Prefix Flag Extension for OSPFv2 and OSPFv3
draft-ietf-lsr-ospf-prefix-extended-flags-06

LSR                                                              R. Chen
Internet-Draft                                                   D. Zhao
Intended status: Standards Track                         ZTE Corporation
Expires: 18 August 2025                                        P. Psenak
                                                           K. Talaulikar
                                                           Cisco Systems
                                                                 L. Gong
                                                            China mobile
                                                        14 February 2025

              Prefix Flag Extension for OSPFv2 and OSPFv3
              draft-ietf-lsr-ospf-prefix-extended-flags-06

Abstract

   Each OSPF prefix can be advertised with an 8-bit field to indicate
   specific properties of that prefix.  However, all the OSPFv3 Prefix
   Options bits have already been assigned and only a few bits remain
   unassigned in the flags field of the OSPFv2 Extended Prefix TLV.

   This document solves the problem of insufficient prefix options bits
   by defining variable-length Prefix Attribute Flags Sub-TLV for OSPF.

Status of This Memo

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   This Internet-Draft will expire on 18 August 2025.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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 carefully, as they describe your rights
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Variable-Length Prefix Attribute Flags Sub-TLVs . . . . . . .   3
   3.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   4
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  OSPFv2 Prefix Attribute Flags Sub-TLV Registry  . . . . .   5
       5.1.1.  OSPFv2 Prefix Extended Flags Field Registry . . . . .   5
     5.2.  OSPFv3 Prefix Attribute Flags Sub-TLV Registry  . . . . .   5
       5.2.1.  OSPFv3 Prefix Extended Flags Field Registry . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Each OSPF prefix can be advertised with an 8-bit field to indicate
   specific properties of that prefix.  This is done using the OSPFv3
   Prefix Options [RFC5340] and the flags field in the OSPFv2 Extended
   Prefix TLV [RFC7684].  The rest of this document refers to these
   8-bit fields in both OSPFv2 and OSPFv3 as the "existing fixed-size
   prefix attribute flags".

   However, all the OSPFv3 Prefix Options bits have already been
   assigned (see OSPFv3 Prefix Options IANA registries [IANA-OSPFv3-PO]
   and only 5 bits remain unassigned (at the time of publication of this
   document) in the flags field of the OSPFv2 Extended Prefix TLV (see
   OSPFv2 Extended Prefix TLV Flags IANA registries [IANA-OSPFv2-EPF]).

   This document solves the problem of insufficient flag bits for the
   signaling of prefix properties in OSPF by defining variable-length
   Prefix Attribute Flags Sub-TLVs for OSPFv2 and OSPFv3.

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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.

2.  Variable-Length Prefix Attribute Flags Sub-TLVs

   This document defines variable-Length Prefix Attribute Flags Sub-TLVs
   for OSPFv2 and OSPFv3.  These Sub-TLVs specify the variable-flag
   fields to advertise additional attributes associated with OSPF
   prefixs i.e., the advertisement and processing of the existing fixed-
   size prefix attribute flags remains unchanged.

   The format of OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLVs is:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Type             |            Length             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     //                 Prefix Attribute Flags (Variable)           //
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   Type: 11 for OSPFv2 and 37 for OSPFv3.

   Length: Variable, dependent on the included Prefix Attribute Flags.
   This indicates the length of the value portion in bytes.  The length
   MUST be a multiple of 4 octets.  If the length is not a multiple of 4
   octets, the LSA MUST be considered malformed.

   Prefix Attribute Flags: Variable.  The extended flag field.  This
   contains a variable number of 32-bit flags.  Currently, no bits are
   defined in this document.

   Unassigned bits MUST be set to zero on transmission and MUST be
   ignored on receipt.

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   An implementation MUST limit the length of the sub-TLV so as to
   signal the bits that are set to 1.  Defined prefix flags that are not
   transmitted due to being beyond the transmitted length MUST be
   treated as being set to 0.  If any trailing 32-bit block(s) are
   received without any bit being set in it, then the LSA MUST be
   considered malformed.

   OSPFv2 Prefix Attribute Flags Sub-TLV is advertised as a Sub-TLV of
   the OSPFv2 Extended Prefix TLV as defined in [RFC7684].

   OSPFv3 Prefix Attribute Flags Sub-TLV is advertised as a Sub-TLV of
   the following OSPFv3 TLVs:

   *  Inter-Area-Prefix TLV [RFC8362].

   *  Intra-Area-Prefix TLV [RFC8362].

   *  External-Prefix TLV [RFC8362].

   *  SRv6 Locator TLV [RFC9513].

   When multiple instances of an OSPFv2/OSPFv3 Prefix Attribute Flags
   Sub-TLVs are received within the same TLV, an implementation MUST use
   only the first occurrence of the Sub-TLV and MUST ignore all
   subsequent instances of the Sub-TLV.

