INTERNET-DRAFT Sami Boutros
Intended Status: Standard Track Ali Sajassi
Samer Salam
Cisco Systems
John Drake
Juniper Networks
Jeff Tantsura
Ericsson
Dirk Steinberg
Steinberg Consulting
Thomas Beckhaus
Deutsche Telecom
J. Rabadan
Alcatel-Lucent
Expires: August 3, 2015 January 30, 2015
VPWS support in EVPN
draft-ietf-bess-evpn-vpws-00.txt
Abstract
This document describes how EVPN can be used to support virtual
private wire service (VPWS) in MPLS/IP networks. EVPN enables the
following characteristics for VPWS: single-active as well as all-
active multi-homing with flow-based load-balancing, eliminates the
need for single-segment and multi-segment PW signaling, and provides
fast protection using data-plane prefix independent convergence upon
node or link failure.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
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Internet-Drafts are draft documents valid for a maximum of six months
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
2. BGP Extensions . . . . . . . . . . . . . . . . . . . . . . . . 6
3 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4 EVPN Comparison to PW Signaling . . . . . . . . . . . . . . . . 8
5 ESI Bandwidth . . . . . . . . . . . . . . . . . . . . . . . . . 8
6 Failure Scenarios . . . . . . . . . . . . . . . . . . . . . . . 9
6.1 Single-Homed CEs . . . . . . . . . . . . . . . . . . . . . . 9
6.1 Multi-Homed CEs . . . . . . . . . . . . . . . . . . . . . . 9
7 VPWS with multiple sites . . . . . . . . . . . . . . . . . . . . 9
8 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10
9 Security Considerations . . . . . . . . . . . . . . . . . . . . 10
10 IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
11 References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1 Normative References . . . . . . . . . . . . . . . . . . . 10
11.2 Informative References . . . . . . . . . . . . . . . . . . 10
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1 Introduction
This document describes how EVPN can be used to support virtual
private wire service (VPWS) in MPLS/IP networks. The use of EVPN
mechanisms for VPWS brings the benefits of EVPN to p2p services.
These benefits include single-active redundancy as well as all-active
redundancy with flow-based load-balancing. Furthermore, the use of
EVPN for VPWS eliminates the need for signaling single-segment and
multi-segment PWs for p2p Ethernet services.
[EVPN] has the ability to forward customer traffic to/from a given
customer Attachment Circuit (AC), aka Ethernet Segment in EVPN
terminology, without any MAC lookup. This capability is ideal in
providing p2p services (aka VPWS services). [MEF] defines Ethernet
Virtual Private Line (EVPL) service as p2p service between a pair of
ACs (designated by VLANs) and Ethernet Private Line (EPL) service, in
which all traffic flows are between a single pair of ESes. EVPL can
be considered as a VPWS with only two ACs. In delivering an EVPL
service, the traffic forwarding capability of EVPN based on the
exchange of a pair of Ethernet AD routes is used; whereas, for more
general VPWS, traffic forwarding capability of EVPN based on the
exchange of a group of Ethernet AD routes (one Ethernet AD route per
AC/segment) is used. In a VPWS service, the traffic from an
originating Ethernet Segment can be forwarded only to a single
destination Ethernet Segment; hence, no MAC lookup is needed and the
MPLS label associated with the per-EVI Ethernet AD route can be used
in forwarding user traffic to the destination AC.
