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Versions: (draft-farinacci-lisp-signal-free-multicast) 00 01 02 03 04

Network Working Group                                          V. Moreno
Internet-Draft                                             Cisco Systems
Intended status: Experimental                               D. Farinacci
Expires: November 7, 2017                                    lispers.net
                                                             May 6, 2017

                       Signal-Free LISP Multicast


   When multicast sources and receivers are active at LISP sites, the
   core network is required to use native multicast so packets can be
   delivered from sources to group members.  When multicast is not
   available to connect the multicast sites together, a signal-free
   mechanism can be used to allow traffic to flow between sites.  The
   mechanism within here uses unicast replication and encapsulation over
   the core network for the data-plane and uses the LISP mapping
   database system so encapsulators at the source LISP multicast site
   can find de-capsulators at the receiver LISP multicast sites.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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 November 7, 2017.

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Copyright Notice

   Copyright (c) 2017 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definition of Terms . . . . . . . . . . . . . . . . . . . . .   4
   3.  Reference Model . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  General Procedures  . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  General Receiver-Site Procedures  . . . . . . . . . . . .   8
       4.1.1.  Multicast Receiver Detection  . . . . . . . . . . . .   8
       4.1.2.  Receiver-Site Registration  . . . . . . . . . . . . .   8
       4.1.3.  Consolidation of the Replication-List . . . . . . . .   9
     4.2.  General Source-Site Procedures  . . . . . . . . . . . . .  10
       4.2.1.  Multicast Tree Building at the Source-Site  . . . . .  10
       4.2.2.  Multicast Destination Resolution  . . . . . . . . . .  10
     4.3.  General LISP Notification Procedures  . . . . . . . . . .  10
   5.  Source Specific Multicast Trees . . . . . . . . . . . . . . .  11
     5.1.  Source Directly Connected to Source-ITRs  . . . . . . . .  11
     5.2.  Source not Directly Connected to Source-ITRs  . . . . . .  12
   6.  Multi-Homing Considerations . . . . . . . . . . . . . . . . .  12
     6.1.  Multiple ITRs at a Source-Site  . . . . . . . . . . . . .  12
     6.2.  Multiple ETRs at a Receiver-Site  . . . . . . . . . . . .  13
     6.3.  Multiple RLOCs for an ETR at a Receiver-Site  . . . . . .  13
   7.  PIM Any Source Multicast Trees  . . . . . . . . . . . . . . .  14
   8.  Signal-Free Multicast for Replication Engineering . . . . . .  15
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     12.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Appendix A.  Document Change Log  . . . . . . . . . . . . . . . .  20
     A.1.  Changes to draft-ietf-lisp-signal-free-multicast-04 . . .  20
     A.2.  Changes to draft-ietf-lisp-signal-free-multicast-03 . . .  20
     A.3.  Changes to draft-ietf-lisp-signal-free-multicast-02 . . .  20

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     A.4.  Changes to draft-ietf-lisp-signal-free-multicast-01 . . .  20
     A.5.  Changes to draft-ietf-lisp-signal-free-multicast-00 . . .  21
     A.6.  Changes to draft-farinacci-lisp-signal-free-multicast-04   21
     A.7.  Changes to draft-farinacci-lisp-signal-free-multicast-03   21
     A.8.  Changes to draft-farinacci-lisp-signal-free-multicast-02   21
     A.9.  Changes to draft-farinacci-lisp-signal-free-multicast-01   21
     A.10. Changes to draft-farinacci-lisp-signal-free-multicast-00   21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   When multicast sources and receivers are active at LISP sites, and
   the core network between the sites does not provide multicast
   support, a signal-free mechanism can be used to create an overlay
   that will allow multicast traffic to flow between sites and connect
   the multicast trees at the different sites.

   The signal-free mechanism here proposed does not extend PIM over the
   overlay as proposed in [RFC6831], nor does the mechanism utilize
   direct signaling between the Receiver-ETRs and Sender-ITRs as
   described in [I-D.farinacci-lisp-mr-signaling].  The signal-free
   mechanism proposed reduces the amount of signaling required between
   sites to a minimum and is centered around the registration of
   Receiver-sites for a particular multicast-group or multicast-channel
   with the LISP Mapping System.

   Registrations from the different receiver-sites will be merged at the
   Mapping System to assemble a multicast-replication-list inclusive of
   all RLOCs that lead to receivers for a particular multicast-group or
   multicast-channel.  The replication-list for each specific multicast-
   entry is maintained as a LISP database mapping entry in the Mapping

   When the ITR at the source-site receives multicast traffic from
   sources at its site, the ITR can query the mapping system by issuing
   Map-Request messages for the (S,G) source and destination addresses
   in the packets received.  The Mapping System will return the RLOC
   replication-list to the ITR, which the ITR will cache as per standard
   LISP procedure.  Since the core is assumed to not support multicast,
   the ITR will replicate the multicast traffic for each RLOC on the
   replication-list and will unicast encapsulate the traffic to each
   RLOC.  The combined function or replicating and encapsulating the
   traffic to the RLOCs in the replication-list is referred to as "rep-
   encapsulation" in this document.

