Internet Working Group                         Ali Sajassi(Editor)
   Internet Draft                                         Samer Salam
                                                     Clarence Filsfils
   Category: Standards Track                                    Cisco
                                                   R. Aggarwal(Editor)
                                                      Juniper Networks
                                                           Nabil Bitar
                                                            Jim Uttaro
                                                          Aldrin Isaac
                                                        Wim Henderickx
   Expires: April 17, 2011                           October 17, 2010
                   Requirements for Ethernet VPN (E-VPN)
   Status of this Memo
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   Copyright (c) 2010 IETF Trust and the persons identified as the
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   draft-sajassi-raggarwa-evpn-req-00.txt                    June 2010
   document authors. All rights reserved.
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   than English.
   The widespread adoption of Ethernet L2VPN services and the advent of
   new applications for the technology (e.g. data center interconnect)
   have culminated in a new set of requirements that are not readily
   addressable by the current VPLS solution. In particular, multi-
   homing with all-active forwarding is not supported and there's no
   existing solution to leverage MP2MP LSPs for optimizing the delivery
   of multi-destination frames. Furthermore, the provisioning of VPLS,
   even in the context of BGP-based auto-discovery, requires network
   operators to specify various network parameters on top of the access
   configuration. This document specifies the requirements for an
   Ethernet VPN (E-VPN) solution which addresses the above issues.
   Table of Contents
   1. Specification of Requirements................................... 3
   2. Introduction.................................................... 3
   3. Terminology..................................................... 4
   4. Redundancy Requirements......................................... 4
   4.1. Flow-based Load Balancing..................................... 4
   4.2. Flow-based Multi-pathing...................................... 5
   4.3. Geo-redundant PE Nodes........................................ 5
   4.4. Optimal Traffic Forwarding.................................... 6
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   4.5. Flexible Redundancy Grouping Support.......................... 6
   4.6. Multi-homed Network........................................... 6
   5. Multicast Optimization Requirements............................. 7
   6. Ease of Provisioning Requirements............................... 7
   7. New Service Interface Requirements.............................. 8
   8. Fast Convergence................................................ 9
   9. Flood Suppression............................................... 9
   10. Supporting Flexible VPN Topologies and Policies............... 10
   11. Security Considerations....................................... 10
   12. IANA Considerations........................................... 10
   13. Normative References.......................................... 10
   14. Informative References........................................ 11
   15. Authors' Addresses............................................ 11
      Specification of Requirements
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].
   VPLS, as defined in [RFC4664][RFC4761][RFC4762], is a proven and
   widely deployed technology. However, the existing solution has a
   number of limitations when it comes to redundancy, multicast
   optimization and provisioning simplicity. Furthermore, new
   applications are driving several new requirements for a VPLS
   In the area of multi-homing current VPLS can only support multi-
   homing with active/standby resiliency model, for e.g. as described
   in [VPLS-BGP-MH]. Flexible multi-homing with all-active Attachment
   Circuits (ACs) cannot be supported by current VPLS solution.
   In the area of multicast optimization, [VPLS-MCAST] describes how
   multicast LSPs can be used in conjunction with VPLS. However, this
   solution is limited to P2MP LSPs, as there's no defined solution for
   leveraging MP2MP LSPs with VPLS.
   In the area of provisioning simplicity, current VPLS does offer a
   mechanism for single-sided provisioning by relying on BGP-based
   service auto-discovery [RFC4761][L2VPN-Sig]. This, however, still
   requires the operator to configure a number of network-side
   parameters on top of the access-side Ethernet configuration.
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   Furthermore, data center interconnect applications are driving the
   need for new service interface types which are a hybrid combination
   of VLAN Bundling and VLAN-based service interfaces. These are
   referred to as "VLAN-aware Bundling" service interfaces.
   Also virtualization applications are fueling an increase in the
   volume of MAC addresses that are to be handled by the network, which
   gives rise to the requirement for having the network re-convergence
   upon failure be independent of the number of MAC addresses learned
   by the PE.
   In addition, there are requirements for minimizing the amount of
   flooding of multi-destination frames and localizing the flooding to
   the confines of a given site.
   Moreover, there are requirements for supporting flexible VPN
   topologies and policies beyond those currently covered by (H-)VPLS.
   The focus of this document is on defining the requirements for a new
   solution, namely Ethernet VPN (E-VPN), which addresses the above
   Section 2 provides a summary of the terminology used. Section 3
   discusses the redundancy requirements. Section 4 describes the
   multicast optimization requirements. Section 5 articulates the ease
   of provisioning requirements. Section 6 focuses on the new service
   interface requirements. Section 7 highlights the fast convergence
   requirements. Section 8 describes the flood suppression requirement,
   and finally section 9 discusses the requirements for supporting
   flexible VPN topologies and policies.
