PIM Join Attributes for Locator/ID Separation Protocol (LISP) Environments
draft-ietf-pim-rfc8059-9798bis-00

Internet Engineering Task Force                              V. Govindan
Internet-Draft                                                 S. Venaas
Updates: 8059, 9798 (if approved)                                  Cisco
Intended status: Standards Track                          4 January 2026
Expires: 8 July 2026

     PIM Join Attributes for Locator/ID Separation Protocol (LISP)
                              Environments
                   draft-ietf-pim-rfc8059-9798bis-00

Abstract

   This document defines two PIM Join/Prune attributes that support the
   construction of multicast distribution trees where the root and
   receivers are located in different Locator/ID Separation Protocol
   (LISP) sites.  These attributes allow the receiver site to select
   between unicast and multicast underlying transport, to convey the
   RLOC (Routing Locator) address of the receiver ETR (Egress Tunnel
   Router) to the control plane of the root ITR (Ingress Tunnel Router)
   and to signal the underlay multicast group to the control plane of
   the root ITR.  This document updates RFC 8059 and RFC 9798.

Status of This Memo

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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  PIM Join/Prune Attributes . . . . . . . . . . . . . . . . . .   4
   3.  The Transport Attribute . . . . . . . . . . . . . . . . . . .   4
     3.1.  Transport Attribute Format  . . . . . . . . . . . . . . .   4
     3.2.  Using the Transport Attribute . . . . . . . . . . . . . .   5
   4.  Receiver ETR RLOC Attribute . . . . . . . . . . . . . . . . .   5
     4.1.  Using the Received ETR RLOC Attribute for Unicast
           Underlays . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Using the Received ETR RLOC Attribute for Multicast
           Underlays . . . . . . . . . . . . . . . . . . . . . . . .   6
       4.2.1.  Multicast Address Range constraints:  . . . . . . . .   6
     4.3.  Receiver RLOC Attribute format  . . . . . . . . . . . . .   7
     4.4.  Using the Receiver RLOC Attribute . . . . . . . . . . . .   8
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The construction of multicast distribution trees where the root and
   receivers are located in different LISP sites [RFC9300] is defined in
   [I-D.ietf-lisp-rfc6831bis].  Creation of (root-EID,G) state in the
   root site requires that unicast LISP-encapsulated Join/Prune messages
   be sent from an ETR on the receiver site to an ITR on the root site.
   The term "EID" is short for "Endpoint ID".  [RFC9300] specifies that
   (root-EID,G) data packets are to be LISP- encapsulated into (root-
   RLOC,G) multicast packets.  However, a wide deployment of multicast
   connectivity between LISP sites is unlikely to happen any time soon.
   In fact, some implementations are initially focusing on unicast
   transport with head-end replication between root and receiver sites.

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   The unicast LISP-encapsulated Join/Prune message specifies the (root-
   EID,G) state that needs to be established in the root site, but
   conveys nothing about the receiver's capability or desire to use
   multicast as the underlying transport.  This document specifies a
   Join/Prune attribute that allows the receiver ETR to select the
   desired transport.

   The term "transport" in this document is intentionally somewhat
   vague.  Currently, it is used just to indicate whether multicast or
   head-end replication is used; this means that the outer destination
   address is either a unicast or multicast address.  Future documents
   may specify how other types of delivery, encapsulation, or underlay
   are used.

   Knowledge of the receiver ETR's RLOC address is essential to the
   control plane of the root ITR.  The RLOC address determines the
   downstream destination for unicast head-end replication and
   identifies the receiver ETR that needs to be notified should the root
   ITR of the distribution tree move to another site.  The root ITR can
   change when the source EID is roaming to another LISP site.