   The document describes the General Procedures and information
   encoding that are required at the Receiver-sites and Source-sites to
   achieve signal-free multicast interconnectivity.  The General

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   Procedures for Mapping System Notifications to different sites are
   also described.  A section dedicated to the specific case of SSM
   trees discusses the implications to the General Procedures for SSM
   multicast trees over different topological scenarios.  A section on
   ASM support is included to identify the constraints that come along
   with supporting it using LISP Signal-Free multicast.

   There is a section dedicated to Replication Engineering.  A mechanism
   to reduce the impact of head-end replication.  The mapping system,
   via LISP Signal-Free mechanisms, can be used to build a layer of

2.  Definition of Terms

   LISP related terms, notably Map-Request, Map-Reply, Ingress Tunnel
   Router (ITR), Egress Tunnel Router (ETR), Map-Server (MS) and Map-
   Resolver (MR) are defined in the LISP specification [RFC6830].

   Extensions to the definitions in [RFC6830] for their application to
   multicast routing are documented in [RFC6831].

   Terms defining interactions with the LISP Mapping System are defined
   in [RFC6833].

   The following terms are consistent with the definitions in [RFC6830]
   and [RFC6831].  The terms are specific cases of the general terms and
   are here defined to facilitate the descriptions and discussions
   within this particular document.

   Source: Multicast source end-point.  Host originating multicast

   Receiver: Multicast group member end-point.  Host joins multicast
   group as a receiver of multicast packets sent to the group.

   Receiver-site: LISP site where multicast receivers are located.

   Source-site: LISP site where multicast sources are located.

   RP-site: LISP site where an ASM PIM Rendezvous Point is located.  The
   RP-site and the Source-site may be the same in some situations.

   Receiver-ETR: LISP xTR at the Receiver-site.  This is a multicast

   Source-ITR: LISP xTR at the Source-site.  This is a multicast ITR.

   RP-xTR: LISP xTR at the RP-site.  This is typically a multicast ITR.

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   Replication-list: Mapping-entry containing the list of RLOCs that
   have registered Receivers for a particular multicast-entry.

   Multicast-entry: A tuple identifying a multicast tree.  Multicast-
   entries are in the form of (S-prefix, G-prefix).

   Rep-encapsulation: The process of replicating and then encapsulating
   traffic to multiple RLOCs.

   Re-encapsulating Tunnel Router (RTR): An RTR is a router that
   implements the re-encapsulating tunnel function detailed in Section 8
   of the main LISP specification [RFC6830].  A LISP RTR performs packet
   re-routing by chaining ETR and ITR functions, whereby it first
   removes the LISP header of an ingress packet and then prepends a new
   LISP header to an egress packet.

   RTR Level: An RTR level is encoded in a Replication-List-Entry (RLE)
   LCAF Type detailed in [RFC8060].  Each entry in the replication list
   contains an address of an xTR and a level value.  Level values are
   used to create a replication hierarchy so that ITRs at source LISP
   sites replicate to the lowest (smaller value) level number RTRs in a
   RLE entry.  And then RTRs at a given level replicate to the next
   higher level of RTRs.  The number of RTRs at each level are
   engineered to control the fan-out or replication factor so a tradeoff
   between the width of the level versus the number of levels can be

3.  Reference Model

   The reference model that will be used for the discussion of the
   Signal-Free multicast tree interconnection is illustrated in
   Figure 1.

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                                 |   |
            +---+     +---+      +---+      +---+      +---+
  Src-1 ----| R1|-----|ITR|        |        |ETR|------| R2|------ Rcv-2
            +---+     +---+        |        +---+      +---+
                           \       |       /
            Source-site-1   \      |      /    Receiver-site-2
                             \     |     /
                              \    |    /
                               \   |   /
                               /       \
                              /         \
                             /           \
                            /             \
                           /               \
                      +---+                 +---+
  Src-3 --------------|ITR|                 |ETR|----------------- Rcv-4
                      +---+                 +---+

             Source-site-3                       Receiver-site-4

             Figure 1: LISP Multicast Generic Reference Model

   Sites 1 and 3 are Source-sites.

   Source-site-3 presents a Source (Src-3) that is directly connected to
   the Source-ITR

   Source-site-1 presents a Source (Src-1) that is one hop or more away
   from the Source-ITR

   Receiver-site-2 and 4 are receiver sites with not-directly connected
   and directly connected Receiver end-points respectively

   R1 is a router in Source-site-1.

