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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
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
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
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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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