Internet DRAFT - draft-filsfils-spring-large-scale-interconnect
draft-filsfils-spring-large-scale-interconnect
Network Working Group C. Filsfils, Ed.
Internet-Draft S. Previdi
Intended status: Informational Cisco Systems, Inc.
Expires: September 6, 2019 G. Dawra, Ed.
LinkedIn
W. Henderickx
Nokia
D. Cooper
Level 3
March 5, 2019
Interconnecting Millions Of Endpoints With Segment Routing
draft-filsfils-spring-large-scale-interconnect-13
Abstract
This document describes an application of Segment Routing to scale
the network to support hundreds of thousands of network nodes, and
tens of millions of physical underlay endpoints. This use-case can
be applied to the interconnection of massive-scale DCs and/or large
aggregation networks. Forwarding tables of midpoint and leaf nodes
only require a few tens of thousands of entries. This may be
achieved by inherert scaleable nature of Segment Routing and designed
proposed in this document.
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Reference Design . . . . . . . . . . . . . . . . . . . . . . 3
4. Control Plane . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Illustration of the scale . . . . . . . . . . . . . . . . . . 5
6. Design Options . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Segment Routing Global Block(SRGB) Size . . . . . . . . . 6
6.2. Redistribution of Agg nodes routes . . . . . . . . . . . 6
6.3. Sizing and hierarchy . . . . . . . . . . . . . . . . . . 6
6.4. Local Segments to Hosts/Servers . . . . . . . . . . . . . 7
6.5. Compressed SRTE policies . . . . . . . . . . . . . . . . 7
7. Deployment Model . . . . . . . . . . . . . . . . . . . . . . 7
8. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Simplified operations . . . . . . . . . . . . . . . . . . 8
8.2. Inter-domain SLA . . . . . . . . . . . . . . . . . . . . 8
8.3. Scale . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.4. ECMP . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10. Manageability Considerations . . . . . . . . . . . . . . . . 9
11. Security Considerations . . . . . . . . . . . . . . . . . . . 9
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
14. Informative References . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
This document describes how SR can be used to interconnect millions
of endpoints.The following terminology is used in this document:
2. Terminology
The following terms and abbreviations are used in this document:
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Term Definition
---------------------------------------------------------
Agg Aggregation
BGP Border Gateway Protocol
DC Data Center
DCI Data Center Interconnect
ECMP Equal Cost MultiPathing
FIB Forwarding Information Base
LDP Label Distribution Protocol
LFIB Label Forwarding Information Base
MPLS Multi-Protocol Label Switching
PCE Path Computation Element
PCEP Path Computation Element Protocol
PW Pseudowire
SLA Service level Agreement
SR Segment Routing
SRTE Policy Segment Routing Traffic Engineering Policy
TE Traffic Engineering
TI-LFA Topology Independent - Loop Free Alternative
3. Reference Design
The network diagram here below describes the reference network
topology used in this document:
+-------+ +--------+ +--------+ +-------+ +-------+
A DCI1 Agg1 Agg3 DCI3 Z
| DC1 | | M1 | | C | | M2 | | DC2 |
| DCI2 Agg2 Agg4 DCI4 |
+-------+ +--------+ +--------+ +-------+ +-------+
Figure 1: Reference Topology
The following applies to the reference topology above:
Independent ISIS-OSPF/SR instance in core (C) region.
Independent ISIS-OSPF/SR instance in Metro1 (M1) region.
Independent ISIS-OSPF/SR instance in Metro2 (M2) region.
BGP/SR in DC1.
BGP/SR in DC2.
Agg routes (Agg1, Agg2, Agg3, Agg4) are redistributed from C to M
(M1 and M2) and from M to DC domains.
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No other route is advertised or redistributed between regions.
The same homogeneous SRGB is used throughout the domains (e.g.
16000-23999).
Unique SRGB sub-ranges are allocated to each metro (M) and core
(C) domains:
16000-16999 range is allocated to the core (C) domain/region.
17000-17999 range is allocated to the M1 domain/region.
18000-18999 range is allocated to the M2 domain/region.
Specifically, Agg1 router has SID 16001 allocated and Agg2
router has SID 16002 allocated.
Specifically, Agg3 router has SID 16003 allocated and the
anycast SID for Agg3 and Agg4 is 16006.
Specifically, DCI3 router has SID 18003 allocated and the
anycast SID for DCI3 and DCI4 is 18006.
Specifically, at Agg1 router Binding SID 4001 leads to DCI Pair
DCI3, DCI4 via specific low-latency path {16002, 16003, 18006}.
The same SRGB sub-range is re-used within each DC (DC1 and DC2)
region. for each DC: e.g. 20000-23999. Specifically, nodes A and
Z both have SID 20001 allocated to them.
