Requirements for Ethernet VPN (E-VPN)
draft-ietf-l2vpn-evpn-req-02

Internet Working Group                                        A. Sajassi
INTERNET-DRAFT                                                     Cisco
Category: Informational                                                 
                                                             R. Aggarwal
J. Uttaro                                                         Arktan
AT&T                                                                    
                                                                N. Bitar
W. Henderickx                                                    Verizon
Alcatel-Lucent                                                          
                                                            Aldrin Isaac
                                                               Bloomberg
                                                                        
                                                                        
Expires: August 24, 2013                               February 24, 2013

                 Requirements for Ethernet VPN (E-VPN) 
                    draft-ietf-l2vpn-evpn-req-02.txt

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Abstract

   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 . . . . . . . . . . . . . . . . . .  6
     4.4.  Optimal Traffic Forwarding . . . . . . . . . . . . . . . .  6
     4.5.  Flexible Redundancy Grouping Support . . . . . . . . . . .  7
     4.6.   Multi-homed Network . . . . . . . . . . . . . . . . . . .  7
   5. Multicast Optimization Requirements . . . . . . . . . . . . . .  7
   6. Ease of Provisioning Requirements . . . . . . . . . . . . . . .  8
   7. New Service Interface Requirements  . . . . . . . . . . . . . .  8
   8. Fast Convergence  . . . . . . . . . . . . . . . . . . . . . . . 10
   9. Flood Suppression . . . . . . . . . . . . . . . . . . . . . . . 10
   10. Supporting Flexible VPN Topologies and Policies  . . . . . . . 11
   11. Contributers . . . . . . . . . . . . . . . . . . . . . . . . . 11
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   14. Normative References . . . . . . . . . . . . . . . . . . . . . 11
   14. Informative References . . . . . . . . . . . . . . . . . . . . 12
   15. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 12

 

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1. Specification of requirements

   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].

2. Introduction

   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 other L2VPN
   services such as E-TREE, VPWS, and VPMS. 

   In the area of multi-homing current VPLS can only support multi-
   homing with active/standby resiliency model, for example 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][RFC6074]. This, however, still
   requires the operator to configure a number of network-side
   parameters on top of the access-side Ethernet configuration. 

   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
 

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   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
   issues.

   Section 3 provides a summary of the terminology used. Section 4
   discusses the redundancy requirements. Section 5 describes the
   multicast optimization requirements. Section 6 articulates the ease
   of provisioning requirements. Section 7 focuses on the new service
   interface requirements. Section 8 highlights the fast convergence
   requirements. Section 9 describes the flood suppression requirement,
   and finally section 10 discusses the requirements for supporting
   flexible VPN topologies and policies.

3. Terminology

   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
   MP2MP: Multipoint to Multipoint
   P2MP: Point to Multipoint
   P2P:Point to Point

4. Redundancy Requirements

4.1.  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
   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
 

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   ii.  Layer 3: Source IP Address, Destination IP Address
   iii. Layer 4: UDP or TCP Source Port, Destination Port

   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. It
   should be noted that when a CE is multi-homed to several PEs, there
   could be multiple ECMP paths from each remote PE to each multi-homed
   PE. Furthermore, for active/active multi-homed site, a remote PE can
   choose any of the multi-homed PEs for sending traffic destined to the
   multi-homed sites. Therefore, when a solution supports active/active
   multi-homing, it MUST exercise as many of these paths as possible for
   traffic destined to a multi-homed site.

   A solution MAY support flow-based load balancing among PEs that are
   member of a redundancy group spanning multiple ASes. 

4.2.  Flow-based Multi-pathing 

   Any solution that meets the active-active flow based load balancing
   requirement described in section 4.1 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 among those LSPs on a per
   flow basis. Similarly, if LDP is being used as the signaling protocol
   for transport LSP, then the solution MUST be able to leverage those
   LDP signaled equal cost LSPs. 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
   [ENTROPY-LABEL]. 

   It is worth pointing out that flow-based multi-pathing complements
   flow-based load balancing described in the previous section.

 

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4.3.  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),
   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 a cost standpoint. Furthermore, the
   IGP cost from remote PEs to the pair of PEs in the dual-homed setup
   cannot be assumed to be the same when those latter PEs are geo-
   redundant.

   A solution MUST support active/active multi-homing without the need
   for a dedicated control/data link among the PEs in the multi-homed
   group.

   A solution MUST NOT assume that the IGP cost from a remote PE to each
   of the PEs in the multi-homed group is the same. 

   A solution MUST support multi-homing across different IGP domains
   within the same Autonomous System.

   A solution SHOULD support multi-homing across multiple Autonomous
   Systems.

4.4.  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 LAG) is a group of
   PEs supporting a multi-homed CE.
 

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4.5.  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.

4.6.   Multi-homed Network

   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
   Multiple Spanning Tree Protocol [802.1Q] or Ethernet Ring Protection
   Switching [G.8032]. The PEs may or may not participate in the control
   protocol of the Ethernet network. For a multi-homed network running
   [802.1Q] or [G.8032], these protocols require that each VLAN to be
   active only on one of the multi-homed links.  

