Inter-Domain Routing K. Talaulikar, Ed.
Internet-Draft Arrcus Inc
Intended status: Standards Track P. Psenak
Expires: October 30, 2022 Cisco Systems
J. Tantsura
Microsoft
April 28, 2022
Application-Specific Attributes Advertisement with BGP Link-State
draft-ietf-idr-bgp-ls-app-specific-attr-10
Abstract
Various link attributes have been defined in link-state routing
protocols like OSPF and IS-IS in the context of the MPLS Traffic
Engineering (TE) and GMPLS. BGP Link-State (BGP-LS) extensions have
been defined to distribute these attributes along with other topology
information from these link-state routing protocols.
New extensions have been defined for link-state routing protocols
that enable distribution of application-specific link attributes for
existing as well as newer applications such as Segment Routing. This
document defines extensions to BGP-LS to enable the advertisement of
these application-specific attributes as a part of the topology
information from the network.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 30, 2022.
Talaulikar, et al. Expires October 30, 2022 [Page 1]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
Copyright Notice
Copyright (c) 2022 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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Application Specific Link Attributes TLV . . . . . . . . . . 3
3. Application-Specific Link Attributes . . . . . . . . . . . . 5
4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Deployment Considerations . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Manageability Considerations . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
BGP Link-State [RFC7752] enables the distribution of the link-state
topology information from link-state routing protocols (viz., IS-IS
[RFC1195], OSPFv2 [RFC2328] and OSPFv3 [RFC5340]) to an application
like a controller or Path Computation Engine (PCE) via BGP. The
controller/PCE gets the end-to-end topology information across IGP
domains so it can perform path computations for use cases like end-
to-end traffic engineering (TE).
The link-state topology information distributed via BGP-LS includes
link attributes that were originally defined for traditional MPLS
Traffic Engineering (i.e., using RSVP-TE [RFC3209]) or GMPLS
[RFC4202]) applications. In recent years new applications, such as
Segment Routing (SR) Policy [RFC8402] and Loop-Free Alternates (LFA)
[RFC5286], that also make use of link attributes have been
Talaulikar, et al. Expires October 30, 2022 [Page 2]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
introduced. [RFC8919] and [RFC8920] define extensions for IS-IS and
OSPF respectively that enable advertising application-specific link
attributes for these and other future applications. This has
resulted in the need for a similar BGP-LS extension to include this
additional link-state topology information from the link-state
routing protocols.
This document defines the BGP-LS extensions for the advertisement of
application-specific link attributes. It describes the advertisement
of these link attributes as top-level TLVs (i.e., as TLVs of the BGP-
LS Attribute) and as sub-TLVs of the new (top-level) Application
Specific Link Attributes TLV. The document also describes the
procedures for the advertisement of these attributes from the
underlying IGPs and discusses their deployment aspects.
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. Application Specific Link Attributes TLV
The BGP-LS [RFC7752] specifies the Link NLRI for the advertisement of
links and their attributes using the BGP-LS Attribute. The
Application-Specific Link Attributes (ASLA) TLV is a new optional
top-level BGP-LS Attribute TLV that is introduced for Link NLRIs. It
is defined such that it may act as a container for certain existing
and future link attributes that require application-specific
definition.
The format of this TLV is as follows and is similar to the
corresponding ASLA sub-TLVs defined for OSPF and IS-IS in [RFC8920]
and [RFC8919] respectively.
Talaulikar, et al. Expires October 30, 2022 [Page 3]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SABM Length | UDABM Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Standard Application Identifier Bit Mask (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| User-Defined Application Identifier Bit Mask (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Attribute sub-TLVs //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Application-Specific Link Attributes TLV
where:
o Type: 1122
o Length: variable.
o SABM Length : Standard Application Identifier Bit Mask Length in
octets as defined in [RFC8920].
o UDABM Length : User-Defined Application Identifier Bit Mask Length
in octets as defined in [RFC8920].
o Standard Application Identifier Bit Mask : An optional set of bits
(of size 0, 4, or 8 octets as indicated by the SABML), where each
bit represents a single standard application as defined in
[RFC8919].
o User-Defined Application Identifier Bit Mask : An optional set of
bits (of size 0, 4, or 8 octets as indicated by the UDABML), where
each bit represents a single user-defined application as defined
in [RFC8919].
o Link Attribute sub-TLVs : BGP-LS Attribute TLVs corresponding to
the Link NLRI that are application-specific (including existing
ones as specified in Section 3) are included as sub-TLVs of the
ASLA TLV.
