Internet DRAFT - draft-boutros-eline-services-over-sr
draft-boutros-eline-services-over-sr
BESS Workgroup S. Boutros, Ed.
Internet-Draft S. Sivabalan, Ed.
Intended status: Standards Track Ciena Corporation
Expires: May 6, 2021 J. Uttaro
AT&T
D. Voyer
Bell Canada
B. Wen
Comcast
L. Jalil
Verizon
November 2, 2020
A Simplified Scalable E-Line Service Model with Segment Routing Underlay
draft-boutros-eline-services-over-sr-00
Abstract
This document proposes a new approach for realizing Ethernet line
(E-Line) services over Segment Routing (SR) networks. This approach
significantly improves scalability and convergence of control plane,
and simplifies network operation. Furthermore, it naturally yields
All-Active multi-homing support for E-Line services without relying
on any overlay techniques.
Status of This Memo
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Copyright Notice
Copyright (c) 2020 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Control Plane Behavior . . . . . . . . . . . . . . . . . . . 5
4.1. Service discovery . . . . . . . . . . . . . . . . . . . . 5
4.2. All-Active Service Redundancy . . . . . . . . . . . . . . 5
4.3. E-Line Attributes . . . . . . . . . . . . . . . . . . . . 5
4.4. Service withdrawal . . . . . . . . . . . . . . . . . . . 6
5. Data Plane Behavior . . . . . . . . . . . . . . . . . . . . . 6
5.1. Data Packet Format . . . . . . . . . . . . . . . . . . . 6
5.2. Aliasing . . . . . . . . . . . . . . . . . . . . . . . . 7
5.3. Single-Homed CE . . . . . . . . . . . . . . . . . . . . . 7
5.4. Multi-Homed CE . . . . . . . . . . . . . . . . . . . . . 7
6. Benefits of E-Line services over SR . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Historically, E-Line services are realized as Virtual Private Wire
Services (VPWS) using point-to-point (P2P) Pseudo-Wires (PWs). A PW
identifies both the service type and the service termination nodes in
both control and data planes. A PW can be dynamically established
via LDP or BGP. Ethernet VPN (EVPN) signaling mechanisms via BGP can
be used to provide VPWS with Single-Active and All-Active multihoming
redundancy as well as Inter-Autonomous System (AS) support.
This document proposes a new approach for supporting E-Line services
over Segment Routing (SR) networks. It reduces BGP signaling
overhead by at least by two orders of magnitudes compared to the
current EVPN-VPWS signaling mechanisms and hence yields better
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control plane scalabilty. Furthermore, it eliminates the need to
associate Route Distinguisher (RD) and Route Target (RT) with EVPN
routes, and hence leads to simpler network operations. The proposed
approach enables the benefit of All-Active redundancy and aliasing
for the Multi-Home (MH) sites. This proposal makes use of the
properties of SR anycast SID to achieve redundancy and fast
convergence at the transport level. Anycast SIDs provide the ability
to discover nodes supporting multihoming and perform Designated
Forwarder (DF) election. As such, the need for any overlay mechanism
to achieve redundancy and fast convergence is eliminated. Also, the
proposed approach supports auto-discovery and single-sided service
provisioning.
In the proposed approach, an E-Line service instance is represented
by a Segment ID (SID) which is referred to "Service SID" in the rest
of the document. Such a SID can be:
o an MPLS label for SR-MPLS.
o a uSID (micro SID) for SRv6 representing network function
associated with an E-Line service instance. A new SRv6 network
programming function will be specified in the next version of this
document.
In the present form, classical VPWS service is incapable of
supporting All-Active multihoming. However, thanks to SR anycast SID
capability, the proposed approach natively provides such redundancy
at transport layer.
A Service SID is unique within a service domain. A node can
advertise service SID(s) of the E-Line instance(s) that it hosts via
BGP for auto-discovery purpose. In the case of SR-MPLS, a service
SID can be carried as a range of absolute MPLS label values or an
index into an Segment Routing Global Block (SRGB), and in the case of
SRv6, a service SID can be carried as uSID in BGP update.
