Internet DRAFT - draft-ketant-idr-bgp-ls-flex-algo
draft-ketant-idr-bgp-ls-flex-algo
Inter-Domain Routing K. Talaulikar
Internet-Draft P. Psenak
Intended status: Standards Track Cisco Systems
Expires: August 26, 2019 S. Zandi
G. Dawra
LinkedIn
February 22, 2019
Flexible Algorithm Definition Advertisement with BGP Link-State
draft-ketant-idr-bgp-ls-flex-algo-01
Abstract
Flexible Algorithm is a solution that allows routing protocols (viz.
OSPF and IS-IS) to compute paths over a network based on user-defined
(and hence, flexible) constraints and metrics. The computation is
performed by routers participating in the specific network in a
distribute manner using a Flex Algorithm definition. This definition
provisioned on one or more routers and propagated (viz. OSPF and IS-
IS flooding) through the network.
BGP Link-State (BGP-LS) enables the collection of various topology
information from the network. This draft defines extensions to BGP-
LS address-family to advertise the Flexible Algorithm Definition as a
part of the topology information from the network.
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.
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
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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 August 26, 2019.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. BGP-LS Extensions for Flex Algo Definition . . . . . . . . . 4
2.1. Flex Algo Exclude Any Affinity . . . . . . . . . . . . . 5
2.2. Flex Algo Include Any Affinity . . . . . . . . . . . . . 6
2.3. Flex Algo Include All Affinity . . . . . . . . . . . . . 7
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
4. Manageability Considerations . . . . . . . . . . . . . . . . 8
4.1. Operational Considerations . . . . . . . . . . . . . . . 8
4.2. Management Considerations . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
IGP protocols (OSPF and IS-IS) traditionally compute best paths over
the network based on the IGP metric assigned to the links. Many
network deployments use RSVP-TE [RFC3209] based or Segment Routing
(SR) Policy [I-D.ietf-spring-segment-routing-policy] based solutions
to enforce traffic over a path that is computed using different
metrics or constraints than the shortest IGP path.
[I-D.ietf-lsr-flex-algo] defines the Flexible Algorithm solution that
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allows IGPs themselves to compute constraint based paths over the
network.
Flexible Algorithm is called so as it allows a user the flexibility
to define
o the type of calculation to be used (e.g. shortest path)
o the metric type to be used (e.g. IGP metric or TE metric)
o the set of constraints to be used (e.g. inclusion or exclusion of
certain links using affinities)
The operations of the flexible algorithm solution is described in
detail in [I-D.ietf-lsr-flex-algo] and a high level summary of the
same is described here for clarity. The network operator enables the
participation of specific nodes in the network for a specific
algorithm and then provisions the definition of that flexible
algorithm on one or more of these nodes. The nodes where the
flexible algorithm definition is advertised then flood these
definitions via respective IGP (IS-IS and OSPFv2/v3) mechanisms to
all other nodes in the network. The nodes select the definition for
each algorithm based on the flooded information in a deterministic
manner and thus all nodes participating in a flexible algorithm
computation arrive at a common understanding of the type of
calculation that they need to use.
When using Segment Routing (SR) [RFC8402] forwarding plane, the
result of a flex algorithm computation is the provisioning of the
Prefix SIDs associated with that algorithm with paths based on the
topology computed based on that algorithm. This flex algorithm
computation is within an IGP area or level similar to the default
shortest path tree (SPT) algorithm.
The BGP-LS extensions for SR are defined in
[I-D.ietf-idr-bgp-ls-segment-routing-ext] and includes the
o SR Algorithm TLV to indicate the participation of a node in a flex
algorithm computation
o Prefix SID TLV to indicate the association of the Prefix-SIDs to a
specific flex algorithm
Thus a controller or a Path Computation Engine (PCE) is aware of the
IGP topology across multiple domains which includes the above
information related to the flexible algorithm. This draft defines
extensions to BGP-LS for carrying the Flexible Algorithm Definition
information so that it enables the controller/PCE to learn the
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mapping of the flex algorithm number to its definition in each area/
domain of the underlying IGP. The controller/PCE also learns the
type of computation used and the constraints for the same. This
information can then be leveraged by it for setting up SR Policy
paths end to end across domains by leveraging the appropriate Flex
Algorithm specific Prefix SIDs in its Segment List
[I-D.ietf-spring-segment-routing-policy]. e.g. picking the Flex
Algorithm Prefix SID or ABRs/ASBRs corresponding to a definition that
optimizes on the delay metric enables the PCE/controller to build an
end to end low latency path across IGP domains with minimal Prefix-
SIDs in the SID list.
