L2VPN Working Group
     Internet Draft
     Intended status: Informational
     Expires: April 2014
                                                   Nabil Bitar
                                                   Verizon
     
                                                   Florin Balus
                                                   Marc Lasserre
                                                   Wim Henderickx
     John Drake                                    Alcatel-Lucent
     Juniper Networks
                                                   Ali Sajassi
                                                   Luyuan Fang
                                                   Cisco
     Lucy Yong
     Huawei
                                                   Yuichi Ikejiri
     Susan Hare                                    NTT Communications
     ADARA
                                                   Mircea Pisica
                                                   BT
     
                                                   October 21, 2013
     
          Cloud Networking: VPN Applicability and NVo3 Gap Analysis
                  draft-bitar-nvo3-vpn-applicability-02.txt
     
     
     Abstract
     
        Multi-tenant data centers and clouds provide computing,
        storage and network resources dedicated per tenant. The
        current focus in the evolution of multi-tenant data-center and
        cloud networks is to (1) support a large number of tenants
        with a large number of communicating systems, (2) provide
        isolation among tenant virtual networks, (3) provide for
        efficient network utilization, and (4) support virtual machine
        mobility and network elasticity that match compute and storage
        elasticity.
     
     
        The NVo3 work effort is initially targeted to identify the
        requirements for large multi-tenant data centers, and develop
        a framework architecture that addresses those requirements. In
        addition, it is targeted to identify existing or evolving
        solutions used in cloud networking, their applicability to
        NVo3, and any gaps that they may have in addressing the NVo3
        requirements. This document describes the applicability of
        existing work in various IETF Working Groups (e.g., RFCs and
        drafts developed or evolving in IETF L2VPN and L3VPN Working
        Groups) to cloud networking and NVo3, as well as the gaps and
        problems that need to be further addressed.
     
     
     
     
     
     
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     Status of this Memo
     
        This Internet-Draft is submitted in full conformance with the
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        This Internet-Draft will expire on April 21, 2014.
     
     Copyright Notice
     
        Copyright (c) 2013 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
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     Table of Contents
     
        1. Introduction.............................................. 4
        2. General terminology....................................... 6
           2.1. Conventions used in this document.................... 7
        3. Brief overview of Ethernet, L2VPN and L3VPN deployments... 7
        4. Generic Cloud Networking Architecture..................... 9
        5. Challenges in Existing Deployments....................... 13
           5.1. VLAN Space Limitation............................... 14
           5.2. MAC, IP, and ARP Issues............................. 14
           5.3. Per VLAN flood containment.......................... 17
           5.4. Convergence and multipath support................... 17
           5.5. Optimal traffic forwarding.......................... 18
           5.6. Efficient multicast................................. 20
           5.7. L3 virtualization................................... 21
           5.8. Connectivity to existing tenant VPN sites........... 21
           5.9. DC Inter-connect requirements....................... 22
           5.10. VM Mobility........................................ 22
        6. L2VPN Applicability to Cloud Networking.................. 24
           6.1. VLANs and L2VPN toolset............................. 24
           6.2. E-VPN............................................... 27
           6.3. PBB and L2VPN toolset............................... 30
              6.3.1. Addressing VLAN space exhaustion and MAC
              explosion............................................. 32
              6.3.2. Fast convergence and L2 multi-pathing.......... 32
              6.3.3. Per ISID flood containment..................... 34
              6.3.4. Efficient multicast support.................... 34
              6.3.5. Tunneling options for PBB ELAN: Ethernet, IP and
              MPLS.................................................. 34
              6.3.6. Use Case examples.............................. 35
              6.3.7. NVo3 applicability............................. 38
              6.3.8. Connectivity to existing VPN sites and Internet 40
              6.3.9. DC Interconnect................................ 43
              6.3.10. Interoperating with existing DC VLANs......... 44
           6.4. TRILL and L2VPN toolset............................. 46
        7. L3VPN applicability to Cloud Networking.................. 47
        8. VM Mobility with E-VPN................................... 50
           8.1. Layer 2 Extension Solution.......................... 50
           8.2. VM Default Gateway Solutions........................ 53
              8.2.1. VM Default Gateway Solution 1.................. 53
              8.2.2. VM Default Gateway Solution 2.................. 54
        9. Solutions and Considerations for other DC challenges..... 55
           9.1. Addressing IP/ARP explosion......................... 55
           9.2. Optimal traffic forwarding.......................... 55
           9.3. VM Mobility......................................... 55
           9.4. Dynamic provisioning of network services............ 56
     
     
     
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           9.5. Considerations for Layer2 and Layer3 VPNS on End-
           systems.................................................. 57
        10. Operator Considerations................................. 57
        11. Security Considerations................................. 58
        12. IANA Considerations..................................... 58
        13. References.............................................. 58
           13.1. Normative References............................... 58
           13.2. Informative References............................. 59
        14. Acknowledgments......................................... 61
     
     1. Introduction
     
     
     
     The initial Data Center (DC) networks were built to address the
     needs of individual enterprises and/or individual applications.
     Ethernet VLANs and regular IP routing were used to provide
     connectivity between compute, storage resources and the related
     customer sites.
     
     
     
     The virtualization of compute resources in a Data Center (DC)
     environment provides the foundation for providing compute and
     storage resources to multiple tenants (customers), and/or for
     providing application services to multiple tenants. For example,
     a tenant may be provided a group of Virtual Machines (VMs) that
     may reside on server blades distributed throughout a DC or across
     DCs. In this latter case, the DCs may be owned and operated by a
     cloud service provider connected to one or more network service
     providers, two or more cloud service providers each connected to
     one or more network service providers, or a hybrid of DCs
     operated by the customer and the cloud service provider(s). In
     addition, multiple tenants may be assigned resources on the same
     compute and storage hardware.
     
     
     
     In order to provide access for multiple tenants to the
     virtualized compute and storage resources, the DC network and DC
     interconnect have to evolve from the basic VLAN and IP routing
     architecture to provide equivalent connectivity virtualization at
     a large scale.
     
     
     
     
     
     
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     [NVo3-problem-statement] describes the problems faced in large
     multi-tenant data centers, and motivates the need for overlays to
     address these problems. The main problems highlighted are: (1)
     support for a large number of tenants, (2) network infrastructure
     scale, (3) isolation among tenant virtual networks with
     overlapping address spaces across tenants, and (4) support for
     virtual machine mobility, network elasticity, and accompanying
     dynamic network provisioning. [NVo3-fmwk] describes a framework
     architecture for NVo3, while [NVo3-dp-reqts] and [NVo3-cp-reqts]
     describe NVo3 data plane and control plane requirements,
     respectively. Prior to the NVo3 effort initiation, a number of
     technologies had been used to address network virtualization.
     Some had also been deployed in data centers and cloud networks,
     and/or had been further evolved to address requirements of large
     multi-tenant data centers and cloud networks. The natural
     question is how these technologies address multi-tenant cloud
     networking problems as described in [NVo3-problem-statement],
     what challenges or gaps they need to still further address, and
     how they compare to the NVo3 architecture framework [NVo3-frmwk].
     This document addresses that question. Further evolution of this
     document may target a more detailed comparison of these
     technologies to the evolving NVo3 data plane and control plane
     requirements.
     
     
     
     Virtual LAN bridging and Virtual Private Network (VPN)
     technologies had been developed and deployed to support virtual
     networks with overlapping address spaces over a common
     infrastructure. Some of these technologies also use various
     overlay technologies to enable the sharing and scale of an
     undelay network infrastructure. Those technologies have been used
     in data-center and cloud networks. However, these technologies
     originally developed for relatively static environments in terms
     of communicating endpoints, do not address all the requirements
     arising in cloud-computing environments, and specifically multi-
     tenant environments.
     
     
     
     This document starts with a brief overview of Ethernet, Layer2
     and Layer3 VPN deployments. It then describes generic data center
     architecture. This architecture is used in subsequent sections as
     basis for describing how different VPN technologies apply in DCs
     and cloud networks, and what problems described in [Nvo3-problem-
     statement] they address. In addition, it provides a comparison
     
     
     
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     among these technologies and the NVo3 architecture framework at
     the functional level.
     
