RFC 9356 PROPOSED STANDARD OSPF · ROUTING · LINK BUNDLES
OSPF L2 Bundle Members: Advertising Layer 2 Bundle Member Link Attributes in OSPF
How OSPF can tell outside systems about the individual physical links inside a Layer 2 bundle, without changing how routes are computed.
RFC EDITOR
Talaulikar, K., Ed. and P. Psenak, "Advertising Layer 2 Bundle Member Link Attributes in OSPF", RFC 9356, DOI 10.17487/RFC9356, January 2023, <https://www.rfc-editor.org/info/rfc9356>.
BIBTEX
@misc{rfc9356,
series = {Request for Comments},
number = 9356,
howpublished = {RFC 9356},
publisher = {RFC Editor},
doi = {10.17487/RFC9356},
url = {https://www.rfc-editor.org/info/rfc9356},
author = {K. Talaulikar and P. Psenak},
title = {{Advertising Layer 2 Bundle Member Link Attributes in OSPF}},
pagetotal = 12,
year = 2023,
month = jan,
} LINEAGE · FROM THE RFC INDEXOpen full graph →
RFC text
Contents
Internet Engineering Task Force (IETF) K. Talaulikar, Ed.
Request for Comments: 9356 P. Psenak
Updates: 9085 Cisco Systems
Category: Standards Track January 2023
ISSN: 2070-1721
Advertising Layer 2 Bundle Member Link Attributes in OSPF
Abstract
There are deployments where the Layer 3 (L3) interface on which OSPF
operates is a Layer 2 (L2) interface bundle. Existing OSPF
advertisements only support advertising link attributes of the L3
interface. If entities external to OSPF wish to control traffic
flows on the individual physical links that comprise the L2 interface
bundle, link attribute information for the bundle members is
required.
This document defines the protocol extensions for OSPF to advertise
the link attributes of L2 bundle members. The document also
specifies the advertisement of these OSPF extensions via the Border
Gateway Protocol - Link State (BGP-LS) and thereby updates RFC 9085.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9356.
Copyright Notice
Copyright (c) 2023 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
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 described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
1.1. Requirements Language
2. L2 Bundle Member Attributes
3. BGP-LS Advertisement
4. IANA Considerations
5. Operational Considerations
6. Security Considerations
7. References
7.1. Normative References
7.2. Informative References
Acknowledgements
Authors' Addresses
1. Introduction
There are deployments where the L3 interface on which an OSPF
adjacency is established is a L2 interface bundle, for instance, a
Link Aggregation Group (LAG) [IEEE802.1AX]. This reduces the number
of adjacencies that need to be maintained by the OSPF protocol in
cases where there are parallel links between the neighbors. Entities
external to OSPF such as Path Computation Elements (PCEs) [RFC4655]
may wish to control traffic flows on individual L2 member links of
the underlying bundle interface (e.g., LAG). To do so, link
attribute information for individual bundle members is required. The
protocol extensions defined in this document provide the means to
advertise this information.
This document defines sub-TLVs to advertise link attribute
information for each of the L2 bundle members that comprise the L3
interface on which OSPF operates. Similar capabilities were
introduced for IS-IS in [RFC8668].
[RFC8665] and [RFC8666] introduced the Adjacency Segment Identifier
(Adj-SID) link attribute for OSPFv2 and OSPFv3, respectively, which
can be used as an instruction to forward traffic over a specific link
[RFC8402]. This document enables the advertisement of the Adj-SIDs
using the same Adj-SID sub-TLV at the granularity level of each L2
bundle member link so that traffic may be steered over that specific
member link.
Note that the advertisements at the L2 bundle member link level
defined in this document are intended to be provided to entities
external to OSPF and do not alter or change the OSPF route
computation. The following items are intentionally not defined in
and are outside the scope of this document:
* What link attributes will be advertised. This is determined by
the needs of the external entities.
* A minimum or default set of link attributes.