2. BGP-LS Extensions for Flex Algo Definition
The BGP-LS [RFC7752] specifies the Node NLRI for advertisement of
nodes and their attributes using the BGP-LS Attribute. The Flexible
Algorithm Definition (FAD) advertised by a node are considered as its
node level attributes and advertised as such.
This document defines a new BGP-LS Attribute TLV called the Flexible
Algorithm Definition (FAD) TLV and its format is as follows:
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Flex-Algorithm | Metric-Type | Calc-Type | Priority |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-TLVs ... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Flex Algorithm Definition TLV
where:
o Type: TBD (see IANA Considerations Section 3)
o Length: variable. Minimum of 8 octets.
o Flex-Algorithm : 1 octet value in the range between 128 and 255
inclusive which is the range defined for Flexible Algorithms in
the IANA "IGP Parameters" registries under the "IGP Algorithm
Types" registry [I-D.ietf-lsr-flex-algo].
o Metric-Type : 1 octet value indicating the type of the metric used
in the computation. Values allowed come from the IANA "IGP
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Parameters" registries under the "Flexible Algorithm Definition
Metric-Type" registry [I-D.ietf-lsr-flex-algo].
o Calculation-Type : 1 octet value in the range between 0 and 127
inclusive which is the range defined for the standard algorithms
in the IANA "IGP Parameters" registries under the "IGP Algorithm
Types" registry [I-D.ietf-lsr-flex-algo].
o Priority : 1 octet value between 0 and 255 inclusive that
specifies the priority of the FAD.
o sub-TLVs : zero or more sub-TLVs may be included as described
further in this section.
The FAD TLV can only be added to the BGP-LS Attribute of the Node
NLRI if the corresponding node originates the underlying IGP TLV/sub-
TLV as described below. This information is derived from the
protocol specific advertisements as below..
o IS-IS, as defined by the ISIS Flexible Algorithm Definition sub-
TLV in [I-D.ietf-lsr-flex-algo].
o OSPFv2/OSPFv3, as defined by the OSPF Flexible Algorithm
Definition TLV in [I-D.ietf-lsr-flex-algo].
The following sub-sections define the sub-TLVs for the FAD TLV.
2.1. Flex Algo Exclude Any Affinity
The Flex Algo Exclude Any Affinity sub-TLV is an optional sub-TLV
that is used to carry the affinity constraints [RFC2702] associated
with the flex algo definition and enable the exclusion of links
carrying any of the specified affinities from the computation of the
specific algorithm as described in [I-D.ietf-lsr-flex-algo]. The
affinity is expressed in terms of Extended Admin Group (EAG) as
defined in [RFC7308].
The 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Exclude-Any EAG (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
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o Type: TBD (see IANA Considerations Section 3)
o Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets.
o Exclude-Any EAG : the bitmask used to represent the affinities to
be excluded.
The information in the Flex Algo Exclude Any Affinity sub-TLV is
derived from the IS-IS and OSPF protocol specific Flexible Algorithm
Exclude Admin Group sub-TLV as defined in [I-D.ietf-lsr-flex-algo].
2.2. Flex Algo Include Any Affinity
The Flex Algo Incude Any Affinity sub-TLV is an optional sub-TLV that
is used to carry the affinity constraints [RFC2702] associated with
the flex algo definition and enable the inclusion of links carrying
any of the specified affinities in the computation of the specific
algorithm as described in [I-D.ietf-lsr-flex-algo]. The affinity is
expressed in terms of Extended Admin Group (EAG) as defined in
[RFC7308].