   R2 is a PIM router at the Receiver-site.

   The Map-Servers and Resolvers are reachable in the RLOC space in the
   Core, only one is shown for illustration purposes, but these can be
   many or even part of a DDT tree.

   The procedures for interconnecting multicast Trees over an overlay
   can be broken down into three functional areas:

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   o  Receiver-site procedures

   o  Source-site procedures

   o  LISP notification procedures

   The receiver site procedures will be common for most tree types and

   The procedures at the source site can vary depending on the type of
   trees being interconnected as well as based on the topological
   relation between sources and source-site xTRs.  For ASM trees, a
   special case of the Source-site is the RP-site for which a variation
   of the Source-site procedures may be necessary if ASM trees are to be
   supported in future specifications of LISP Signal-Free multicast.

   The LISP notification procedures between sites are normalized for the
   different possible scenarios.  Certain scenarios may benefit from a
   simplified notification mechanism or no notification requirement at

4.  General Procedures

   The interconnection of multicast trees across different LISP sites
   involves the following procedures to build the necessary multicast
   distribution trees across sites.

   1.  The presence of multicast Receiver end-points is detected by the
       Receiver-ETRs at the Receiver-sites.

   2.  Receiver-ETRs register their RLOCs as part of the replication-
       list for the multicast-entry the detected Receivers subscribe to.

   3.  The Mapping-system merges all receiver-ETR or delivery-group
       RLOCs to build a comprehensive replication-list inclusive of all
       Receiver-sites for each multicast-entry.

   4.  LISP Map-Notify messages should be sent to the Source-ITR
       informing of any changes in the replication-list.

   5.  Multicast-tree building at the Source-site is initiated when the
       Source-ITR receives the LISP Notification.

   Once the multicast distribution trees are built, the following
   forwarding procedures may take place:

   1.  The Source sends multicast packets to the multicast group
       destination address.

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   2.  Multicast traffic follows the multicast tree built at the Source-
       site and makes its way to the Source-ITRs.

   3.  The Source-ITR will issue a map-request to resolve the
       replication-list for the multicast-entry.

   4.  The Mapping System responds to the Source-ITR with a map-reply
       containing the replication-list for the multicast group

   5.  The Source-ITR caches the replication-list received in the map-
       reply for the multicast-entry.

   6.  Multicast traffic is rep-encapsulated.  That is, the packet is
       replicated for each RLOC in the replication-list and then
       encapsulated to each one.

4.1.  General Receiver-Site Procedures

4.1.1.  Multicast Receiver Detection

   When the Receiver-ETRs are directly connected to the Receivers (e.g.
   Receiver-site-4 in Figure 1), the Receiver-ETRs will receive IGMP
   Reports from the Receivers indicating which group the Receivers wish
   to subscribe to.  Based on these IGMP Reports, the receiver-ETR is
   made aware of the presence of Receivers as well as which group they
   are interested in.

   When the Receiver-ETRs are several hops away from the Receivers (e.g.
   Receiver-site-2 in Figure 1), the Receiver-ETRs will receive PIM join
   messages which will allow the Receiver-ETR to know that there are
   multicast Receivers at the site and also learn which multicast group
   the Receivers are for.

4.1.2.  Receiver-Site Registration

   Once the Receiver-ETRs detect the presence of Receivers at the
   Receiver-site, the Receiver-ETRs will issue Map-Register messages to
   include the Receiver-ETR RLOCs in the replication-list for the
   multicast-entry the Receivers joined.

   The Map-Register message will use the multicast-entry (Source, Group)
   tuple as its EID record type with the Receiver-ETR RLOCs conforming
   the locator set.

   The EID in the Map-Register message must be encoded using the
   Multicast Information LCAF type defined in [RFC8060].

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   The RLOC in the Map-Register message must be encoded using the
   Replication List Entry (RLE) LCAF type defined in [RFC8060] with the
   Level Value fields for all entries set to 128 (decimal).

   The encoding described above must be used consistently for Map-
   Register messages, entries in the Mapping Database, Map-reply
   messages as well as the map-cache at the Source-ITRs.

   The Map-Register messages [RFC6830] sent by the receiver-ETRs should
   have the following bits set as here specified:

   1.  merge-request-bit set to 1.  The Map-Register messages must be
       sent with "Merge Semantics".  The Map-Server will receive
       registrations from a multitude of Receiver-ETRs.  The Map-Server
       will merge the registrations for common EIDs and maintain a
       consolidated replication-list for each multicast-entry.

