VPWS support in E-VPN
draft-boutros-l2vpn-evpn-vpws-02

INTERNET-DRAFT                                              Sami Boutros
Intended Status: Standard Track                              Ali Sajassi
                                                             Samer Salam
                                                           Cisco Systems

                                                              John Drake
                                                        Juniper Networks

                                                           Jeff Tantsura
                                                                Ericsson
Expires: April 24, 2014                                 October 21, 2013

                         VPWS support in E-VPN 
                 draft-boutros-l2vpn-evpn-vpws-02.txt 

Abstract

   This document describes how E-VPN can be used to support virtual
   private wire service (VPWS) in MPLS/IP networks. E-VPN 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.

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Copyright and License Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. BGP Extensions  . . . . . . . . . . . . . . . . . . . . . . . .  4
   3 Operation  . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4 EVPN Comparison to PW Signaling  . . . . . . . . . . . . . . . .  5
   5 ESI Bandwidth  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   6 ESI value derivation . . . . . . . . . . . . . . . . . . . . . .  6
   7 VPWS with multiple sites . . . . . . . . . . . . . . . . . . . .  6
   8 Security Considerations  . . . . . . . . . . . . . . . . . . . .  6
   9  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  7
   10  References . . . . . . . . . . . . . . . . . . . . . . . . . .  7
     10.1  Normative References . . . . . . . . . . . . . . . . . . .  7
     10.2  Informative References . . . . . . . . . . . . . . . . . .  7
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . .  7

 

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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). 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.  

   In current PW redundancy mechanisms, convergence time is a function
   of control plane convergence characteristics. However, with EVPN it
   is possible to attain faster convergence through the use of data-
   plane prefix independent convergence, upon node or link failure.

   This document proposes the use of the Ethernet AD route to signal
   labels for P2P Ethernet services. As with EVPN, the Ethernet Segment
   route can be used to synchronize state between the PEs attached to
   the same multi-homed Ethernet Segment.

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.
 

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   PE: Provide Edge Node.

   CE: Customer Edge device e.g., host or router or switch.

   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".

2. BGP Extensions

   [EVPN] defines a new BGP NLRI for advertising different route types
   for EVPN operation. This document does not define any new BGP
   messages, but rather re-purposes one of the routes as described next.

   This document proposes the use of the per EVI Ethernet AD route to
   signal P2P services. The Ethernet Segment Identifier field is set to
   the ESI of the attachment circuit of the VPWS service instance. The
   Ethernet Tag field is set to 0 in the case of an Ethernet Private
   Wire service, and to the VLAN identifier associated with the service
   for Ethernet Virtual Private Wire service. The route is associated
   with a Route-Target (RT) extended community attribute that identifies
   the service instance (together with the Ethernet Tag field when non-
   zero).

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 |
 

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      |    |-------+-----+      +-----+  +-----+   +-----+-------|    |
      +----+ |     | 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 EVPN
   Ethernet A-D routes - one route per AC. The ASBRs re-advertise the
   Ethernet A-D 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. This interface is set up as a trunk
   with multiple VLANs.

   A VPWS with multiple sites or multiple EVPL services on the same CE
   port can be included in one EVI between 2 or more PEs. An Ethernet
   Tag corresponding to each P2P connection and known to both PEs is
   used to identify the services multiplexed in the same EVI.

   For CE multi-homing, the Ethernet AD Route encodes the ESI associated
   with the CE. This allows flow-based load-balancing of traffic between
   PEs connected to the same multi-homed CE. The VPN ID MUST be the same
   on both PEs attached to the site. The Ethernet Segment route may be
   used too, for discovery of multi-homed CEs. In all cases traffic
   follows the transport paths, which may be asymmetric.

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 primary
   and secondary PEs. Upon link or node failure, EVPN can trigger
   failover with the withdrawal of a single BGP route per service,
 

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   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

   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".

6 ESI value derivation

   The 10 bytes ESI value will contain:-

   1) 6-byte System-ID that is globally unique. These 6 bytes can be
   auto derived using  a mechanism similar to the one used for
   automating B-MAC Address Assignment in [PBB-EVPN].

   2) 4-byte Local-AC-ID that is unique within each PE.

   The combination of System-ID and Local-AC-ID makes the associated AC-
   ID globally unique. A pair of such globally unique AC-ID identifies a
   point-to-point service (EVPL or EPL) uniquely in the provider
   network.

7 VPWS with multiple sites

   The future revision of this draft will describe how a VPWS among
   multiple sites (full mesh of P2P connections - one per pair of sites)
   can be setup automatically without any explicit provisioning of P2P
   connections among the sites. 

8 Security Considerations
 

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   This document does not introduce any additional security constraints.
9  IANA Considerations

   TBD

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.

10.2  Informative References

   [EVPN-REQ] A. Sajassi, R. Aggarwal et. al., "Requirements for      
   Ethernet VPN", draft-ietf-l2vpn-evpn-req-00.txt.

   [EVPN] A. Sajassi, R. Aggarwal et. al., "BGP MPLS Based Ethernet
   VPN", draft-ietf-l2vpn-evpn-04.txt.

   [PBB-EVPN] A. Sajassi et. al., "PBB-EVPN", draft-ietf-l2vpn-pbb-evpn-
   05.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 
   170 West Tasman Drive
   San Jose, CA  95134, US
   Email: sboutros@cisco.com

   Ali Sajassi
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134, US 
   Email: sajassi@cisco.com

   Samer Salam
   Cisco 
   595 Burrard Street, Suite 2123
   Vancouver, BC V7X 1J1, Canada
   Email: ssalam@cisco.com
 

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   John Drake
   Juniper Networks
   Email: jdrake@juniper.net

   Jeff Tantsura
   Ericsson
   Email: jeff.tantsura@ericsson.com

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