     
     
     2. General terminology
     
     
     
        Some general terminology is defined here; most of the
        terminology used is from [802.1ah], [RFC4026] and [NVo3-fmwk].
        Terminology specific to this memo is introduced as needed in
        later sections.
     
     
     
        DC: Data Center
     
     
     
        ELAN: MEF ELAN, multipoint-to-multipoint Ethernet service
     
     
     
        EVPN: Ethernet VPN as defined in [EVPN]
     
     
     
        PBB: Provider Backbone Bridging, new Ethernet encapsulation
        designed to address VLAN exhaustion and MAC explosion issues;
        specified in IEEE 802.1ah [802.1ah]
     
     
     
        PBB-EVPN: defines how EVPN can be used to transport PBB frames
     
     
     
        BMAC: Backbone MACs, the backbone source or destination MAC
        address fields defined in the 802.1ah provider MAC
        encapsulation header.
     
     
     
     
     
     
     
     
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        CMAC: Customer MACs, the customer source or destination MAC
        address fields defined in the 802.1ah customer MAC
        encapsulation header.
     
     
     
        BEB: A backbone edge bridge positioned at the edge of a
        provider backbone bridged network. It is usually the point in
        the network where PBB encapsulation is added or removed from
        the frame.
     
     
     
        BCB: A backbone core bridge positioned in the core of a
        provider backbone bridged network. It performs regular
        Ethernet switching using the outer Ethernet header.
     
     
     
     2.1. Conventions used in this document
     
     
     
        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].
     
     
     
        In this document, these words will appear with that
        interpretation only when in ALL CAPS. Lower case uses of
        these words are not to be interpreted as carrying RFC-2119
        significance.
     
     
     
     3. Brief overview of Ethernet, L2VPN and L3VPN deployments
     
     
     
        Initial Ethernet networks have been deployed in LAN
        environments, where the total number of hosts (hence MAC
        addresses) to manage was limited. Physical Ethernet topologies
        in LANs were pretty simple. Hence, a simple loop resolution
        protocol such as the Spanning Tree Protocol (STP) was
     
     
     
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        sufficient in the early days. Efficient utilisation of
        physical links was not a major concern in LANs, while at the
        same time leveraging existing and mature technologies.
     
     
     
        As more hosts got connected to a LAN, or the need arose to
        create multiple LANs on the same physical infrastructure, it
        became necessary to partition the physical topology into
        multiple Virtual LANs (VLANs) [802.1q]. A VLAN is identified
        by a VLAN ID in the 802.1q VLAN tag inserted in the Ethernet
        header. STP evolved to cope with multiple VLANs with Multiple-
        STP (MSTP). Bridges/Switches evolved to learn behind which
        VLAN specific MACs resided, a process known as qualified
        learning, requiring MACs to be unique only in the VLAN
        context. As Ethernet LANs moved into the provider space, the
        12-bit VLAN space limitation (i.e. a total of 4094 VLANs,
        VLANs 0 and 4095 reserved) led to VLAN stacking (Q-in-Q) and
        later to Provider backbone Bridging (PBB).
     
     
     
        With PBB, not only can over 16M virtual LAN instances (24-bit
        Service I-SID) be supported, but also a clean separation
        between customer and provider domains has been defined with
        separate MAC address spaces (Customer-MACs (CMACs) versus
        Provider Backbone-MACs (BMACs)). CMACs are only learned at the
        edge of the PBB network on PBB Backbone Edge Bridges (BEBs) in
        the context of an I-component while only B-MACs are learnt by
        PBB Backbone Core Bridges (BCBs). This results in BEB switches
        creating MAC-in-MAC tunnels to carry customer traffic, thereby
        hiding C-MACs in the core.
     
     
     
        In the meantime, interconnecting L2 domains across
        geographical areas has become a necessity. VPN technologies
        have been defined to carry both L2 and L3 traffic across
        IP/MPLS core networks. The same technologies could also be
        used within the same data center to provide for scale or for
        interconnecting services across L3 domains, as needed. Virtual
        Private LAN Service (VPLS) has been used to provide
        transparent LAN services over IP/MPLS WANs while IP VPNs,
        including BGP/MPLS IP VPNs and IPsec VPNs, have been used to
        provide virtual IP routing instances over a common IP/MPLS
        core network.
     
     
     
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        All these technologies have been combined to maximize their
        respective benefits. At the edge of the network, such as in
        access networks, VLAN and PBB are commonly used technologies.
        Aggregation networks typically use VPLS or BGP/MPLS IP VPNs to
        groom traffic on a common IP/MPLS core.
     
     
     
        It should be noted that Ethernet has kept evolving because of
        its attractive features, specifically its auto-discovery
        capabilities and the ability of hosts to physically relocate
        on the same LAN without requiring renumbering. In addition,
        Ethernet switches have become commodity, creating a financial
        incentive for interconnecting hosts in the same community with
        Ethernet switches. The network layer (layer3), on the other
        hand, has become pre-dominantly IP. Thus, communication across
        LANs uses IP routing.
     
     
     
     4. Generic Cloud Networking Architecture
     
     
     
        A generic architecture for Cloud Networking is depicted in
        Figure 1.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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                                 ,---------.
                               ,'           `.
                              (    IP/MPLS    )
                               `.           ,'
                                 `-+------+'
                              +--+--+   +-+---+
                              | GW  |+-+| GW  |
                              +-+---+   +-----+
                                 /         \
                           +----+---+   +---+-----+
                           | Core   |   |  Core   |
                           | SW/Rtr |   | SW/Rtr  |
                           +-+----`.+   +-+---+---+
                             /      \   .'     \
                        +---+--+   +-`.+--+  +--+----+
                        | ToR  |   | ToR  |  |  ToR  |
                        +-+--`.+   +-+-`.-+  +-+--+--+
                        .'     \   .'    \   .'    `.
                     __/_      _i./       i./_      _\__
                    :VSw :    :VSw :     :VSw :    :VSw :
                    '----'    '----'     '----'    '----'
     
            Figure 1 : A Generic Architecture for Cloud Networking
     
     
     
        A cloud network is composed of intra-Data Center (DC) networks
        and network services, and inter-DC network connectivity. DCs
        may belong to a cloud service provider connected to one or
        more network service providers, different cloud service
        providers each connected to one or more network service
        providers, or a hybrid of DCs operated by the enterprise
        customers and the cloud service provider(s). It may also
        provide access to the public and/or enterprise customers.
     
     
     
        The following network components are present in a DC:
     
     
     
           - VSw or virtual switch: software based Ethernet switch
             running inside the server blades. VSw may be single or
             dual-homed to the Top of Rack switches (ToRs). The
             individual VMs appear to a VSw as IP hosts connected via
     
     
     
     
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             logical Ethernet interfaces. The VSw may evolve to
             support IP routing functionality.
     
           - ToR or Top of Rack: hardware-based Ethernet switch
             aggregating all Ethernet links from the server blades in
             a rack representing the entry point in the physical DC
             network for the hosts. ToRs may also perform routing
             functionality. ToRs are usually dual-homed to the Core
             SW. Other deployment scenarios may use an EoR (End of
             Row) switch to provide a similar function as a ToR.
     
     
     
           - Core SW (switch): high capacity core node aggregating
             multiple ToRs. This is usually a cost effective Ethernet
             switch. Core switches can also support IP routing
             capabilities.
     
     
     
           - DC GW: gateway to the outside world providing DC
             Interconnect and connectivity to Internet and VPN
             customers. In the current DC network model, this may be a
             Router with Virtual Routing capabilities and/or an IPVPN
             [RFC4364]/L2VPN [RFC7461][RFC[4762] Provider Edge [PE].
     
     
     
        A DC network also contains other network services, such as
        firewalls, load-balancers, IPsec gateways, and SSL
        acceleration gateways. These network services are not
        currently discussed in this document as the focus is on the
        routing and switching services. The traditional DC deployment
        employs VLANs to isolate different VM groups throughout the
        Ethernet switching network within a DC. The VM Groups are
        mapped to VLANs in the vSws. The ToRs and Core SWs may employ
        VLAN trunking to eliminate provisioning touches in the DC
        network. In some scenarios, IP routing is extended down to the
        ToRs, and may be further extended to the hypervisor as
        discussed earlier. However, this routing unless it provides
        for virtual forwarding function, it would require it to be
        limited to one IP domain addressed from the same address
        realm.
     