   2.  want-map-notify-bit (M) set to 0.  This tells the Mapping System
       that the receiver-ETR does not expect to receive Map-Notify
       messages as it does not need to be notified of all changes to the

   3.  proxy-reply-bit (P) set to 1.  The merged replication-list is
       kept in the Map-Servers.  By setting the proxy-reply bit, the
       receiver-ETRs instruct the Mapping-system to proxy reply to map-
       requests issued for the multicast entries.

   Map-Register messages for a particular multicast-entry should be sent
   for every receiver detected, even if previous receivers have been
   detected for the particular multicast-entry.  This allows the
   replication-list to remain up to date.

   Receiver-ETRs must be configured to know what Map-Servers Map-
   Register messages are sent to.  The configuration is likely to be
   assocated with an S-prefix that multiple (S,G) entries match to and
   are more specific for.  Therefore, the S-prefix determines the Map-
   Server set in the least number of configuration statements.

4.1.3.  Consolidation of the Replication-List

   The Map-Server will receive registrations from a multitude of
   Receiver-ETRs.  The Map-Server will merge the registrations for
   common EIDs and consolidate a replication-list for each multicast-

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4.2.  General Source-Site Procedures

   Source-ITRs must register the unicast EIDs of any Sources or
   Rendezvous Points that may be present on the Source-site.  In other
   words, it is assumed that the Sources and RPs are LISP EIDs.

   The registration of the unicast EIDs for the Sources or Rendezvous
   Points allows the map-server to know where to send Map-Notify
   messages to.  Therefore, the Source-ITR must register the unicast
   S-prefix EID with the want-map-notify-bit set in order to receive
   Map-Notify messages whenever there is a change in the replication-

4.2.1.  Multicast Tree Building at the Source-Site

   When the source site receives the Map-Notify messages from the
   mapping system as described in Section 4.3, it will initiate the
   process of building a multicast distribution tree that will allow the
   multicast packets from the Source to reach the Source-ITR.

   The Source-ITR will issue a PIM join for the multicast-entry for
   which it received the Map-Notify message.  The join will be issued in
   the direction of the source or in the direction of the RP for the SSM
   and ASM cases respectively.

4.2.2.  Multicast Destination Resolution

   On reception of multicast packets, the source-ITR must obtain the
   replication-list for the (S,G) addresses in the packets.

   In order to obtain the replication-list, the Source-ITR must issue a
   Map-Request message in which the EID is the (S,G) multicast tuple
   which is encoded using the Multicast Info LCAF type defined in

   The Mapping System (most likely the Map-Server) will Map-reply with
   the merged replication-list maintained in the Mapping System.  The
   Map-reply message must follow the format defined in [RFC6830], its
   EID must be encoded using the Multicast Info LCAF type and the
   corresponding RLOC-records must be encoded using the RLE LCAF type.
   Both LCAF types defined in [RFC8060].

4.3.  General LISP Notification Procedures

   The Map-Server will issue LISP Map-Notify messages to inform the
   Source-site of the presence of receivers for a particular multicast
   group over the overlay.

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   Updated Map-Notify messages should be issued every time a new
   registration is received from a Receiver-site.  This guarantees that
   the source-sites are aware of any potential changes in the multicast-
   distribution-list membership.

   The Map-Notify messages carry (S,G) multicast EIDs encoded using the
   Multicast Info LCAF type defined in [RFC8060].

   Map-Notify messages will be sent by the Map-Server to the RLOCs with
   which the unicast S-prefix EID was registered.  In the case when
   sources are discovered dynamically [I-D.portoles-lisp-eid-mobility],
   xTRs must register sources explicitly with the want-map-notify-bit
   set.  This is so the ITR in the site the source has moved to can get
   the most current replication list.

   When both the Receiver-sites and the Source-sites register to the
   same Map-Server, the Map-Server has all the necessary information to
   send the Map-Notify messages to the Source-site.

   When the Map-Servers are distributed in a DDT, the Receiver-sites may
   register to one Map-Server while the Source-site registers to a
   different Map-Server.  In this scenario, the Map-Server for the
   receiver sites must resolve the unicast S-prefix EID in the DDT per
   standard LISP lookup procedures and obtain the necessary information
   to send the Map-Notify messages to the Source-site.  The Map-Notify
   messages must be sent with an authentication length of 0 as they
   would not be authenticated.

   When the Map-Servers are distributed in a DDT, different Receiver-
   sites may register to different Map-Servers.  This is an unsupported
   scenario with the currently defined mechanisms.

5.  Source Specific Multicast Trees

   The interconnection of Source Specific Multicast (SSM) Trees across
   sites will follow the General Receiver-site Procedures described in
   Section 4.1 on the Receiver-sites.

   The Source-site Procedures will vary depending on the topological
   location of the Source within the Source-site as described in
   Section 5.1 and Section 5.2 .