   CE: Customer Edge
   E-VPN: Ethernet Virtual Private Network
   MHD: Multi-homed Device
   MHN: Multi-homed Network
   LACP: Link Aggregation Control Protocol
   LSP: Label Switched Path
   PE: Provider Edge
   PoA: Point of Attachment
   PW: Pseudowire
      Redundancy Requirements
        Flow-based Load Balancing
   A common mechanism for multi-homing a CE node to a set of PE nodes
   involves leveraging multi-chassis Ethernet link aggregation groups
   based on [802.1AX] LACP. [PWE3-ICCP] describes one such scheme. In
   Ethernet link aggregation, the load-balancing algorithms by which a
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   CE distributes traffic over the Attachment Circuits connecting to
   the PEs are quite flexible. The only requirement is for the
   algorithm to ensure in-order frame delivery for a given traffic
   flow. In typical implementations, these algorithms involve selecting
   an outbound link within the bundle based on a hash function that
   identifies a flow based on one or more of the following fields:
   i.   Layer 2: Source MAC Address, Destination MAC Address, VLAN
   ii.  Layer 3: Source IP Address, Destination IP Address
   iii. Layer 4: UDP or TCP Source Port, Destination Port
   iv.  Combinations of the above.
   A key point to note here is that [802.1AX] does not define a
   standard load-balancing algorithm for Ethernet bundles, and as such
   different implementations behave differently. As a matter of fact, a
   bundle operates correctly even in the presence of asymmetric load-
   balancing over the links. This being the case, the first requirement
   for active/active multi-homing is the ability to accommodate
   flexible flow-based load-balancing from the CE node based on L2, L3
   and/or L4 header fields.
   A solution MUST be capable of supporting flexible flow-based load
   balancing from the CE as described above. Further the MPLS network
   MUST be able to support flow-based load-balancing of traffic
   destined to the CE, even when the CE is connected to more than one
   PE. Thus the solution MUST be able to exercise multiple links
   connected to the CE, irrespective of the number of PEs that the CE
   is connected to.
        Flow-based Multi-pathing
   Any solution that meets the active-active flow based load balancing
   requirement described in section 3.1 MUST also be able to exercise
   multiple paths between a given pair of PEs. For instance if there
   are multiple RSVP-TE LSPs between a pair of PEs then the solution
   MUST be capable of load balancing traffic between those LSPs on a
   per flow basis. Similarly if LDP is being used as the transport LSP
   protocol, then the solution MUST be able to leverage LDP ECMP
   capabilities. The solution MUST also be able to leverage work in the
   MPLS WG that is in progress to improve the load balancing
   capabilities of the network based on entropy labels.
   It is worth pointing out that flow-based multi-pathing complements
   flow-based load balancing described in the previous section.
        Geo-redundant PE Nodes
   The PE nodes offering multi-homed connectivity to a CE or access
   network may be situated in the same physical location (co-located),
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   or may be spread geographically (e.g. in different COs or POPs). The
   latter is desirable when offering a geo-redundant solution that
   ensures business continuity for critical applications in the case of
   power outages, natural disasters, etc. An active/active multi-homing
   mechanism SHOULD support both co-located as well as geo-redundant PE
   placement. The latter scenario often means that requiring a
   dedicated link between the PEs, for the operation of the multi-
   homing mechanism, is not appealing from cost standpoint.
   Furthermore, the IGP cost from remote PEs to the pair of PEs in the
   multi-homed setup cannot be assumed to be the same when those latter
   PEs are geo-redundant.
        Optimal Traffic Forwarding
   In a typical network, and considering a designated pair of PEs, it
   is common to find both single-homed as well as multi-homed CEs being
   connected to those PEs. An active/active multi-homing solution
   SHOULD support optimal forwarding of unicast traffic for all the
   following scenarios:
   i.   single-homed CE to single-homed CE
   ii.  single-homed CE to multi-homed CE
   iii. multi-homed CE to single-homed CE
   iv.  multi-homed CE to multi-homed CE
   This is especially important in the case of geo-redundant PEs, where
   having traffic forwarded from one PE to another within the same
   multi-homed group introduces additional latency, on top of the
   inefficient use of the PE node's and core nodes' switching capacity.
   A multi-homed group (also known as a multi-chassis LACP group) is a
   group of PEs supporting a multi-homed CE.
        Flexible Redundancy Grouping Support
   In order to simplify service provisioning and activation, the multi-
   homing mechanism SHOULD allow arbitrary grouping of PE nodes into
   redundancy groups where each redundancy group represents all multi-
   homed groups that share the same group of PEs. This is best
   explained with an example: consider three PE nodes - PE1, PE2 and
   PE3. The multi-homing mechanism MUST allow a given PE, say PE1, to
   be part of multiple redundancy groups concurrently. For example,
   there can be a group (PE1, PE2), a group (PE1, PE3), and another
   group (PE2, PE3)  where CEs could be multi-homed to any one of these
   three redundancy groups.
