LSR R. Chen
Internet-Draft D. Zhao
Intended status: Standards Track ZTE Corporation
Expires: 30 July 2025 P. Psenak
K. Talaulikar
Cisco Systems
L. Gong
China mobile
26 January 2025
Prefix Flag Extension for OSPFv2 and OSPFv3
draft-ietf-lsr-ospf-prefix-extended-flags-05
Abstract
Each OSPF prefix is advertised with an 8-bit options field, using the
Prefix Options (OSPFv3) and the flag field in the OSPFv2 Extended
Prefix TLV (OSPFv2). However for OSPFv3, all the Prefix Options bits
have already been assigned, and for OSPFv2, there are not many bits
left unassigned in the OSPFv2 Extended Prefix TLV.
This document solves the problem of insufficient options bit by
defining variable-length Prefix Attribute Flags Sub-TLVs for OSPFv2
and OSPFv3.
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 30 July 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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Variable-Length Prefix Attribute Flags Sub-TLVs . . . . . . . 4
2.1. OSPFv2 Prefix Attribute Flags Sub-TLV . . . . . . . . . . 4
2.2. OSPFv3 Prefix Attribute Flags Sub-TLV . . . . . . . . . . 5
3. Processing . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Backward Compatibility . . . . . . . . . . . . . . . . . . . 7
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1. OSPFv2 Prefix Attribute Flags Sub-TLV Registry . . . . . 7
6.1.1. OSPFv2 Prefix Extended Flags Field Registry . . . . . 8
6.2. OSPFv3 Prefix Attribute Flags Sub-TLV Registry . . . . . 8
6.2.1. OSPFv3 Prefix Extended Flags Field Registry . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Each OSPF prefix is advertised with an 8-bit options field, using the
Prefix Options [RFC5340] **in OSPFv3** and the flag field in the
OSPFv2 Extended Prefix TLV [RFC7684]. However for OSPFv3, all the
Prefix Options bits have already been assigned, and for OSPFv2, at
the time of writing, only 4 bits remain undefined in the OSPFv2
Extended Prefix TLV.
For OSPFv2, as defined in [RFC7684], the length of the Flag field is
8 bits, and the flags defined in the OSPFv2 Extended Prefix TLV are
listed in Table 1.
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+=======+==================+=============================+
| Value | Description | Reference |
+=======+==================+=============================+
| 0x80 | A | [RFC7684] |
+-------+------------------+-----------------------------+
| 0x40 | N | [RFC7684] |
+-------+------------------+-----------------------------+
| 0x20 | E-Flag(ELC Flag) | [RFC9089] |
+-------+------------------+-----------------------------+
| TBD | AC | [I-D.ietf-lsr-anycast-flag] |
+-------+------------------+-----------------------------+
Table 1: OSPFv2 Extended Prefix TLV Flags (8 bits)
For OSPFv3 [RFC5340] and [RFC8362], the length of the Flag field is 8
bits, and all of the bits have already been defined as shown in
Table 2.
+=======+===================+===========+
| Value | Description | Reference |
+=======+===================+===========+
| 0x01 | NU-bit | [RFC5340] |
+-------+-------------------+-----------+
| 0x02 | LA-bit | [RFC5340] |
+-------+-------------------+-----------+
| 0x04 | Deprecated | [RFC5340] |
+-------+-------------------+-----------+
| 0x08 | P-bit | [RFC5340] |
+-------+-------------------+-----------+
| 0x10 | DN-bit | [RFC5340] |
+-------+-------------------+-----------+
| 0x20 | N-bit | [RFC8362] |
+-------+-------------------+-----------+
| 0x40 | E-Flag (ELC Flag) | [RFC9089] |
+-------+-------------------+-----------+
| 0x80 | AC-bit | [RFC9513] |
+-------+-------------------+-----------+
Table 2: OSPFv3 Prefix Options (8 bits)
This document solves the problem of insufficient flag bit by defining
variable-length Prefix Attribute Flags Sub-TLVs for OSPFv2 and
OSPFv3.