* How these attributes are configured.
* How the advertisements are used.
* What impact the use of these advertisements may have on traffic
flow in the network.
* How the advertisements are passed to external entities.
BGP Link State (BGP-LS) [RFC7752] was extended for the advertisement
of L2 bundle members and their attributes in [RFC9085], which covered
only IS-IS. This document updates [RFC9085] by specifying the
advertisement from OSPF (refer to Section 3).
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. L2 Bundle Member Attributes
A new L2 Bundle Member Attributes sub-TLV is introduced to advertise
L2 bundle member attributes in both OSPFv2 and OSPFv3. In the case
of OSPFv2, this sub-TLV is an optional sub-TLV of the OSPFv2 Extended
Link TLV that is used to describe link attributes via the OSPFv2
Extended Link Opaque LSA (Link State Advertisement) [RFC7684]. In
the case of OSPFv3, this sub-TLV is an optional sub-TLV of the
Router-Link TLV of the OSPFv3 E-Router-LSA [RFC8362].
When the OSPF adjacency is associated with an L2 bundle interface,
this sub-TLV is used to advertise the underlying L2 bundle member
links along with their respective link attributes. The inclusion of
this information implies that the identified link is a member of the
L2 bundle associated with an OSPF L3 link and that the member link is
operationally up. Therefore, advertisements of member links MUST NOT
be done when the member link becomes operationally down or is no
longer a member of the identified L2 bundle.
The advertisement of the L2 Bundle Member Attributes sub-TLV may be
asymmetric for an OSPF link, depending on the underlying L2
connectivity, i.e., advertised by the router on only one end.
The L2 Bundle Member Attributes 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 Bundle Member Descriptor |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Member Link Attribute sub-TLVs (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: L2 Bundle Member Attributes Sub-TLV Format
Where:
Type: 24 for OSPFv2 and 29 for OSPFv3
Length: The total length (in octets) of the value portion of the TLV
including nested sub-TLVs.
L2 Bundle Member Descriptor: A 4-octet link-local identifier for the
member link. This identifier is described as "link local
identifier" in [RFC4202] and used as "Local Interface ID" in
[RFC8510].
Link attributes for L2 bundle member links are advertised as sub-TLVs
of the L2 Bundle Member Attributes sub-TLV.
In the case of OSPFv2, the L2 Bundle Member Attributes sub-TLV shares
the sub-TLV space of the Extended Link TLV, and the sub-TLVs of the
Extended Link TLV MAY be used to describe the attributes of the
member link. Table 1 lists sub-TLVs and their applicability for L2
bundle member links. The sub-TLVs that are not applicable MUST NOT
be used as sub-TLVs for the L2 Bundle Member Attributes sub-TLV.
Specifications that introduce new sub-TLVs of the Extended Link TLV
MUST indicate their applicability to the L2 Bundle Member Attributes
sub-TLV. Typically, attributes that have L3 semantics would not be
applicable, but L2 attributes would apply. An implementation MUST
ignore any sub-TLVs received that are not applicable in the context
of the L2 Bundle Member Attributes sub-TLV.