   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 VLAN-based load balancing among PEs that are
   member of a redundancy group spanning multiple ASes. 

   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).

5. Multicast Optimization Requirements

   There are environments where the usage of MP2MP LSPs may be desirable
   for optimizing multicast, broadcast and unknown unicast traffic in
   order to reduce the amount of multicast states in the core routers.
   [VPLS-MCAST] precludes the usage of MP2MP LSPs since current VPLS
   solutions require an egress PE to perform learning when it receives
 

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   unknown unicast 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.

6. Ease of Provisioning Requirements

   As L2VPN technologies expand into enterprise deployments, ease of
   provisioning becomes paramount. Even though current VPLS has auto-
   discovery mechanism, 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) for 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
   configuration.

   - Implementations SHOULD revert to using default values for
   parameters as and where applicable.

7. 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
 

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   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. 

   [RFC4762] 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.

   - The service interface MUST guarantee customer VLAN transparency
   end-to-end.

   - 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:

 

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   - 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
   instance.

8. 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 the PE.

9. 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
   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
 

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   paths for a given MAC address.

10. 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 E-TREE topology where one or more sites in the VPN
   are roots and the others as leafs. The roots are allowed to send
   traffic to other roots and to leafs, while leafs can communicate only
   with other roots. The solution MUST provide the ability to support E-
   TREE topology. 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.

   A solution MUST be capable of supporting both inter-AS option-C and
   inter-AS option-B scenarios as described in [RFC 4364]. 

11. Contributers

   Samer Salam, Cisco John Drake, Juniper Clarence Filsfils, Cico

12. Security Considerations

   For scenarios where MAC learning is performed in data-plane, there
   are no additional security aspects beyond those considered in
   [RFC4761] and [RFC4762]. And for scenarios where MAC learning is
   performed in control plane (via BGP), there are no additional
   security aspects beyond those considered in [RFC4364].

13. IANA Considerations

   None.

14. Normative References
   [RFC2119] "Key words for use in RFCs to Indicate Requirement Levels",
              August 1996.

   [RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
              (VPLS) Using BGP for Auto-Discovery and Signaling", RFC
              4761, January 2007.

   [RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service
              (VPLS) Using Label Distribution Protocol (LDP) Signaling",
 

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              RFC 4762, January 2007.

   [RFC4364] "BGP/MPLS IP Virtual Private Networks (VPNs)", February
              2006.

   [802.1AX] IEEE Std. 802.1AX-2008, "IEEE Standard for Local and
              metropolitan area networks - Link Aggregation", IEEE
              Computer Society, November 2008.

   [802.1Q] IEEE Std. 802.1Q-2011, "IEEE Standard for Local and
              metropolitan area networks - Virtual Bridged Local Area
              Networks", 2011.

   [RFC6074] E. Rosen and B. Davie, "Provisioning, Auto-Discovery, and
              Signaling in Layer 2 Virtual Private Networks (L2VPNs)",
              January 2011.

14. Informative References
   [RFC4664] "Framework for Layer 2 Virtual Private Networks (L2VPNs)",
              September 2006.

   [VPLS-BGP-MH] Kothari et al., "BGP based Multi-homing in Virtual
              Private LAN Service", draft-ietf-l2vpn-vpls-multihoming-
              03, work in progress, November, 2009.

   [PWE3-ICCP] Martini et al., "Inter-Chassis Communication Protocol for
              L2VPN PE Redundancy", draft-ietf-pwe3-iccp-09.txt, work in
              progress, Octoer, 2009.

   [VPLS-MCAST] R. Aggarwal, et al., "Multicast in VPLS", draft-ietf-
              l2vpn-vpls-mcast-11.txt, work in progress, July 2012.

   [MEF] MEF 6.1 Technical Specification, "Ethernet Service
              Definitions",  April 2008.

   [ENTROPY-LABEL] K. Kompella et al., "The Use of Entropy Labels in
              MPLS Forwarding", draft-ietf-mpls-entropy-label-06.txt,
              September 6, 2012.

15. Author's Address

      Ali Sajassi
      Cisco
      Email: sajassi@cisco.com

      Rahul Aggarwal
 

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      Email: raggarwa_1@yahoo.com

      Wim Henderickx
      Alcatel-Lucent
      e-mail: wim.henderickx@alcatel-lucent.com

      Aldrin Isaac
      Bloomberg
      Email: aisaac71@bloomberg.net

      James Uttaro
      AT&T
      200 S. Laurel Avenue
      Middletown, NJ  07748
      USA
      Email: uttaro@att.com

      Nabil Bitar
      Verizon Communications
      Email : nabil.n.bitar@verizon.com

      John Drake
      Juniper Networks
      1194 N. Mathilda Ave.
      Sunnyvale, CA  94089 US
      Email: jdrake@juniper.net

      Clarence Filsfils
      Cisco
      Email: cfilsfil@cisco.com

      Samer Salam
      Cisco
      Email: ssalam@cisco.com

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