Both services are supported by using the Ethernet A-D per EVI route
which contains an Ethernet Segment Identifier, in which the customer
ES is encoded, and an Ethernet Tag, in which the VPWS service
instance identifier is encoded. I.e., for both EPL and EVPL
services, a specific VPWS service instance is identified by a pair of
Ethernet A-D per EVI routes which together identify the VPWS service
instance endpoints and the VPWS service instance. In the control
plane the VPWS service instance is identified using the VPWS service
instance identifiers advertised by each PE and in the data plane the
MPLS label advertised by one PE is used by the other PE to send
traffic for that VPWS service instance. As with the Ethernet Tag in
standard EVPN, the VPWS service instance identifier has uniqueness
within an EVPN instance. Unlike standard EVPN where the Ethernet Tag
MUST be carried in the MPLS encapsulated frames, VPWS does not use
the Ethernet Tag value in the data plane. The MPLS label is enough to
identify the VPWS service instance and provide egress tag translation
at the disposition PE, if required. The Ethernet Segment identifier
encoded in the Ethernet A-D per EVI route is not used to identify the
service, however it can be used for flow-based load-balancing and
mass withdraw functions.
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As with standard EVPN, the Ethernet A-D per ES route is used for fast
convergence upon link or node failure and the Ethernet Segment route
is used for auto-discovery of the PEs attached to a given multi-homed
CE and to synchronize state between them.
1.1 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 RFC 2119 [RFC2119].
MAC: Media Access Control
MPLS: Multi Protocol Label Switching.
OAM: Operations, Administration and Maintenance.
PE: Provide Edge Node.
CE: Customer Edge device e.g., host or router or switch.
EVPL: Ethernet Virtual Private Line.
EPL: Ethernet Private Line.
VPWS: Virtual private wire service.
EVI: EVPN Instance.
Single-Active Mode: When a device or a network is multi-homed to two
or more PEs and when only a single PE in such redundancy group can
forward traffic to/from the multi-homed device or network for a given
VLAN, then such multi-homing or redundancy is referred to as "Single-
Active".
All-Active: When a device is multi-homed to two or more PEs and when
all PEs in such redundancy group can forward traffic to/from the
multi-homed device for a given VLAN, then such multi-homing or
redundancy is referred to as "All-Active".
1.2 Requirements
1. EPL service access circuit maps to the whole Ethernet port.
2. EVPL service access circuits are VLANs on single or double tagged
trunk ports. Each VLAN individually will be considered to be an
endpoint for an EVPL service, without any direct dependency on any
other VLANs on the trunk. Other VLANs on the same trunk could also be
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used for EVPL services, but could also be associated with other
services.
3. If multiple VLANs on the same trunk are associated with EVPL
services, the respective remote endpoints of these EVPLs could be
dispersed across any number of PEs, i.e. different VLANs may lead to
different destinations.
4. The VLAN tag on the access trunk only has PE-local significance.
The VLAN tag on the remote end could be different, and could also be
double tagged when the other side is single tagged.
5. Also, multiple EVPL service VLANs on the same trunk could belong
to the same EVPN instance (EVI), or they could belong to different
EVIs. This should be purely an administrative choice of the network
operator.
6. A given access trunk could have hundreds of EVPL services, and a
given PE could have thousands of EVPLs configured. It must be
possible to configure multiple EVPL services within the same EVI.
7. Local access circuits configured to belong to a given EVPN
instance could also belong to different physical access trunks.
8. EPL-LAN and EVP-LAN are possible on the same system and also ESIs
can be shared between EVPL and EVP-LANs.
2. BGP Extensions
This document proposes the use of the Ethernet A-D per EVI route to
signal VPWS services. The Ethernet Segment Identifier field is set to
the customer ES and the Ethernet Tag ID 32-bit field is set to the
24-bit VPWS service instance identifier. For both EPL and EVPL
services, for a given VPWS service instance the pair of PEs
instantiating that VPWS service instance will each advertise an
Ethernet A-D per EVI route with its VPWS service instance identifier
and will each be configured with the other PE's VPWS service instance
identifier. When each PE has received the other PE's Ethernet A-D per
EVI route the VPWS service instance is instantiated. It should be
noted that the same VPWS service instance identifier may be
configured on both PEs.