     
     
     
     
     
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        Any new DC and cloud networking technology should to be able
        to fit as seamlessly as possible with this existing DC model,
        at least in a non-greenfield environment. In particular, it
        should be possible to introduce enhancements to various tiers
        in this model in a phased approach without disrupting the
        other elements.
     
     
     
        Depending upon the scale, DC distribution, operations model,
        Capex and Opex aspects, DC switching elements can act as
        strict L2 switches and/or provide IP routing capabilities,
        including VPN routing and/or MPLS support if the operation
        environment allows. In smaller DCs, it is likely that some
        tier layers get collapsed, and that Internet connectivity,
        inter-DC connectivity and VPN support will be handled by Core
        Nodes that perform the DC GW role as well.
     
     
     
        The DC network architecture described in this section can be
        used to provide generic L2-L3 service connectivity to each
        tenant as depicted in Figure 2:
     
     
     
                           ---+--.                      ---+---
                  ....( VRF1 )......               (  VRF2 )
                      |    '-----'      |               '-----'
                      |     Tenant1     |ELAN12     Tenant1|
                  |ELAN11       ....|........          |ELAN13
                  '':'''''''':'       |        |     '':'''''''':'
               ,'.      ,'.      ,+.      ,+.     ,'.      ,'.
              (VM )....(VM )    (VM )... (VM )   (VM )....(VM )
               `-'      `-'      `-'      `-'     `-'      `-'
     
            Figure 2 : Logical Service connectivity for one tenant
     
     
     
        In this example one or more virtual routing contexts
        distributed on multiple DC GWs and one or more ELANs (e.g.,
        one per Application) running on DC switches are assigned for
        DC tenant 1. ELAN is a generic term for Ethernet multipoint
        service, which in the current DC environment is implemented
     
     
     
     
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        using 12-bit VLAN tags. Other possible ELAN technologies are
        discussed in section 6.
     
     
     
        For a multi-tenant DC, this type of service connectivity or a
        variation could be used for each tenant. In some cases only L2
        connectivity is required, i.e., only an ELAN may be used to
        interconnect VMs and customer sites.
     
     
     
     5. Challenges in Existing Deployments
     
     
     
        This section summarizes the challenges faced with the present
        mode of operation described in the previous section and the
        issues arising for next generation DC networks as described in
        [NVo3-problem-statement].
     
     
     
        With the introduction of multi-tenant DCs, providing each
        tenant dedicated virtual compute and storage resources and/or
        application services, the DC network must also provide each
        tenant access to these resources and services. In addition,
        some tenants may require some aspect of their services
        available to other businesses in a B-to-B model or to the
        public. Every tenant requires service connectivity to its own
        resources with secure separation from other tenant domains.
        Connectivity needs to support various deployment models,
        including interconnecting customer-hosted data center
        resources to Cloud Service Provider (CSP) hosted resources
        (Virtualized DC for the tenant). This connectivity may be at
        layer2 or layer3.
     
     
     
        Currently, large DCs are often built on a service architecture
        where each tenant is assigned two or more VLANs. VLANs
        configured in Ethernet edge and core switches are
        interconnected by IP routing running in a few centralized
        routers. There may be some cases though where IP routing might
        be used in the DC core nodes or even in the TORs inside a DC.
     
     
     
     
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     5.1. VLAN Space Limitation
     
     
     
        Existing DC deployments provide customer separation and flood
        containment, including support for DC infrastructure
        interconnectivity, using Ethernet VLANs [802.1q]. A 12-bit
        VLAN tag provides support for a maximum of 4094 VLANs.
     
     
     
        4094 VLANs are inadequate for a CSP looking to expand its
        customer base. For example, there are a number of VPN
        deployments (VPLS and IP VPN) that serve more than 20K
        customers. If a VPN service provider with 20K VPN customers
        wants to provide cloud services to these customers or teams up
        with an independent CSP that does, and If 50% (10k) of these
        customers are likely to become cloud customers each requiring
        multiple VLANs in a multi-tenant DC, 4094 VLANs will not be
        able to support the demand. In general, 4094 VLANs will
        support less than 4K tenants in a multi-tenant DC unless
        constraints are imposed on the VM placement so that the DC is
        subdivided into multiple non-congruent domains, each with 4K
        VLANs.
     
     
     
        The cloud networking infrastructure needs to provide support
        for a much bigger number of virtual Layer2 (L2) domains than
        4K, as discussed in [NVo3-problem-statement] Section 2.7,
        allowing for resource placement flexibility and efficient
        resource utilization as discussed in [NVo3-problem-statement]
        Section 2.2.
     
     
     
     5.2. MAC, IP, and ARP Issues
     
     
     
        Virtual Machines are the basic compute blocks provided to
        cloud tenants. Every server blade typically supports 16-40 VMs
        today with 100 or more VMs per server blade possibly becoming
        common in the near future. Every VM may have multiple
     
     
     
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        interfaces for provider and enterprise management, VM mobility
        and tenant access, each with its own MAC and IP addresses. For
        a sizable DC, this may translate into millions of VM IP and
        MAC addresses. From a cloud network viewpoint, this scale
        number will be an order of magnitude higher.
     
     
     
        Supporting this amount of IP and MAC addresses, including the
        associated dynamic behavior (e.g., ARP), throughout the DC
        Ethernet switches and routers is very challenging in an
        Ethernet VLAN and regular routing environment.
     
     
     
        A Core Ethernet switch supporting VLAN bridging domains
        [802.1q] learns the MAC addresses for every single VM
        interface that sends traffic through the switch albeit in the
        context of VLANs to which these MACs belong. VLANs, as
        discussed earlier, provide for MAC address separation across
        tenants and therefore address the problem in [NVo3-problem-
        statement] Section 2.5 for L2 bridged domains.  Throwing
        memory to increase the MAC Forwarding DataBase (FDB) size
        affects the cost of these switches, and there could still be a
        scale constraint. MAC address table scale is highlighted in
        [NVo3-problem-statemnt] Section 2.3. In addition, as the
        number of MACs that switches need to learn increases,
        convergence time could increase, and flooding activity will
        increase upon a topology change as the core switches flush and
        re-learn the MAC addresses. Simple operational mistakes may
        lead to duplicate MAC entries within the same VLAN domain and
        security issues due to administrative MAC assignment used
        today for VM interfaces. Similar concerns about memory
        requirements and related cost apply to DC Edge switches
        (ToRs/EoRs) and DC GWs.
     
     
     
        From a router perspective, it is important to maximize the
        utilization of available resources in both control and data
        planes through flexible mapping of VMs and related VLANs to
        routing interfaces. This is not easily done in the current
        VLAN based deployment environment where the use of VLAN
        trunking limits the allocation of VMs to only local routers.
     
     
     
     
     
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        The amount of ARP traffic grows linearly with the number of
        hosts on a LAN. For 1 million VM hosts, it can be expected
        that the amount of ARP traffic will be in the range of half
        million ARPs per second at the peak, which corresponds to over
        200 Mbps of ARP traffic [MYERS]. Similarly, on a server, the
        amount of ARP traffic grows linearly with the number of
        virtual L2 domains/ELANs instantiated on that server and the
        number of VMs in that domain. Besides the link capacity
        wasted, which may be small compared to the link capacities
        deployed in DCs, the computational burden may be prohibitive.
        In a large-DC environment, the large number of hosts and the
        distribution of ARP traffic may lead to a number of
        challenges:
     
     
     
           - Processing overload and overload of ARP entries on the
             Server/Hypervisor. This is caused by the increased number
             of VMs per server blade and the size of related ELAN
             domains. For example, a server blade with 100 VMs, each
             in a separate L2 domain with 100 VMs each would need to
             support 10K ARP entries and the associated ARP processing
             while performing the other compute tasks.
           - Processing overload and exhaustion of ARP entries on the
             Routers/PEs and any other L3 Service Appliances (Firewall
             (FW), Load-Balancer (LB) etc.). This issue is magnified
             by the L3 virtualization at the service gateways. For
             example, a gateway PE handling 10K ELANs each with 10 VMs
             will result in 100K hosts sending/receiving traffic
             to/from the PE, thus requiring the PE to learn 100K ARP
             entries. It should be noted that if the PE supports
             Integrated Routing and Bridging (IRB), it must support
             the associated virtual IP RIBs/FIBs and MAC FDBs for
             these hosts in addition to the ARP entries.
           - Flood explosion throughout Ethernet switching network.
             This is caused by the use of VLAN trunking and implicitly
             by the lack of per VPN flood containment.
     