+=======+======================================+===============+
| Value | Description | Applicability |
+=======+======================================+===============+
| 1 | SID/Label | N |
+-------+--------------------------------------+---------------+
| 2 | Adj-SID | Y |
+-------+--------------------------------------+---------------+
| 3 | LAN Adj-SID/Label | Y |
+-------+--------------------------------------+---------------+
| 4 | Network-to-Router Metric | N |
+-------+--------------------------------------+---------------+
| 5 | RTM Capability | N |
+-------+--------------------------------------+---------------+
| 6 | OSPFv2 Link MSD | N |
+-------+--------------------------------------+---------------+
| 7 | Graceful-Link-Shutdown | N |
+-------+--------------------------------------+---------------+
| 8 | Remote IPv4 Address | N |
+-------+--------------------------------------+---------------+
| 9 | Local/Remote Interface ID | N |
+-------+--------------------------------------+---------------+
| 10 | Application-Specific Link Attributes | Y |
+-------+--------------------------------------+---------------+
| 11 | Shared Risk Link Group | Y |
+-------+--------------------------------------+---------------+
| 12 | Unidirectional Link Delay | Y |
+-------+--------------------------------------+---------------+
| 13 | Min/Max Unidirectional Link Delay | Y |
+-------+--------------------------------------+---------------+
| 14 | Unidirectional Delay Variation | Y |
+-------+--------------------------------------+---------------+
| 15 | Unidirectional Link Loss | Y |
+-------+--------------------------------------+---------------+
| 16 | Unidirectional Residual Bandwidth | Y |
+-------+--------------------------------------+---------------+
| 17 | Unidirectional Available Bandwidth | Y |
+-------+--------------------------------------+---------------+
| 18 | Unidirectional Utilized Bandwidth | Y |
+-------+--------------------------------------+---------------+
| 19 | Administrative Group | Y |
+-------+--------------------------------------+---------------+
| 20 | Extended Administrative Group | Y |
+-------+--------------------------------------+---------------+
| 22 | TE Metric | Y |
+-------+--------------------------------------+---------------+
| 23 | Maximum Link Bandwidth | Y |
+-------+--------------------------------------+---------------+
| 24 | L2 Bundle Member Attributes | N |
+-------+--------------------------------------+---------------+
Table 1: Applicability of OSPFv2 Link Attribute Sub-TLVs for
L2 Bundle Members
Applicability:
Y: This sub-TLV MAY appear in the L2 Bundle Member Attributes sub-
TLV.
N: This sub-TLV MUST NOT appear in the L2 Bundle Member Attributes
sub-TLV.
In the case of OSPFv3, the L2 Bundle Member Attributes sub-TLV shares
the sub-TLV space of the Router-Link TLV, and the sub-TLVs of the
Router-Link TLV MAY be used to describe the attributes of the member
link. Table 2 lists sub-TLVs that are applicable to the Router-Link
TLV and their applicability for L2 bundle member links. The sub-TLVs
that are not applicable MUST NOT be used as sub-TLVs for the L2
Bundle Member Attributes sub-TLV. Specifications that introduce new
sub-TLVs of the Router-Link TLV MUST indicate their applicability to
the L2 Bundle Member Attributes sub-TLV. An implementation MUST
ignore any sub-TLVs received that are not applicable in the context
of the L2 Bundle Member Attributes sub-TLV.
+=======+=========================================+===============+
| Value | Description | Applicability |
+=======+=========================================+===============+
| 1 | IPv6-Forwarding-Address | X |
+-------+-----------------------------------------+---------------+
| 2 | IPv4-Forwarding-Address | X |
+-------+-----------------------------------------+---------------+
| 3 | Route-Tag | X |
+-------+-----------------------------------------+---------------+
| 4 | Prefix SID | X |
+-------+-----------------------------------------+---------------+
| 5 | Adj-SID | Y |
+-------+-----------------------------------------+---------------+
| 6 | LAN Adj-SID | Y |
+-------+-----------------------------------------+---------------+
| 7 | SID/Label | N |
+-------+-----------------------------------------+---------------+
| 8 | Graceful-Link-Shutdown | N |
+-------+-----------------------------------------+---------------+
