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Versions: (draft-hfa-bier-pim-signaling) 00 01 02 03 04 05

BIER Workgroup                                           H. Bidgoli, Ed.
Internet Draft                                               A. Dolganow
Intended status: Standard Track                              J. Kotalwar
                                                                   Nokia
                                                              Fengman Xu
                                                                 Verizon
                                                             IJ. Wijnand
                                                     Cisco Systems, Inc.
                                                        Mankamana Mishra
                                                      Cisco System, Inc.


Expires: August 27, 2018                               February 23, 2018


                    PIM Signaling Through BIER Core
                    draft-ietf-bier-pim-signaling-00

Abstract

   Bit Index Explicit Replication (BIER) is an architecture that
   provides multicast forwarding through a "BIER domain" without
   requiring intermediate routers to maintain multicast related per-flow
   state.  Neither does BIER require an explicit tree-building protocol
   for its operation.  A multicast data packet enters a BIER domain at a
   "Bit-Forwarding Ingress Router" (BFIR), and leaves the BIER domain at
   one or more "Bit-Forwarding Egress Routers" (BFERs).  The BFIR router
   adds a BIER header to the packet.  Such header contains a bit-string
   in which each bit represents exactly one BFER to forward the packet
   to.  The set of BFERs to which the multicast packet needs to be
   forwarded is expressed by the according set of bits switched on in
   BIER packet header.

   This document describes the procedure needed for PIM Joins and Prunes
   to be signaled through a BIER core. Allowing PIM routers to run
   traditional PIM multicast services through a BIER core.


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), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.




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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on October 8, 2017.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   described in the Simplified BSD License.


Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Conventions used in this document . . . . . . . . . . . . . . .  3
     2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . .  4
   3. PIM Signaling Through BIER domain . . . . . . . . . . . . . . .  5
     3.1. Ingress BBR procedure . . . . . . . . . . . . . . . . . . .  6
       3.1.1. BIER packet construction at IBBR  . . . . . . . . . . .  7
     3.2. Signaling PIM through the BIER domain procedure . . . . . .  8
     3.3 Procedure to determine EBBR on IBBR  . . . . . . . . . . . .  8
       3.3.1 EBBR identification via next-hop . . . . . . . . . . . .  8
         3.3.1.1 Static Route . . . . . . . . . . . . . . . . . . . .  8
         3.3.1.2 Interior Border Gateway Protocol (iBGP)  . . . . . .  8
       3.3.2 Route summarization at EBBR  . . . . . . . . . . . . . .  9
       3.3.4 Constrain shortest path first  . . . . . . . . . . . . .  9
     3.4. EBBR procedure  . . . . . . . . . . . . . . . . . . . . . .  9
   4. Datapath Forwarding . . . . . . . . . . . . . . . . . . . . . . 10
     4.1. BFIR tracking of (S,G)  . . . . . . . . . . . . . . . . . . 10
     4.2. Datapath traffic flow . . . . . . . . . . . . . . . . . . . 10
   5. PIM-ASM behavior  . . . . . . . . . . . . . . . . . . . . . . . 10



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   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   7. Security Considerations . . . . . . . . . . . . . . . . . . . . 11
   8. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     8.1. Normative References  . . . . . . . . . . . . . . . . . . . 11
     8.2. Informative References  . . . . . . . . . . . . . . . . . . 11
   7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11



1. Introduction

   Greenfield deployment of BIER might not be possible for some large
   network. These networks deploy traditional PIM multicast services in
   GRT or in mvpns such as multicast vpns rfc 6037. Typically, each
   portion of these large networks have their own mandates and
   requirements.

   Consider the case of converged core, where single core is used for
   fixed, business and wireless services. In this case there is a desire
   for next generation "lean" core. Where a single IGP protocol or SDN
   controller could enable unicast and multicast services. BIER is a
   natural fit for this core. That said because of cost and operational
   complexity the migration to BIER might fall into below categories:

     1.Gradual migration of the network to BIER, starting with the
     "lean" core and eventually to access networks.

     2.Migrating only the core to BIER and keeping traditional pim
     services in access. As an example, in wireless networks where there
     are thousands of cell site routers. Each cell site router is a leaf
     as such for scaling and cost it might be desired to keep
     traditional PIM multicast services in the access network.

   This draft explains the procedure to signal PIM joins and prunes
   through a BIER core, as such enable provisioning of traditional pim
   services through a BIER core.

   It should be noted that this "lean" core is usually a single IGP
   area. As such the procedures in this draft is concentrating on a
   single BIER IGP area.

2. Conventions used in this document

   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].




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2.1. Definitions

   Some of the terminology specified in [I-D. rfc8279] is replicated
   here and extended by necessary definitions:

   BIER:

          Bit Index Explicit Replication (The overall architecture of
          forwarding multicast using a Bit Position).