     
     
          DC and DC-interconnect technologies, including control
          plane, that minimize the negative impact of ARP, MAC and IP
          entry explosion on individual network elements in a DC or
          cloud network hierarchy are needed.
     
     
     
     
     
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     5.3. Per VLAN flood containment
     
     
     
        From an operational perspective, DC operators try to minimize
        the provisioning touches required for configuring a VLAN
        domain by employing VLAN trunks on the L2 switches. This comes
        at the cost of flooding broadcast, multicast and unknown
        unicast frames outside of the boundaries of the actual VLAN
        domain. Containment of a broadcast domain identified by a VLAN
        ID to a POD, and connecting a broadcast domain to a local
        router limits the L2 broadcast domain span but also limits the
        flexibility of placing VMs across PODs in a DC or a cloud.
        This is the problem identified in [NVo3-problem-statement]
        Section 3.4.
     
     
     
        The cloud-networking infrastructure needs to prevent
        unnecessary traffic from being sent/leaked to undesired
        locations.
     
     
     
     5.4. Convergence and multipath support
     
     
     
        Spanning Tree is used in the current DC environment for loop
        avoidance in the Ethernet switching domain.
     
     
     
        STP can take 30 to 50 seconds to repair a topology. Practical
        experience shows that Rapid STP (RSTP) can also take multiple
        seconds to converge, such as when the root bridge fails.
     
     
     
        STP eliminates loops by disabling ports. The result is that
        only one path is used to carry traffic. The capacity of
        disabled links cannot be utilized, leading to inefficient use
        of resources.
     
     
     
     
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        In a small DC deployment, multi-chassis LAG (MC-LAG) support
        may be sufficient initially to provide for loop-free
        redundancy as an STP alternative. However, in medium or large
        DCs it is challenging to use MC-LAGs solely across the network
        to provide for resiliency and loop-free paths without
        introducing a layer2 routing protocol: i.e. for multi-homing
        of server blades to ToRs, ToRs to Core SWs, Core SWs to DC
        GWs. MC-LAG may work as a local mechanism but it has no
        knowledge of the end-to-end paths so it does not provide any
        degree of traffic steering across the network.
     
     
     
        Efficient and mature link-state protocols, such as IS-IS,
        provide rapid failover times, can compute optimal paths and
        can fully utilize multiple parallel paths to forward traffic
        between 2 nodes in the network.
     
     
     
        Unlike OSPF, IS-IS runs directly at L2 (i.e. no reliance on
        IP) and does not require any configuration. Therefore, IS-IS
        based DC networks are to be favored over STP-based networks.
        IEEE Shortest Path Bridging (SPB), based on IEEE 802.1aq and
        IEEE 802.1Qbp, and IETF TRILL [RFC6325] are technologies that
        enable Layer2 networks using IS-IS for Layer2 routing.
     
     
     
     5.5. Optimal traffic forwarding
     
     
     
        Optimal traffic forwarding requires (1) efficient utilization
        of all available link capacity in a DC and DC-interconnect,
        and (2) traffic forwarding on the shortest path between any
        two communicating VMs within the DC or across DCs.
     
     
     
        Optimizing traffic forwarding between any VM pair in the same
        virtual domain is dependent on (1) the placement of these VMs
        and their relative proximity from a network viewpoint, and (2)
        the technology used for computing the routing/switching path
     
     
     
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        between these VMs. The latter is especially important in the
        context of VM Mobility, moving a VM from one network location
        to another, while maintaining its layer2 and Layer3 (IP)
        addresses.
     
     
     
        Ethernet-based forwarding between two VMs in traditional DCs
        relies on the MAC-destination Address that is unique per VM
        interface in the context of a virtual domain (e.g., VLAN). In
        traditional IEEE technologies (e.g., 802.1q, 802.1ad, 802.1ah)
        and IETF L2VPN (i.e., VPLS), Ethernet MAC reachability is
        always learnt in the data plane. Other IEEE and IETF
        technologies allow MAC reachability to be learnt in the
        control plane as discussed further in Section 6. . In all
        these cases, it is important that as a VM is moved from one
        location to another: (1) VM MAC reachability convergence
        happens fast to minimize traffic black-holing, and (2)
        forwarding takes the shortest path.
     
     
     
        IP-based forwarding relies on the destination IP address. ECMP
        load balancing relies on flow-based criteria. An IP host
        address is unique per VM interface. However, hosts on a LAN
        share a subnet mask, and IP routing entries are based on that
        subnet address. Thus, when VMs are on the same LAN and
        traditional forwarding takes place, these VMs forward traffic
        to each other by relying on ARP or IPv6 Neighbor discovery to
        identify the MAC address of the destination and on the
        underlying layer2 network to deliver the resulting MAC frame
        to is destination. However, when VMs, as IP hosts across
        layer2 virtual domains, need to communicate they rely on the
        underlying IP routing infrastructure.
     
     
     
        In addition, when a DC is an all-IP DC, VMs are assigned a
        host address with /32 subnet in the IPv4 case, or /64 or /128
        host address in the IPv6 case, and rely on the IP routing
        infrastructure to route the IP packets among VMs. In this
        latter case, there is really no need for layer2 awareness
        potentially beyond the hypervisor switch at the server hosting
        the VM. In either case, when a VM moves location from one
        physical router to another while maintaining its IP identity
        (address), the underlying IP network must be able to route the
     
     
     
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        traffic to the destination and must be able to do that on the
        shortest path.
     
     
     
        Thus, in the case of IP address aggregation as in a subnet,
        optimality in traffic forwarding to a VM will require
        reachability to the VM host address rather than only the
        subnet. That is what is often referred to as punching a hole
        in the aggregate at the expense of routing and forwarding
        table size increase.
     
     
     
        As in layer2, layer3 may capitalize on hierarchical tunneling
        to optimize the routing/FIB resource utilization at different
        places in the network. If a hybrid of subnet-based routing and
        host-based routing (host-based routing here is used to refer
        to hole-punching in the aggregate) is used, then during VM
        mobility, routing transition can take place, and traffic may
        be routed to a location based on subnet reachability or to a
        location where the VM used to be attached. In either of these
        cases, traffic must not be black-holed. It must be directed
        potentially via tunneling to the location where the VM is.
        This requires that the old routing gateway knows where the VM
        is currently attached. How to obtain that information can be
        based on different techniques with tradeoffs. However, this
        traffic triangulation is not optimal and must only exist in
        the transition until the network converges to a shortest path
        to the destination.
     
     
     
     5.6. Efficient multicast
     
     
     
        STP bridges typically perform IGMP and/or PIM snooping in
        order to optimize multicast data delivery. However, this
        snooping is performed locally by each bridge following the STP
        topology where all the traffic goes through the root bridge.
        This may result in sub-optimal multicast traffic delivery. In
        addition, each customer multicast group is associated with a
        forwarding tree throughout the Ethernet switching network.
        Solutions must provide for efficient Layer2 multicast. In an
        all-IP network, explicit multicast trees in the DC network can
     
     
     
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        be built via multicast signaling protocols (e.g., PIM-SSM)
        that follows the shortest path between the destinations and
        source(s). In an IPVPN context, Multicast IPVPN based on
        [MVPN] can be used to build multicast trees shared among
        IPVPNs, specific to VPNs, and/or shared among multicast groups
        across IPVPNs.
     
