INTERNET-DRAFT Sami Boutros
Intended Status: Standard Track VMware
Ali Sajassi
Samer Salam
Cisco Systems
John Drake
Juniper Networks
Jeff Tantsura
Individual
Dirk Steinberg
Steinberg Consulting
Thomas Beckhaus
Deutsche Telecom
J. Rabadan
Nokia
Expires: December 9, 2016 June 7, 2016
VPWS support in EVPN
draft-ietf-bess-evpn-vpws-05.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 traditional way of PW signaling, and provides fast
protection 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.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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Copyright and License Notice
Copyright (c) 2016 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
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Service interface . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 VLAN-Based Service Interface . . . . . . . . . . . . . . . . 7
2.2 VLAN Bundle Service Interface . . . . . . . . . . . . . . . 7
2.2.1 Port-Based Service Interface . . . . . . . . . . . . . . 7
2.3 VLAN-Aware Bundle Service Interface . . . . . . . . . . . . 8
3. BGP Extensions . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1 EVPN Layer 2 attributes extended community . . . . . . . . . 8
4 Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5 EVPN Comparison to PW Signaling . . . . . . . . . . . . . . . . 11
6 Failure Scenarios . . . . . . . . . . . . . . . . . . . . . . . 12
6.1 Single-Homed CEs . . . . . . . . . . . . . . . . . . . . . . 12
6.2 Multi-Homed CEs . . . . . . . . . . . . . . . . . . . . . . 12
7 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 12
8 Security Considerations . . . . . . . . . . . . . . . . . . . . 12
9 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 12
10 References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1 Normative References . . . . . . . . . . . . . . . . . . . 13
10.2 Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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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 traditional way of PW signaling
for p2p Ethernet services, as described in section 4.
[EVPN] has the ability to forward customer traffic to/from a given
customer Attachment Circuit (AC), 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 ports, that in EVPN terminology would mean 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/ES) 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 per EVI Ethernet A-D 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
per EVI Ethernet A-D 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
value of 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 EVPN where Ethernet Tag ID in EVPN routes are set to zero for
Port-based, vlan-based, and vlan-bundle interface mode and it is set
to non-zero Ethernet tag ID for vlan-aware bundle mode, in EVPN-VPWS,
for all the four interface modes, Ethernet tag ID in the Ethernet A-D
route MUST be set to a valid value in all the service interface
types.
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In terms of route advertisement and MPLS label lookup behavior, EVPN-
VPWS resembles the vlan-aware bundle mode of [RFC 7432] such that
when a PE advertises per EVI Ethernet A-D route, the VPWS service
instance serves as a 24-bit normalized Ethernet tag ID. The value of
the MPLS label in this route represents both the EVI and the VPWS
service instance, so that upon receiving an MPLS encapsulated packet,
the disposition PE can identify the egress AC from the lookup of the
MPLS label alone and perform any required tag translation. For EVPL
service, the Ethernet frames transported over an MPLS/IP network
SHOULD remain tagged with the originating VID and any VID translation
is performed at the disposition PE. For EPL service, the Ethernet
frames are transported as is and the tags are not altered.
The MPLS label value in the Ethernet A-D route can be set to the VNI
for VxLAN encap, and this VNI may have a global scope or local scope
per PE and may also be made equal to the VPWS service instance
identifier set in the Ethernet A-D route.
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.
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.
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EP-LAN: Ethernet Private LAN.
EVP-LAN: Ethernet Virtual Private LAN.
VPWS: Virtual Private Wire Service.
EVI: EVPN Instance.
ES: Ethernet Segment on a PE refer to the link attached to it, this
link can be part of a set of links attached to different PEs in multi
home cases, or could be a single link in single home cases.
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 (or <S-VLAN,C-VLAN> combination)
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 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.
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6. 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. EP-LAN and EVP-LAN are possible on the same system and also ESIs
can be shared between EVPL and EVP-LANs.
2 Service interface
2.1 VLAN-Based Service Interface
With this service interface, a VPWS instance identifier corresponds
to only a single VLAN on a specific interface. Therefore, there is a
one-to-one mapping between a VID on this interface and the VPWS
service instance identifier. The PE provides the cross-connect
functionality between MPLS LSP identified by the VPWS service
instance identifier and a specific <port,VLAN>. If the VLAN is
represented by different VIDs on different PEs. (e.g., a different
VID per Ethernet segment per PE), then each PE needs to perform VID
translation for frames destined to its Ethernet segment. In such
scenarios, the Ethernet frames transported over an MPLS/IP network
SHOULD remain tagged with the originating VID, and a VID translation
MUST be supported in the data path and MUST be performed on the
disposition PE.
2.2 VLAN Bundle Service Interface
With this service interface, a VPWS service instance identifier
corresponds to multiple VLANs on a specific interface. The PE
provides the cross-connect functionality between MPLS label
identified by the VPWS service instance identifier and a group of
VLANs on a specific interface. For this service interface, each VLAN
is presented by a single VID which means no VLAN translation is
allowed. The receiving PE, can direct the traffic based on EVPN label
alone to a specific port. The transmitting PE can cross connect
traffic from a group of VLANs on a specific port to the MPLS label.
The MPLS-encapsulated frames MUST remain tagged with the originating
VID.
2.2.1 Port-Based Service Interface
This service interface is a special case of the VLAN bundle service
interface, where all of the VLANs on the port are mapped to the same
VPWS service instance identifier. The procedures are identical to
those described in Section 2.2.
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2.3 VLAN-Aware Bundle Service Interface
Contrary to EVPN, in EVPN-VPWS this service interface maps to VLAN-
based service interface (defined in section 2.1) and thus this
service interface is not used in EVPN-VPWS. In other words, if one
tries to define data-plane and control plane behavior for this
service interface, he would realize that it is the same as that of
VLAN-based service.