| 9 | OSPFv3 Link MSD | N |
+-------+-----------------------------------------+---------------+
| 11 | Application-Specific Link Attributes | Y |
+-------+-----------------------------------------+---------------+
| 12 | Shared Risk Link Group | Y |
+-------+-----------------------------------------+---------------+
| 13 | Unidirectional Link Delay | Y |
+-------+-----------------------------------------+---------------+
| 14 | Min/Max Unidirectional Link Delay | Y |
+-------+-----------------------------------------+---------------+
| 15 | Unidirectional Delay Variation | Y |
+-------+-----------------------------------------+---------------+
| 16 | Unidirectional Link Loss | Y |
+-------+-----------------------------------------+---------------+
| 17 | Unidirectional Residual Bandwidth | Y |
+-------+-----------------------------------------+---------------+
| 18 | Unidirectional Available Bandwidth | Y |
+-------+-----------------------------------------+---------------+
| 19 | Unidirectional Utilized Bandwidth | Y |
+-------+-----------------------------------------+---------------+
| 20 | Administrative Group | Y |
+-------+-----------------------------------------+---------------+
| 21 | Extended Administrative Group | Y |
+-------+-----------------------------------------+---------------+
| 22 | TE Metric | Y |
+-------+-----------------------------------------+---------------+
| 23 | Maximum Link Bandwidth | Y |
+-------+-----------------------------------------+---------------+
| 24 | Local Interface IPv6 Address | N |
+-------+-----------------------------------------+---------------+
| 25 | Remote Interface IPv6 Address | N |
+-------+-----------------------------------------+---------------+
| 26 | Flexible Algorithm Prefix Metric (FAPM) | X |
+-------+-----------------------------------------+---------------+
| 27 | Prefix Source OSPF Router-ID | X |
+-------+-----------------------------------------+---------------+
| 28 | Prefix Source Router Address | X |
+-------+-----------------------------------------+---------------+
| 29 | L2 Bundle Member Attributes | N |
+-------+-----------------------------------------+---------------+
| 33 | OSPF Flexible Algorithm ASBR Metric | X |
+-------+-----------------------------------------+---------------+
Table 2: Applicability of OSPFv3 Link Attribute Sub-TLVs for L2
Bundle Members
Applicability:
Y: This sub-TLV MAY appear in the L2 Bundle Member Attributes sub-
TLV.
N: This sub-TLV MUST NOT appear in the L2 Bundle Member Attributes
sub-TLV.
X: This is not a sub-TLV of the Router-Link TLV; it MUST NOT appear
in the L2 Bundle Member Attributes sub-TLV.
3. BGP-LS Advertisement
The BGP-LS extensions for the advertisement of L2 bundle members and
their attributes were specified in [RFC9085]. Using the OSPF L2
Bundle Member Attributes sub-TLV defined in this document, the L2
bundle member information can now be advertised from OSPF into BGP-LS
on the same lines as discussed for IS-IS in Section 2.2.3 of
[RFC9085].
4. IANA Considerations
IANA has allocated the following code point in the "OSPFv2 Extended
Link TLV Sub-TLVs" subregistry under the "Open Shortest Path First v2
(OSPFv2) Parameters" registry:
Value: 24
Designation: L2 Bundle Member Attributes
IANA has allocated the following code point in the "OSPFv3 Extended-
LSA Sub-TLVs" subregistry under the "Open Shortest Path First v3
(OSPFv3) Parameters" registry:
Value: 29
Description: L2 Bundle Member Attributes
IANA has also introduced a column titled "L2BM" in the "OSPFv2
Extended Link TLV Sub-TLVs" registry. The "L2BM" column indicates
applicability to the L2 Bundle Attributes Member sub-TLV. The
initial allocations (Y/N) for this column are indicated in Table 1.
The following explanatory note has been added to the registry:
| The "L2BM" column indicates applicability to the L2 Bundle
| Attributes Member sub-TLV. The options for the "L2BM" column are:
|
| Y - This sub-TLV MAY appear in the L2 Bundle Member Attributes
| sub-TLV.
|
| N - This sub-TLV MUST NOT appear in the L2 Bundle Member
| Attributes sub-TLV.
Similarly, IANA has introduced a column titled "L2BM" in the "OSPFv3
Extended-LSA Sub-TLVs" registry. The "L2BM" column indicates
applicability to the L2 Bundle Attributes Member sub-TLV. The
initial allocations (Y/N/X) for this column are indicated in Table 2.