         Multi-homed Network
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   There are applications which require an Ethernet network, rather
   than a single device, to be multi-homed to a group of PEs. The
   Ethernet network would typically run a resiliency mechanism such as
   MST or [G.8032] Ring Automated Protection Switching. The PEs may or
   may not participate in the control protocol of the Ethernet network.
   A solution MUST support multi-homed network connectivity with
   active/standby redundancy.
   A solution MUST also support multi-homed network with active/active
   VLAN-based load-balancing (i.e. disjoint VLAN sets active on
   disparate PEs).
   A solution MAY support multi-homed network with active/active MAC-
   based load-balancing (i.e. different MAC addresses on a VLAN are
   reachable via different PEs).
      Multicast Optimization Requirements
   There are environments where the usage of MP2MP LSPs may be
   desirable for optimizing multicast, broadcast and unknown unicast
   traffic. [VPLS-LSM] precludes the usage of MP2MP LSPs since current
   VPLS solutions require an egress PE to perform learning when it
   receives unknown uncast packets over a LSP. This is challenging when
   MP2MP LSPs are used as MP2MP LSPs do not have inherent mechanisms to
   identify the sender. The usage of MP2MP LSPs for multicast
   optimization becomes tractable if the need to identify the sender
   for performing learning is lifted. A solution MUST be able to
   provide a mechanism that does not require learning when packets are
   received over a MP2MP LSP. Further a solution MUST be able to
   provide procedures to use MP2MP LSPs for optimizing delivery of
   multicast, broadcast and unknown unicast traffic.
      Ease of Provisioning Requirements
   As L2VPN technologies expand into enterprise deployments, ease of
   provisioning becomes paramount. Even though current VPLS has auto-
   discovery mechanisms which allow for single-sided provisioning,
   further simplifications are required, as outlined below:
   - Single-sided provisioning behavior MUST be maintained
   - For deployments where VLAN identifiers are global across the MPLS
   network (i.e. the network is limited to a maximum of 4K services),
   it is required that the devices derive the MPLS specific attributes
   (e.g. VPN ID, BGP RT, etc.) from the VLAN identifier. This way, it
   is sufficient for the network operator to configure the VLAN
   identifier(s) on the access circuit, and all the MPLS and BGP
   parameters required for setting up the service over the core network
   would be automatically derived without any need for explicit
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   - Implementations SHOULD revert to using default values for
   parameters as and where applicable.
      New Service Interface Requirements
   [MEF] and [IEEE 802.1Q] have the following services specified:
   - Port mode: in this mode, all traffic on the port is mapped to a
     single bridge domain and a single corresponding L2VPN service
     instance. Customer VLAN transparency is guaranteed end-to-end.
   - VLAN mode: in this mode, each VLAN on the port is mapped to a
     unique bridge domain and corresponding L2VPN service instance.
     This mode allows for service multiplexing over the port and
     supports optional VLAN translation.
   - VLAN  bundling: in this mode, a group of VLANs on the port are
     collectively mapped to a unique bridge domain and corresponding
     L2VPN service instance. Customer MAC addresses must be unique
     across all VLANs mapped to the same service instance.
   For each of the above services a single bridge domain is assigned
   per service instance on the PE supporting the associated service.
   For example, in case of the port mode, a single bridge domain is
   assigned for all the ports belonging to that service instance
   regardless of number of VLANs coming through these ports.
   It is worth noting that the term 'bridge domain' as used above
   refers to a MAC forwarding table as defined in the IEEE bridge
   model, and does not denote or imply any specific implementation.
   [RFC 4762] defines two types of VPLS services based on "unqualified
   and qualified learning" which in turn maps to port mode and VLAN
   mode respectively.
   A solution is required to support the above three service types plus
   two additional service types which are primarily intended for hosted
   data center applications and are described below.
   For hosted data center interconnect applications, network operators
   require the ability to extend Ethernet VLANs over a WAN using a
   single L2VPN instance while maintaining data-plane separation
   between the various VLANs associated with that instance. This gives
   rise to two new service interface types: VLAN-aware Bundling without
   Translation, and VLAN-aware Bundling with Translation.
   The VLAN-aware Bundling without Translation service interface has
   the following characteristics:
   - The service interface MUST provide bundling of customer VLANs into
   a single L2VPN service instance.
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   - The service interface MUST guarantee customer VLAN transparency
   - The service interface MUST maintain data-plane separation between
   the customer VLANs (i.e. create a dedicated bridge-domain per VLAN).
   - In the special case of all-to-one bundling, the service interface
   MUST not assume any a priori knowledge of the customer VLANs. In
   other words, the customer VLANs shall not be configured on the PE,
   rather the interface is configured just like a port-based service.