4. Control Plane
This section provides a high-level description of a how a control
plane could be implemented using protocol components already defined
in other RFCs.
The mechanism through which SRTE Policies are defined, computed and
programmed in the source nodes, are outside the scope of this
document.
Typically, a controller or a service orchestration system programs
node A with a pseudowire (PW) to a remote next-hop Z with a given SLA
contract (e.g. low-latency path, be disjoint from a specific core
plane, be disjoint from a different PW service, etc.).
Node A automatically detects that it does not have reachability to Z.
It then automatically sends a PCEP request to an SR PCE for an SRTE
policy that provides reachability to Z with the requested SLA.
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The SR PCE [RFC4655] is made of two components. A multi-domain
topology and a computation engine. The multi-domain topology is
continuously refreshed through BGP-LS [RFC7752] feeds from each
domain. The computing engine is desined to implemet Traffic
Engineering (TE) algorithms and provide output in SR Path format.
Upon receiving the PCEP [RFC5440] request, the SR PCE computes the
requested path. The path is expressed through a list of segments
(e.g. {16003, 18006, 20001} and provided to node A.
The SR PCE logs the request as a stateful query and hence is capable
to recompute the path at each network topology change.
Node A receives the PCEP reply with the path (expressed as a segment
list). Node A installs the received SRTE policy in the dataplane.
Node A then automatically steers the PW into that SRTE policy.
5. Illustration of the scale
According to the reference topology described in Figure 1 the
following assumptions are made:
There's 1 core domain and 100 leaf (metro) domains.
The core domain includes 200 nodes.
Two nodes connect each leaf (metro) domain. Each node connecting
a leaf domain has a SID allocated. Each pair of nodes connecting
a leaf domain also has a common anycast SID. This brings up to
300 prefix segments in total.
A core node connects only one leaf domain.
Each leaf domain has 6000 leaf node segments. Each leaf-node has
500 endpoints attached, thus 500 adjacency segments. In total, it
is 3 millions endpoints for a leaf domain.
Based on the above, the network scaling numbers are as follows:
6,000 leaf node segments multiplied by 100 leaf domains: 600,000
nodes.
600,000 nodes multiplied by 500 endpoints: 300 millions of
endpoints.
The node scaling numbers are as follows:
Leaf node segment scale: 6,000 leaf node segments + 300 core node
segments + 500 adjacency segments = 6,800 segments
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Core node segment scale: 6,000 leaf domain segments + 300 core
domain segments = 6,300 segments
In the above calculations, the link adjacency segments are not taken
into account. These are local segments and, typically, less than 100
per node.
It has to be noted that, depending on leaf node FIB capabilities,
leaf domains could be split into multiple smaller domains. In the
above example, the leaf domains could be split into 6 smaller domains
so that each leaf node only need to learn 1000 leaf node segments +
300 core node segments + 500 adjacency segments which gives a total
of 1,800 segments.
6. Design Options
This section describes multiple design options to the illustration of
previous section.
6.1. Segment Routing Global Block(SRGB) Size
In the simplified illustrations of this document, we picked a small
homogeneous SRGB range of 16000-23999. In practice, a large-scale
design would use a bigger range such as 16000-80000, or even larger.
Larger range provides allocations for various Traffic Engineering
applications within a given domain
6.2. Redistribution of Agg nodes routes
The operator might choose to not redistribute the Agg nodes routes
into the Metro/DC domains. In that case, more segments are required
in order to express an inter-domain path.
For example, node A would use an SRTE Policy {DCI1, Agg1, Agg3, DCI3,
Z} in order to reach Z instead of {Agg3, DCI3, Z} in the reference
design.
6.3. Sizing and hierarchy
The operator is free to choose among a small number of larger leaf
domains, a large number of small leaf domains or a mix of small and
large core/leaf domains.
The operator is free to use a 2-tier design (Core/Metro) or a 3-tier
(Core/Metro/DC).
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6.4. Local Segments to Hosts/Servers
Local segments can be programmed at any leaf node (e.g. node Z) in
order to identify locally-attached hosts (or VM's). For example, if
node Z has bound a local segment 40001 to a local host ZH1, then node
A uses the following SRTE Policy in order to reach that host: {16006,
18006, 20001, 40001}. Such local segment could represent the NID
(Network Interface Device) in the context of the SP access network,
or VM in the context of the DC network.
6.5. Compressed SRTE policies
As an example and according to Section 3, we assume node A can reach
node Z (e.g., with a low-latency SLA contract) via the SRTE policy
consisting of the path: Agg1, Agg2, Agg3, DCI3/4(anycast), Z. The
path is represented by the segment list: {16001, 16002, 16003, 18006,
20001}.