In OSPFv2, the structure is extended to include OSPFv2 Prefix
Attribute Flags Sub-TLV as follows:
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OSPFv2 Extended Prefix Opaque LSA->OSPFv2 Extended Prefix TLV
extended to
OSPFv2 Extended Prefix Opaque LSA->OSPFv2 Extended Prefix
TLV->OSPFv2 Prefix Attribute Flags Sub-TLV
In OSPFv3, the structure is extended to include OSPFv3 Prefix
Attribute Flags Sub-TLV as follows:
E-Inter-Area-Prefix-LSA->The Inter-Area-Prefix TLV->PrefixOptions
E-Link-LSA & E-Intra-Area-Prefix-LSA->Intra-Area-Prefix
TLV->PrefixOptions
E-AS-External-LSA & E-NSSA-LSA->External-Prefix TLV->PrefixOptions
extended to
E-Inter-Area-Prefix-LSA->The Inter-Area-Prefix TLV->OSPFv3 Prefix
Attribute Flags Sub-TLV
E-Link-LSA & E-Intra-Area-Prefix-LSA->Intra-Area-Prefix
TLV->OSPFv3 Prefix Attribute Flags Sub-TLV
E-AS-External-LSA & E-NSSA-LSA->External-Prefix TLV->OSPFv3 Prefix
Attribute Flags Sub-TLV
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 the 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.
2.1. OSPFv2 Prefix Attribute Flags Sub-TLV
The format of OSPFv2 Prefix Attribute Flags Sub-TLV is:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Prefix Attribute Flags (Variable) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: TBD1.
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 OSPFv2 Prefix Attribute Flags
Sub-TLV is recognized but its length is not a multiple of 4 octets,
the LSA SHOULD 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.
Defined prefix flags that are not transmitted due to exceeding the
transmitted length MUST be treated as if they are set to 0 upon
receipt. If they are not treated as 0, logging SHOULD be performed.
OSPFv2 Prefix Attribute Flags Sub-TLV is a Sub-TLV of the OSPFv2
Extended Prefix TLV as defined in [RFC7684].
2.2. OSPFv3 Prefix Attribute Flags Sub-TLV
The format of OSPFv3 Prefix Attribute Flags Sub-TLV 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) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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where:
Type: TBD2.
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 OSPFv3 Prefix Attribute Flags
Sub-TLV is recognized but its length is not a multiple of 4 octets,
the LSA SHOULD be considered malformed.
Prefix Attribute Flags: Variable. The extended flag fields. This
contains a variable number of 32-bit flags. Currently, no bits are
defined.
Unassigned bits MUST be set to zero on transmission and MUST be
ignored on receipt.
Defined prefix flags that are not transmitted due to exceeding the
transmitted length MUST be treated as if they are set to 0 upon
receipt. If they are not treated as 0, logging SHOULD be performed.
OSPFv3 Prefix Attribute Flags Sub-TLV is a Sub-TLV of the following
OSPFv3 TLVs as defined in [RFC8362]:
* Intra-Area-Prefix TLV
* Inter-Area-Prefix TLV
* External-Prefix TLV
3. Processing
The Extended Flags field is a variable-length field in multiples of
32 bits, with bits allocated as flags starting from the most
significant bit. Future documents will assign these bits; this
document does not define any flags. Unrecognized flags in the Prefix
Attribute Flags Sub-TLVs for OSPFv2 and OSPFv3 MUST be forwarded
without modification. Specifically, the entire flag field MUST be
copied unchanged into outgoing messages, regardless of whether the
implementation recognizes any or all flags.
Implementations MUST handle variable-length Prefix Attribute Flags
Sub-TLVs. Any portion of the field beyond the length supported by
the implementation MUST be ignored.