   BFR:

          Bit Forwarding Router (A router that participates in Bit Index
          Multipoint Forwarding).A BFR is identified by a unique BFR-
          prefix in a BIER domain.

   BFIR:

          Bit Forwarding Ingress Router (The ingress border router that
          inserts the BM into the packet). Each BFIR must have a valid
          BFR-id assigned. In this draft BIER will be used for
          forwarding and tunneling of control plain packet (i.e. PIM)
          and forwarding dataplane packets. BFIR is term used for
          dataplane packet forwarding.

   BFER:

          Bit Forwarding Egress Router. A router that participates in
          Bit Index Forwarding as leaf. Each BFER must be a BFR.  Each
          BFER must have a valid BFR-id assigned. In this draft BIER
          will be used for forwarding and tunneling of control plain
          packet (i.e. PIM) and forwarding dataplain packets. BFIR is
          term used for dataplain packet forwarding.

   BBR:

          BIER Boundary router. The router between the PIM domain and
          BIER domain. Maintains PIM adjacency for all routers attached
          to it on the PIM domain and terminates the PIM adjacency
          toward the BIER domain.

   IBBR:

          Ingress BIER Boundary Router. The ingress router from
          signaling point of view. It maintains PIM adjacency toward the
          PIM domain and determines if PIM joins and prunes arriving
          from PIM domain need to be signaled across the BIER domain. If
          so it terminates the PIM adjacency toward the BIER domain and



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          signals the PIM joins/prunes through the BIER core.

   EBBR:

          Egress BIER Boundary Router. The egress router in BIER domain
          from signaling point of view. It terminates the BIER packet
          and forwards the signaled joins and prunes into PIM Domain.

   BFT:

          Bit Forwarding Tree used to reach all BFERs in a domain.

   BIFT:

          Bit Index Forwarding Table.

   BIER sub-domain:

          A further distinction within a BIER domain identified by its
          unique sub-domain identifier.  A BIER sub-domain can support
          multiple BitString Lengths.



   BFR-id:

          An optional, unique identifier for a BFR within a BIER sub-
          domain.


3. PIM Signaling Through BIER domain

                      bbr                   bbr
        |--pim Domain--|-----bier domain-----|--pim domain--|
   S--( A )----------( B ) ---- ( C ) ---- ( D )----------( E )--h


                      ebbr                  ibbr
   Sig   <-----PIM-----|<--Bier Tunneling----|<----PIM------
   (new)

                      bfir                  bfer
         ------------->|--------BIER-------->|------------->  Datapatah
                                                             (no change)

                     Figure 1: bier boundary router

   As per figure 1, the procedures of PIM signaling is done at the BIER



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   boundary router. The BIER boundary router (BBR) are connected to PIM
   capable routers toward the pim domain and BIER routers toward the
   bier domain. PIM routers in pim domain continue to send PIM state
   messages to the BBR. The BBR will create pim adjacency between all
   the PIM routers attach to it on the pim domain. That said the BBR
   does not propagate all PIM packets natively into the BIER domain.
   Instead when it determines that the PIM join or prune messages needs
   to be signaled through the BIER domain it will tunnel the PIM packet
   through BIER network. This tunneling is only done for signaling
   purposes and not for creating a PIM adjacency between the two
   disjoint pim domains through the bier domain.

   The terminology ingress BBR (ibbr) and egress BBR (ebbr) are relative
   from signaling point of view.

   The ingress BBR will determine if an arriving pim join or prune needs
   to be signaled across the bier domain. While the egress BBR will
   determine if the bier packet is a signaling packet and propagate the
   packet to its attach pim domain.

   The BFER and BFIR are BBR from datapath point of view. It should be
   noted the new procedures in this draft are only applicable to
   signaling and there are no changes from datapath point of view.



3.1. Ingress BBR procedure


   IBBR will create pim adjacency to all pim routers attach to it toward
   the pim domain.

   When a PIM join or prune for certain (S,G) arrives, the IBBR first
   determines weather the join or prune is meant for a source that is
   reachable through the bier domain. As an example, this source is
   located on a disjoint PIM domain that is reachable through the BIER
   domain. If so the ibbr will try to resolve the source via an ebbr
   closest to the source.

   The procedure to find the ebbr (BFIR from datapath point of view) can
   be via many mechanisms explained in more detail in upcoming sections.
   It should be noted that in most cases the BIER domain is a single IGP
   area. The PIM domains are part of the same IGP area as BIER
   domain(single area) or are stitched to the BIER domain via an ABR or
   ASBR. in either case the BBRs are all located in the same area as
   bier domain. Below are two examples of resolving ebbrs:

   1.The ebbr can be an ABR or ASBR router in the same IGP area as bier



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     domain. In this case the ebbr summarizes the route to the source,
     and as such the ebbr is the IGP source of this route. The IGP
     source information can be used for identifying the ebbr and
     resolving it.