   The VLAN-aware Bundling with Translation service interface has the
   following characteristics:
   - The service interface MUST provide bundling of customer VLANs into
   a single L2VPN service instance.
   - The service interface MUST maintain data-plane separation between
   the customer VLANs (i.e. create a dedicated bridge-domain per VLAN).
   - The service interface MUST support customer VLAN translation to
   handle the scenario where different VLAN Identifiers (VIDs) are used
   on different interfaces to designate the same customer VLAN.
   The main difference, in terms of service provider resource
   allocation, between these new service types and the previously
   defined three types is that the new services require several bridge
   domains to be allocated (one per customer VLAN) per L2VPN service
   instance as opposed to a single bridge domain per L2VPN service
      Fast Convergence
   A solution MUST provide the ability to recover from PE-CE attachment
   circuit failures as well as PE node failure for the case of both
   multi-homed device and multi-homed network. The recovery
   mechanism(s) MUST provide convergence time that is independent of
   the number of MAC addresses learned by the PE. This is particularly
   important in the context of virtualization applications which are
   fueling an increase in the number of MAC addresses to be handled by
   the Layer 2 network.
   Furthermore, the recovery mechanism(s) SHOULD provide convergence
   time that is independent of the number of service instances
   associated with the attachment circuit or PE.
      Flood Suppression
   The solution SHOULD allow the network operator to choose whether
   unknown unicast frames are to be dropped or to be flooded. This
   attribute need to be configurable on a per service instance basis.
   In addition, for the case where the solution is used for data-center
   interconnect, it is required to minimize the flooding of broadcast
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   frames outside the confines of a given site. Of particular interest
   is periodic ARP traffic.
   Furthermore, it is required to eliminate any unnecessary flooding of
   unicast traffic upon topology changes, especially in the case of
   multi-homed site where the PEs have a priori knowledge of the backup
   paths for a given MAC address.
       Supporting Flexible VPN Topologies and Policies
   A solution MUST be capable of supporting flexible VPN topologies
   that are not constrained by the underlying mechanisms of the
   solution. One example of this is hub and spoke where one or more
   sites in the VPN are hubs and the others as spokes. The hubs are
   allowed to send traffic to other hubs and to spokes, while spokes
   can communicate only with other hubs. The solution MUST provide the
   ability to support hub and spoke. Further the solution MUST provide
   the ability to apply policies at the MAC address granularity to
   control which PEs in the VPN learn which MAC address and how a
   specific MAC address is forwarded. It MUST be possible to apply
   policies to allow only some of the member PEs in the VPN to send or
   receive traffic for a particular MAC address.
       Security Considerations
   There are no additional security aspects beyond those of VPLS/H-VPLS
   that need to be discussed here.
       IANA Considerations
       Normative References
   [RFC4664] "Framework for Layer 2 Virtual Private Networks (L2VPNs)",
      September 2006.
   [RFC4761] "Virtual Private LAN Service (VPLS) Using BGP for Auto-
      discovery and Signaling", January 2007.
   [RFC4762] "Virtual Private LAN Service (VPLS) Using Label
      Distribution Protocol (LDP) Signaling", January 2007.
   [802.1AX] IEEE Std. 802.1AX-2008, "IEEE Standard for Local and
      metropolitan area networks - Link Aggregation", IEEE Computer
      Society, November, 2008.
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       Informative References
   [VPLS-BGP-MH] Kothari et al., "BGP based Multi-homing in Virtual
   Private LAN Service", draft-ietf-l2vpn-vpls-multihoming-00, work in
   progress, November, 2009.
   [VPLS-MCAST] Aggarwal et al., "Multicast in VPLS", draft-ietf-l2vpn-
   vpls-mcast-06.txt, work in progress, March, 2010.
   [PWE3-ICCP] Martini et al., "Inter-Chassis Communication Protocol
   for L2VPN PE Redundancy", draft-ietf-pwe3-iccp-02.txt, work in
   progress, Octoer, 2009.
   [PWE3-FAT-PW] Bryant et al., "Flow Aware Transport of Pseudowires
      over an MPLS PSN", draft-ietf-pwe3-fat-pw-03.txt, work in
      progress, January 2010.
       Authors' Addresses
   Ali Sajassi
   170 West Tasman Drive
   San Jose, CA  95134, USA
   Samer Salam
   595 Burrard Street, Suite 2123
   Vancouver, BC V7X 1J1, Canada
   Rahul Aggarwal
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089, USA
   Nabil Bitar
   Verizon Communications
   Email :
   James Uttaro
   200 S. Laurel Avenue
   Middletown, NJ  07748, USA
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   Aldrin Isaac
   Clarence Filsfils
   Wim Henderickx
   Sajassi-Aggarwal, et al.                                  [Page 12]