The following explanatory note has been added to the registry:
| The "L2BM" column indicates applicability to the L2 Bundle
| Attributes Member sub-TLV. The options for the "L2BM" column are:
|
| Y - This sub-TLV MAY appear in the L2 Bundle Member Attributes
| sub-TLV.
|
| N - This sub-TLV MUST NOT appear in the L2 Bundle Member
| Attributes sub-TLV.
|
| X - This is not a sub-TLV of the Router-Link TLV; it MUST NOT
| appear in the L2 Bundle Member Attributes sub-TLV.
Future allocations in these two registries are required to indicate
the applicability of the introduced sub-TLV to the L2 Bundle Member
Attributes sub-TLV. IANA has added this document as a reference for
both registries.
5. Operational Considerations
Implementations MUST NOT enable the advertisement of L2 bundle member
links and their attributes in OSPF LSAs by default and MUST provide a
configuration option to enable their advertisement on specific links.
[RFC9129] specifies the base YANG data model for OSPF. The required
configuration and operational elements for this feature are expected
to be introduced as augmentation to this base YANG data model for
OSPF.
6. Security Considerations
The OSPF protocol has supported the advertisement of link attribute
information, including link identifiers, for many years. The
advertisements defined in this document are identical to the existing
advertisements defined in [RFC3630], [RFC4203], [RFC5329], [RFC7471],
[RFC8665], and [RFC8666], but they are associated with L2 links that
are part of a bundle interface on which the OSPF protocol operates.
Therefore, the security considerations of these documents are
applicable, and there are no new security issues introduced by the
extensions in this document.
As always, if the protocol is used in an environment where
unauthorized access to the physical links on which OSPF packets are
sent occurs, then attacks are possible. The use of authentication as
defined in [RFC5709], [RFC7474], [RFC4552], and [RFC7166] is
recommended for preventing such attacks.
7. References
7.1. Normative References
[IEEE802.1AX]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks--Link Aggregation", IEEE Std 802.1AX,
DOI 10.1109/IEEESTD.2020.9105034, May 2020,
<https://doi.org/10.1109/IEEESTD.2020.9105034>.
[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>.
[RFC4202] Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
<https://www.rfc-editor.org/info/rfc4202>.
[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>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
December 2019, <https://www.rfc-editor.org/info/rfc8666>.
[RFC9085] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Gredler,
H., and M. Chen, "Border Gateway Protocol - Link State
(BGP-LS) Extensions for Segment Routing", RFC 9085,
DOI 10.17487/RFC9085, August 2021,
<https://www.rfc-editor.org/info/rfc9085>.
7.2. Informative References
[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>.
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
<https://www.rfc-editor.org/info/rfc4203>.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[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>.
[RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, DOI 10.17487/RFC5709, October
2009, <https://www.rfc-editor.org/info/rfc5709>.
[RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting
Authentication Trailer for OSPFv3", RFC 7166,
DOI 10.17487/RFC7166, March 2014,
<https://www.rfc-editor.org/info/rfc7166>.
[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
<https://www.rfc-editor.org/info/rfc7471>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<https://www.rfc-editor.org/info/rfc7474>.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8510] Psenak, P., Ed., Talaulikar, K., Henderickx, W., and P.
Pillay-Esnault, "OSPF Link-Local Signaling (LLS)
Extensions for Local Interface ID Advertisement",
RFC 8510, DOI 10.17487/RFC8510, January 2019,
<https://www.rfc-editor.org/info/rfc8510>.
[RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
M., and E. Aries, "Advertising Layer 2 Bundle Member Link
Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
December 2019, <https://www.rfc-editor.org/info/rfc8668>.
[RFC9129] Yeung, D., Qu, Y., Zhang, Z., Chen, I., and A. Lindem,
"YANG Data Model for the OSPF Protocol", RFC 9129,
DOI 10.17487/RFC9129, October 2022,
<https://www.rfc-editor.org/info/rfc9129>.
