Internet DRAFT - draft-ietf-idr-bgp-ls-segment-routing-rld
draft-ietf-idr-bgp-ls-segment-routing-rld
IDR Working Group G. Van de Velde, Ed.
Internet-Draft W. Henderickx
Intended status: Standards Track M. Bocci
Expires: February 21, 2020 Nokia
K. Patel
Arrcus
August 20, 2019
Signalling ERLD using BGP-LS
draft-ietf-idr-bgp-ls-segment-routing-rld-05
Abstract
This document defines the attribute encoding to use for BGP-LS to
expose ERLD "Entropy capable Readable Label Depth" from a node to a
centralised controller (PCE/SDN).
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1].
Status of This Memo
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Copyright Notice
Copyright (c) 2019 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
4. Advertising of ERLD in BGP-LS . . . . . . . . . . . . . . . . 3
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
8.1. Normative References . . . . . . . . . . . . . . . . . . 4
8.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
When Segment Routing tunnels are computed by a centralised
controller, it is beneficial that the controller knows the ERLD
(Entropy Readable Label Depth) of each node or link a tunnel
traverses. A network node signalling an ERLD MUST support the
ability to read the signalled number of labels before any action is
done upon the packet and SHOULD support entropy awareness found
within the signalled ERLD depth.
ERLD awareness of each node will allow a network SDN controller to
influence the path used for each tunnel. The SDN controller may for
example only create tunnels with a label stack smaller or equal as
the ERLD of each node on the path. This will allow the network to
behave accordingly (e.g. make use of Entropy Labels to improve ECMP)
upon the imposed Segment Routing label stack on each packet.
This document describes how to use BGP-LS to expose the ERLD of a
node.
2. Conventions used in this document
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2.1. Terminology
BGP-LS: Distribution of Link-State and TE Information using Border
Gateway Protocol
ERLD: Entropy capable Readable Label Depth
ELC: Entropy Label Capability
MSD: Maximum SID Depth
SID: Segment Identifier
3. Problem Statement
For Segment Routing technology both ISIS [7] and OSPF [6] have
proposed extensions to signal the ERLD (Entropy Readable Label Depth)
and ELC (Entropy Label Capability) of a node. However, if a network
SDN controller is connected to the network through a BGP-LS session
and not through either ISIS or OSPF technology, then both ERLD and
ELC needs to be signalled using BGP-LS encoding. This document
describes the extension BGP-LS requires to signal ERLD.
A network SDN controller having awareness of the ERLD can for example
use it as a constraint on path computation to make sure that high
bandwidth LSPs are not placed on LAG (Link Aggregation Group),
containing links with smaller member bandwidth, if they know the
entropy label cannot be processed by the node at the ingress to the
link.
4. Advertising of ERLD in BGP-LS
Both ISIS [7] and OSPF [6] have proposed extensions to signal the
ERLD (Entropy Readable Label Depth) and ELC (Entropy Label
Capability) using new MSD-type of the Node MSD sub-Type TLV RFC8491
[4] or RFC8476 [3].
This document defines a new node BGP MSD sub-type TLV from draft-
ietf-idr-bgp-ls-segment-routing-msd [5] to signal the ERLD.
A BGP-LS router exporting the IGP LSDB, MUST NOT encode the IGP ERLD
value in an BGP-LS ERLD attribute, if the associated ELC is not
signalled.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type=TBD | ERLD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1
The BGP-LS ERLD is encoded as a node MSD sub-type defined in the IANA
registry titled "IGP MSD-Types" under the "Interior Gateway Protocol
(IGP) Parameters" registry created by RFC8491 [4].
The ERLD-Value field in the range between 0 to 255 is set to the BGP-
LS imported IGP ERLD. The value of 0 represents lack of ability to
read a label stack of any depth, any other value represents the
readable label depth of the node.
5. Security Considerations
This document does not introduce security issues beyond those
discussed in RFC7752 [2]
6. Acknowledgements
Thanks to discussions with Acee Lindem, Jeff Tantsura, Stephane
Litkowski, Bruno Decraene, Kireeti Kompella, John E. Drake and
Carlos Pignataro to bring the concept of combining ELC and RLD into a
single ERLD signalled parameter more suitable for SDN controller
based networks.
7. IANA Considerations
This document requests assigning new BGP MSD sub-TLV code-points as
described in section 4.
Note: placeholder IANA request
8. References
8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://xml.resource.org/public/rfc/html/rfc2119.html>.
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[2] 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>.
[3] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
DOI 10.17487/RFC8476, December 2018,
<https://www.rfc-editor.org/info/rfc8476>.
[4] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>.
[5] Tantsura, J., Chunduri, U., Talaulikar, K., Mirsky, G.,
and N. Triantafillis, "draft-ietf-idr-bgp-ls-segment-
routing-msd", June 2019.
8.2. Informative References
[6] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "draft-ietf-ospf-mpls-elc", May 2019.
[7] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "draft-ietf-isis-mpls-elc", May 2019.
Authors' Addresses
Gunter Van de Velde (editor)
Nokia
Antwerp
BE
Email: gunter.van_de_velde@nokia.com
Wim Henderickx
Nokia
Belgium
Email: wim.henderickx@nokia.com
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Matthew Bocci
Nokia
Shoppenhangers Road
Maidenhead, Berks
UK
Email: matthew.bocci@nokia.com
Keyur Patel
Arrcus
USA
Email: keyur@arrcus.com
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