     
     
     5.7. L3 virtualization
     
     
     
        In order to provide tenant L3 separation while supporting
        overlapping IP addressing and privacy across tenants, as
        discussed in [NV03-roblem-statement] Section 2.5, a number of
        schemes were implemented in the DC environment. Some of these
        schemes, such as double NATing are operationally complex and
        prone to operator errors. Virtual Routing contexts, Virtual
        Device contexts, or dedicated hardware-routers are positioned
        in the DC environment as an alternative to these mechanisms.
        Every customer is assigned a dedicated routing context with
        associated control plane protocols. For instance, every
        customer gets an IP routing instance controlled by its own
        routing. Assigning virtual or hardware routers to each
        customer, while supporting thousands of customers in a DC,
        is neither scalable nor cost-efficient. Section 6 further
        discusses the applicability of BGP/MPLS IP VPNs to
        L3vitualization.
     
     
     
     5.8. Connectivity to existing tenant VPN sites
     
     
     
        It is expected that cloud services will have to span larger
        geographical areas in the near future and that existing VPN
        customers will require access to VM and storage facilities
        for virtualized data center applications. Hence, the DC
        network virtualization must interoperate with deployed and
        evolving VPN solutions (e.g., IP VPN, VPLS, VPWS, PBB-VPLS,
        E-VPN and PBB-EVPN).
     
     
     
     
     
     
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        Section 6 discusses this type of connectivity.
     
     
     
     5.9. DC Inter-connect requirements
     
     
     
        Cloud computing requirements such as VM Mobility across DCs,
        Management connectivity, and support for East-West traffic
        between customer applications located in different DCs imply
        that inter-DC connectivity must be supported. These DCs can be
        part of a hybrid cloud operated by the cloud service
        provider(s) and/or the end-customers.
     
     
     
        Mature VPN technologies can be used to provide L2/L3 DC
        interconnect among VLANs/virtual domains located in different
        DCs. DC-interconnect using existing VPN technologies is
        described in Section 6.
     
     
     
     5.10. VM Mobility
     
     
     
        The ability to move VMs within a resource pool, whether it is
        a local move within the same DC to another server or to a
        distant DC, offers multiple advantages for a number of
        scenarios, for example:
     
     
     
        - In the event of a possible natural disaster, moving VMs to a
          safe DC location decreases downtime and allows for meeting
          Service Level Agreement (SLA) requirements.
        -
        - Optimized resource location: VMs can be moved to locations
          that offer significant cost reduction (e.g. power savings),
          or locations close to the application users. They can also
          be moved to simply load-balance across different locations.
     
     
     
     
     
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        When VMs change location, it is often important to maintain
        the existing client sessions. The VM MAC and IP addresses must
        be preserved, and the state of the VM sessions must be copied
        to the new location.
     
     
     
        Current VM mobility tools like VMware VMotion require L2
        connectivity among the hypervisors on the servers
        participating in a VMotion pool. This is in addition to
        "tenant ELAN" connectivity that provides for communication
        between the VM and the client(s).
     
     
     
        A VMotion ELAN might need to cross multiple DC networks to
        provide the required protection or load-balancing. In
        addition, in the current VMotion procedure, the new VM
        location must be part of the tenant ELAN domain. When the new
        VM is activated, a Gratuitous ARP is sent so that the MAC FIB
        entries in the tenant ELAN are updated to direct traffic
        destined to that VM to the new VM location. In addition, if a
        portion of the path requires IP forwarding, the VM
        reachability information must be updated to direct the traffic
        on the shortest path to the VM.
     
     
     
        VM mobility requirements may be addressed through the use of
        Inter-DC VLANs to address VMotion and "tenant ELANs". However,
        expanding "tenant ELANs" across two or more DCs will
        accelerate VLAN exhaustion and MAC explosion issues. In
        addition, STP needs to run across DCs leading to increased
        convergence times and the blocking of expensive WAN bandwidth.
        VLAN trunking used throughout the network creates
        indiscriminate flooding across DCs.
     
     
     
        L2 VPN solutions over IP/MPLS are designed to interconnect
        sites located across the WAN as described in Section 6.
     
     
     
     
     
     
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     6. L2VPN Applicability to Cloud Networking
     
     
     
        The following sections will discuss different solution
        alternatives, re-using IEEE and IETF technologies that can
        provide a gradual migration path from the current Ethernet
        switching VLAN-based model to more advanced Ethernet switching
        and IP/MPLS based models. In addition, they discuss how these
        solutions compare to the NVo3 framework [NVo3-fmwk] and the
        problems in [Nvo3-problem-statement] that they would still
        need to address. This evolution is targeted to address inter-
        DC requirements, cost considerations, and the efficient use of
        processing/memory resources on DC networking components.
     
     
     
     6.1. VLANs and L2VPN toolset
     
     
     
        One approach to address some of the DC challenges discussed in
        the previous section is to gradually deploy additional
        technologies within existing DC networks. For example, an
        operator may start by breaking its DC VLAN domains into
        different VLAN islands so that each island can support up to
        4K VLANs. VLAN Domains can then be interconnected via VPLS
        using the DC GW as a VPLS PE [RFC4761][RFC4762]. An ELAN
        service can be identified with one VLAN ID in one island and
        another VLAN ID in another island with the appropriate VLAN ID
        processed at the GW.
     
     
     
        As the number of tenants in individual VLAN islands surpasses
        4K and no further sub-division of VLAN domains is feasible or
        desired, the operator could push VPLS deployment deeper in the
        DC network closer to tenant systems as defined in [NVo3-fmwk],
        it is possible in the end to retain existing VLAN-based
        solution only in VSw and to provide L2VPN support starting at
        the ToRs. The ToR and DC core elements need to be MPLS enabled
        with existing VPLS solutions.
     
     
     
     
     
     
     
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        VPLS represents a mature virtualization and overlay technology
        for private LAN services. This is the way it has been deployed
        in service provider networks. It also addresses many of the
        problems described in Section 5 and in [NVo3-problem-
        statement] but still lacks some capabilities to address
        others.
     
     
     
        Table 1 provides a comparison between the VPLS functional
        elements and the NVo3 framework functional elements [NVo3-
        fmwk].
     
        Table 1: Functional comparison between VPLS and NVo3 framework
     
     
        Nvo3 Function                      Matching VPLS Function
     
       -----------------------------------------------------------
       Virtual Access Point (VAP)         Attachment Circuit (AC)
     
     
       Network Virtual Edge (NVE)          Provider Edge (PE)
     
     
       Virtual Network Instance (VNI)     Virtual Switching Instance
                                           (VSI)
     
     
        Virtual Network Context (VN        A 20-bit MPLS label
        Context) identifier
     
        Overlay Module and tunneling       -PWE3 over IP/GRE in an IP
                                           network
     
                                           -PWE3 and MPLS in an MPLS
                                           network
     
     
         Control Plane: TBD                 Control plane:
     
                                           Service signaling
     
                                         - PWE3 T-LDP or MP-BGP
                                           Core Routing:
     
                                           - IGP: OSPF/ISIS -(TE)
     
                                           Core Signaling:
     
                                         - RSVP or LDP for MPLS
                                           LSPs
     
     
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        Depending on the implementation model, VPLS can address some
        of the issues described in Section 5 and in [NVo3-problem-
        statement], but not all:
     
     
     
             -Dynamic Provisioning as described in [NVo3-problem-
             statement] Section 2.1: This is not addressed today in
             VPLS solutions, as it has not been in scope of that work.
             VPLS provisioning today requires management of both VLAN
             and L2VPN addressing, and mapping of service profiles.
             Per VLAN, per port and per VPLS configurations are
             required at the ToR, increasing the time it takes to
             bring up service connectivity and complicating the
             operational model. However, a mechanism may be developed
             to perform such provisioning dynamically as compute
             resources are configured. It should be noted that VPLS
             currently supports auto-discovery of PEs with instances
             of the same VPLS service, as a component of the dynamic
             provision of a VPLS service.
     
     
             -VM Mobility as also defined in [NVo3-problem-statement]
             section 2.2: VPLS supports MAC discovery as in any LAN
             switch based on MAC learning in the data plane. Thus, as
             a VM moves, a VPLS may lean the location of a new MAC
             from an ARP message initiated by the VM or by seeing
             Ethernet frames from that VM.
     