Acknowledgements
This document leverages similar work done for IS-IS, and the authors
of this document would like to acknowledge the contributions of the
authors of [RFC8668].
The authors would like to thank Anoop Ghanwani, Paul Kyzivat, Dan
Romascanu, and Russ Mundy for their review and feedback on this
document. The authors would also like to thank Acee Lindem for his
detailed shepherd review of this document. The authors would also
like to thank John Scudder for his AD review and the discussion
related to the applicability of TLVs/sub-TLVs to the L2 Bundle Member
Attributes sub-TLV.
Authors' Addresses
Ketan Talaulikar (editor)
Cisco Systems
India
Email: ketant.ietf@gmail.com
Peter Psenak
Cisco Systems
Apollo Business Center
Mlynske nivy 43
821 09 Bratislava
Slovakia
Email: ppsenak@cisco.com
AI ELI5
On this page
PROBLEMWhen OSPF runs over a Layer 2 bundle such as a LAG, it sees one link, so external systems like a Path Computation Element cannot learn about or steer traffic onto individual member links.
MECHANISMA new L2 Bundle Member Attributes sub-TLV (type 24 in OSPFv2, 29 in OSPFv3) carries a 4-octet member descriptor plus nested sub-TLVs with that member's link attributes, such as Adj-SIDs.
WHY IT MATTERSThe information is meant for external entities and does not change OSPF route computation. It can also be passed on through BGP-LS, and it is off by default.
§1Why Bundle Members Need Advertising
Sometimes the Layer 3 interface carrying an OSPF adjacency is a Layer 2 bundle, for example a Link Aggregation Group (LAG). That reduces the number of adjacencies OSPF must maintain when there are parallel links between neighbors. But entities outside OSPF, such as Path Computation Elements (PCEs), may want to control traffic on individual member links, and for that they need attribute information for each member.
This document defines sub-TLVs to advertise that information. Similar capabilities were introduced for IS-IS in RFC 8668. It also lets the Adjacency Segment Identifier (Adj-SID) of RFC 8665 and RFC 8666 be advertised per member link, so traffic can be steered over that specific member.
When many wires are tied together, the router sees one fat cable. Helpers outside the router may want to pick one wire, so each wire needs its own description.
§1.1What Is and Is Not Covered
The advertisements are for entities external to OSPF and do not alter or change OSPF route computation. The RFC deliberately leaves out several things:
- which link attributes get advertised, since that depends on the external entities
- a minimum or default set of attributes
- how the attributes are configured
- how the advertisements are used and what impact they have on traffic
- how the advertisements are passed to external entities
This RFC only says how to describe each wire. It does not say who reads the description or what they do with it.
§2The L2 Bundle Member Attributes Sub-TLV
The new L2 Bundle Member Attributes sub-TLV works in both OSPFv2 and OSPFv3. In OSPFv2 it is an optional sub-TLV of the Extended Link TLV in the Extended Link Opaque LSA (RFC 7684). In OSPFv3 it is an optional sub-TLV of the Router-Link TLV of the E-Router-LSA (RFC 8362).
It has a Type (24 for OSPFv2, 29 for OSPFv3), a Length covering the value including nested sub-TLVs, a 4-octet L2 Bundle Member Descriptor, and then the member link attribute sub-TLVs. The descriptor is a link-local identifier for the member link, as in RFC 4202 and as the Local Interface ID in RFC 8510.
Including a member means that it is part of the bundle and operationally up. So a router MUST NOT advertise a member that is operationally down or no longer in the bundle. The advertisement may be asymmetric, made by the router on only one end of the link.
Each wire gets a name tag number, followed by a list of facts about that wire. Only working wires in the bundle get listed.