The 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-Any EAG (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: TBD (see IANA Considerations Section 3)
o Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets.
o Include-Any EAG : the bitmask used to represent the affinities to
be included.
The information in the Flex Algo Include Any Affinity sub-TLV is
derived from the IS-IS and OSPF protocol specific Flexible Algorithm
Include-Any Admin Group sub-TLV as defined in
[I-D.ietf-lsr-flex-algo].
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2.3. Flex Algo Include All Affinity
The Flex Algo Incude All Affinity sub-TLV is an optional sub-TLV that
is used to carry the affinity constraints [RFC2702] associated with
the flex algo definition and enable the inclusion of links carrying
all of the specified affinities in the computation of the specific
algorithm as described in [I-D.ietf-lsr-flex-algo]. The affinity is
expressed in terms of Extended Admin Group (EAG) as defined in
[RFC7308].
The 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Include-All EAG (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
o Type: TBD (see IANA Considerations Section 3)
o Length: variable, dependent on the size of the Extended Admin
Group. MUST be a multiple of 4 octets.
o Include-All EAG : the bitmask used to represent the affinities to
be included.
The information in the Flex Algo Include All Affinity sub-TLV is
derived from the IS-IS and OSPF protocol specific Flexible Algorithm
Include-All Admin Group sub-TLV as defined in
[I-D.ietf-lsr-flex-algo].
3. IANA Considerations
This document requests assigning code-points from the registry "BGP-
LS Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs" based on table below. The column "IS-IS TLV/Sub-TLV" defined
in the registry does not require any value and should be left empty.
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+------------+----------------------------------------+----------+
| Code Point | Description | Length |
+------------+----------------------------------------+----------+
| TBD | Flex Algorithm Definition TLV | variable |
| TBD | Flex Algo Exclude Any Affinity sub-TLV | variable |
| TBD | Flex Algo Include Any Affinity sub-TLV | variable |
| TBD | Flex Algo Include All Affinity sub-TLV | variable |
+------------+----------------------------------------+----------+
4. Manageability Considerations
This section is structured as recommended in [RFC5706].
The new protocol extensions introduced in this document augment the
existing IGP topology information that was distributed via [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 encompass the new TLVs for the
BGP-LS NLRI in this document.
4.1. Operational Considerations
No additional operation considerations are defined in this document.
4.2. Management Considerations
No additional management considerations are defined in this document.
5. Security Considerations
The new protocol extensions introduced in this document augment the
existing IGP topology information that was distributed via [RFC7752].
Procedures and protocol extensions defined in this document do not
affect the BGP security model other than as discussed in the Security
Considerations section of [RFC7752].
6. Acknowledgements
The authors would like to thank Les Ginsberg for his reviews and
contributions to this work.
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7. References
7.1. Normative References
[I-D.ietf-lsr-flex-algo]
Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
algo-01 (work in progress), November 2018.
[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>.
7.2. 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-11
(work in progress), October 2018.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
bogdanov@google.com, b., and P. Mattes, "Segment Routing
Policy Architecture", draft-ietf-spring-segment-routing-
policy-02 (work in progress), October 2018.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, DOI 10.17487/RFC2702, September 1999,
<https://www.rfc-editor.org/info/rfc2702>.
[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>.
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[RFC5706] Harrington, D., "Guidelines for Considering Operations and
Management of New Protocols and Protocol Extensions",
RFC 5706, DOI 10.17487/RFC5706, November 2009,
<https://www.rfc-editor.org/info/rfc5706>.
[RFC7308] Osborne, E., "Extended Administrative Groups in MPLS
Traffic Engineering (MPLS-TE)", RFC 7308,
DOI 10.17487/RFC7308, July 2014,
<https://www.rfc-editor.org/info/rfc7308>.
[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
Cisco Systems
Email: ketant@cisco.com
Peter Psenak
Cisco Systems
Slovakia
Email: ppsenak@cisco.com
Shawn Zandi
LinkedIn
USA
Email: szandi@linkedin.com
Gaurav Dawra
LinkedIn
USA
Email: gdawra.ietf@gmail.com
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