             -MAC table sizes in Switches as also described in [NVo3-
             problem-statement] Section 2.3: As opposed to an 802.1q
             based core Ethernet network, tenant VM addresses are only
             learned at a VPLS PE with a corresponding service
             instance.  This is because VPLS is built as an overlay on
             a core IP/MPLS network and the core interconnecting the
             PEs will have no knowledge of the tenant MACs.
     
             -VLAN limitation as also described in [NV03-proble-
             statement] Section 2.7: VPLS enables service instance
             scale in a DC as it connects VLAN domains as described
             earlier and as the service identifier for a VPLS instance
             at a PE is based on a 20-bit MPLS label.
     
     
     
     
     
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     This model does not solve the potential MAC explosion on VPLS
     PEs, depending on how close to the tenant systems the PE
     functionality is deployed.  The closer to the systems, the
     smaller the number of VPLS instances that need to be supported on
     a VPLS PE, and the lower should be the MAC scale need.
     
     
     
     6.2. E-VPN
     
     
     
     Ethernet VPN (E-VPN) [E-VPN] is evolving work in IETF L2VPN WG.
     Ethernet VPN provides private LAN service over an IP/MPLS core.
     E-VPN was driven by some gaps in the existing VPLS solution, and
     by large multi-tenant DC requirements. E-VPN, similar to VPLS, is
     provided on a PE where an E-VPN instance (EVI) provides the
     virtual LAN bridging service. E-VPN defines types of EVIs
     depending on the bridging domains supported in an EVI. As opposed
     to VPLS, E-VPN provides for active-active multi-homing of CEs to
     different PEs while eliminating loops and traffic duplications.
     In addition, it provides for effective load-balancing across the
     IP/MPLS core to PEs with access to the same MAC address on
     connected CEs. In addition, as opposed to IEEE 802.1q/ad/ah
     standards and VPLS where MAC reachability is learned in the data
     plane, E-VPNS distributes MAC reachability across the IP/MPLS
     core using MP-BGP extensions. Along with MAC address
     distribution, E-VPN also distributes the IP address(es)
     associated with the MAC, equivalent in IPv4 to ARP entries. In
     addition, as opposed to VPLS, and more in synergy with BGP/MPLS
     VPNs [RFC4364], E-VPN uses (MP)-BGP extensions to discover and
     signal the service MPLS label(s) among PEs across the IP/MPLS
     core and does not require a Pseudowire (PW) mesh among PEs per E-
     VPN. E-VPN also allows an option for flooding suppression of BUM
     traffic.
     
     
     
     E-VPN, can be implemented at the same network elements as VPLS
     discussed in the previous section. However, with reduced set of
     protocols needed, namely PW signaling via T-LDP, and in synergy
     with [endsystem], E-VPN could more likely be implemented at an
     end-system than VPLS.
     
     
     
     
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     E-VPN represents an evolving virtualization and overlay
     technology for private LAN services, albeit capitalizing on the
     synergy with mature BGP/MPLS IPVPNs. It also addresses many of
     the problems described in Section 5 and in [NVo3-problem-
     statement] and some of the VPLS problems, but still lacks some
     capabilities to address others.
     
     
     
     Table 2 provides a comparison between the E-VPN functional
     elements and the NVo3 framework functional elements [NVo3-fmwk].
     
     
     
        Table 2: Functional comparison between E-VPN and NVo3
        framework
     
     
        Nvo3 Function                      Matching E-VPN Function
        -----------------------------------------------------------
     
        Virtual Access Point (VAP)         Attachment Circuit (AC)
                                           based on VLAN ID
     
     
        Network Virtual Edge (NVE)         PE
     
     
        Virtual Network Instance (VNI)     EVPN Instance (EVI)
     
     
        Virtual Network Context (VN        A 20-bit MPLS label
        Context) identifier
     
        Overlay Module and tunneling       -MPLS over MPLS tunnels
     
                                           -MPLS over IP/GRE in an
                                           IP network
     
     
        Control Plane: TBD                 Control plane:
     
                                           - MP-BGP for E-VPN
     
                                           Core Routing:
     
                                           - IGP: OSPF/ISIS -(TE)
     
                                           Core Signaling:
     
     
     
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                                         - RSVP or LDP for MPLS LSPs
     
     
     
     
        Depending on the implementation model, E-VPN can address some
        of the issues described in Section 5 and in [NVo3-problem-
        statement], but not all:
     
     
     
       -Dynamic Provisioning as described in [NVo3-problem-statement]
       Section 2.1: This is not addressed today in E-VPN solutions,
       as it has not been in scope of that work. E-VPN provisioning
       today requires management of VLAN and service profiles. Per
       VLAN, per port and per E-VPN configurations are required,
       increasing the time it takes to bring up service connectivity
       and complicating the operational model. However, a mechanism
       may be developed to perform such provisioning dynamically as
       compute resources are configured. It should be noted that E-
       VPN currently supports auto-discovery of PEs with instances of
       the same E-VPN service, as a component of the dynamic
       provisioning of an E-VPN service.
     
       -VM Mobility as also defined in [NVo3-problem-statement]
       section 2.2: E-VPN supports VM mobility as described in
       Section 8.
     
       -MAC-table sizes in Switches as also described in [NVo3-
       problem-statement] Section 2.3: As opposed to an 802.1q based
       core Ethernet network, tenant VM addresses are only learned at
       a E-VPN PE with a corresponding service instance.  This is
       because E-VPN is built as an overlay on a core IP/MPLS network
       and the core interconnecting the PEs will have no knowledge of
       the tenant MACs.
     
       -VLAN limitation as also described in [NV03-proble-statement]
       Section 2.7: E-VPN enables service instance scale in a DC as
       it connects VLAN domains similarly to VPLS and as the service
       identifier for an E-VPN instance at a PE is based on a 20-bit
       MPLS label.
     
     
     
     This model does not solve the potential MAC explosion on E-VPN
     PEs, depending on how close to the tenant systems the PE
     
     
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     functionality is deployed.  The closer to the systems, the
     smaller the number of VPLS instances that need to be supported on
     a VPLS PE, and the lower should be the MAC scale need. E-VPN
     could be potentially implemented at an end-system hosting the VMs
     to which the E-VPN services are provided.
     
     
     
     6.3. PBB and L2VPN toolset
     
     
     
        As highlighted in Section 5, the expected large number of VM
        MAC addresses in the DC calls out for a VM MAC hiding solution
        so that the ToRs and the Core Switches only need to handle a
        limited number of MAC addresses.
     
     
     
        PBB IEEE 802.1ah encapsulation is a standard L2 technique
        developed by IEEE to achieve this goal. It was designed also
        to address other limitations of VLAN-based encapsulations
        while maintaining the native Ethernet operational model
        deployed in the DC network.
     
     
     
        A conceptual PBB encapsulation is described in Figure 3 (for
        detailed encapsulation see [802.1ah]):
     
     
     
                                  +-------------+
                         Backbone | BMAC DA,SA  |12B
                         Ethernet |-------------|
                          Header  |BVID optional| 4B
                                  |-------------|
                        Service ID|  PBB I-tag  | 6B
                                  |-------------|
                          Regular |VM MAC DA,SA |
                          Payload |-------------|
                                  |             |
                                  |VM IP Payload|
                                  |             |
                                  +-------------+
     
                          Figure 3 PBB encapsulation
     
     
     
     
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        The original Ethernet packet used in this example for Inter-VM
        communication is encapsulated in the following PBB header:
     
     
     
           - I-tag field - organized similarly with the 802.1q VLAN
             tag; it includes the Ethertype, PCP and DEI bits and a 24
             bit ISID tag which replaces the 12 bit VLAN tag,
             extending the number of virtual L2 domain support to 16
             Million. It should be noted that the PBB I-Tag includes
             also some reserved bits, and most importantly the C-MAC
             DA and SA. What is designated as 6 bytes in the figure is
             the I-tag information excluding the C-MAC DA and SA.
     
     
     
           - An optional Backbone VLAN field (BVLAN) may be used if
             grouping of tenant domains is desired.
     
     
     
           - An outer Backbone MAC header contains the source and
             destination MAC addresses for the related server blades,
             assuming the PBB encapsulation is done at the hypervisor
             virtual switch on the server blade.
     