5.1.  Source Directly Connected to Source-ITRs

   When the Source is directly connected to the source-ITR, it is not
   necessary to trigger signaling to build a local multicast tree at the
   Source-site.  Therefore Map-Notify messages may not be required to
   initiate building of the multicast tree at the Source-site.

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   Map-Notify messages are still required to ensure that any changes to
   the replication-list are communicated to the Source-site so that the
   map-cache at the Source-ITRs is kept updated.

5.2.  Source not Directly Connected to Source-ITRs

   The General LISP Notification Procedures described in Section 4.3
   must be followed when the Source is not directly connected to the
   source-ITR.  On reception of Map-Notify messages, local multicast
   signaling must be initiated at the Source-site per the General Source
   Site Procedures for Multicast Tree building described in
   Section 4.2.1.

   In the SSM case, the IP address of the Source is known and it is also
   registered with the LISP mapping system.  Thus, the mapping system
   may resolve the mapping for the Source address in order to send Map-
   Notify messages to the correct source-ITR.

6.  Multi-Homing Considerations

6.1.  Multiple ITRs at a Source-Site

   When multiple ITRs exist at a source multicast site, care should be
   taken that more than one ITR does not head-end replicate packets else
   receiver multicast sites will receive duplicate packets.  The
   following procedures will be used for each topology scenarios:

   o  When more than one ITR is directly connected to the source host,
      either the PIM DR or the IGMP querier (when PIM is not enabled on
      the ITRs) is responsible for packet replication.  All other ITRs
      silently drop the packet.  In the IGMP querier case, it is
      required to configure the source LAN to have one of the ITRs be
      the IGMP querier.

   o  When more than one ITR is multiple hops away from the source host
      and one of the ITRs is the PIM Rendezvous Point, then the PIM RP
      is responsible for packet replication.

   o  When more than one ITR is multiple hops away from the source host
      and the PIM Rendezvous Point is not one of the ITRs, then one of
      the ITRs must join to the RP.  When a Map-Notify is received from
      the Map-Server by an ITR, only the highest RLOC addressed ITR will
      join toward the PIM RP or toward the source.

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6.2.  Multiple ETRs at a Receiver-Site

   When multiple ETRs exist in a receiver multicast site, and each
   create multicast join state, they each Map-Register their RLOC
   addresses to the mapping system.  In this scenario, the replication
   happens on the overlay causing multiple ETR entry points to replicate
   to all receivers versus a single ETR entry point replicating to all
   receivers.  If an ETR does not create join state, because it has not
   received PIM joins or IGMP reports, it will not Map-Register its RLOC
   addresses to the mapping system.  The same procedures in Section 4.1
   should be followed.

   When multiple ETRs exist on the same LAN as a receiver host, then the
   PIM DR, when PIM is enabled, or the IGMP querier is responsible for
   sending a Map-Register for its RLOC.  In the IGMP case, it is
   required that the LAN is configured with one of the ETRs as IGMP

6.3.  Multiple RLOCs for an ETR at a Receiver-Site

   It may be desirable to have multiple underlay paths to an ETR for
   multicast packet delivery.  This can be done by having multiple RLOCs
   assigned to an ETR and having the ETR send Map-Registers for all its
   RLOCs.  By doing this, an ITR can choose a specific path based on
   underlay performance and/or RLOC reachability.

   It is suggested that an ETR sends a Map-Register with a single RLOC-
   record that uses the ELP LCAF type [RFC8060] that is nested inside
   RLE entry LCAF.  For example say ETR1 has assigned RLOC1 and RLOC2
   for a LISP receiver site.  And there is ETR2 in another LISP receiver
   site, that has RLOC3.  The two receiver sites have the same (S,G)
   being joined.  Here is how the RLOC-record is encoded on each ETR:

   ETR1: EID-record: (S,G)
         RLOC-record: RLE[ ELP{ (RLOC1,s,p), (RLOC2,s,p) } ]

   ETR2: EID-record: (S,G)
         RLOC-record: RLE[ RLOC3 ]

   And here is how the entry is merged and stored on the Map-Server
   since the Map-Registers have an RLE encoded RLOC-record:

   MS: EID-record: (S,G)
       RLOC-record: RLE[ RLOC3, ELP{ (RLOC1,s,p), (RLOC2,s,p) } ]

   When the ITR receives a packet from a multicast source S for group G,
   it uses the merged RLOC-record, returned from the Map-Server.  The
   ITR replicates the packet to (RLOC3 and RLOC1) or (RLOC3 and RLOC2).

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   Since it is required for the s-bit to be set for RLOC1, the ITR must
   replicate to RLOC1 if it is reachable.  When the required p-bit is
   also set, the RLOC-reachability mechanisms from [RFC6830] are
   followed.  If the ITR determines that RLOC1 is unreachable, it uses
   RLOC2, as long as RLOC2 is reachable.

