Prefix Flag Extension for OSPFv2 and OSPFv3
draft-ietf-lsr-ospf-prefix-extended-flags-07

LSR                                                              R. Chen
Internet-Draft                                                   D. Zhao
Intended status: Standards Track                         ZTE Corporation
Expires: 10 October 2025                                       P. Psenak
                                                           K. Talaulikar
                                                           Cisco Systems
                                                                 L. Gong
                                                            China mobile
                                                            8 April 2025

              Prefix Flag Extension for OSPFv2 and OSPFv3
              draft-ietf-lsr-ospf-prefix-extended-flags-07

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 this problem by defining variable-length Prefix
   Attribute Flags sub-TLV for OSPF.  This sub-TLV is applicable to
   OSPFv2 and OSPFv3.

Status of This Memo

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Copyright Notice

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

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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.  Variable-Length Prefix Attribute Flags Sub-TLV  . . . . . . .   3
   3.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   4
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  OSPFv2  . . . . . . . . . . . . . . . . . . . . . . . . .   5
       5.1.1.  OSPFv2 Prefix Attribute Flags Sub-TLV Registry  . . .   5
       5.1.2.  OSPFv2 Prefix Extended Flags Field Registry . . . . .   5
     5.2.  OSPFv3  . . . . . . . . . . . . . . . . . . . . . . . . .   6
       5.2.1.  OSPFv3 Prefix Attribute Flags Sub-TLV Registry  . . .   6
       5.2.2.  OSPFv3 Prefix Extended Flags Field Registry . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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 (Appendix A.4.1.1 of [RFC5340]) and the flags field in
   the OSPFv2 Extended Prefix TLV (Section 2.1 of [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 (8 bits)" IANA registry
   [IANA-OSPFv3-PO]).  Also, 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
   registry [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-TLV

   This document defines variable-Length Prefix Attribute Flags sub-TLV
   for OSPFv2 and OSPFv3.  Such sub-TLV specifies the variable-flag
   fields to advertise additional attributes associated with OSPF
   prefixes.  The advertisement and processing of the existing fixed-
   size prefix attribute flags remain unchanged.

   The format of OSPFv2/OSPFv3 Prefix Attribute Flags sub-TLVs is shown
   in Figure 1.

    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)           //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 1: Format of OSPFv2/OSPFv3 Prefix Attribute Flags Sub-TLV

   where:

   Type (2 octets): 11 for OSPFv2 and 37 for OSPFv3.

   Length (2 octets): Variable, dependent on the included Prefix
   Attribute Flags.  This indicates the length of the prefix attributes
   flags in octets.  The length MUST be a multiple of 4 octets.  If the
   length is not a multiple of 4 octets, the Link State Advertisement
   (LSA) is malformed and MUST be ignored.

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   Prefix Attribute Flags (Variable): The extended flag field.  This
   field contains a variable number of flags, grouped in 4-octet blocks.
   The bits are numbered starting from bit 0 as the most significant bit
   of the first 32-bit block.  If a Prefix Attribute Flags field's
   length exceeds 4 octets, numbering for the additional bits picks up
   where the previous 4-octet block left off.  For example, the most
   significant bit in the fifth octet of an 8-octet Prefix Attribute
   Flags is referred to as bit 32.  Currently, no bits are defined in
   this document.

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

   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.

   OSPFv2 Prefix Attribute Flags sub-TLV is advertised as a sub-TLV of
   the OSPFv2 Extended Prefix TLV defined in [RFC7684].  Additional
   OSPFv2 prefix flags SHOULD be allocated from the unused bits in the
   Flags field of the OSPFv2 Extended Prefix TLV prior to allocating
   flags in the OSPFv2 Prefix Attribute Flags sub-TLV.

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

   *  Inter-Area-Prefix TLV (Section 3.4 of [RFC8362]).

   *  External-Prefix TLV (Section 3.6 of [RFC8362]).

   *  Intra-Area-Prefix TLV (Section 3.7 of [RFC8362]).

   *  SRv6 Locator TLV [RFC9513].

   When multiple instances of the 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.  Errors SHOULD be logged subject
   to rate limiting.

3.  Backward Compatibility

   The Prefix Attribute Flags sub-TLV does not introduce any backward
   compatibility issues.  An implementation that does not recognize the
   OSPFv2/OSPFv3 Prefix Attribute Flags sub-TLV would ignore the sub-TLV
   as per normal TLV processing operations (refer Section 6.3 of
   [RFC3630] and Section 2.3.2 of [RFC8362]).

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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 registries.

5.1.  OSPFv2

5.1.1.  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        RFC to be

5.1.2.  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" registry group.  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 of the first block)
        *  Description
        *  Reference

   No bits are currently defined.  Bits 0-31 are to be initially marked
   as "Unassigned".  The flags defined in this document may use either a
   single bit or multiple bits to represent a state, as determined by
   the specific requirements of the document defining them.  IANA is
   requested to add subsequent blocks of 32 bits upon exhaustion of the
   preceding 32-bit block.

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5.2.  OSPFv3

5.2.1.  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         RFC to be

5.2.2.  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)" registry
   group.  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 of the first block )
        *  Description
        *  Reference

   No bits are currently defined.  Bits 0-31 are to be initially marked
   as "Unassigned".  The flags defined in this document may use either a
   single bit or multiple bits to represent a state, as determined by
   the specific requirements of the document defining them.  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

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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>.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

   [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>.

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

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   [IANA-OSPFv3-PO]
              "OSPFv3 Prefix Options (8 bits)",
              <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
   Apollo Business Center
   Mlynske nivy 43
   Bratislava 821 09
   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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