



Internet Engineering Task Force (IETF)                         V. Kamath
Request for Comments: 9465                                        VMware
Category: Standards Track                   R. Chokkanathapuram Sundaram
ISSN: 2070-1721                                      Cisco Systems, Inc.
                                                              R. Banthia
                                                                  Apstra
                                                                A. Gopal
                                                     Cisco Systems, Inc.
                                                          September 2023


                       PIM Null-Register Packing

Abstract

   In PIM Sparse Mode (PIM-SM) networks, PIM Null-Register messages are
   sent by the Designated Router (DR) to the Rendezvous Point (RP) to
   signal the presence of multicast sources in the network.  There are
   periodic PIM Null-Registers sent from the DR to the RP to keep the
   state alive at the RP as long as the source is active.  The PIM Null-
   Register message carries information about a single multicast source
   and group.

   This document defines a standard to send information about multiple
   multicast sources and groups in a single PIM message.  This document
   refers to the new messages as the "PIM Packed Null-Register message"
   and "PIM Packed Register-Stop message".

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9465.

Copyright Notice

   Copyright (c) 2023 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
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   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must
   include Revised BSD License text as described in Section 4.e of the
   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
     1.1.  Conventions Used in This Document
     1.2.  Terminology
   2.  Packing Capability
   3.  PIM Packed Null-Register Message Format
   4.  PIM Packed Register-Stop Message Format
   5.  Protocol Operation
   6.  Operational Considerations
     6.1.  PIM Anycast RP Considerations
     6.2.  Interoperability between Different Versions
     6.3.  Disabling PIM Packed Message Support at RP and/or DR
   7.  Fragmentation Considerations
   8.  Security Considerations
   9.  IANA Considerations
   10. Normative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   The DR periodically sends PIM Null-Registers to keep the state of
   existing multicast sources active on the RP.  As the number of
   multicast sources increases, the number of PIM Null-Register messages
   that are sent also increases.  This results in more PIM packet
   processing at the RP and the DR.

   This document specifies a method to efficiently pack the content of
   multiple PIM Null-Register and Register-Stop messages [RFC7761] into
   a single message.

   The document also discusses interoperability between PIM routers that
   support PIM Packed Null-Registers and PIM Packed Register-Stops and
   PIM routers that do not.

1.1.  Conventions Used in This Document

   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.

1.2.  Terminology

   RP:  Rendezvous Point

   DR:  Designated Router

   MSDP:  Multicast Source Discovery Protocol

   PIM-SM:  PIM Sparse Mode

2.  Packing Capability

   The RP indicates its ability to receive PIM Packed Null-Register
   messages (Section 3) and send PIM Packed Register-Stop messages
   (Section 4) with a Packing Capability bit (P-bit) in the PIM
   Register-Stop message.  The P-bit is allocated in Section 9.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |PIM Ver| Type  |7 6 5 4 3 2 1|P|           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Group Address (Encoded-Group format)              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Source Address (Encoded-Unicast format)            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     Figure 1: PIM Register-Stop Message with Packing Capability Option

   The Group Address and Source Address fields in the PIM Register-Stop
   message are defined in Section 4.9.4 of [RFC7761].  The common header
   is defined in [RFC9436].

   Packing Capability bit (P-bit; flag bit 0):  When set, it indicates
      the ability of the RP to receive PIM Packed Null-Register messages
      and send PIM Packed Register-Stop messages.

3.  PIM Packed Null-Register Message 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |PIM Ver| Type  |Subtype|  FB   |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Group Address[1]   (Encoded-Group format)                 |
   |     Source Address[1]  (Encoded-Unicast format)               |
   .                                                               .
   .                                                               .
   .                                                               .
   .                                                               .
   .     Group Address[N]                                          .
   |     Source Address[N]                                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 2: PIM Packed Null-Register Message Format

   The Group Address and Source Address fields in the PIM Packed Null-
   Register message are defined in Section 4.9.4 of [RFC7761].  The
   common header is defined in [RFC9436].

   Type, Subtype:  PIM Packed Null-Register (13.0).

   N:  The total number of records; a record consists of a Group Address
       and Source Address pair.

