10.17487/RFC8556, April
              2019, <https://www.rfc-editor.org/info/rfc8556>.

8.2.  Informative References

   [I-D.eckert-bier-te-frr]
              Eckert, T., Cauchie, G., Braun, W., and M. Menth,
              "Protection Methods for BIER-TE", Work in Progress,
              Internet-Draft, draft-eckert-bier-te-frr-03, 5 March 2018,
              <https://www.ietf.org/archive/id/draft-eckert-bier-te-frr-
              03.txt>.

   [I-D.ietf-rtgwg-segment-routing-ti-lfa]
              Litkowski, S., Bashandy, A., Filsfils, C., Francois, P.,
              Decraene, B., and D. Voyer, "Topology Independent Fast
              Reroute using Segment Routing", Work in Progress,
              Internet-Draft, draft-ietf-rtgwg-segment-routing-ti-lfa-
              07, 29 June 2021, <https://www.ietf.org/archive/id/draft-
              ietf-rtgwg-segment-routing-ti-lfa-07.txt>.










Chen, et al.              Expires 25 April 2022                [Page 20]


Internet-Draft               BIER-TE for LAN                October 2021


   [I-D.ietf-spring-segment-protection-sr-te-paths]
              Hegde, S., Bowers, C., Litkowski, S., Xu, X., and F. Xu,
              "Segment Protection for SR-TE Paths", Work in Progress,
              Internet-Draft, draft-ietf-spring-segment-protection-sr-
              te-paths-01, 11 July 2021,
              <https://www.ietf.org/archive/id/draft-ietf-spring-
              segment-protection-sr-te-paths-01.txt>.

   [RFC8296]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
              for Bit Index Explicit Replication (BIER) in MPLS and Non-
              MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
              2018, <https://www.rfc-editor.org/info/rfc8296>.

   [RFC8401]  Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z.
              Zhang, "Bit Index Explicit Replication (BIER) Support via
              IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018,
              <https://www.rfc-editor.org/info/rfc8401>.

   [RFC8444]  Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A.,
              Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2
              Extensions for Bit Index Explicit Replication (BIER)",
              RFC 8444, DOI 10.17487/RFC8444, November 2018,
              <https://www.rfc-editor.org/info/rfc8444>.

Authors' Addresses

   Huaimo Chen
   Futurewei
   Boston, MA,
   United States of America

   Email: Huaimo.chen@futurewei.com


   Mike McBride
   Futurewei

   Email: michael.mcbride@futurewei.com


   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing
   102209
   China




Chen, et al.              Expires 25 April 2022                [Page 21]


Internet-Draft               BIER-TE for LAN                October 2021


   Email: wangaj3@chinatelecom.cn


   Gyan S. Mishra
   Verizon Inc.
   13101 Columbia Pike
   Silver Spring,  MD 20904
   United States of America

   Phone: 301 502-1347
   Email: gyan.s.mishra@verizon.com


   Lei Liu
   Fujitsu
   United States of America

   Email: liulei.kddi@gmail.com


   Xufeng Liu
   Volta Networks
   McLean, VA
   United States of America

   Email: xufeng.liu.ietf@gmail.com

























Chen, et al.              Expires 25 April 2022                [Page 22]