IDR Working Group G. Van de Velde, Ed.
Internet-Draft W. Henderickx
Intended status: Standards Track M. Bocci
Expires: December 14, 2018 Nokia
K. Patel
Arrcus
June 12, 2018
Signalling ERLD using BGP-LS
draft-ietf-idr-bgp-ls-segment-routing-rld-02
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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
4. Origination of ERLD in BGP-LS . . . . . . . . . . . . . . . . 3
5. ERLD support by a node . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
9.1. Normative References . . . . . . . . . . . . . . . . . . 5
9.2. 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 capable 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.
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2. Conventions used in this document
2.1. Terminology
BGP-LS: Distribution of Link-State and TE Information using Border
Gateway Protocol
ERLD: Entropy capable Readable Label Depth
PCC: Path Computation Client
PCE: Path Computation Element
PCEP: Path Computation Element Protocol
SID: Segment Identifier
SR: Segment routing
3. Problem Statement
In existing technology both ISIS [4] and OSPF [3] have proposed
extensions to signal the RLD (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
ISIS or OSPF technology, then both RLD and ELC needs to be signalled
using BGP-LS encoding. This document describes the extension BGP-LS
requires to transport the combined RLD and ELC into an ERLD (Entropy
capable Readable Label Depth) attribute.
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. Origination of ERLD in BGP-LS
Both ISIS [4] and OSPF [3] have proposed extensions to signal the RLD
(Readable Label Depth) and ELC (Entropy Label Capability) for a node.
A BGP-LS router exporting the IGP LSDB, MUST NOT encode the IGP RLD
value in an BGP-LS ERLD attribute, if the associated node ELC is not
signalled.
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5. ERLD support by a node
Node ERLD is encoded in a new Node Attribute TLV, as defined in
RFC7752 [2].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ERLD |
+-+-+-+-+-+-+-+-+
Figure 1
Type : A 2-octet field specifying code-point of the new TLV type.
Code-point: TBA from BGP-LS Node Descriptor, Link Descriptor,
Prefix Descriptor, and Attribute TLVs registry
Length: A 2-octet field that indicates the length of the value
portion
ERLD: Node ERLD is a number in the range of 0-254. 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.
6. Security Considerations
This document does not introduce security issues beyond those
discussed in RFC7752 [2]
7. 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.
8. IANA Considerations
This document requests assigning a new code-points from the BGP-LS
Node Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs registry as specified in section 5.
Note: placeholder IANA request
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Request Node ERLD codepoint
BGP-LS TLV Code Point: TBD1
ISIS TLV 242/TBD2
Note: There is nothing in IANA from draft draft-ietf-isis-mpls-elc
Note: Draft talks only about ELC/RLD and that is mismatch with ERLD
OSPF RI TLV TBD5
OSPF ELC in Non-OSPF functionality Capability Bits (TBD6)
9. References
9.1. 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>.
[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>.
9.2. Informative References
[3] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "draft-ietf-ospf-mpls-elc", January 2018.
[4] Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "draft-ietf-isis-mpls-elc", January 2018.
Authors' Addresses
Gunter Van de Velde (editor)
Nokia
Antwerp
BE
Email: gunter.van_de_velde@nokia.com
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Wim Henderickx
Nokia
Belgium
Email: wim.henderickx@nokia.com
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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