   After parsing the PIM common header, individual records are then
   parsed one by one until the end of the PIM Packed Null-Register
   message.  This length is inferred from the IP layer.

   Sending or receiving a PIM Packed Null-Register message has the
   equivalent effect of sending or receiving an individual Null-Register
   message for each record represented in the PIM Packed Null-Register
   message.

4.  PIM Packed Register-Stop Message 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |PIM Ver| Type  |Subtype|  FB   |           Checksum            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Group Address[1]  (Encoded-Group format)                  |
   |     Source Address[1]  (Encoded-Unicast format)               |
   .                                                               .
   .                                                               .
   .                                                               .
   .                                                               .
   .     Group Address[N]                                          .
   |     Source Address[N]                                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 3: PIM Packed Register-Stop Message Format

   The Group Address and Source Address fields in the PIM Packed
   Register-Stop message are defined in Section 4.9.4 of [RFC7761].  The
   common header is defined in [RFC9436].

   Type, Subtype:  PIM Packed Register-Stop (13.1).

   N:  The total number of records; a record consists of a Group Address
       and Source Address pair.

   After parsing the PIM common header, individual records are then
   parsed one by one until the end of the PIM Packed Register-Stop
   message.  This length is inferred from the IP layer.

   Sending or receiving a PIM Packed Register-Stop message has the
   equivalent effect of sending or receiving an individual Null-Register
   message for each record represented in the PIM Packed Register-Stop.

5.  Protocol Operation

   As specified in [RFC7761], the DR sends PIM Register messages towards
   the RP when a new source is detected.

   When this feature is enabled/configured, an RP supporting this
   specification MUST set the P-bit (flag bit 0) in all Register-Stop
   messages.

   When a Register-Stop message with the P-bit set is received, the DR
   SHOULD send PIM Packed Null-Register messages (Section 3) to the RP
   instead of multiple Register messages with the N-bit set [RFC7761].
   The DR MAY use a mixture of PIM Packed Null-Register messages and
   Register messages.  The decision is up to the implementation and out
   of the scope of this document.  However, it is RECOMMENDED to stick
   to the PIM Packed Null-Register and PIM Packed Register-Stop formats
   as long as the RP and DR have the feature enabled.

   After receiving a PIM Packed Null-Register message, the RP SHOULD
   start sending PIM Packed Register-Stop messages (Section 4) to the
   corresponding DR instead of individual Register-Stop messages.  The
   RP MAY use a mixture of PIM Packed Register-Stop messages and
   individual Register-Stop messages.  The decision is up to the
   implementation and out of the scope of this document.  However, it is
   RECOMMENDED to stick to the PIM Packed Null-Register and PIM Packed
   Register-Stop formats as long as the RP and DR have the feature
   enabled.

6.  Operational Considerations

6.1.  PIM Anycast RP Considerations

   The PIM Packed Null-Register packet format should be enabled only if
   it is supported by all the routers in the Anycast-RP set [RFC4610].
   This consideration applies to PIM Anycast RP with Multicast Source
   Discovery Protocol (MSDP) [RFC3446] as well.

6.2.  Interoperability between Different Versions

   A router (DR) can decide to use the PIM Packed Null-Register message
   format based on the Packing Capability received from the RP as part
   of the PIM Register-Stop.  This ensures compatibility with routers
   that do not support processing of the new packet format.  The Packing
   Capability information MUST be indicated by the RP via the PIM
   Register-Stop message sent to the DR.  Thus, a DR will switch to the
   new packet format only when it learns that the RP is capable of
   handling the PIM Packed Null-Register messages.

   Conversely, a DR that does not support the packed format can continue
   generating the PIM Null-Register as defined in Section 4.4 of
   [RFC7761].

6.3.  Disabling PIM Packed Message Support at RP and/or DR

   Consider a PIM RP router that supports PIM Packed Null-Registers and
   PIM Packed Register-Stops.  In scenarios where this router no longer
   supports this feature, for example, in case of a software downgrade,
   it will not send a PIM Register-Stop message to the DR in response to
   a PIM Packed Null-Register message.