3. BGP Extensions
This document proposes the use of the per EVI Ethernet A-D 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 a per
EVI Ethernet A-D 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 per EVI Ethernet
A-D 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 per EVI
Ethernet A-D 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
given EVPN instance. However, a given EVPN instance MUST NOT be
configured with both VPWS service instances and standard EVPN multi-
point services.
3.1 EVPN Layer 2 attributes extended community
This draft proposes a new extended community, defined below, to be
included with the per EVI Ethernet A-D route. This attribute is
mandatory if multihoming is enabled.
+------------------------------------+
| Type(0x06)/Sub-type(0x04)(2 octet)|
+------------------------------------+
| Control Flags (2 octets) |
+------------------------------------+
| L2 MTU (2 octets) |
+------------------------------------+
| Reserved (2 octets) |
+------------------------------------+
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ |C|P|B| (MBZ = MUST Be Zero)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The following bits in the Control Flags are defined; the remaining
bits MUST be set to zero when sending and MUST be ignored when
receiving this community.
Name Meaning
P If set to 1 in multihoming single-active scenarios, it
indicates that the advertising PE is the Primary PE.
SHOULD be set to 1 for multihoming all-active scenarios.
B If set to 1 in multihoming single-active scenarios, it
indicates that the advertising PE is the Backup PE.
C If set to 1, a Control word [RFC 4448] MUST be present
when sending EVPN packets to this PE.
A received L2 MTU=0 means no MTU checking against local MTU is
needed. A received non-zero MTU SHOULD be checked against local MTU
and if there is a mismatch, the local PE MUST not add the remote PE
as the EVPN destination for the corresponding VPWS service instance.
The usage of the Per ES Ethernet AD route is unchanged from its usage
in [RFC7432], i.e. the "Single-Active" bit in the flags of the ESI
Label extended community will indicate if single-active or all-active
redundancy is used for this ES.
In a multihoming all-active scenario, there is no DF election, and
all the PEs in the ES that are active and ready to forward traffic
to/from the CE will set the P bit to 1. A remote PE will do per-flow
load balancing to the PEs that send P=1 for the same Ethernet Tag and
ESI.
In multihoming single-active scenario, the DF election will determine
who the primary and the backup PEs are, and only those PEs will set
the P bit and B bit respectively. A remote PE will forward the
traffic to the primary PE and switch over to the backup PE as soon as
it receives an Ethernet A-D route withdrawal from the primary PE in
the Ethernet Segment.
In multihoming single-active scenario, during transient situations, a
remote PE receiving P=1 from more than one PE will select the last
advertising PE as the primary PE when forwarding traffic. A remote PE
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receiving B=1 from more than one PE will select only one backup PE. A
remote PE MUST receive P=1 from at least one PE before forwarding
traffic.
As per [RFC6790], if a network uses entropy labels then the control
word (C bit set) SHOULD not be used when sending EVPN-encapsulated
packets over a P2P LSP.
4 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 per EVI
Ethernet A-D 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
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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 per EVI Ethernet A-D route the
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 per EVI Ethernet A-D 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 per EVI Ethernet A-D route MUST either be
unique across all ASs, or an ASBR needs to perform a translation when
the per EVI Ethernet A-D route is re-advertised by the ASBR from one
AS to the other AS.
Per ES Ethernet A-D route can be used for mass withdraw to withdraw
all per EVI Ethernet A-D routes associated with the multi-home site
on a given PE.
5 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.
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Finally, EVPN may employ data plane egress link protection mechanisms
not available in VPWS. This can be done by the primary PE (on local
AC down) using the label advertised in the per EVI Ethernet A-D route
by the backup PE to encapsulate the traffic and direct it to backup
PE.
6 Failure Scenarios
On a link or port failure between the CE and the PE for both single
and multi-homed CEs, unlike [EVPN] 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 per EVI Ethernet A-D routes.
6.2 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 a per ES
Ethernet A-D 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 Acknowledgements
The authors would like to acknowledge Jeffrey Zhang, Wen Lin, Nitin
Singh, Senthil Sathappan and Vinod Prabhu for their feedback and
contributions to this document.
8 Security Considerations
The mechanisms in this document use EVPN control plane as defined in
[RFC7432]. Security considerations described in [RFC7432] are equally
applicable.
This document uses MPLS and IP-based tunnel technologies to support
data plane transport. Security considerations described in [RFC7432]
and in [ietf-evpn-overlay] are equally applicable.
9 IANA Considerations
IANA has allocated the following EVPN Extended Community sub-type in
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[RFC7153].
0x04 EVPN Layer 2 attributes [RFCXXXX]
10 References
10.1 Normative References
[KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7432] A. Sajassi, R. Aggarwal et. al., "BGP MPLS Based Ethernet
VPN".
10.2 Informative References
[RFC7209] A. Sajassi, R. Aggarwal et. al., "Requirements for Ethernet
VPN".
[RFC7623] A. Sajassi et. al., "PBB-EVPN", "Provider Backbone Bridging
Combined with Ethernet VPN (PBB-EVPN)".
[RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling", RFC4761, January
2007.
Authors' Addresses
Sami Boutros
VMware, Inc.
Email: sboutros@vmware.com
Ali Sajassi
Cisco
Email: sajassi@cisco.com
Samer Salam
Cisco
Email: ssalam@cisco.com
John Drake
Juniper Networks
Email: jdrake@juniper.net
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Jeff Tantsura
Individual
Email: jefftant@gmail.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
Ryan Bickhart
Juniper Networks
Email: rbickhart@juniper.net
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