It is clear that the control-plane solution can install an SRTE
Policy {16002, 16003, 18006} at Agg1, collect the Binding SID
allocated by Agg1 to that policy (e.g. 4001) and hence program node A
with the compressed SRTE Policy {16001, 4001, 20001}.
From node A, 16001 leads to Agg1. Once at Agg1, 4001 leads to the
DCI pair (DCI3, DCI4) via a specific low-latency path {16002, 16003,
18006}. Once at that DCI pair, 20001 leads to Z.
Binding SID's allocated to "intermediate" SRTE Policies allow to
compress end-to-end SRTE Policies.
The segment list {16001, 4001, 20001} expresses the same path as
{16001, 16002, 16003, 18006, 20001} but with 2 less segments.
The Binding SID also provides for an inherent churn protection.
When the core topology changes, the control-plane can update the low-
latency SRTE Policy from Agg1 to the DCI pair to DC2 without updating
the SRTE Policy from A to Z.
7. Deployment Model
It is expected that this design be deployed as a green field but as
well in interworking (brown field) with MPLS design across multiple
domains.
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8. Benefits
The design options illustrated in this document allow the
interconnection on a very large scale. Millions of endpoints across
different domains can be interconnected.
8.1. Simplified operations
Two protocols are not needed in this design: LDP and RSVP-TE. No new
protocol has been introduced. The design leverages the core IP
protocols: ISIS, OSPF, BGP, PCEP with straightforward SR extensions.
8.2. Inter-domain SLA
Fast reroute and resiliency is provided by TI-LFA with sub-50msec FRR
upon Link/Node/SRLG failure. TI-LFA is described in
[I-D.bashandy-rtgwg-segment-routing-ti-lfa].
The use of anycast SIDs also provides an improvement in availability
and resiliency.
Inter-domain SLA's can be delivered, e.g., latency vs. cost optimized
path, disjointness from backbone planes, disjointness from other
services, disjointness between primary and backup paths.
Existing inter-domain solutions do not provide any support for SLA
contracts. They just provide a best-effort reachability across
domains.
8.3. Scale
In addition to having eliminated two control plane protocols, per-
service midpoint states have also been removed from the network.
8.4. ECMP
Each policy (intra or inter-domain, with or without TE) is expressed
as a list of segments. Since each segment is optimized for ECMP,
then the entire policy is optimized for ECMP. The ECMP gain of
anycast prefix segment should also be considered (e.g. 16001 load-
shares across any gateway from M1 leaf domain to Core and 16002 load-
shares across any gateway from Core to M1 leaf domain).
9. IANA Considerations
This document does not make any IANA request.
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10. Manageability Considerations
This document describes an application of Segment Routing over the
MPLS data plane. Segment Routing does not introduce any change in
the MPLS data plane. Manageability considerations described in
[RFC8402] apply to the MPLS data plane when used with Segment
Routing.
11. Security Considerations
This document does not introduce additional security requirements and
mechanisms other than the ones described in [RFC8402].
12. Acknowledgements
We would like to thank Giles Heron, Alexander Preusche, Steve Braaten
and Francis Ferguson for their contribution to the content of this
document.
13. Contributors
The following people have substantially contributed to the editing of
this document:
Dennis Cai
Individual
Tim Laberge
Individual
Steven Lin
Google Inc.
Steven Lin
Google Inc.
Bruno Decraene
Orange
Luay Jalil
Verizon
Jeff Tantsura
Individual
Rob Shakir
Google
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14. Informative References
[I-D.bashandy-rtgwg-segment-routing-ti-lfa]
Bashandy, A., Filsfils, C., Decraene, B., Litkowski, S.,
Francois, P., daniel.voyer@bell.ca, d., Clad, F., and P.
Camarillo, "Topology Independent Fast Reroute using
Segment Routing", draft-bashandy-rtgwg-segment-routing-ti-
lfa-05 (work in progress), October 2018.
[RFC4655] Farrel, A., Vasseur, J., 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>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[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>.
Authors' Addresses
Clarence Filsfils (editor)
Cisco Systems, Inc.
Brussels
Belgium
Email: cfilsfil@cisco.com
Stefano Previdi
Cisco Systems, Inc.
Via Del Serafico, 200
Rome 00142
Italy
Email: stefano@previdi.net
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Gaurav Dawra (editor)
LinkedIn
USA
Email: gdawra.ietf@gmail.com
Wim Henderickx
Nokia
Copernicuslaan 50
Antwerp 2018
Belgium
Email: wim.henderickx@nokia.com
Dave Cooper
Level 3
Email: Dave.Cooper@Level3.com
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