The Route-Target (RT) extended community with which the Ethernet A-D
per EVI route is tagged identifies the EVPN instance in which the
VPWS service instance is configured. It is the operator's choice as
to how many and which VPWS service instances are configured in a
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given EVPN instance. However, a given EVPN instance MUST NOT be
configured with both VPWS service instances and standard EVPN multi-
point services.
3 Operation
The following figure shows an example of a P2P service deployed with
EVPN.
Ethernet Ethernet
Native |<--------- EVPN Instance ----------->| Native
Service | | Service
(AC) | |<-PSN1->| |<-PSN2->| | (AC)
| V V V V V V |
| +-----+ +-----+ +-----+ +-----+ |
+----+ | | PE1 |======|ASBR1|==|ASBR2|===| PE3 | | +----+
| |-------+-----+ +-----+ +-----+ +-----+-------| |
| CE1| | | |CE2 |
| |-------+-----+ +-----+ +-----+ +-----+-------| |
+----+ | | PE2 |======|ASBR3|==|ASBR4|===| PE4 | | +----+
^ +-----+ +-----+ +-----+ +-----+ ^
| Provider Edge 1 ^ Provider Edge 2 |
| | |
| | |
| EVPN Inter-provider point |
| |
|<---------------- Emulated Service -------------------->|
iBGP sessions are established between PE1, PE2, ASBR1 and ASBR3,
possibly via a BGP route-reflector. Similarly, iBGP sessions are
established between PE3, PE4, ASBR2 and ASBR4. eBGP sessions are
established among ASBR1, ASBR2, ASBR3, and ASBR4.
All PEs and ASBRs are enabled for the EVPN SAFI and exchange Ethernet
A-D per EVI routes, one route per VPWS service instance. For inter-
AS option B, the ASBRs re-advertise these routes with Next Hop
attribute set to their IP addresses. The link between the CE and the
PE is either a C-tagged or S-tagged interface, as described in
[802.1Q], that can carry a single VLAN tag or two nested VLAN tags
and it is configured as a trunk with multiple VLANs, one per VPWS
service instance. It should be noted that the VLAN ID used by the
customer at either end of a VPWS service instance to identify that
service instance may be different and EVPN doesn't perform that
translation between the two values. Rather, the MPLS label will
identify the VPWS service instance and if translation is needed, it
should be done by the Ethernet interface for each service.
For single-homed CE, in an advertised Ethernet A-D per EVI route the
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ESI field is set to 0 and the Ethernet Tag field is set to the VPWS
service instance identifier that identifies the EVPL or EPL service.
For a multi-homed CE, in an advertised Ethernet A-D per EVI route the
ESI field is set to the CE's ESI and the Ethernet Tag field is set to
the VPWS service instance identifier, which MUST have the same value
on all PEs attached to that ES. This allows an ingress PE to perform
flow-based load-balancing of traffic flows to all of the PEs attached
to that ES. In all cases traffic follows the transport paths, which
may be asymmetric.
The VPWS service instance identifier encoded in the Ethernet Tag
field in an advertised Ethernet A-D per EVI route MUST either be
unique across all ASs, or an ASBR needs to perform a translation when
the Ethernet A-D per EVI route is re-advertised by the ASBR from one
AS to the other AS.
Ethernet A-D per ES route can be used for mass withdraw to withdraw
all Ethernet A-D per EVI routes associated with the multi-home site
on a given PE.
4 EVPN Comparison to PW Signaling
In EVPN, service endpoint discovery and label signaling are done
concurrently using BGP. Whereas, with VPWS based on [RFC4448], label
signaling is done via LDP and service endpoint discovery is either
through manual provisioning or through BGP.
In existing implementation of VPWS using pseudowires(PWs), redundancy
is limited to single-active mode, while with EVPN implementation of
VPWS both single-active and all-active redundancy modes can be
supported.
In existing implementation with PWs, backup PWs are not used to carry
traffic, while with EVPN, traffic can be load-balanced among
different PEs multi-homed to a single CE.
