PIM Null-Register packing
draft-ietf-pim-null-register-packing-11

Network Working Group                                          V. Kamath
Internet-Draft                                                    VMware
Intended status: Standards Track            R. Chokkanathapuram Sundaram
Expires: 11 May 2022                                 Cisco Systems, Inc.
                                                              R. Banthia
                                                                  Apstra
                                                                A. Gopal
                                                     Cisco Systems, Inc.
                                                         7 November 2021

                       PIM Null-Register packing
                draft-ietf-pim-null-register-packing-11

Abstract

   In 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 multiple Multicast source
   and group information in a single PIM Packed Null-Register message.
   We will refer to the new packed formats as the PIM Packed Null-
   Register format and PIM Packed Register-Stop format throughout the
   document.  This document also discusses interoperability between the
   PIM routers which do not understand the PIM Packed Null-Register
   format and routers which do understand it.

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
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   This Internet-Draft will expire on 11 May 2022.

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Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions used in this document . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Packed Null-Register Capability . . . . . . . . . . . . . . .   3
   3.  PIM Packed Null-Register message format . . . . . . . . . . .   4
   4.  PIM Packed Register-Stop message format . . . . . . . . . . .   5
   5.  Protocol operation  . . . . . . . . . . . . . . . . . . . . .   6
   6.  Operational Considerations  . . . . . . . . . . . . . . . . .   7
   7.  PIM Anycast RP Considerations . . . . . . . . . . . . . . . .   7
   8.  PIM RP router version downgrade . . . . . . . . . . . . . . .   7
   9.  Fragmentation Considerations  . . . . . . . . . . . . . . . .   7
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   8
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     13.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     13.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   PIM Null-Registers are sent by the DR periodically for Multicast
   streams to keep the states active on the RP, as long as the multicast
   source is alive.  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.

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   The control plane policing (COPP), monitors the packets that are
   processed by the control plane.  The high rate at which Null-
   Registers are received at the RP can lead to COPP drops of Multicast
   PIM Null-Register messages.  This draft proposes a method to
   efficiently pack multiple PIM Null-Registers [RFC7761] (Section 4.4)
   and Register-Stops [RFC7761](Section 3.2) into a single message as
   these packets anyway do not contain encapsulated data.

   The draft also discusses interoperability with PIM routers that do
   not understand the new packet format.

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

2.  Packed Null-Register Capability

   A router (DR) can decide to pack multiple Null-Register messages
   based on the 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 format.  The capability information can
   be indicated by the RP via the PIM Register-Stop message sent to the
   DR.  Thus a DR will switch to the new 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 [RFC7761]
   (Section 4.4).  To exchange the capability information in the
   Register-Stop message, the "Reserved" field can be used to indicate
   this capability in those Register-Stop messages.  One bit of the
   Reserved field is used to indicate the "packing" capability (P bit).
   The rest of the bits in the "Reserved" field will be retained for
   future use.

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       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  |P|  Reserved   |           Checksum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Group Address (Encoded-Group format)              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Source Address (Encoded-Unicast format)            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 1: PIM Register-Stop message with capability option

   PIM Version, Type, Checksum, Group Address, Source Address:

      Same as [RFC7761] (Section 4.9.4)

   P:

      Capability bit (flag bit 7) used to indicate support for the
      Packed Null-Register Capability

3.  PIM Packed Null-Register message format

   PIM Packed Null-Register message format includes a count to indicate
   the number of Null-Register records in the message.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Count       |              Reserved                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     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

   PIM Version, Reserved, Checksum:

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      Same as [RFC7761] (Section 4.9.3)

   Type, SubType:

      The new packed Null-Register Type and SubType values TBD.
      [RFC8736]

   Count:

      The number of packed Null-Register records.  A record consists of
      a Group Address and Source Address pair.

   Group Address, Source Address:

      Same as [RFC7761] (Section 4.9.4)

4.  PIM Packed Register-Stop message format

   The PIM Packed Register-Stop message includes a count to indicate the
   number of records that are present in the message.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     Count     |          Reserved                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     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

   PIM Version, Reserved, Checksum:

      Same as [RFC7761] (Section 4.9.4)

   Type:

      The new Register Stop Type and SubType values TBD

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   Count:

      The number of PIM packed Register-Stop records.  A record consists
      of a Group Address and Source Address pair.

   Group Address, Source Address:

      Same as [RFC7761] (Section 4.9.4)

5.  Protocol operation

   The following combinations exist -

   1.  DR and RP both support the PIM Packed Null-Register and PIM
       Packed Register-Stop formats:

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

       *  An RP supporting this specification MUST set the P-bit in the
          corresponding 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 RP, after receiving a PIM Packed Null-Register message
          SHOULD start sending PIM Packed Register-Stop messages
          (Section 4) to the corresponding DR instead of individual
          Register-Stop messages.

