LSR R. Chen
Internet-Draft D. Zhao
Intended status: Standards Track ZTE Corporation
Expires: 8 May 2022 P. Psenak
K. Talaulikar
Cisco Systems
4 November 2021
Updates to Anycast Property advertisement for OSPF
draft-chen-lsr-anycast-flag-01
Abstract
Each prefix is advertised along with an 8-bit field of
capabilities,by using the Prefix Options[RFC8362] and the flag flield
in the OSPFv2 Extended Prefix TLV [RFC7684], but the definition of
anycast flag to identify the prefix as anycast has not yet been
defined. However, Almost all bits of the Flag field has been
assigned already. Thus, it is also required to extend the flag field
for future use.
This document updates [RFC7684] and [RFC8362], by defining a new
variable length Prefix attributes Sub-TLVs for OSPFv2 and OSPFv3 and
a new flag in the Prefix attributes Sub-TLV to advertise the anycast
property.
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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and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on 8 May 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . 3
2. Variable length Prefix attributes Sub-TLV . . . . . . . . . . 3
3. Processing . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. OSPFv2 Extended Prefix Sub-TLV Registry . . . . . . . . . 6
5.2. OSPFv3 Extended LSA Sub-TLV Registry . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Both SR-MPLS prefixes-SID and IPv4/IPv6 prefix may be configured as
anycast and as such the same value can be advertised by multiple
routers. It is useful for other routers to know that the
advertisement is for an anycast identifier.
[RFC7684] defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV)
tuples that can be used to associate additional attributes with
prefixes or links.8-bit field of the OSPFv2 Extended Prefix TLV is
used to advertise additional attributes associated with the prefix,
but the definition of anycast flag to identify the prefix as anycast
has not yet been defined. However, three bits have been defined.
[RFC8362] extends the LSA format by encoding the existing OSPFv3 LSA
information in Type-Length-Value (TLV) tuples and allowing
advertisement of additional information with additional TLVs. Each
prefix is advertised along with an 8-bit field of capabilities, by
using the Prefix Options, but the definition of anycast flag to
identify the prefix as anycast has not yet been defined.
However,only the final bit in the Prefix Options is not allocated.
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This document updates [RFC7684] and [RFC8362], by defining a new
variable length Prefix attributes Sub-TLVs for OSPFv2 and OSPFv3 and
a new flag in the Prefix attributes Sub-TLV to advertise the anycast
property.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Variable length Prefix attributes Sub-TLV
This document creates a new variable length Prefix attributes Sub-TLV
for OSPFv2 and OSPFv3. This Sub-TLV specifies a variable flag fields
to advertise additional attributes associated with the prefix.
The format of each 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| attributes(variable)... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
where:
Type: TBA.
Length: Variable, dependent on the included attributes.
Attributes: Variable.The extended flag fields, and the first 8 bits
are reserved for the flag field previously defined by OSPFv2 and
OSPFv3.
In the case of OSPFv2,the Prefix attributes Sub-TLVs is a sub-TLV of
the OSPFv2 Extended Prefix TLV as defined in [RFC7684].Figure 2 below
is the definition of attribute field.
Attributes:The following flags are defined and the first 8 bits are
reserved for the previously defined one-octet field contains flags in
OSPFv2 Extended Prefix TLV [RFC7684]:
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| A| N| E| | | | | |AC| | | | | | | |......
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 2
Where:
E-Flag: Refer to [RFC9089] .
N/A-Flag: Refer to [RFC7684].
AC-flag: A new flag is used to advertise the anycast property. When
the prefix is configured as anycast, the AC-flag SHOULD be set.
Otherwise, this flag MUST be clear.If both N-flag and AC-flag are
set, the receiving routers MUST ignore the N-flag.
AC-flag MUST be preserved when the prefix is propagated between
areas.
The same prefix can be advertised by multiple routers, and that if at
least one of them sets the AC-Flag in its advertisement, the prefix
SHOULD be considered as anycast.
The other bits are reserved for future use.
In the case of OSPFv3, the Prefix attributes Sub-TLVs is a sub-TLV of
the following OSPFv3 TLVs as defined in [RFC8362]:
* Intra-Area Prefix TLV
* Inter-Area Prefix TLV
* External Prefix TLV
Figure 3 below is the definition of attribute field.
Attributes:The following flags are defined and the first 8 bits are
reserved for the previously defined OSPFv3 Prefix Options:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| | E| N|DN| P| x|LA|NU|AC| | | | | | | |......
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 3
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Where:
E-Flag: Refer to [RFC9089] in section 3.1.
N-Flag: Refer to [RFC8362] in section 3.1.1.
P/x/LA/NU-Flag: Refer to [RFC5340].
AC-Flag: A new flag is used to advertise the anycast property. When
the prefix is configured as anycast, the AC-flag SHOULD be set.
Otherwise, this flag MUST be clear.If both N-flag and AC-flag are
set, the receiving routers MUST ignore the N-flag.
AC-flag MUST be preserved when the prefix is propagated between
areas.
The same prefix can be advertised by multiple routers, and that if at
least one of them sets the AC-Flag in its advertisement, the prefix
SHOULD be considered as anycast.
The other bits are reserved for future use.
3. Processing
If there is an device in the network that does not support the
Extension of the Prefix attributes Sub-TLV, then the device that
support the Extension of the Prefix attributes Sub-TLV should
advertise the field of capabilities of the Prefix by using prefix-
options[RFC8362]or prefix-flags[RFC7684], and the Prefix attributes
Sub-TLV. Otherwise, only use the Prefix attributes Sub-TLV to
advertise the field of capabilities of the Prefix.
If prefix is advertised along with the field of capabilities, by
using the Prefix attributes Sub-TLV, then the field of capabilities
of the Prefix in the OSPFv2/OSPFv3 Prefix attributes Sub-TLV shall
prevail.
As long as the Prefix attributes Sub-TLV is used to advertise the
field of capabilities and the device support the Extension of the
Prefix attributes Sub-TLV, then the field of capabilities in the
Prefix attributes Sub-TLV shall prevail.
If prefix is advertised along with the field of capabilities, by
using only the prefix-options[RFC8362]or prefix-flags[RFC7684], then
the field of capabilities in the prefix-options[RFC8362]or prefix-
flags[RFC7684] shall prevail.
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4. Acknowledgements
TBD.
5. IANA Considerations
This document requests allocation for the following registry.
5.1. OSPFv2 Extended Prefix Sub-TLV Registry
This document requests allocation for OSPFv2 Extended Prefix Sub-TLV
Registry:
Value Description Reference
------ ---------------------------------- --------------
TBA OSPFv2 Prefix attributes Sub-TLV This document
Figure 4
This document adds a new bit in the "OSPFv2 Prefix attributes Sub-
TLV" registry:
AC-flag (Anycast Flag).
5.2. OSPFv3 Extended LSA Sub-TLV Registry
This document requests allocation for OSPFv3 Extended LSA Sub-TLV
Registry:
Value Description Reference
------ ---------------------------------- --------------
TBA OSPFv3 Prefix attributes Sub-TLV This document
Figure 5
This document adds a new bit in the "OSPFv3 Prefix attributes TLV"
registry:
AC-flag (Anycast Flag).
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6. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the OSPFv2 , OSPFv3 security model. See the "Security
Considerations"section of [RFC7684] for a discussion of OSPFv2
security, the "Security Considerations"section of [RFC8362] for a
discussion of OSPFv3 security.
7. 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>.
[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>.
[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>.
Authors' Addresses
Ran Chen
ZTE Corporation
Nanjing
China
Email: chen.ran@zte.com.cn
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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@cisco.com
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