   2.If source and ebbr are within a single IGP area, the ebbr can be
     resolved via SPF calculation. As an example, the closest ebbr to
     the source. The ebbr BFR-ID is signaled via IGP to all BFRs, as
     such making it possible to do SFP calculation.

   After discovering the EBBR and its BFR-ID (flooded via IGP BIER
   extension), the IBBR will construct the BIER header via the BIFT. The
   signaling packet, in this case the PIM join/prune packet, is
   encapsulated in the BIER header and transported through BIER domain
   to EBBR.

   On forwarding plane the IBBR will track all the PIM interfaces on the
   attach pim domain which are interested in a certain (S,G). It creates
   multicast states for arriving (S,G)s from pim domain, with incoming
   interface (RPF) as BIER "tunnel" interface and outgoing interface as
   the pim domain interface(s) on which PIM Join(s) were received on. If
   there is another PIM Join for the same multicast (S,G) entry on
   another interface arriving from pim domain, that interface gets added
   in the outgoing interface list as well.




3.1.1. BIER packet construction at IBBR

   The BIER header will be encoded with the BFR-id of the IBBR(with
   appropriate bit set in the bitstring) and the PIM signaling packet is
   then encapsulated in the packet.

        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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              BIFT-id                  | TC  |S|     TTL       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |Nibble |  Ver  |  BSL  |              Entropy                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |OAM|Rsv|    DSCP   |   Proto   |            BFIR-id            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                BitString  (first 32 bits)                     ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                                                               ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                BitString  (last 32 bits)                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   BIERHeader.Proto = IPv4 or IPv6

   BIERHeader.BitString= Bit corresponding to the BFR-ID of the EBBR

   BIERHeader.BFIR-id = BFR-Id of the BER originating the encapsulated
   PIM packet, i.e. the IBBR.

   Rest of the values in the BIER header are determined based on the
   network (MPLS/non-MPLS), capabilities (BSL), and network
   configuration.


3.2. Signaling PIM through the BIER domain procedure

   Throughout the BIER domain the BIER forwarding procedure is in par
   with RFC 8279. No BIER router will examine the BIER packet
   encapsulating the PIM signaling packet. As such there is no multicast
   state build in the BIER domain.

   The packet will be forwarded through the BIER domain until it reaches
   the BER with matching BFR-ID as in the BIERHeader.Bitstring. This BER
   (EBBR) will remove the BIER header and examine the PIM IPv4 or IPv6
   signaling packet farther.

3.3 Procedure to determine EBBR on IBBR

   As it was explained in previous section, IBBR needs to determine the
   EBBR closest to the source. This is needed to encode the BIER header
   BitString field for forwarding of the signaling packet. There can be
   many mechanism to determine the EBBR. This section explain some
   routing methods that can be used to achieve this.

3.3.1 EBBR identification via next-hop

   Assuming on the IBBR the source is resolved via EBBR bier prefix-id
   as its next-hop, the next-hop can be used to lookup the EBBR bit-
   index via the BIFT. In most cases the bier prefix-id is a loopback
   address. The next-hop of the source on IBBR can be set to EBBR via
   multiple methods, including Static Route and BGP.

3.3.1.1 Static Route

   On IBBR there can be a static route configured for the source, with
   source next-hop set as EBBR BIER prefix id.

3.3.1.2 Interior Border Gateway Protocol (iBGP)

   Consider the following topology:



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                      bbr                   bbr
                      ebbr                  ibbr
        |--pim Domain--|-----bier domain-----|--pim domain--|
   S--( A )----------( B ) ---- ( C ) ---- ( D )----------( E )--h


                             Figure 2

   Suppose BGP is enable between EBBR (B) and IBBR (D) and the PIM
   Domain routes are redistributed to the BIER domain via BGP. This
   would include the Multicast Source IP address (S), which resides in
   the PIM Domain. In such case BGP should use the same loopback
   interface as its next-hop as the BBR prefix-id. This will ensure that
   all PIM domain routes, including the Multicast Source IP address (S)
   are resolve via BBR's bier prefix id as thier next-hop. When the host
   (h) triggers a PIM join message to IBBR (D), IBBR tries to resolve
   (S). It resolves (S) via BGP installed route and realizes its next-
   hop is EBBR (B). IBBR will use this next-hop (B) to do a lookup in
   the BIFT and find its corresponding BIER bit index in the BIFT. Next
   IBBR will build the BIER header with corresponding EBBR bit index and
   tunnel the PIM signaling message toward EBBR. This procedure is
   inline with RFC6826 mLDP in-band signaling section 2.