The semantics associated with the standard and user-defined bit masks
as well as the encoding scheme for application-specific attributes
are as specified in [RFC8920].
Talaulikar, et al. Expires October 30, 2022 [Page 4]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
The ASLA TLV and its sub-TLVs can only be added to the BGP-LS
Attribute associated with the Link NLRI of the node that originates
the underlying IGP link attribute TLVs/sub-TLVs. The procedures for
originating link attributes in the ASLA TLV from underlying IGPs are
specified in Section 4.
3. Application-Specific Link Attributes
Several BGP-LS Attribute TLVs corresponding to the Link NLRI are
defined in BGP-LS and more may be added in the future. Those
attributes that have been determined to be, and advertised as
application-specific in the underlying IGPs are also encoded in a
similar manner in BGP-LS.
The following table lists the currently defined BGP-LS Attributes
TLVs corresponding to Link NLRI that can have application-specific
semantics based on the underlying IGP specifications [RFC8919]
[RFC8920]. These were originally defined with semantics for RSVP-TE
and GMPLS applications in BGP-LS by the respective reference
documents.
+---------------+-------------------------------+-------------------+
| TLV Code | Description | Reference |
| Point | | Document |
+---------------+-------------------------------+-------------------+
| 1088 | Administrative group (color) | [RFC7752] |
| 1092 | TE Default Metric | [RFC7752] |
| 1096 | Shared Risk Link Group | [RFC7752] |
| 1114 | Unidirectional Link Delay | [RFC8571] |
| 1115 | Min/Max Unidirectional Link | [RFC8571] |
| | Delay | |
| 1116 | Unidirectional Delay | [RFC8571] |
| | Variation | |
| 1117 | Unidirectional Link Loss | [RFC8571] |
| 1118 | Unidirectional Residual | [RFC8571] |
| | Bandwidth | |
| 1119 | Unidirectional Available | [RFC8571] |
| | Bandwidth | |
| 1120 | Unidirectional Utilized | [RFC8571] |
| | Bandwidth | |
| 1173 | Extended Administrative Group | [RFC9104] |
+---------------+-------------------------------+-------------------+
Table 1: Existing BGP-LS TLVs identified as Application-Specific
All the BGP-LS Attribute TLVs defined in the table above are REQUIRED
to be advertised as a top-level TLV in the BGP-LS Attribute for
carrying link attributes specific to RSVP-TE.
Talaulikar, et al. Expires October 30, 2022 [Page 5]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
BGP-LS Attribute TLVs corresponding to Link NLRI that are identified
as application-specific are REQUIRED to be encoded within an ASLA
TLV.
Link attributes that do not have application-specific semantics MUST
NOT be advertised within the ASLA TLV.
When the same application-specific link attributes are advertised
both within the ASLA TLV and as top-level TLVs in the BGP-LS
Attribute, the attributes advertised within the ASLA TLV take
precedence for the applications indicated in the ASLA TLV encoding.
4. Procedures
The BGP-LS originator learns of the association of an application-
specific attribute to one or more applications from the underlying
IGP protocol LSA/LSPs from which it is advertising the topology
information. [RFC8920] and [RFC8919] specify the mechanisms for
advertising application-specific link attributes in OSPF and IS-IS
respectively.
Application-specific link attributes received from an IGP node
without the use of ASLA encodings continue to be encoded using the
respective BGP-LS top-level TLVs listed in Table 1 as specified in
their respective reference documents.
A BGP-LS originator node that is advertising link-state information
from the underlying IGP using ASLA encodings determines their BGP-LS
encoding based on the following rules:
1. Application-specific link attributes received from an OSPF node
using ASLA sub-TLV or from an IS-IS node using either ASLA sub-
TLV or ASLA SRLG TLV MUST be encoded in the BGP-LS ASLA TLV as
sub-TLVs. Exceptions to this rule are specified in (2)(F) and
(2)(G) below.
2. In the case of IS-IS, the following specific procedures are to be
followed:
A. When application-specific link attributes are received from a
node with the L bit set in the ASLA sub-TLV and application
bits other than RSVP-TE are set in the application bit masks
then the application-specific link attributes advertised in
the corresponding legacy IS-IS TLVs/sub-TLVs MUST be encoded
within the BGP-LS ASLA TLV as sub-TLVs with the application
bits, other than the RSVP-TE bit, copied from the IS-IS ASLA
sub-TLV. The link attributes advertised in the legacy IS-IS
TLVs/sub-TLVs are also advertised in BGP-LS top-level TLVs as
Talaulikar, et al. Expires October 30, 2022 [Page 6]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
per [RFC7752] [RFC8571] [RFC9104]. The same procedure also
applies for the advertisement of the SRLG values from the IS-
IS ASLA SRLG TLV.