     
     
           - The total resulting PBB overhead added to the VM-
             originated Ethernet frame is 18 or 22 Bytes (depending on
             whether the BVID is excluded or not).
     
     
     
           - Note that the original PBB encapsulation allows the use
             of CVLAN and SVLAN in between the VM MACs and IP Payload.
             These fields were removed from Figure 3 since in a VM
             environment these fields do not need to be used on the
             VSw, their function is relegated to the I-SID tag.
     
     
     
     
     
     
     
     
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     6.3.1. Addressing VLAN space exhaustion and MAC explosion
     
     
     
        In a DC environment, PBB maintains traditional Ethernet
        forwarding plane and operational model. For example, a vSw
        implementation of PBB can make use of the 24 bit ISID tag
        instead of the 12 bit VLAN tag to identify the virtual
        bridging domains associated with different VM groups. The vSw
        uplink towards the ToR in Figure 1 can still be treated as an
        Ethernet backbone interface. A frame originated by a VM can be
        encapsulated with the ISID assigned to the VM vSw interface
        and with the outer DA and SA MACs associated with the
        respective destination and source server blades, and then sent
        to the ToR switch. Performing this encapsulation at the vSw
        distributes the VM MAC learning to server blades with
        instances in the corresponding layer2 domain, and therefore
        alleviates this load from ToRs that aggregate multiple server
        blades. Alternatively, the PBB encapsulation can be done at
        the ToR.
     
     
     
        With PBB encapsulation, ToRs and Core SWs do not have to
        handle VM MAC addresses so the size of their MAC FDB tables
        may decrease by two or more orders of magnitude, depending on
        the number of VMs configured in each server blade and the
        number of VM virtual interfaces and associated MACs.
     
     
     
        The original PBB specification [802.1ah] did not introduce any
        new control plane or new forwarding concepts for the PBB core.
        Spanning Tree and regular Ethernet switching based on MAC
        learning and flooding were maintained to provide a smooth
        technology introduction in existing Ethernet networks.
     
     
     
     6.3.2. Fast convergence and L2 multi-pathing
     
     
     
        Additional specification work for PBB control plane has been
        done since then in both IEEE and IETF L2VPN.
     
     
     
     
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        As stated earlier, STP-based layer2 networks underutilize the
        available network capacity as links are put in an idle state
        to prevent loops. Similarly, existing VPLS technology for
        interconnecting Layer2 network-islands over an IP/MPLS core
        does not support active-active dual homing scenarios.
     
     
     
        IS-IS controlled layer2 networks allow traffic to flow on
        multiple parallel paths between any two servers, spreading
        traffic among available links on the path. IEEE 802.1aq
        Shortest Path Bridging (SPB) [802.1aq] and emerging IEEE
        802.1Qbp [802.1Qbp] are PBB control plane technologies that
        utilize different methods to compute parallel paths and
        forward traffic in order to maximize the utilization of
        available links in a DC. In addition, a BGP based solution
        [PBB-EVPN] is progressing in the IETF L2VPN WG.
     
     
     
        One or both mechanisms may be employed as required. IS-IS
        could be used inside the same administrative domain (e.g., a
        DC), while BGP may be employed to provide reachability among
        interconnected Autonomous Systems. Similar architectural
        models have been widely deployed in the Internet and for large
        VPN deployments.
     
     
     
        IS-IS and/or BGP are also used to advertise Backbone MAC
        addresses and to eliminate B-MAC learning and unknown unicast
        flooding in the forwarding plane, albeit with tradeoffs. The
        B-MAC FIB entries are populated as required from the resulting
        IS-IS or BGP RIBs.
     
     
     
        Legacy loop avoidance schemes using Spanning Tree and local
        Active/Active MC-LAG are no longer required as their function
        (layer2 routing) is replaced by the indicated routing
        protocols (IS-IS and BGP).
     
     
     
     
     
     
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     6.3.3. Per ISID flood containment
     
     
     
        Service auto-discovery provided by 802.1aq SPB [802.1aq] and
        BGP [PBB-EVPN] is used to distribute ISID related information
        among DC nodes, eliminating any provisioning touches
        throughout the PBB infrastructure. This implicitly creates
        backbone distribution trees that provide per ISID automatic
        flood and multicast containment.
     
     
     
     6.3.4. Efficient multicast support
     
     
     
        IS-IS [802.1aq] and BGP [PBB-EVPN] could be used to build
        optimal multicast distribution trees. In addition, PBB and
        IP/MPLS tunnel hierarchy may be used to aggregate multiple
        customer multicast trees sharing the same nodes by associating
        them with the same backbone forwarding tree that may be
        represented by a common Group BMAC and optionally a P2MP LSP.
        More details will be discussed in a further version of the
        draft.
     
     
     
     6.3.5. Tunneling options for PBB ELAN: Ethernet, IP and MPLS
     
     
     
        A solution for DC ELAN domains based on PBB ISIDs, PBB
        encapsulation and IS-IS and/or BGP control plane was
        introduced.
     
        IETF L2 VPN specifications [PBB-VPLS] or [PBB-EVPN] enable the
        transport of PBB frames using PW over MPLS or simply MPLS, and
        implicitly allow the use of MPLS Traffic Engineering and
        resiliency toolset to provide for advanced traffic steering
        and faster convergence.
     
     
     
        Transport over IP/L2TPv3 [RFC 4719] or IP/GRE [RFC 4797] is
        also possible as an alternative to MPLS tunneling. Additional
     
     
     
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        header optimization for PBB over IP/GRE encapsulated packets
        may be feasible. These specifications would allow for ISID
        based L2 overlay using a regular IP backbone.
     
     
     
     6.3.6. Use Case examples
     
     6.3.6.1. PBBN in DC, L2VPN in DC GW
     
     
     
        DC environments based on VLANs and native Ethernet operational
        model may want to consider using the native PBB option to
        provide L2 multi-tenancy, in effect the DC ELAN from Figure 2.
        An example of a network architecture that addresses this
        scenario is depicted in Figure 4:
     
                                 ,---------.
                               ,'  Inter-DC  `.
                              (L2VPN (PBB-VPLS)
                               `.or PBB-EVPN),'
                                 `|-------|-'
                              +--+--+   +-+---+
                              |PE GW|+-+|PE GW|
                             .+-----+   +-----+.
                          .'                    `-.
                        .-'                         `\
                      ,'                              `.
                     +          Intra-DC PBBN          \
                     |                                  +
                     :                                  ;
                      `\+------+   +------+  +--+----+-'
                        | ToR  |.. | ToR  |..|  ToR  |
                        +-+--+-+   +-+--+-+  +-+--+--+
                        .'PBB `.   .'PBB `.  .'PBB `.
                    +--+-+    +-+-++     +-++-+    +-+--+
                    |VSw |    :VSw :     :VSw :    :VSw :
                    +----+    +----+     +----+    +----+
     
         Figure 4 PBB in DC, PBB-VPLS or PBB-EVPN for DC Interconnect
     
     
     
        PBB inside the DC core interoperates seamlessly with VPLS used
        for L2 DC-Interconnect to extend ELAN domains across DCs. This
     
     
     
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        expansion may be required to address VM Mobility requirements
        or to balance the load on DC PE gateways. Note than in PBB-
        VPLS case, just one or a handful of infrastructure B-VPLS
        instances are required, providing Backbone VLAN equivalent
        function.
     
     
     
        PBB encapsulation addresses the expansion of the ELAN service
        identification space with 16M ISIDs and solves MAC explosion
        through VM MAC hiding from the Ethernet core.
     
     
     
        PBB SPB [802.1aq] is used for core routing in the ToRs, Core
        SWs and PEs. If the DCs that need to be interconnected at L2
        are part of the same administrative domain, and scaling is not
        an issue, SPB/IS-IS may be extended across the VPLS
        infrastructure. If different AS domains are present, better
        load balancing is required between the DCs and the WAN, or IS-
        IS extension across DCs causes scaling issues, then BGP
        extensions described in [PBB-EVPN] must be employed.
     
     
     
        The forwarding plane, MAC FIB requirements and the Layer2
        operational model in the ToR and Core SW are maintained. The
        VSw sends PBB encapsulated frames to the ToR as described in
        the previous section. ToRs and Core SWs still perform standard
        Ethernet switching using the outer Ethernet header.
     