   2.  DR supports but RP does not support the PIM Packed Null-Register
       and PIM Packed Register-Stop formats:

       *  As specified in [RFC7761], DR sends PIM Null-Registers towards
          the RP.

       *  After receiving DR's PIM Null-Register message, RP sends a
          normal Register-Stop without any capability information.

       *  DR then sends PIM Null-Registers in the unpacked format
          [RFC7761].

   3.  RP supports but DR does not support the PIM Packed Null-Register
       and PIM Packed Register-Stop formats:

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       *  As specified in [RFC7761], DR sends the PIM Null-Register
          towards the RP.

       *  After receiving DR's PIM Null-Register message, RP sends a PIM
          Packed Register-Stop towards the DR that includes capability
          information.

       *  Since DR does not support the new format, it sends PIM Null-
          Registers in the unpacked format [RFC7761].

6.  Operational Considerations

   In case the network manager disables the packed capability at the RP,
   the router should not advertise the 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.  PIM Anycast RP Considerations

   The PIM Packed Null-Register format should be enabled only if it is
   supported by all PIM Anycast RP [RFC4610] members in the RP set for
   the RP address.  This consideration applies to PIM Anycast RP with
   MSDP [RFC3446] as well.

8.  PIM RP router version downgrade

   Consider a PIM RP router that supports PIM Packed Null-Registers and
   PIM Packed Register-Stops.  When this router downgrades to a software
   version which does not support PIM Packed Null-Registers and PIM
   Packed Register-Stops, the DR that sends the PIM Packed Null-Register
   message will not get a PIM Register-Stop message back from the RP.
   In such scenarios the DR can send an unpacked PIM Null-Register and
   check the PIM Register-Stop to see if the capability bit (P-bit) for
   PIM Packed Null-Register is set or not.  If it is not set then the DR
   will continue sending unpacked PIM Null-Register messages.

9.  Fragmentation Considerations

   When building a PIM Packed Null-Register message or PIM Packed
   Register-Stop message, a router should include as many records as
   possible based on the path MTU towards RP, if path MTU discovery is
   done.  Otherwise, the number of records should be limited by the MTU
   of the outgoing interface.

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10.  Security Considerations

   General Register messages security considerations from [RFC7761]
   apply.  As mentioned in [RFC7761], PIM Null-Register messages and
   Register-Stop messages are forwarded by intermediate routers to their
   destination using normal IP forwarding.  Without data origin
   authentication, an attacker who is located anywhere in the network
   may be able to forge a Null-Register or Register-Stop message.  We
   next consider the effect of a forgery of each of these messages.  By
   forging a Register message, an attacker can cause the RP to inject
   forged traffic onto the shared multicast tree.

   By forging a Register-Stop message, an attacker can prevent a
   legitimate DR from registering packets to the RP.  This can prevent
   local hosts on that LAN from sending multicast packets.  The above
   two PIM messages are not changed by intermediate routers and need
   only be examined by the intended receiver.  Thus, these messages can
   be authenticated end-to-end.  Attacks on Register and Register-Stop
   messages do not apply to a PIM-SSM-only implementation, as these
   messages are not used in PIM-SSM.

   There is another case where a spoofed Register-Stop can be sent to
   make it appear that is from the RP, and that the RP supports this new
   packed capability when it does not.  This can cause Null-Registers to
   be sent to an RP that doesnt support this packed format.  But
   standard methods to prevent spoofing should take care of this case.
   For example, uRPF can be used to filter out packets coming from the
   outside from addresses that belong to routers inside.

11.  IANA Considerations

      This document requires the assignment of Capability bit (P-bit),
      flag bit 7 in the PIM Register-Stop message.

      This document requires the assignment of 2 new PIM message types
      for the PIM Packed Null-Register and PIM Packed Register-Stop.

12.  Acknowledgments

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

13.  References

13.1.  Normative References

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   [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>.

   [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>.

   [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>.

   [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>.

   [RFC8736]  Venaas, S. and A. Retana, "PIM Message Type Space
              Extension and Reserved Bits", RFC 8736,
              DOI 10.17487/RFC8736, February 2020,
              <https://www.rfc-editor.org/info/rfc8736>.

13.2.  Informative References

   [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>.

Authors' Addresses

   Vikas Ramesh Kamath
   VMware
   3401 Hillview Ave
   Palo Alto,  CA 94304
   United States of America

   Email: vkamath@vmware.com

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   Ramakrishnan Chokkanathapuram Sundaram
   Cisco Systems, Inc.
   Tasman Drive
   San Jose,  CA 95134
   United States of America

   Email: ramaksun@cisco.com

   Raunak Banthia
   Apstra
   333 Middlefield Rd STE 200
   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

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