   Service providers may implement unicast reverse path forwarding
   (uRPF) policies requiring that the outer source address of the LISP-
   encapsulated Join/Prune message be the address of the receiver ETR's
   core-facing interface used to physically transmit the message.
   However, due to policy and load-balancing considerations, the outer
   source address may not be the RLOC on which the receiver site wishes
   to receive a particular flow.  This document specifies a Join/Prune
   attribute that conveys the appropriate receiver ETR's RLOC address to
   the control plane of the root ITR.

   This document uses terminology defined in [RFC9300] and [RFC9301],
   such as EID, RLOC, ITR, and ETR.

   The construction of multicast distribution trees where the root and
   receivers are located in different LISP sites [RFC9300] is defined in
   [I-D.ietf-lisp-rfc6831bis].

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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2.  PIM Join/Prune Attributes

   PIM Join/Prune attributes are defined in [RFC5384] by introducing a
   new Encoded-Source type that, in addition to the Join/Prune source,
   can carry multiple Type-Length-Value (TLV) attributes.  These
   attributes apply to the individual Join/Prune sources on which they
   are stored.

   The attributes defined in this document conform to the format of the
   encoding type defined in [RFC5384].  The attributes would typically
   be the same for all the sources in the Join/Prune message.  Hence, we
   RECOMMEND using the hierarchical Join/Prune attribute scheme defined
   in [RFC7887].  This hierarchical system allows attributes to be
   conveyed in the Upstream Neighbor Address field, thus enabling the
   efficient application of a single attribute instance to all the
   sources in the Join/Prune message.

   LISP Tunnel Routers (xTRs) do not exchange PIM Hello Messages, and
   hence no Hello option is defined to negotiate support for these
   attributes.  Systems that support unicast head-end replication are
   assumed to support these attributes.

3.  The Transport Attribute

   It is essential that a mechanism be provided by which the desired
   transport can be conveyed by receiver sites.  Root sites with
   multicast connectivity will want to leverage multicast replication.
   However, not all receiver sites can be expected to have multicast
   connectivity.  It is thus desirable that root sites be prepared to
   support (root-EID,G) state with a mixture of multicast and unicast
   output state.  This document specifies a Join/Prune attribute that
   allows the receiver to select the desired underlying transport.

3.1.  Transport Attribute Format

          0                   1                   2
          0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |F|E|  Type = 5 | Length = 1    |  Transport    |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                  Figure 1

   *  F-bit: The Transitive bit.  Specifies whether the attribute is
      transitive or non-transitive.  MUST be set to zero.  This
      attribute is ALWAYS non-transitive.

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   *  End-of-Attributes bit.  Specifies whether this attribute is the
      last.  Set to zero if there are more attributes.  Set to 1 if this
      is the last attribute.
   *  The Transport Attribute type is TBD.
   *  Length: The length of the Transport Attribute value.  MUST be set
      to 1.
   *  Transport: The type of transport being requested.  Set to 0 for
      multicast.  Set to 1 for unicast.  The values from 2 to 255 may be
      assigned in the future.

3.2.  Using the Transport Attribute

   Hierarchical Join/Prune attribute instances [RFC7887] SHOULD be used
   when the same Transport Attribute is to be applied to all the sources
   within the Join/Prune message or all the sources within a group set.
   The root ITR MUST accept Transport Attributes in the Upstream
   Neighbor Encoded-Unicast address, Encoded-Group addresses, and
   Encoded-Source addresses.

   There MUST NOT be more than one Transport Attribute within the same
   encoded address.  If an encoded address has more than one instance of
   the attribute, the root ITR MUST discard all affected Join/Prune
   sources.  The root ITR MUST also discard all affected Join/Prune
   sources if the Transport Attribute value is unknown.

4.  Receiver ETR RLOC Attribute

4.1.  Using the Received ETR RLOC Attribute for Unicast Underlays

   When a receiver ETR requests unicast head-end replication for a given
   (root-EID,G) entry, the PIM control plane of the root ITR must
   maintain an outgoing interface list ("oif-list") entry for the
   receiver ETR and its corresponding RLOC address.  This allows the
   root ITR to perform unicast LISP-encapsulation of multicast data
   packets to each and every receiver ETR that has requested unicast
   head-end replication.

