Internet DRAFT - draft-ietf-lsr-ospf-prefix-originator
draft-ietf-lsr-ospf-prefix-originator
LSR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track A. Lindem
Expires: October 11, 2021 Cisco Systems
J. Dong
Huawei Technologies
P. Psenak
K. Talaulikar, Ed.
Cisco Systems
April 9, 2021
OSPF Prefix Originator Extensions
draft-ietf-lsr-ospf-prefix-originator-12
Abstract
This document defines OSPF extensions to include information
associated with the node originating a prefix along with the prefix
advertisement. These extensions do not change the core OSPF route
computation functionality but provide useful information for network
analysis, troubleshooting, and use-cases like traffic engineering.
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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This Internet-Draft will expire on October 11, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 3
2.1. Prefix Source OSPF Router-ID Sub-TLV . . . . . . . . . . 4
2.2. Prefix Source Router Address Sub-TLV . . . . . . . . . . 5
3. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. Operational Considerations . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Prefix attributes are advertised in OSPFv2 [RFC2328] using the
Extended Prefix Opaque Link State Advertisement (LSA) [RFC7684] and
in OSPFv3 [RFC5340] using the various Extended Prefix LSA types
[RFC8362].
The procedures for identification of the originating router for a
prefix in OSPF vary by the type of the prefix and, currently, it is
not always possible to produce an accurate result. For intra-area
prefixes, the originating router is identified by the Advertising
Router field of the area-scoped LSA used for those prefix
advertisements. However, for the inter-area prefixes advertised by
the Area Border Router (ABR), the Advertising Router field of their
area-scoped LSAs is set to the ABR itself and the information about
the router originating the prefix advertisement is lost in this
process of prefix propagation across areas. For Autonomous System
(AS) external prefixes, the originating router may be considered as
the Autonomous System Border Router (ASBR) and is identified by the
Advertising Router field of the AS-scoped LSA used. However, the
actual originating router for the prefix may be a remote router
outside the OSPF domain. Similarly, when an ABR performs translation
of Not-So-Stubby Area (NSSA) [RFC3101] LSAs to AS-external LSAs, the
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information associated with the NSSA ASBR (or the router outside the
OSPF domain) is not conveyed across the OSPF domain.
While typically the originator of information in OSPF is identified
by its OSPF Router ID, it does not necessarily represent a reachable
address for the router since the OSPF Router ID is a 32-bit number.
There exists a prevalent practice to use one of the IPv4 address of
the node (e.g. a loopback interface) as an OSPF Router ID in the case
of OSPFv2. However, this cannot be always assumed and this approach
does not extend to IPv6 addresses with OSPFv3. The IPv4/IPv6 Router
Address as defined in [RFC3630] and [RFC5329] for OSPFv2 and OSPFv3
respectively provide an address to reach that router.
The primary use case for the extensions proposed in this document is
to be able to identify the originator of a prefix in the network. In
cases where multiple prefixes are advertised by a given router, it is
also useful to be able to associate all these prefixes with a single
router even when prefixes are advertised outside of the area in which
they originated. It also helps to determine when the same prefix is
being originated by multiple routers across areas.
This document proposes extensions to the OSPF protocol for the
inclusion of information associated with the router originating the
prefix along with the prefix advertisement. These extensions do not
change the core OSPF route computation functionality. They provide
useful information for topology analysis and traffic engineering,
especially on a controller when this information is advertised as an
attribute of the prefixes via mechanisms such as Border Gateway
Protocol Link-State (BGP-LS) [RFC7752]
[I-D.ietf-idr-bgp-ls-segment-routing-ext].
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. Protocol Extensions
This document defines the Prefix Source OSPF Router-ID and the Prefix
Source Router Address Sub-TLVs. They are used, respectively, to
include the Router ID of, and a reachable address of, the router that
originates the prefix as a prefix attribute.
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2.1. Prefix Source OSPF Router-ID Sub-TLV
For OSPFv2, the Prefix Source OSPF Router-ID Sub-TLV is an optional
Sub-TLV of the OSPFv2 Extended Prefix TLV [RFC7684]. For OSPFv3, the
Prefix Source OSPF Router-ID Sub-TLV is an optional Sub-TLV of the
Intra-Area-Prefix TLV, Inter-Area-Prefix TLV, and External-Prefix TLV
[RFC8362] when originating either an IPv4 [RFC5838] or an IPv6 prefix
advertisement.