7.  PIM Any Source Multicast Trees

   LISP signal-free multicast can support ASM Trees in limited but
   acceptable topologies.  It is suggested for the simplification of
   building ASM trees across the LISP overlay to have PIM-ASM run
   independently in each LISP site.  What this means, is that a PIM
   Rendezvous Point (RP) is configured in each LISP site so PIM Register
   procedures and (*,G) state maintenance is contained within the LISP

   The following procedure will be used to support ASM in each LISP

   1.  In a Receiver-site, the RP is colocated with the ETR.  RPs for
       different groups can be spread across each ETR, but is not

   2.  When (*,G) state is created in an ETR, the procedures in
       Section 4.1.2 are followed.  In addition, the ETR registers
       (S-prefix,G), where S-prefix is 0/0 (the respective unicast
       default route for the address-family) to the mapping system.

   3.  In a Source-site, the RP is colocated with the ITR.  RPs for
       different groups can be spread across each ITR, but is not

   4.  When a multicast source sends a packet, a PIM Register message is
       delivered to the ITR and the procedures in Section 4.2 are

   5.  When the the ITR sends a Map-Request for (S,G) and no Receiver-
       site has registered for (S,G), the mapping system will return the
       (0/0,G) entry to the ITR so it has a replication list of all the
       ETRs that have received (*,G) state.

   6.  The ITR stores the replication-list in its map-cache for (S,G).
       It replicates packets to all ETRs in the list.

   7.  ETRs decapsulate packets and forward based on (*,G) state in
       their site.

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   8.  When last-hop PIM routers join the newly discovered (S,G), the
       ETR will store the state and follow the procedures in
       Section 4.1.2.

8.  Signal-Free Multicast for Replication Engineering

   The mechanisms in this draft can be applied to the LISP Replication-
   Engineering [I-D.coras-lisp-re] design.  Rather than having the
   layered LISP-RE RTR hierarchy use signaling mechanisms, the RTRs can
   register their availability for multicast tree replication via the
   mapping database system.

   As stated in [I-D.coras-lisp-re], the RTR layered hierarchy is used
   to avoid head-end replication in replicating nodes closest to a
   multicast source.  Rather than have multicast ITRs replicate to each
   ETR in an RLE entry of a (S,G) mapping database entry, it could
   replicate to one or more layer-0 RTRs in the LISP-RE hierarchy.

   This draft documents how the RTR hierarchy is determined but not what
   are the optimal layers of RTRs to use.  Methods for determining
   optimal paths or RTR topological closeness are out of scope for his

   There are two formats an (S,G) mapping database entry could have.
   One format is a 'complete-format' and the other is a 'filtered-
   format'.  A 'complete-format' entails an (S,G) entry having multiple
   RLOC records which contain both ETRs that have registered as well as
   the RTRs at the first level of the LISP-RE hierarchy for the ITR to
   replicate to.  When using 'complete-format', the ITR has the ability
   to select if it replicates to RTRs or to the registered ETRs at the
   receiver sites.  A 'filtered-format' (S,G) entry is one where the
   Map-Server returns the RLOC-records that it decides the ITR should
   use.  So replication policy is shifted from the ITRs to the mapping
   system.  The Map-Servers can also decide for a given ITR, if it uses
   a different set of replication targets per (S,G) entry for which the
   ITR is replicating for.

   The procedure for the LISP-RE RTRs to make themselves available for
   replication can occur before or after any receivers join an (S,G)
   entry or any sources send for a particular (S,G) entry.  Therefore,
   newly configured RTR state will be used to create new (S,G) state and
   inherited into existing (S,G) state.  A set of RTRs can register
   themselves to the mapping system or a third-party can do so on their
   behalf.  When RTR registration occurs, it is done with an (S-prefix,
   G-prefix) entry so it can advertise its replication services for a
   wide-range of source/group combinations.

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   When a Map-Server receives (S,G) registrations from ETRs and
   (S-prefix, G-prefix) registrations from RTRs, it has the option of
   merging the RTR RLOC-records for each (S,G) that is more-specific for
   the (S-prefix, G-prefix) entry or keep them separate.  When merging,
   a Map-Server is ready to return a 'complete-format' Map-Reply.  When
   keeping the entries separate, the Map-Server can decide what to
   include in a Map-Reply when a Map-Request is received.  It can
   include a combination of RLOC-records from each entry or decide to
   use one or the other depending on policy configured.