   The PIM control plane of the root ITR could potentially determine the
   RLOC address of the receiver ETR from the outer source address field
   of the LISP-encapsulated Join/Prune message.  However, receiver ETRs
   are subject to uRPF checks by the network providers on each core-
   facing interface.  The outer source address must therefore be the
   RLOC of the core-facing interface used to physically transmit the
   LISP-encapsulated Join/Prune message.  Due to policy and load-
   balancing considerations, that may not be the RLOC on which the
   receiver site wishes to receive a particular flow.  This document
   specifies a Join/Prune attribute that conveys the appropriate
   receiver RLOC address to the PIM control plane of the root ITR.

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   To support root-EID mobility, receiver ETRs must also be tracked by
   the LISP control plane of the root ITR, regardless of the underlying
   transport.  When the root-EID moves to a new root ITR in a different
   LISP site, the receiver ETRs do not know the root-EID has moved and
   therefore do not know the RLOC of the new root ITR.  This is true for
   both unicast and multicast transport modes.  The new root ITR does
   not have any receiver ETR state.  Therefore, it is the responsibility
   of the old root ITR to inform the receiver ETRs that the root-EID has
   moved.  When the old root ITR detects that the root-EID has moved, it
   sends a LISP Solicit-Map-Request (SMR) message to each receiver ETR.
   The receiver ETRs do a mapping database lookup to retrieve the RLOC
   of the new root ITR.  The old root ITR detects that the root-EID has
   moved when it receives a Map-Notify from the Map-Server.  The
   transmission of the Map-Notify is triggered when the new root ITR
   registers the root-EID [EID-MOBILITY].  When a receiver ETR
   determines that the root ITR has changed, it will send a LISP-
   encapsulated PIM prune message to the old root xTR and a LISP-
   encapsulated PIM join message to the new root xTR.

4.2.  Using the Received ETR RLOC Attribute for Multicast Underlays

   When LISP based Multicast trees are constructed using IP Multicast in
   the underlay, the mapping between the overlay group address and the
   underlay group address becomes a crucial engineering decision:

   Three distinct types of overlay to underlay group mappings are
   possible:

   Many to one mapping:
     Many (root-EID, G) flows originating from an RLOC can be mapped to
     a single underlay multicast (root-RLOC, G-u) flow.

   One to many mapping:
     Conversely a single same overlay flow can be mapped to two or more
     flows, e.g., (root-RLOC, G-u1) and (root-RLOC, G-u2) to cater to
     the requirements of downstream xTR nodes.

   One to one mapping:
     Every (root-EID, G) flow is mapped to a unique (root-RLOC, G-u)
     flow.

4.2.1.  Multicast Address Range constraints:

   Under certain conditions, different subsets of xTRs subscribing to
   the same overlay multicast stream may be constrained to use distinct
   underlay multicast mapping ranges.

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   This introduces a trade-off between replication overhead and the
   flexibility of address range assignment, which may be necessary in
   specific use-cases like Proxy Tunnel Routers or when using nodes with
   limited hardware resources as explained below:

   Inter-site Proxy Tunnel Routers (PxTR):
     When multiple LISP sites are interconnected through a LISP-based
     transit, the site border node (PxTR) connects the site-facing
     interfaces with the external LISP core.  In such cases, different
     ranges of multicast group addresses may be used for constructing
     (S-RLOC, G) trees within the LISP site and in the external LISP
     core.  This distinction is desirable for various operational
     reasons.

   Hardware resource restrictions:
     Platform limitations may necessitate engineering decisions to
     restrict multicast address ranges in the underlay due to hardware
     resource constraints.

4.3.  Receiver RLOC Attribute format

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |F|E|  Type = 6 |    Length     |  Addr Family  |  Receiver RLOC
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-...