The Prefix Source OSPF Router-ID Sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OSPF Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Prefix Source OSPF Router-ID Sub-TLV Format
Where:
o Type: 4 for OSPFv2 and 27 for OSPFv3
o Length: 4
o OSPF Router ID : the OSPF Router ID of the OSPF router that
originated the prefix advertisement in the OSPF domain.
The parent TLV of a prefix advertisement MAY include more than one
Prefix Source OSPF Router-ID sub-TLV, one corresponding to each of
the Equal-Cost Multi-Path (ECMP) nodes that originated the given
prefix.
For intra-area prefix advertisements, the Prefix Source OSPF Router-
ID Sub-TLV MUST be considered invalid and ignored if the OSPF Router
ID field is not the same as the Advertising Router field in the
containing LSA. Similar validation cannot be reliably performed for
inter-area and external prefix advertisements.
A received Prefix Source OSPF Router-ID Sub-TLV with OSPF Router ID
set to 0 MUST be considered invalid and ignored. Additionally,
reception of such Sub-TLV SHOULD be logged as an error (subject to
rate-limiting).
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2.2. Prefix Source Router Address Sub-TLV
For OSPFv2, the Prefix Source Router Address Sub-TLV is an optional
Sub-TLV of the OSPFv2 Extended Prefix TLV [RFC7684]. For OSPFv3, the
Prefix Source Router Address Sub-TLV is an optional Sub-TLV of the
Intra-Area-Prefix TLV, Inter-Area-Prefix TLV, and External-Prefix TLV
[RFC8362] when originating either an IPv4 [RFC5838] or an IPv6 prefix
advertisement.
The Prefix Source Router Address Sub-TLV has the following format:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router Address (4 or 16 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Prefix Source Router Address Sub-TLV Format
Where:
o Type: 5 (suggested) for OSPFv2 and 28 (suggested) for OSPFv3
o Length: 4 or 16
o Router Address: A reachable IPv4 or IPv6 router address for the
router that originated the IPv4 or IPv6 prefix advertisement
respectively. Such an address would be semantically equivalent to
what may be advertised in the OSPFv2 Router Address TLV [RFC3630]
or in the OSPFv3 Router IPv6 Address TLV [RFC5329].
The parent TLV of a prefix advertisement MAY include more than one
Prefix Source Router Address Sub-TLV, one corresponding to each of
the Equal-Cost Multi-Path (ECMP) nodes that originated the given
prefix.
A received Prefix Source Router Address Sub-TLV that has an invalid
length (i.e. not consistent with the prefix's address family) MUST be
considered invalid and ignored. Additionally, reception of such Sub-
TLV SHOULD be logged as an error (subject to rate-limiting).
3. Elements of Procedure
This section describes the procedure for the advertisement of the
Prefix Source OSPF Router-ID and Prefix Source Router Address Sub-
TLVs along with the prefix advertisement.
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The OSPF Router ID of the Prefix Source OSPF Router-ID is set to the
OSPF Router ID of the node originating the prefix in the OSPF domain.
If the originating node is advertising an OSPFv2 Router Address TLV
[RFC3630] or an OSPFv3 Router IPv6 Address TLV [RFC5329], then the
same address MUST be used in the Router Address field of the Prefix
Source Router Address Sub-TLV. When the originating node is not
advertising such an address, implementations can determine a unique
and reachable address (for example, advertised with the N-flag set
[RFC7684] or N-bit set [RFC8362]) belonging to the originating node
to set in the Router Address field.
When an ABR generates inter-area prefix advertisements into its non-
backbone areas corresponding to an inter-area prefix advertisement
from the backbone area, the only way to determine the originating
node information is based on the Prefix Source OSPF Router-ID and
Prefix Source Router Address Sub-TLVs present in the inter-area
prefix advertisement originated into the backbone area by an ABR from
another non-backbone area. The ABR performs its prefix calculation
to determine the set of nodes that contribute to the best prefix
reachability. It MUST use the prefix originator information only
from this set of nodes. The ABR MUST NOT include the Prefix Source
OSPF Router-ID or the Prefix Source Router Address Sub-TLVs when it
is unable to determine the information of the best originating nodes.