                      +---+                 +----+
  Src-1 --------------|ITR|                 |ETR1|----------------- Rcv-1
                      +---+                 +----+
                          \                 /
           Source-site-1   \               /    Receiver-site-1
                            \             /
                             \           /
                  +----+      \         /     +----+
                  |RTR1|       \       /      |RTR2|     Level-0
                  +----+        \     /       +----+
                        \  <^^^^^^^^^^^^^^>  /
                         \ <              > /
                           < Core-Network >
                           <              >
                           /     /   \    \
                          /     /     \    \
                  +----+ /     /       \    \ +----+
                  |RTR3|      /         \     |RTR4|     Level-1
                  +----+     /           \    +----+
                            /             \
                           /               \
                      +----+                +----+
  Rcv-2 --------------|ETR2|                |ETR3|----------------- Rcv-3
                      +----+                +----+

             Receiver-site-2                   Receiver-site-3

                     Figure 2: LISP-RE Reference Model

   Here is a specific example, illustrated in Figure 2, of (S,G) and
   (S-prefix, G-prefix) mapping database entries when a source S is
   behind an ITR and there are receiver sites joined to (S,G) via ETR1,
   ETR2, and ETR3.  And there exists a LISP-RE hierarchy of RTR1 and
   RTR2 at level-0 and RTR3 and RTR4 at level-1:

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       EID-record: (S,G)
           RLOC-record: RLE: (ETR1, ETR2, ETR3), p1
       EID-record: (S-prefix, G-prefix)
           RLOC-record: RLE: (RTR1(L0), RTR2(L0), RTR3(L1), RTR4(L1)), p1

   The above entries are in the form of how they were registered and
   stored in a Map-Server.  When a Map-Server uses 'complete-format', a
   Map-Reply it originates has the mapping record encoded as:

          EID-record: (S,G)
              RLOC-record: RLE: (RTR1(L0), RTR3(L1)), p1
              RLOC-record: RLE: (ETR1, ETR2, ETR3), p1

   The above Map-Reply allows the ITR to decide if it replicates to the
   ETRs or if it should replicate only to level-0 RTR1.  This decision
   is left to the ITR since both RLOC-records have priority 1.  If the
   Map-Server wanted to force the ITR to replicate to RTR1, it would set
   the ETRs RLOC-record to priority greater than 1.

   When a Map_server uses "filtered-format', a Map-Reply it originates
   has the mapping record encoded as:

          EID-record: (S,G)
              RLOC-record: RLE: (RTR1(L0), RTR3(L1)), p1

   An (S,G) entry can contain alternate RTRs.  So rather than
   replicating to multiple RTRs, one of a RTR set may be used based on
   the RTR reachability status.  An ITR can test reachability status to
   any layer-0 RTR using RLOC-probing so it can choose one RTR from a
   set to replicate to.  When this is done the RTRs are encoded in
   different RLOC-records versus together in one RLE RLOC-record.  This
   moves the replication load off the ITRs at the source site to the
   RTRs inside the network infrastructure.  This mechanism can also be
   used by level-n RTRs to level-n+1 RTRs.

   The following mapping would be encoded in a Map-Reply sent by a Map-
   Server and stored in the ITR.  The ITR would use RTR1 until it went
   unreachable and then switch to use RTR2:

          EID-record: (S,G)
              RLOC-record: RTR1, p1
              RLOC-record: RTR2, p2

9.  Security Considerations

   [I-D.ietf-lisp-sec] defines a set of security mechanisms that provide
   origin authentication, integrity and anti-replay protection to LISP's
   EID-to-RLOC mapping data conveyed via mapping lookup process.  LISP-

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   SEC also enables verification of authorization on EID-prefix claims
   in Map-Reply messages.

   Additional security mechanisms to protect the LISP Map-Register
   messages are defined in [RFC6833].

   The security of the Mapping System Infrastructure depends on the
   particular mapping database used.  The [I-D.ietf-lisp-ddt]
   specification, as an example, defines a public-key based mechanism
   that provides origin authentication and integrity protection to the
   LISP DDT protocol.

   Map-Replies received by the source-ITR can be signed (by the Map-
   Server) so the ITR knows the replication-list is from a legit source.

   Data-plane encryption can be used when doing unicast rep-
   encapsulation as described in [RFC8061].  For further study we will
   look how to do multicast rep-encapsulation.

10.  IANA Considerations

   This document has no IANA implications

11.  Acknowledgements

   The authors want to thank Greg Shepherd, Joel Halpern and Sharon
   Barkai for their insightful contribution to shaping the ideas in this
   document.  Thanks also goes to Jimmy Kyriannis, Paul Vinciguerra,
   Florin Coras, and Yan Filyurin for testing an implementation of this

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC3618]  Fenner, B., Ed. and D. Meyer, Ed., "Multicast Source
              Discovery Protocol (MSDP)", RFC 3618,
              DOI 10.17487/RFC3618, October 2003,

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   [RFC4601]  Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
              "Protocol Independent Multicast - Sparse Mode (PIM-SM):
              Protocol Specification (Revised)", RFC 4601,
              DOI 10.17487/RFC4601, August 2006,

   [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
              IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,

12.2.  Informative References

              Coras, F., Cabellos-Aparicio, A., Domingo-Pascual, J.,
              Maino, F., and D. Farinacci, "LISP Replication
              Engineering", draft-coras-lisp-re-08 (work in progress),
              November 2015.