                                Figure 2

   *  F bit: The Transitive bit.  Specifies whether this attribute is
      transitive or non-transitive.  MUST be set to zero.  This
      attribute is ALWAYS non-transitive.
   *  E bit: End-of-Attributes bit.  Specifies whether this attribute is
      the last.  Set to zero if there are more attributes.  Set to 1 if
      this is the last attribute.
   *  Type: The Receiver RLOC Attribute type is TBD[suggested: 6].
   *  Length: The length in octets of the attribute value.  MUST be set
      to the length in octets of the receiver RLOC address plus 1 octet
      to account for the Address Family field.
   *  Addr Family: The PIM Address Family of the receiver RLOC as
      defined in [RFC7761].

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   *  Receiver RLOC: The RLOC address on which the receiver ETR wishes
      to receive the encapsulated flow.  A unicast IP Receiver RLOC
      address is used for unicast-encapsulated flows.  Alternately, a
      multicast IP Receiver RLOC address is used for for multicast-
      encapsulated flows.  A multicast IP address MUST be used only when
      the underlay network of the LISP core supports IP Multicast
      transport.

   When the ITR needs to track the list of ETRs from which the PIM joins
   are received, the ITR MUST use the source IP address field of the
   incoming PIM Join/Prune message.  The source IP address of the PIM
   Join/Prune MUST be an ETR RLOC IP address.

4.4.  Using the Receiver RLOC Attribute

   Hierarchical Join/Prune attribute instances [RFC7887] SHOULD be used
   when the same Receiver RLOC Attribute is to be applied to all the
   sources within the message or all the sources within a group set.
   The root ITR MUST accept Transport Attributes in the Upstream
   Neighbor Encoded-Unicast address, Encoded-Group addresses, and
   Encoded-Source addresses.

   There MUST NOT be more than one Receiver RLOC Attribute within the
   same encoded address.  If an encoded address has more than one
   instance of the attribute, the root ITR MUST discard all affected
   Join/Prune sources.  The root ITR MUST also discard all affected
   Join/Prune sources if the address family is unknown or the address
   length is incorrect for the specified address family.

   When the ETR determines to use the multicast underlay:

   *  It chooses an underlay multicast group that it can join.  This is
      a matter of local decision, beyond the scope of this document.

   *  It identifies the upstream LISP site where the underlay multicast
      tree needs to be rooted.

   *  It constructs the PIM Join/Prune message as specified in RFC 8059
      [RFC8059] and RFC 9798 [RFC9798].  Only the Receiver RLOC
      attribute is encoded as above.

   When the ITR receives a PIM Join/Prune message:

   *  It allocates a new entry in the OutgoingInterfaceList
      [I-D.ietf-lisp-rfc6831bis] for every unique underlay multicast
      mapping.

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   *  The ITR MAY apply local policy to perform any kind of rate-
      limiting on the number of copies it needs to make in the underlay.
      Such actions are beyond the scope of this document.

5.  Acknowledgements

   TBD

6.  IANA Considerations

   Following the guidelines of [RFC8126], IANA is asked to assign values
   as follows:

   Two new PIM Join/Prune attribute types have been requested: value 5
   for the Transport Attribute and value 6 for the Receiver RLOC
   Attribute[RFC8059] and [RFC9798].

   The "PIM Join/Prune Transport Types" registry has been created for
   the Join/Prune Transport attribute.  The registration policy is IETF
   Review [RFC5226], and the values are in the range 0-255.  This
   document requests value 0 for multicast and value 1 for unicast
   [RFC8059] and [RFC9798].

7.  Security Considerations

   Security of Join/Prune attributes is only guaranteed by the security
   of the PIM packet.  The attributes specified herein do not enhance or
   diminish the privacy or authenticity of a Join/Prune message.  A site
   that legitimately or maliciously sends and delivers a Join/Prune
   message to another site will equally be able to append these and any
   other attributes it wishes.  See [RFC5384] for general security
   considerations for Join/Prune attributes.