Upon link or node failure, EVPN can trigger failover with the
withdrawal of a single BGP route per EVPL service or multiple EVPL
services, whereas with VPWS PW redundancy, the failover sequence
requires exchange of two control plane messages: one message to
deactivate the group of primary PWs and a second message to activate
the group of backup PWs associated with the access link. Finally,
EVPN may employ data plane local repair mechanisms not available in
VPWS.
5 ESI Bandwidth
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The ESI Bandwidth will be encoded using the Link Bandwidth Extended
community defined in [draft-ietf-idr-link-bandwidth] and associated
with the Ethernet AD route used to realize the EVPL services.
When a PE receives this attribute for a given EVPL it MUST request
the required bandwidth from the PSN towards the other EVPL service
destination PE originating the message. When resources are allocated
from the PSN for a given EVPL service, then the PSN SHOULD account
for the Bandwidth requested by this EVPL service.
In the case where PSN resources are not available, the PE receiving
this attribute MUST re-send its local Ethernet AD routes for this
EVPL service with the ESI Bandwidth = All FFs to declare that the
"PSN Resources Unavailable".
The scope of the ESI Bandwidth is limited to only one Autonomous
System.
6 Failure Scenarios
On a link or port failure between the CE and the PE for both single
and multi-homed CEs, the PE must withdraw all the associated Ethernet
AD routes for the VPWS service instances on the failed port or link.
6.1 Single-Homed CEs
Unlike [EVPN], EVPN-VPWS uses Ethernet AD route advertisements for
single-homed Ethernet Segments. Therefore, upon a link/port failure
of this single-homed Ethernet Segment, the PE MUST withdraw the
associated Ethernet A-D routes.
6.1 Multi-Homed CEs
For a faster convergence in multi-homed scenarios with either Single-
Active Redundancy or All-active redundancy, mass withdraw technique
as per [EVPN] baseline is used. A PE previously advertising an
Ethernet A-D per ES route, can withdraw this route signaling to the
remote PEs to switch all the VPWS service instances associated with
this multi-homed ES to the backup PE
7 VPWS with multiple sites
The VPWS among multiple sites (full mesh of P2P connections - one per
pair of sites) that can be setup automatically without any explicit
provisioning of P2P connections among the sites is outside the scope
of this document.
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8 Acknowledgements
The authors would like to acknowledge Wen Lin contributions to this
document.
9 Security Considerations
This document does not introduce any additional security constraints.
10 IANA Considerations
TBD.
11 References
11.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
11.2 Informative References
[RFC7209] A. Sajassi, R. Aggarwal et. al., "Requirements for Ethernet
VPN".
[EVPN] A. Sajassi, R. Aggarwal et. al., "BGP MPLS Based Ethernet
VPN", draft-ietf-l2vpn-evpn-11.txt.
[PBB-EVPN] A. Sajassi et. al., "PBB-EVPN", draft-ietf-l2vpn-pbb-evpn-
08.txt.
[draft-ietf-idr-link-bandwidth] P. Mohapatra, R. Fernando, "BGP Link
Bandwidth Extended Community", draft-ietf-idr-link-bandwidth-06.txt
Authors' Addresses
Sami Boutros
Cisco
Email: sboutros@cisco.com
Ali Sajassi
Cisco
Email: sajassi@cisco.com
Samer Salam
Cisco
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Email: ssalam@cisco.com
John Drake
Juniper Networks
Email: jdrake@juniper.net
Jeff Tantsura
Ericsson
Email: jeff.tantsura@ericsson.com
Dirk Steinberg
Steinberg Consulting
Email: dws@steinbergnet.net
Patrice Brissette
Cisco
Email: pbrisset@cisco.com
Thomas Beckhaus
Deutsche Telecom
Email:Thomas.Beckhaus@telekom.de>
Jorge Rabadan
Alcatel-Lucent
Email: jorge.rabadan@alcatel-lucent.com
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