              Farinacci, D. and M. Napierala, "LISP Control-Plane
              Multicast Signaling", draft-farinacci-lisp-mr-signaling-06
              (work in progress), February 2015.

              Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A.
              Smirnov, "LISP Delegated Database Tree", draft-ietf-lisp-
              ddt-09 (work in progress), January 2017.

              Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D.
              Saucez, "LISP-Security (LISP-SEC)", draft-ietf-lisp-sec-12
              (work in progress), November 2016.

              Portoles-Comeras, M., Ashtaputre, V., Moreno, V., Maino,
              F., and D. Farinacci, "LISP L2/L3 EID Mobility Using a
              Unified Control Plane", draft-portoles-lisp-eid-
              mobility-02 (work in progress), April 2017.

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              DOI 10.17487/RFC6830, January 2013,

   [RFC6831]  Farinacci, D., Meyer, D., Zwiebel, J., and S. Venaas, "The
              Locator/ID Separation Protocol (LISP) for Multicast
              Environments", RFC 6831, DOI 10.17487/RFC6831, January
              2013, <http://www.rfc-editor.org/info/rfc6831>.

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   [RFC6833]  Fuller, V. and D. Farinacci, "Locator/ID Separation
              Protocol (LISP) Map-Server Interface", RFC 6833,
              DOI 10.17487/RFC6833, January 2013,

   [RFC8060]  Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
              Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060,
              February 2017, <http://www.rfc-editor.org/info/rfc8060>.

   [RFC8061]  Farinacci, D. and B. Weis, "Locator/ID Separation Protocol
              (LISP) Data-Plane Confidentiality", RFC 8061,
              DOI 10.17487/RFC8061, February 2017,

Appendix A.  Document Change Log

A.1.  Changes to draft-ietf-lisp-signal-free-multicast-04

   o  Posted May 2017.

   o  Make it clear that recieiver-ETRs need configuraiton information
      for what Map-Servers (S,G) entries are registered to.

   o  Make it clear this document indicates what RTR layered hierarchy
      to use and not if its the best hierarchy to use.

A.2.  Changes to draft-ietf-lisp-signal-free-multicast-03

   o  Posted April 2017.

   o  Add "Multi-Homing Considerations" section to describe the case
      where a source LISP site has multiple ITRs and the multicast
      distribution tree at the source site branches to more than one
      ITR.  And at receiver sites where there are multiple ETRs and
      multiple RLOCs per ETR.

A.3.  Changes to draft-ietf-lisp-signal-free-multicast-02

   o  Posted October 2016.

   o  Updated document expiration timer.

A.4.  Changes to draft-ietf-lisp-signal-free-multicast-01

   o  Posted April 2016.

   o  Add text to define RTRs and indicate how RTR level number is used
      for LISP-RE.

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   o  Draw figure 2 that shows a LISP-RE topology.

   o  Indicate that PIM-ASM or (*,G) trees can be supported in LISP
      Signal-Free Multicast.

A.5.  Changes to draft-ietf-lisp-signal-free-multicast-00

   o  Posted late December 2015.

   o  Converted draft-farinacci-lisp-signal-free-multicast-04 into LISP
      working group draft.

A.6.  Changes to draft-farinacci-lisp-signal-free-multicast-04

   o  Posted early December 2015.

   o  Update references and document timer.

A.7.  Changes to draft-farinacci-lisp-signal-free-multicast-03

   o  Posted June 2015.

   o  Update references and document timer.

A.8.  Changes to draft-farinacci-lisp-signal-free-multicast-02

   o  Posted December 2014.

   o  Added section about how LISP-RE can use the mechanisms from
      signal-free-multicast so we can avoid head-end replication and
      avoid signalling across a layered RE topology.

A.9.  Changes to draft-farinacci-lisp-signal-free-multicast-01

   o  Posted June 2014.

   o  Changes based on implementation experience of this draft.

A.10.  Changes to draft-farinacci-lisp-signal-free-multicast-00

   o  Posted initial draft February 2014.

Authors' Addresses

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   Victor Moreno
   Cisco Systems
   170 Tasman Drive
   San Jose, California  95134

   Email: vimoreno@cisco.com

   Dino Farinacci
   San Jose, CA  95120

   Email: farinacci@gmail.com

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