   An attack vector arises where an attacker sends numerous PIM Join
   messages with different group addresses.  This could interfere with
   legitimate multicast traffic if the group addresses overlap.
   Additionally, resource exhaustion may occur if replication is
   requested for a large number of groups, potentially resulting in
   significant resource consumption.

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   To mitigate these risks, PIM authentication mechanisms RFC 5796
   [RFC5796] could be employed to validate join requests.  Furthermore,
   implementations may consider explicit tracking mechanisms to manage
   joins more effectively.  Configurable controls could be introduced,
   allowing for a maximum permissible number of groups for each ETR RLOC
   used as the source of overlay joins.  These controls would limit the
   impact of such attacks and ensure that resource allocation is managed
   appropriately.

8.  Contributors

   Jesus Arango
   TBD
   Email: tbd@tbd.com

   Isidor Kouvelas
   Arista
   Email: kouvelas@arista.com

   Dino Farinacci
   lispers.net
   Email: farinacci@gmail.com

9.  Normative References

   [I-D.ietf-lisp-rfc6831bis]
              Farinacci, D., Meyer, D., Zwiebel, J., Venaas, S., and V.
              P. Govindan, "The Locator/ID Separation Protocol (LISP)
              for Multicast Environments", Work in Progress, Internet-
              Draft, draft-ietf-lisp-rfc6831bis-05, 18 November 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-lisp-
              rfc6831bis-05>.

   [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>.

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   [RFC5384]  Boers, A., Wijnands, I., and E. Rosen, "The Protocol
              Independent Multicast (PIM) Join Attribute Format",
              RFC 5384, DOI 10.17487/RFC5384, November 2008,
              <https://www.rfc-editor.org/info/rfc5384>.

   [RFC5796]  Atwood, W., Islam, S., and M. Siami, "Authentication and
              Confidentiality in Protocol Independent Multicast Sparse
              Mode (PIM-SM) Link-Local Messages", RFC 5796,
              DOI 10.17487/RFC5796, March 2010,
              <https://www.rfc-editor.org/info/rfc5796>.

   [RFC7761]  Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
              Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
              Multicast - Sparse Mode (PIM-SM): Protocol Specification
              (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
              2016, <https://www.rfc-editor.org/info/rfc7761>.

   [RFC7887]  Venaas, S., Arango, J., and I. Kouvelas, "Hierarchical
              Join/Prune Attributes", RFC 7887, DOI 10.17487/RFC7887,
              June 2016, <https://www.rfc-editor.org/info/rfc7887>.

   [RFC8059]  Arango, J., Venaas, S., Kouvelas, I., and D. Farinacci,
              "PIM Join Attributes for Locator/ID Separation Protocol
              (LISP) Environments", RFC 8059, DOI 10.17487/RFC8059,
              January 2017, <https://www.rfc-editor.org/info/rfc8059>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [RFC9300]  Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
              Cabellos, Ed., "The Locator/ID Separation Protocol
              (LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,
              <https://www.rfc-editor.org/info/rfc9300>.

   [RFC9301]  Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
              Ed., "Locator/ID Separation Protocol (LISP) Control
              Plane", RFC 9301, DOI 10.17487/RFC9301, October 2022,
              <https://www.rfc-editor.org/info/rfc9301>.

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   [RFC9798]  Govindan, V. and S. Venaas, "PIM Join/Prune Attributes for
              Locator/ID Separation Protocol (LISP) Environments Using
              Underlay Multicast", RFC 9798, DOI 10.17487/RFC9798, June
              2025, <https://www.rfc-editor.org/info/rfc9798>.

Authors' Addresses

   Vengada Prasad Govindan
   Cisco
   Email: venggovi@cisco.com

   Stig Venaas
   Cisco
   Email: svenaas@cisco.com

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