B. When the ASLA sub-TLV has the RSVP-TE application bit set,
then the link attributes for the corresponding ASLA sub-TLV
MUST be encoded using the respective BGP-LS top-level TLVs as
per [RFC7752] [RFC8571] [RFC9104]. Similarly, when the ASLA
SRLG TLV has the RSVP-TE application bit set, then the SRLG
values within it MUST be encoded using the top-level BGP-LS
SRLG TLV (1096) as per [RFC7752].
C. The SRLGs advertised in IS-IS SRLG ASLA TLVs and the other
link attributes advertised in IS-IS ASLA sub-TLVs are
REQUIRED to be collated, on a per-application basis, for all
applications that have their bit set in the SABM/UDABM in at
least one of the aforementioned TLV types. When performing
this collation, only the TLVs with the application's bit set
in SABM/UDABM MUST be used when such TLVs are available from
either TLV types. If the bit for an application is set in
the SABM/UDABM of only one of the TLV types, then the
attributes from the other TLV type with zero-length
application bit mask MUST be also collated for that
application, if such TLV is available. Such collated link
attributes are advertised in a per-application instance of
the BGP-LS ASLA TLV.
D. If the resulting set of collated link attributes and SRLG
values is common across multiple applications, they MAY be
advertised in a common BGP-LS ASLA TLV instance where the
bits for all such applications would be set in the
application bit mask.
E. Both the SRLG values from IS-IS ASLA SRLG TLVs and the link
attributes from IS-IS ASLA sub-TLVs, with the zero-length
application bit mask, MUST be advertised into a BGP-LS ASLA
TLV with a zero-length application bit mask, independent of
the collation described above.
F. [RFC8919] allows the advertisement of the Maximum Link
Bandwidth within an ASLA sub-TLV even though it is not an
application-specific attribute. However, when originating
the Maximum Link Bandwidth into BGP-LS, the attribute MUST be
encoded only in the top-level BGP-LS Maximum Link Bandwidth
TLV (1089) and MUST NOT be advertised within the BGP-LS ASLA
TLV.
Talaulikar, et al. Expires October 30, 2022 [Page 7]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
G. [RFC8919] also allows the advertisement of the Maximum
Reservable Link Bandwidth and the Unreserved Bandwidth within
an ASLA sub-TLV even though these attributes are specific to
RSVP-TE application. However, when originating the Maximum
Reservable Link Bandwidth and Unreserved Bandwidth into BGP-
LS, these attributes MUST be encoded only in the BGP-LS top-
level Maximum Reservable Link Bandwidth TLV (1090) and
Unreserved Bandwidth TLV (1091) respectively and not within
the BGP-LS ASLA TLV.
These rules ensure that a BGP-LS originator performs the
advertisement for all application-specific link attributes from the
IGP nodes that support or do not support the ASLA extension.
Furthermore, it also ensures that the top-level BGP-LS TLVs defined
for RSVP-TE and GMPLS applications continue to be used for
advertisement of their application-specific attributes.
A BGP-LS speaker would normally advertise all the application-
specific link attributes corresponding to RSVP-TE and GMPLS
applications as existing top-level BGP-LS TLVs while for other
applications they are encoded in ASLA TLV(s) with appropriate
applicable bit mask setting. The application-specific attribute
value received via sub-TLVs within the ASLA TLV have preference over
the value received via the top-level TLVs.
5. Deployment Considerations
BGP-LS sources the link-state topology information (including the
extensions introduced by this document) from the underlying link-
state IGP protocols. The various deployment aspects related to the
advertisement and use of application-specific link attributes are
discussed in the Deployment Considerations sections of [RFC8920] and
[RFC8919]. The IGP backward compatibility aspects described in those
documents associated with application-specific link attributes along
with the BGP-LS procedures specified in this document enable backward
compatibility in deployments of existing implementations of [RFC7752]
[RFC8571] [RFC9104] for applications such as RSVP-TE, SR Policy, and
LFA.
It is recommended that nodes supporting this specification are
selected as originators of BGP-LS information when advertising the
link-state information from the IGPs.
BGP-LS consumers that do not support this specification can continue
to use the existing top-level TLVs for link attributes for existing
applications as discussed above. They would, however, not be able to
support neither the application-specific link attributes nor newer
applications that may be encoded only using the ASLA TLV.