3.  Backward Compatibility

   The Prefix Attribute Flags Sub-TLVs defined in this document does not
   introduce any backward compatibility issues.  An implementation that
   does not recognize the OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLV
   MUST ignore the Sub-TLV.

4.  Acknowledgements

   The authors thank Shraddha Hegde, Changwang Lin, Tom Petch and many
   others for their suggestions and comments.

   The authors would like to thank Acee Lindem for aligning the
   terminology with existing OSPF documents and for editorial
   improvements.

5.  IANA Considerations

   This document requests allocation for the following registry.

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5.1.  OSPFv2 Prefix Attribute Flags Sub-TLV Registry

   This document requests IANA to make permanent the early allocation of
   the following codepoint for the "OSPFv2 Prefix Attribute Flags" in
   the "OSPFv2 Extended Prefix TLV Sub-TLVs" registry to be made
   permanent:

       Value            Description                     Reference
     ---------  -----------------------------------   ---------------
        11         OSPFv2 Prefix Attribute Flags        This document

5.1.1.  OSPFv2 Prefix Extended Flags Field Registry

   This document requests the creation of "OSPFv2 Prefix Extended Flag
   Field" Registry under "Open Shortest Path First v2 (OSPFv2)
   Parameters".  The registry defines the bits in the Prefix Attribute
   Flags field in the OSPFv2 Prefix Attribute Flags Sub-TLV as specified
   in section 2.  The bits are to be allocated via IETF Review
   [RFC8126].  Each bit definition will include:

      *  Bit number (counting from bit 0 as the most significant bit)
      *  Description
      *  Reference

   No bits are currently defined.  Bits 0-31 are to be initially marked
   as "Unassigned".  IANA is requested to add subsequent blocks of 32
   bits upon exhaustion of the preceding 32-bit block.

5.2.  OSPFv3 Prefix Attribute Flags Sub-TLV Registry

   This document requests IANA to make permanent the early allocation of
   the following codepoint for the "OSPFv3 Prefix Attribute Flags" in
   the "OSPFv3 Extended-LSA Sub-TLVs" registry:

     Value            Description                         Reference
    --------   ----------------------------------       --------------
      37         OSPFv3 Prefix Attribute Flags           This document

5.2.1.  OSPFv3 Prefix Extended Flags Field Registry

   This document requests the creation of "OSPFv3 Prefix Extended Flag
   Field" registry under "Open Shortest Path First v3 (OSPFv3)"
   Parameters.  The registry defines the bits in the Prefix Attribute
   Flags field in the OSPFv2 Prefix Attribute Flags Sub-TLV as specified
   in section 2.  The bits are to be allocated via IETF Review
   [RFC8126].  Each bit definition will include:

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      *  Bit number (counting from bit 0 as the most significant bit)
      *  Description
      *  Reference

   No bits are currently defined.  Bits 0-31 are to be initially marked
   as "Unassigned".  IANA is requested to add subsequent blocks of 32
   bits upon exhaustion of the preceding 32-bit block.

6.  Security Considerations

   Procedures and protocol extensions defined in this document do not
   affect the OSPFv2 or OSPFv3 security models.  See the "Security
   Considerations" section of [RFC7684] for a discussion of OSPFv2 TLV-
   encoding considerations, and the "Security Considerations" section of
   [RFC8362] for a discussion of OSPFv3 security.

7.  References

7.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <https://www.rfc-editor.org/info/rfc7684>.

   [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>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

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   [RFC9513]  Li, Z., Hu, Z., Talaulikar, K., Ed., and P. Psenak,
              "OSPFv3 Extensions for Segment Routing over IPv6 (SRv6)",
              RFC 9513, DOI 10.17487/RFC9513, December 2023,
              <https://www.rfc-editor.org/info/rfc9513>.

7.2.  Informative References

   [IANA-OSPFv2-EPF]
              "", <https://www.iana.org/assignments/ospfv2-parameters/
              ospfv2-parameters.xhtml#extended-prefix-tlv-flags>.

   [IANA-OSPFv3-PO]
              "", <https://www.iana.org/assignments/ospfv3-parameters/
              ospfv3-parameters.xhtml#ospfv3-parameters-4>.

Authors' Addresses

   Ran Chen
   ZTE Corporation
   Nanjing
   China
   Email: chen.ran@zte.com.cn

   Detao Zhao
   ZTE Corporation
   Nanjing
   China
   Email: zhao.detao@zte.com.cn

   Peter Psenak
   Cisco Systems
   Slovakia
   Email: ppsenak@cisco.com

   Ketan Talaulikar
   Cisco Systems
   India
   Email: ketant.ietf@gmail.com

   Liyan Gong
   China mobile
   China
   Email: gongliyan@chinamobile.com

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