081624
| Field | Name | Size | Value | Description |
|---|---|---|---|---|
TYPE | Type | 2 bytes | 24 for OSPFv2, 29 for OSPFv3. | |
LENGTH | Length | 2 bytes | Octets in the value, including nested sub-TLVs. | |
DESCRIPTOR | L2 Bundle Member Descriptor | 4 bytes | A 4-octet link-local identifier for the member link. |
§2Which Attributes Apply to Members
The nested sub-TLVs come from the sub-TLV space of the parent TLV. Not all make sense per member. Typically, attributes with Layer 3 semantics do not apply, but Layer 2 attributes do. Tables in the RFC list each existing sub-TLV as Y (MAY appear), N (MUST NOT appear) or, for OSPFv3, X (not a Router-Link sub-TLV, so MUST NOT appear).
Examples marked as allowed include Adj-SID, LAN Adj-SID, Shared Risk Link Group, the unidirectional delay, loss and bandwidth sub-TLVs, Administrative Group, TE Metric and Maximum Link Bandwidth. Not allowed are, for instance, SID/Label, Graceful-Link-Shutdown, the Link MSD, Remote IPv4 Address and the L2 Bundle Member Attributes sub-TLV itself.
An implementation MUST ignore any received sub-TLV that is not applicable. Future specifications that add sub-TLVs to the Extended Link TLV or Router-Link TLV MUST state whether they apply to the L2 Bundle Member Attributes sub-TLV.
Some facts make sense for one wire, like how fast it is. Others only make sense for the whole cable. The RFC has a checklist saying which is which.
§3Passing It On via BGP-LS
BGP Link State (BGP-LS, RFC 7752) was extended in RFC 9085 to advertise L2 bundle members and their attributes, but that covered only IS-IS. This document updates RFC 9085 so the OSPF sub-TLV can be advertised into BGP-LS in the same way as described for IS-IS in Section 2.2.3 of that RFC.
Another system collects maps from many routers. This lets it also collect the wire-by-wire details from routers that speak OSPF.
§5Operations and IANA
Implementations MUST NOT enable the advertisement of L2 bundle members by default, and MUST provide a configuration option to enable it on specific links. The base YANG model for OSPF is RFC 9129, and the configuration for this feature is expected to be added as an augmentation of it.
IANA allocated value 24 in the OSPFv2 Extended Link TLV Sub-TLVs registry and value 29 in the OSPFv3 Extended-LSA Sub-TLVs registry. It also added an L2BM column to both registries to record applicability, and future allocations must say whether the new sub-TLV applies.
The feature starts switched off. A network operator turns it on for just the cables where it is needed.
§6Security Considerations
The advertisements are identical to existing link attribute advertisements, such as those in RFC 3630, RFC 7471, RFC 8665 and RFC 8666, but they are associated with member links of a bundle. The RFC concludes that the security considerations of those documents apply and that no new security issues are introduced.
As always, an environment where unauthorized access to the physical links carrying OSPF occurs allows attacks. The RFC recommends the authentication mechanisms of RFC 5709, RFC 7474, RFC 4552 and RFC 7166 to prevent them.
Describing each wire adds no new way to cheat. The usual locks on OSPF still apply.
§8References
[RFC7684]RFC 7684Psenak, P., et al., "OSPFv2 Prefix/Link Attribute Advertisement", RFC 7684, November 2015.November 2015[RFC8362]RFC 8362Lindem, A., et al., "OSPFv3 Link State Advertisement (LSA) Extensibility", RFC 8362, April 2018.April 2018[RFC8668]RFC 8668Ginsberg, L., Ed., et al., "Advertising Layer 2 Bundle Member Link Attributes in IS-IS", RFC 8668, December 2019.December 2019[RFC9085]RFC 9085Previdi, S., et al., "Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing", RFC 9085, August 2021.August 2021[RFC8665]RFC 8665Psenak, P., Ed., et al., "OSPF Extensions for Segment Routing", RFC 8665, December 2019.December 2019[RFC8666]RFC 8666Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions for Segment Routing", RFC 8666, December 2019.December 2019[RFC7752]RFC 7752Gredler, H., Ed., et al., "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, March 2016.March 2016