Talaulikar, et al. Expires October 30, 2022 [Page 8]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
6. IANA Considerations
IANA has assigned, through the early allocation process, the
following code-point from the "BGP-LS Node Descriptor, Link
Descriptor, Prefix Descriptor, and Attribute TLVs" registry. This
document requests that the allocation be made permanent. The column
"IS-IS TLV/Sub-TLV" defined in the registry does not require any
value and should be left empty.
+------------+------------------------------------------+----------+
| Code Point | Description | Length |
+------------+------------------------------------------+----------+
| 1122 | Application-Specific Link Attributes TLV | variable |
+------------+------------------------------------------+----------+
Table 2: ASLA TLV Code-Point Allocation
7. Manageability Considerations
The new protocol extensions introduced in this document augment the
existing IGP topology information defined in [RFC7752]. Procedures
and protocol extensions defined in this document do not affect the
BGP protocol operations and management other than as discussed in the
Manageability Considerations section of [RFC7752]. Specifically, the
malformed NLRIs attribute tests in the Fault Management section of
[RFC7752] now encompasses the BGP-LS TLVs defined in this document.
The extensions specified in this document do not specify any new
configuration or monitoring aspects in BGP or BGP-LS. The
specification of BGP models is an ongoing work based on
[I-D.ietf-idr-bgp-model].
8. Security Considerations
Security considerations for acquiring and distributing BGP-LS
information are discussed in [RFC7752].
The TLVs introduced in this document are used to propagate the
application-specific link attributes IGP extensions defined in
[RFC8919] and [RFC8920]. It is assumed that the IGP instances
originating these TLVs will support all the required security (as
described in [RFC8919] and [RFC8920]) to prevent any security issues
when propagating the TLVs into BGP-LS.
This document defines a new way to advertise link attributes.
Tampering with the information defined in this document may affect
applications using it, including impacting traffic engineering, which
Talaulikar, et al. Expires October 30, 2022 [Page 9]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
uses various link attributes for its path computation. As the
advertisements defined in this document limit the scope to specific
applications, the impact of tampering is similarly limited in scope.
The advertisement of the link attribute information defined in this
document presents no significant additional risk beyond that
associated with the existing link attribute information already
supported in [RFC7752].
9. Acknowledgements
The authors would like to thank Les Ginsberg, Baalajee S, Amalesh
Maity, Acee Lindem, Keyur Patel, Paul Wouters, and Rudy Selderslaghs
for their review and feedback on this document. The authors would
also like to thank Alvaro Retana for his very detailed AD review and
comments for improving this document.
10. References
10.1. 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>.
[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>.
[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>.
[RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
IGP Traffic Engineering Performance Metric Extensions",
RFC 8571, DOI 10.17487/RFC8571, March 2019,
<https://www.rfc-editor.org/info/rfc8571>.
[RFC8919] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
J. Drake, "IS-IS Application-Specific Link Attributes",
RFC 8919, DOI 10.17487/RFC8919, October 2020,
<https://www.rfc-editor.org/info/rfc8919>.
Talaulikar, et al. Expires October 30, 2022 [Page 10]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
[RFC8920] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
J., and J. Drake, "OSPF Application-Specific Link
Attributes", RFC 8920, DOI 10.17487/RFC8920, October 2020,
<https://www.rfc-editor.org/info/rfc8920>.
[RFC9104] Tantsura, J., Wang, Z., Wu, Q., and K. Talaulikar,
"Distribution of Traffic Engineering Extended
Administrative Groups Using the Border Gateway Protocol -
Link State (BGP-LS)", RFC 9104, DOI 10.17487/RFC9104,
August 2021, <https://www.rfc-editor.org/info/rfc9104>.
10.2. Informative References
[I-D.ietf-idr-bgp-model]
Jethanandani, M., Patel, K., Hares, S., and J. Haas, "BGP
YANG Model for Service Provider Networks", draft-ietf-idr-
bgp-model-13 (work in progress), March 2022.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[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>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008,
<https://www.rfc-editor.org/info/rfc5286>.
[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>.
Talaulikar, et al. Expires October 30, 2022 [Page 11]
Internet-Draft BGP-LS Extns for App Specific Attributes April 2022
[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>.
Authors' Addresses
Ketan Talaulikar (editor)
Arrcus Inc
India
Email: ketant.ietf@gmail.com
Peter Psenak
Cisco Systems
Slovakia
Email: ppsenak@cisco.com
Jeff Tantsura
Microsoft
Email: jefftant.ietf@gmail.com
Talaulikar, et al. Expires October 30, 2022 [Page 12]