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An OSPFv2 router receiving multiple OSPFv2 Prefix Attribute Flags
Sub-TLVs in the same OSPFv2 Extended Prefix TLV MUST use only the
first occurrence of the Sub-TLV and MUST ignore all subsequent
instances of that Sub-TLV.
An OSPFv3 router receiving multiple OSPFv3 Prefix Attribute Flags
Sub-TLVs within a subsuming TLV MUST use only the first occurrence of
the Sub-TLV and MUST ignore all subsequent instances in that
subsuming TLV.
4. 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 Prefix Attribute Flags Sub-TLV MUST ignore the
Sub-TLV.
Further, any additional bits in the OSPFv2/OSPFv3 Prefix Attribute
Flags Sub-TLV that are not recognized by an implementation MUST be
ignored.
5. 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.
6. IANA Considerations
This document requests allocation for the following registry.
6.1. OSPFv2 Prefix Attribute Flags Sub-TLV Registry
This document requests the allocation of "OSPFv2 Prefix Attribute
Flags" in the "OSPFv2 Extended Prefix TLV Sub-TLVs" registry:
The following flag (TEMPORARY - registered 2024-04-05, expires
2025-04-05) has been allocated by IANA:
Value Description Reference
--------- ----------------------------------- ---------------
TBD1=11 OSPFv2 Prefix Attribute Flags This document
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6.1.1. OSPFv2 Prefix Extended Flags Field Registry
This document requests an allocation of "OSPFv2 Prefix Extended Flag
Field" Registry under "Open Shortest Path First v2 (OSPFv2)
Parameters". The registry defines the bits in the 32-bit Flags field
in the OSPFv2 Prefix Attribute Flags Sub-TLV. Additionaly bits can
be allocated via IETF Review or IESG Approval [RFC8126]. Each bit
definition will include:
* Bit number (counting from bit 0 as the most significant bit)
* Description
* Reference
No values are currently defined. Bits 0-31 are initially marked as
"Unassigned". Bits with an ordinal higher than 31 will be added to
the registry as required by future documents.
6.2. OSPFv3 Prefix Attribute Flags Sub-TLV Registry
This document requests the allocation of "OSPFv3 Prefix Attribute
Flags" in the "OSPFv3 Extended-LSA Sub-TLVs" registry:
The following flag (TEMPORARY - registered 2024-04-05, expires
2025-04-05) has been allocated by IANA:
Value Description Reference
-------- ---------------------------------- --------------
TBD2=37 OSPFv3 Prefix Attribute Flags This document
6.2.1. OSPFv3 Prefix Extended Flags Field Registry
This document requests an allocation of "OSPFv3 Prefix Extended Flag
Field" registry under "Open Shortest Path First v3 (OSPFv3)
Parameters". Additional bits can be allocated via IETF Review or
IESG Approval [RFC8126]. Each bit definition will include:
* Bit number (counting from bit 0 as the most significant bit)
* Description
* Reference
Bits 0-31 are initially marked as "Unassigned". Bits with an ordinal
higher than 31 will be added to the registry as required by future
documents.
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7. 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.
8. References
8.1. 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>.
8.2. Informative References
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[I-D.ietf-lsr-anycast-flag]
Chen, R., Zhao, D., Psenak, P., Talaulikar, K., and C.
Lin, "Updates to Anycast Property advertisement for
OSPFv2", Work in Progress, Internet-Draft, draft-ietf-lsr-
anycast-flag-01, 20 October 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-lsr-
anycast-flag-01>.
[RFC9089] Xu, X., Kini, S., Psenak, P., Filsfils, C., Litkowski, S.,
and M. Bocci, "Signaling Entropy Label Capability and
Entropy Readable Label Depth Using OSPF", RFC 9089,
DOI 10.17487/RFC9089, August 2021,
<https://www.rfc-editor.org/info/rfc9089>.
[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>.
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
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Liyan Gong
China mobile
China
Email: gongliyan@chinamobile.com
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