A node advertising E-Line service routes packs information about as
many service instances as possible at the time of advertisement in a
single route. The objective is to reduce the volume of signaling
messages advertised as well as processed in control plane. E-Line
service SIDs are represented as an array. A service route contains
SID value at the start of the array and a bitmask where each bit
represents an index in the array. The SID value for an E-Line
service instance can be derived from the start and the index of the
array. When advertising routes to E-Line services, a node sends the
initial value of the SID array and sets the bitmask to indicate all
E-Line services instances that it hosts along with its node SID which
may be anycast SID for MH case. For FXC, a route containing the
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start normalized VID and the bitmask of VIDs in association with the
E-Line service SID is advertised. The necessary BGP extension will
be described in a future version of this document.
Each node attached to the MH site advertises the same anycast SID to
allow other nodes to discover the redundancy group membership (auto-
discovery).
The proposed solution can also be applicable to the existing EVPN
control plane without compromising its benefits such as All-Active
multihoming on access, aliasing in the core, auto-provisioning and
auto-discovery, etc. With this approach, the need for advertising of
EVPN route types 1 and 4 as well Split-Horizon (SH) label is
eliminated which simplifies EVPN-VPWS operations.
In the following sections, we will describe the functionalities of
the proposed approach in detail.
2. Terminology
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 [RFC2119].
3. Abbreviations
CE: Customer Edge node e.g., host or router or switch.
E-Line: Ethernet virtual private line.
EVPN: Ethernet VPN.
MH: Multi-Home.
OAM: Operations, Administration and Maintenance.
PE: Provide Edge Node.
SID: Segment Identifier.
SR: Segment Routing.
VPWS: Virtual Private Wire Service.
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4. Control Plane Behavior
____ CE3
/ ____CE1
-------- PE3 --------- /
/ PE1
/ | \
PE5 | \
/| | \ CE2
/ | Service Provider Network | /
CE5 | | /
\ | | /
\| PE2
PE6 /
/ -------- PE4 --------
CE6___ / CE4_____/
Figure 1: A reference network used for the examples below
4.1. Service discovery
A node (e.g., PE5 in Figure 1) can discover E-Line instances as well
as the associated service SIDs on other nodes (e.g., PE1, PE2, etc in
Figure 1) via configuration or auto-discovery. With the latter, the
service SIDs may be advertised using BGP.
4.2. All-Active Service Redundancy
An anycast SID per Ethernet Segment (ES) will be configured on all
nodes attached to a Multi-Home (MH) site. For example, in Figure 1,
PE1 and PE2 are configured with an anycast SID representing the
multi-homed site CE2. The ES anycast SIDs will be advertised in BGP
by nodes (e.g., PE1 and PE2) connected to the MH site.
Upon receiving advertisement containing ES anycast SID, a node (e.g.,
PE5 in Figure 1) learns the nodes (e.g., PE1 and PE2) hosting MH
sites, and performs DF election. Aliasing is natively achieved at
transport layer.
4.3. E-Line Attributes
Layer 2 extended community can be advertised with E-Line service
routes. Such a route includes the start of service SID and the
bitmap of all other Services enabled on the advertising node. This
will be elaborated more in the next revision of this document. As
mentioned earlier, the goal is to pack information about as many
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E-Line services hosted on the advertising node as possible to reduce
the overall amount of signaling messages.
4.4. Service withdrawal
Node failure can be detected due via IGP convergence. For faster
detection of node failure, mechanism like BFD can be deployed. The
proposed approach does not require additional service withdrawal
mechanism.
On PE-CE link failure, the PE node withdraws the route to the
corresponding ES in BGP in order to stop receiving traffic to that
ES.
With MH case with anycast SID, upon detecting a failure on PE-CE
link, a PE node may forward incoming traffic to the impacted ES(s) to
another PE node which is part of the anycast group until it withdraws
routes to the impacted ES(s) for faster convergence. For example, in
Figure 1, assuming PE5 and PE6 are part of an anycast group, upon
link failure between PE5 and CE5, PE5 can forward the received
packets from the core to PE6 until it withdraws the anycast SID
associated with the MH site.
5. Data Plane Behavior
5.1. Data Packet Format
The proposed method requires unicast data packet be formed as shown
in Figure 2.