   When the DR switches to Data Registers from Null-Registers, it MUST
   start a Packed_Register_Probe_Time timer.  If no PIM Packed Register-
   Stop or Register-Stop with the P-bit set is received within
   Packed_Register_Probe_Time seconds, the DR can decide that the RP no
   longer supports PIM Packed Null-Registers.  The
   Packed_Register_Probe_Time timer is configurable; its default value
   is 60 seconds.

   When Packed_Register_Probe_Time expires, the DR MAY also send an
   unpacked PIM Null-Register and check the PIM Register-Stop to see if
   the P-bit is set or not.  If it is not set, then the DR will continue
   sending unpacked PIM Null-Register messages.

   In case the network manager disables the Packing Capability at the RP
   (or in other words, disables the feature from the RP), the router
   MUST NOT advertise the Packing Capability.  However, an
   implementation MAY choose to still parse any packed registers if they
   are received.  This may be particularly useful in the transitional
   period after the network manager disables it.

7.  Fragmentation Considerations

   As explained in Section 4.4.1 of [RFC7761], the DR may perform Path
   MTU Discovery to the RP before sending PIM Packed Null-Register
   messages.  Similarly, the RP may perform Path MTU Discovery to the DR
   before sending PIM Packed Register-Stop messages.  In both cases, the
   number of records in a message should be limited such that it can fit
   within the Path MTU.

8.  Security Considerations

   The Security Considerations in [RFC7761] apply to this document.  In
   particular, the effect of forging a PIM Packed Null-Register or
   Register-Stop message would be amplified to all the records included
   instead of just one.

   By forging a PIM Register-Stop message and setting the P-bit, an
   attacker can trigger the use of PIM Packed Null-Register messages by
   a DR, thus creating unnecessary churn in the network.

9.  IANA Considerations

   IANA has assigned a Packing Capability bit (0) in the PIM Register-
   Stop common header in the "PIM Message Types" registry.

   IANA has assigned a PIM message type (13.0) for PIM Packed Null-
   Register in the "PIM Message Types" registry.  Flag bits 0-3 for this
   message type are "Unassigned".

   IANA has assigned a PIM message type (13.1) for PIM Packed Register-
   Stop in the "PIM Message Types" registry.  The flag bits 0-3 for this
   message type are "Unassigned".

10.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3446]  Kim, D., Meyer, D., Kilmer, H., and D. Farinacci, "Anycast
              Rendevous Point (RP) mechanism using Protocol Independent
              Multicast (PIM) and Multicast Source Discovery Protocol
              (MSDP)", RFC 3446, DOI 10.17487/RFC3446, January 2003,
              <https://www.rfc-editor.org/info/rfc3446>.

   [RFC4610]  Farinacci, D. and Y. Cai, "Anycast-RP Using Protocol
              Independent Multicast (PIM)", RFC 4610,
              DOI 10.17487/RFC4610, August 2006,
              <https://www.rfc-editor.org/info/rfc4610>.

   [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>.

   [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>.

   [RFC9436]  Venaas, S. and A. Retana, "PIM Message Type Space
              Extension and Reserved Bits", RFC 9436,
              DOI 10.17487/RFC9436, August 2023,
              <https://www.rfc-editor.org/info/rfc9436>.

Acknowledgments

   The authors would like to thank Stig Venaas, Alvaro Retana, Anish
   Peter, Zheng Zhang, and Umesh Dudani for their helpful comments on
   the document.

Authors' Addresses

   Vikas Ramesh Kamath
   VMware
   3401 Hillview Ave
   Palo Alto, CA 94304
   United States of America
   Email: vkamath@vmware.com


   Ramakrishnan Chokkanathapuram Sundaram
   Cisco Systems, Inc.
   Tasman Drive
   San Jose, CA 95134
   United States of America
   Email: ramaksun@cisco.com


   Raunak Banthia
   Apstra
   Suite 200
   333 Middlefield Rd
   Menlo Park, CA 94025
   United States of America
   Email: rbanthia@apstra.com


   Ananya Gopal
   Cisco Systems, Inc.
   Tasman Drive
   San Jose, CA 95134
   United States of America
   Email: ananygop@cisco.com