Implementations may support the propagation of the originating node
information along with a redistributed prefix into the OSPF domain
from another routing domain. The details of such mechanisms are
outside the scope of this document. Such implementations may also
provide control on whether the Router Address in the Prefix Source
Router Address Sub-TLV is set as the ABSR node address or as the
address of the actual node outside the OSPF domain that owns the
prefix.
When translating the NSSA prefix advertisements [RFC3101] to the AS
external prefix advertisements, the NSSA ABR, follows the same
procedures as an ABR generating inter-area prefix advertisements for
the propagation of the originating node information.
4. Security Considerations
Since this document extends the OSPFv2 Extended Prefix LSA, the
security considerations for [RFC7684] are applicable. Similarly,
since this document extends the OSPFv3 E-Intra-Area-Prefix-LSA, E-
Inter-Area-Prefix-LSA, E-AS-External LSA, and E-NSSA-LSA, the
security considerations for [RFC8362] are applicable. The new sub-
TLVs introduced in this document are optional and do not affect the
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OSPF route computation and therefore do not affect the security
aspects of OSPF protocol operations.
A rogue node that can inject prefix advertisements may use the new
extensions introduced in this document to indicate an incorrect
prefix source information.
5. Operational Considerations
Consideration should be given to the operational impact of the
increase in the size of the OSPF Link-State Database as a result of
the protocol extensions in this document. Based on deployment design
and requirements, a subset of prefixes may be identified for which
the originating node information needs to be included with their
prefix advertisements.
The propagation of the prefix source node information when doing
prefix advertisements across OSPF area or domain boundaries results
in the exposure of node information outside of an area or domain
within which it is normally hidden or abstracted by the base OSPF
protocol. Based on deployment design and requirements, a subset of
prefixes may be identified for which the propagation of the
originating node information across area or domain boundaries is
disabled at the ABRs or ASBRs respectively.
The identification of the node that is originating a specific prefix
in the network may aid in debugging of issues related to prefix
reachability within an OSPF network.
6. IANA Considerations
This document requests IANA for the allocation of the codepoints from
the "OSPFv2 Extended Prefix TLV Sub-TLVs" registry under the "Open
Shortest Path First v2 (OSPFv2) Parameters" registry.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Description | IANA Allocation |
| Point | | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4 | Prefix Source OSPF Router-ID | early allocation done |
| 5 | Prefix Source Router Address | suggested |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Codepoints in OSPFv2 Extended Prefix TLV Sub-TLVs
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This document requests IANA for the allocation of the codepoints from
the "OSPFv3 Extended-LSA Sub-TLVs" registry under the "Open Shortest
Path First v3 (OSPFv3) Parameters" registry.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Description | IANA Allocation |
| Point | | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 27 | Prefix Source OSPF Router-ID | early allocation done |
| 28 | Prefix Source Router Address | suggested |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Codepoints in OSPFv3 Extended-LSA Sub-TLVs
7. Acknowledgement
Many thanks to Les Ginsberg for his suggestions on this draft. Also
thanks to Jeff Tantsura, Rob Shakir, Gunter Van De Velde, Goethals
Dirk, Smita Selot, Shaofu Peng, John E Drake and Baalajee S for their
review and valuable comments. The authors would also like to thank
Alvaro Retana for his detailed review and suggestions for the
improvement of this document.
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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[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>.
[RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
"Traffic Engineering Extensions to OSPF Version 3",
RFC 5329, DOI 10.17487/RFC5329, September 2008,
<https://www.rfc-editor.org/info/rfc5329>.
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[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>.
[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
[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
(work in progress), June 2019.
[RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
RFC 3101, DOI 10.17487/RFC3101, January 2003,
<https://www.rfc-editor.org/info/rfc3101>.
[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
R. Aggarwal, "Support of Address Families in OSPFv3",
RFC 5838, DOI 10.17487/RFC5838, April 2010,
<https://www.rfc-editor.org/info/rfc5838>.
[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
Authors' Addresses
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Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing 102209
China
Email: wangaj3@chinatelecom.cn
Acee Lindem
Cisco Systems
301 Midenhall Way
Cary, NC 27513
USA
Email: acee@cisco.com
Jie Dong
Huawei Technologies
Beijing
China
Email: jie.dong@huawei.com
Peter Psenak
Cisco Systems
Pribinova Street 10
Bratislava, Eurovea Centre, Central 3 81109
Slovakia
Email: ppsenak@cisco.com
Ketan Talaulikar (editor)
Cisco Systems
India
Email: ketant@cisco.com
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