Network Working Group                                          V. Kamath
Internet-Draft                                                    VMware
Intended status: Standards Track            R. Chokkanathapuram Sundaram
Expires: September 23, 2021                          Cisco Systems, Inc.
                                                              R. Banthia
                                                                  Apstra
                                                                A. Gopal
                                                     Cisco Systems, Inc.
                                                          March 22, 2021


                       PIM Null-Register packing
                draft-ietf-pim-null-register-packing-08

Abstract

   In PIM-SM networks PIM 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 Null-Register message, in a
   packed format.  This document also discusses the interoperability
   between the PIM routers which do not understand the packed message
   format with multiple multicast source and group details.

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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   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 September 23, 2021.






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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/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   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  . . . . . . . . . . . . . .   4
   4.  PIM Packed Register-Stop message format . . . . . . . . . . .   5
   5.  Protocol operation  . . . . . . . . . . . . . . . . . . . . .   6
   6.  PIM Anycast RP considerations . . . . . . . . . . . . . . . .   7
   7.  PIM RP router version downgrade . . . . . . . . . . . . . . .   7
   8.  Fragmentation consideration . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   12. Normative References  . . . . . . . . . . . . . . . . . . . .   8
   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.

   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




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   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] 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 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 packed Null-Register messages.

   Conversely, a DR that does not support the new format can continue
   generating the PIM Null-Register the current way.  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

   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:

      Same as [RFC7761] (Section 4.9.3)



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   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

   Count:



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      The number of 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 format

       *  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 MAY send 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 Packed Null-Register message MAY
          start sending Packed Register-Stop messages (Section 4) to the
          corresponding DR instead of individual Register-Stop messages.

   2.  DR supports but RP does not support PIM Packed Null-Register
       format

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

       *  RP sends a normal Register-Stop without any capability
          information.

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

   3.  RP supports but DR doesn't support the new PIM Packed Null-
       Register format

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

       *  P sends a PIM Packed Register-Stop towards the DR that
          includes capability information.




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

6.  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.

7.  PIM RP router version downgrade

   Consider a PIM RP router that supports PIM Register Packing and then
   downgrades to a software version which does not support PIM Register
   Packing.  The DR that sends the PIM Packed Null-Register message will
   not get a PIM Register-Stop message back.  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.

8.  Fragmentation consideration

   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.

9.  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.



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   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.

10.  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.

11.  Acknowledgments

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

12.  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>.

   [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>.

   [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>.








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Authors' Addresses

   Vikas Ramesh Kamath
   VMware
   3401 Hillview Ave
   Palo Alto  CA 94304
   USA

   Email: vkamath@vmware.com


   Ramakrishnan Chokkanathapuram Sundaram
   Cisco Systems, Inc.
   Tasman Drive
   San Jose  CA 95134
   USA

   Email: ramaksun@cisco.com


   Raunak Banthia
   Apstra
   333 Middlefield Rd STE 200
   Menlo Park  CA 94025
   USA

   Email: rbanthia@apstra.com


   Ananya Gopal
   Cisco Systems, Inc.
   Tasman Drive
   San Jose  CA 95134
   USA

   Email: ananygop@cisco.com















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