+-------------------------------+
| SID(s) to reach destination |
+-------------------------------+
| Service SID |
+-------------------------------+
| Layer-2 Payload |
+-------------------------------+
Figure 2: Data packet format for sending traffic to a destination
o SID(s) to reach destination: depends on the intent of the underlay
transport:
* IGP shortest path: node SID of the destination. The
destination can belong to an anycast group.
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* IGP path with intent: Flex-Algo SID if the destination can be
reached using the Flex-Algo SID for a specific intent (e.g.,
low latency path). The destination can belong to an anycast
group.
* SR policy: a SID-list for the SR policy that can be used to
reach the destination.
o Service SID: The SID that uniquely identifies a E-Line service
instance in an SR domain.
5.2. Aliasing
Packets destined to a MH CE is distributed to the PE nodes attached
to the CE for load-balancing (UCMP/ECMP) purpose. This is achieved
implicitly due to the use of anycast SIDs for both ES as well as PE
attached to the ES. In our example, traffic destined to CE5 is
distributed via PE5 and PE6.
5.3. Single-Homed CE
Referring to Figure 1, PE3 and PE4 provide an E-Line service to
connect CE3 to CE4. If PE3 wants to forward a packet received from
CE3 to CE4, it formulates the packet as shown in Figure 3.
+-----------------------------+
|Transport SID(s) to reach PE4|
+-----------------------------+
| Service SID |
+-----------------------------+
| Layer-2 Packet |
+-----------------------------+
Figure 3: Data packet format for forwarding traffic from PE3 to CE4
5.4. Multi-Homed CE
Referring to Figure 1, PE5 and PE6 and PE1 and PE2 provide to provide
E-Line services to connect CE2 and CE5. PE5 and PE6 share an anycast
SID, and PE1 and PE2 share another anycast SID.
Packets sent from CE2 to CE5 are load-balanced (ECMP/UCMP) between
PE5 and PE6 assuming that PE1 and PE2 learned the corresponding
E-Line Service SID from PE5 and PE6.
The following diagram shows SID stack for a L2 packet sent from CE2
to CE5.
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+--------------------------------+
|Anycast Node SID for PE5 and PE6|
+--------------------------------+
| Service SID |
+--------------------------------+
| Layer-2 Packet |
+--------------------------------+
Figure 4: Data packet format for forwarding traffic from PE1 or PE2 to CE5
In case of FXC the signaled normalized VID will be encoded in the
Layer 2 packet.
6. Benefits of E-Line services over SR
The proposed approach eliminates the need for establishing and
maintaining PWs as with legacy VPWS technology. This yields
significant reduction in control plane overhead. The proposed
approach provides the benefits as such fast convergence. Finally,
using anycast SID, the proposed approach provides All-Active
multihoming as well as aliasing.
7. Security Considerations
The mechanisms in this document use Segment Routing control plane as
defined in Security considerations described in Segment Routing
control plane are equally applicable.
8. IANA Considerations
TBD.
9. Acknowledgements
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>.
[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>.
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[RFC8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC8660, December 2019,
<https://www.rfc-editor.org/info/rfc8660>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
10.2. Informative References
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-08 (work in progress),
July 2020.
[RFC4664] Andersson, L., Ed. and E. Rosen, Ed., "Framework for Layer
2 Virtual Private Networks (L2VPNs)", RFC 4664,
DOI 10.17487/RFC4664, September 2006,
<https://www.rfc-editor.org/info/rfc4664>.
[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
Rabadan, "Virtual Private Wire Service Support in Ethernet
VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
<https://www.rfc-editor.org/info/rfc8214>.
Authors' Addresses
Sami Boutros (editor)
Ciena Corporation
USA
Email: sboutros@ciena.com
Siva Sivabalan (editor)
Ciena Corporation
Canada
Email: ssivabal@ciena.com
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James Uttaro
AT&T
USA
Email: ju1738@att.com
Daniel Voyer
Bell Canada
Canada
Email: daniel.voyer@bell.ca
Bin Wen
Comcast
USA
Email: bin_wen@cable.comcast.com
Luay Jalil
Verizon
USA
Email: luay.jalil@verizon.com
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