3.3.2 Route summarization at EBBR

   The BIER domain can be an IGP area, in this case the EBBRs and IBBRs
   would act as an area boundary router (ABR). ABR could summarize
   routes and/or generate new routes with advertising router field set
   to EBBR bier prefix-id. When IBBR resolves the Source it can use the
   advertising router field to generate the BIER BitString Header for
   the EBBR closest to the source.

3.3.4 Constrain shortest path first

   In the BIER domain the edge BIER routers use IGP or BGP to advertise
   BIER extension TLVs. As such the routing protocols have a view of the
   EBBR closest to the source in PIM domain. To find the EBBR, IBBR can
   do a lookup for the source and ask for the closest EBBR on the path
   to the source. This look up can be a CSPF lookup. The IGP should
   return the EBBR closest to the source as part of this lookup.

3.4. EBBR procedure

   After receiving the BIER packet and determining this packet is a
   signaling packet. As such the EBBR will remove the BIER header from
   PIM packet and does a route lookup for the source of the pim packet,
   if the source is on a local attach pim domain, it forwards the PIM



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   packet toward the source.

   With same token the EBBR creates a multicast state with incoming
   interface as same interface that PIM join packet was forwarded and
   outgoing interfaces of BIER tunnel with BIER-Header.BFIR-id as one of
   the BFER of the tunnel.

   The EBBR will also build a BIER reverse path forwarding table, using
   the BIERHeader.BFIR-id and the arriving PIM packet (S,G). This is
   explained in section 4.1.

   It should be noted EBBR will maintain PIM adjacency toward the PIM
   domain and all PIM routers which are connected to it.

   At this point the end-to-end multicast traffic flow setup is
   complete.

4. Datapath Forwarding

4.1. BFIR tracking of (S,G)

   For a specific Source and Group, BFIR (EBBR)should track all the
   interested BFERs via arriving PIM signaling from BIER Domain. BFIR
   should build its multicast tree with incoming interface (IIF) as PIM
   interface (in PIM domain) and out going interfaces OIFs set as the
   <SD, BFR-ID> of the interested BFERs (in BIER Domain).

4.2. Datapath traffic flow

   When the multicast data traffic arrives on the BFIR (EBBR) the router
   will find all the interested BFERs for that specific (S,G). The
   router then constructs the BIERHeader.BitString with all the BFER
   interested in the group and will forward the packet to the BIER
   domain. The BFER(s) will accept the packets and remove the BIER
   header and forward the multicast packet as per pre-build multicast
   state for (G) and its outgoing interfaces.

5. PIM-ASM behavior

   In case of PIM ASM the procedure for LEAFs joining RP is same as
   above. The unicast (source registration) traffic from source to RP
   will be flooded throughout the BIER domain as regular unicast traffic
   without BIER involvement.

6.  IANA Considerations

   This document contains no actions for IANA.




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7. Security Considerations

   TBD

8. References

8.1. Normative References

   [BIER_ARCH] Wijnands, IJ., Rosen, E., Dolganow, A., Przygienda, T.,
   and S. Aldrin, "Multicast using Bit Index Explicit Replication", rfc
   8279, October 2016.

8.2. 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-ietf-bier-mvpn-08, January 2017.

   [ISIS_BIER_EXTENSIONS] Ginsberg, L., Przygienda, T., Aldrin, S., and
   Z. Zhang, "BIER Support via ISIS", internet-draft draft-ietf-bier-
   isis-extensions-06.txt, March 2017.

   [OSPF_BIER_EXTENSIONS] Psenak, P., Kumar, N., Wijnands, IJ.,
   Dolganow, A., Przygienda, T., Zhang, Z., and S. Aldrin, "OSPF
   Extensions for Bit Index Explicit Replication", internet-draft draft-
   ietf-ospf-bier-extensions-09.txt, March 2017.

7. Acknowledgments <Add any acknowledgements>

Authors' Addresses

   Hooman Bidgoli (editor)
   Nokia
   600 March Rd.
   Ottawa, Ontario K2K 2E6
   Canada

   Email: hooman.bidgoli@nokia.com

   Fengman Xu
   Verizon
   400 International PKWY
   Richardson, Tx 75081
   US

   Email: fengman.xu@verizon.com

   Jayant Kotalwar



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   Nokia
   380 N Bernardo Ave,
   Mountain View, CA 94043
   US

   Email: jayant.kotalwar@nokia.com

   Andrew Dolganow
   Nokia
   750D Chai Chee Rd
   06-06, Viva Business Park
   Singapore 469004

   Email: Andrew.dolganow@nokia.com

   IJsbrand Wijnands
   Cisco Systems
   De Kleetlaan 6a
   Diegem  1831
   Belgium

   Email: ice@cisco.com

   Mankamana Mishra
   Cisco System
   821 alder drive,
   Milpitas California
   USA

   Email: mankamis@cisco.com





















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