     
     
        From a control plane perspective, VSw uses a default gateway
        configuration to send traffic to the ToR, as in regular IP
        routing case. VSw BMAC learning on the ToR is done through
        either LLDP or VM Discovery Protocol (VDP) described in
        [802.1Qbg]. Identical mechanisms may be used for the ISID.
        Once this information is learned on the ToR it is
        automatically advertised through SPB. If PBB-EVPN is used in
        the DC GWs, MultiProtcol (MP)-BGP will be used to advertise
        the ISID and BMAC over the WAN as described in [PBB-EVPN].
     
     
     
     
     
     
     
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     6.3.6.2. PBBN in vSw, L2VPN in the ToR
     
     
     
        A variation of the use case example from the previous section
        is depicted in Figure 5:
     
                                 ,---------.
                               ,'  Inter-DC  `.
                              (L2VPN (PBB-VPLS)
                               `.or PBB-EVPN),'
                                 `|-------|-'
                              +--+--+   +-+---+
                              |PE GW|+-+|PE GW|
                             .+-----+   +-----+.
                          .'                    `-.
                        .-'                         `\
                      ,'                              `.
                     +        Intra-DC L2VPN over       \
                    |        IP or MPLS tunneling       +
                     :                                  ;
                      `\+------+   +------+  +--+----+-'
                        | ToR  |.. | ToR  |..|  ToR  |
                        +-+--+-+   +-+--+-+  +-+--+--+
                        .'PBB `.   .'PBB `.  .'PBB `.
                    +--+-+    +-+-++     +-++-+    +-+--+
                    |VSw |    :VSw :     :VSw :    :VSw :
                    +----+    +----+     +----+    +----+
     
                    Figure 5 PBB in VSw, L2VPN at the ToR
     
     
     
        The procedures from the previous section are used at the VSw:
        PBB encapsulation and Ethernet BVLANs can be used on the VSw
        uplink. L2VPN infrastructure is replacing the BVLAN at the ToR
        enabling the use of IP (GRE or L2TP) or MPLS tunneling.
     
     
     
        L2 networking still has the same control plane choices: IS-IS
        [802.1aq] and/or BGP [PBB-EVPN], independently from the
        tunneling choice.
     
     
     
     
     
     
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     6.3.7. NVo3 applicability
     
     
     
     Table 3 provides a comparison between the PBB-VPLS VPN functional
     elements and the NVo3 framework functional elements [NVo3-fmwk].
     
     
     
        Table 3: Functional comparison between PBB-VPLS and NVo3
        framework
     
     
        Nvo3 Function                      Matching PBB-VPLS
                                           Function
     
       ----------------------------------------------------------
       Virtual Access Point (VAP)         Attachment Circuit (AC)
                                           based on I-SID
     
     
        Network Virtual Edge (NVE)         PE
     
     
        Virtual Network Instance (VNI)     VSI
     
     
        Virtual Network Context (VN        MPLS-label for PBB-VSI
        Context) identifier                and I-SID if the PE is
                                           PBB edge
     
     
        Overlay Module and tunneling       -MPLS over MPLS tunnels
     
                                           -MPLS over IP/GRE in an
                                           IP network
     
     
        Control Plane: TBD                 Control plane:
     
                                              - MP-BGP for auto-
                                                 discovery
                                              - PWE3 T-LDP for PW
                                                 signaling
     
                                           Core Routing:
     
                                           - IGP: OSPF/ISIS -(TE)
     
                                           Core Signaling:
     
                                         - RSVP or LDP for MPLS LSPs
     
     
     
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     Table 4 provides a comparison between the PBB-EVPN functional
     elements and the NVo3 framework functional elements [NVo3-fmwk].
     
     
     
        Table 4: Functional comparison between E-VPN and NVo3
        framework
     
     
        Nvo3 Function                      Matching PBB-EVPN
                                           Function
     
        ----------------------------------------------------------
        Virtual Access Point (VAP)         Attachment Circuit (AC)
                                           based on I-SID
     
     
     
        Network Virtual Edge (NVE)         PE
     
     
        Virtual Network Instance (VNI)     EVPN Instance (EVI)
     
     
        Virtual Network Context (VN        MPLS label for PBB-EVI
        Context) identifier                and I-SID if the PE is
                                           PBB edge
     
     
        Overlay Module and tunneling       -MPLS over MPLS tunnels
     
                                           -MPLS over IP/GRE in an
                                           IP network
     
     
        Control Plane: TBD                 Control plane:
     
                                           - MP-BGP for E-VPN
     
                                           Core Routing:
     
                                           - IGP: OSPF/ISIS -(TE)
     
                                           Core Signaling:
     
                                         - RSVP or LDP for MPLS LSPs
     
     
     
     
     
     
     
     
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        Depending on the implementation model, PBB-EVPN and PBB-VPLS
        can address some of the issues described in Section 5 and in
        [NVo3-problem-statement], but not all:
     
     
     
             -Dynamic Provisioning as described in [NVo3-problem-
             statement] Section 2.1: This is not addressed today in
             PBB and PBB-VPN solutions, as it has not been in scope of
             the work for either. However, a mechanism may be
             developed to perform such provisioning dynamically as
             compute resources are configured. It should be noted that
             PBB-VPLS and PBB-EVPN currently support auto-discovery of
             PEs with instances of the same VPLS or E-VPN service, as
             a component of the dynamic provisioning of a VPLS/E-VPN
             service.
     
             -VM Mobility as also defined in [NVo3-problem-statement]
             section 2.2: PBB-EVPN and PBB-VPLS support VM MAC
             mobility as the 802.1q and VPLS solution do based on MAC
             learning in the data plane.
     
             -MAC table sizes in Switches as also described in [NVo3-
             problem-statement] Section 2.3: As opposed to an 802.1q-
             based core Ethernet network, tenant VM addresses are only
             learned at a PBB edge. If the VsW implements PBB edge
             functionality and the ToR implements PBB-EVPN or PBB-
             VPLS, then the vsW will learn the MAC addresses of other
             VMs and devices in the same LAN, but the ToR will also
             learn the MAC addresses of Backbone bridges that will be
             on the order of number of servers not VMs, conserving MAC
             FDB entries on the ToR. This is because there are two
             layers of overlay, one at the VsW for PBB, and one at the
             ToR for VPLS or E-VPN, on a core IP/MPLS network.
     
             -VLAN limitation as also described in [NV03-proble-
             statement] Section 2.7: The number of service instances
             that can supported is 16 Millions.
     
     
     
     6.3.8. Connectivity to existing VPN sites and Internet
     
     
     
     
     
     
     
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        The main reason for extending the ELAN space beyond the 4K
        VLANs is to be able to serve multiple DC tenants whereby the
        total number of service domains needed exceeds 4K. Figure 6
        represents the logical service view where PBB ELANs are used
        inside one or multiple DCs to connect to existing IP VPN
        sites. It should be noted that the PE GW should be able to
        perform integrated routing in a VPN context and bridging in
        VSI context:
     
     
     
                     Tenant 1 sites connected over IP VPN
     
                           ,--+-'.              ;-`.--.
                           (  PE  ) VRFs on PEs .  PE  )
                               '-----'              '-----'
                              |                    |
                      ,-------------------------------.
                     (     IP VPN over IP/MPLS WAN     )
                      `---.'-----------------------`.-'
                       +--+--+ IP VPN VRF on PE GWs +-+---+
                  .....|PE GW|......                |PE GW|
        DC with PBB   |    +-----+      |               +--+--+
        Tenant 1      |                 |PBB ELAN12        |
        view       PBB|ELAN11     ......|......         PBB|ELAN13
                  '':'''''''':'       |        |     '':'''''''':'
               ,'.      ,'.      ,+.      ,+.     ,'.      ,'.
              (VM )....(VM )    (VM )... (VM )   (VM )....(VM )
               `-'      `-'      `-'      `-'     `-'      `-'
                         Compute Resources inside DC
     
                  Figure 6 Logical Service View with IP VPN
     
     
     
        DC ELANs are identified with 24-bit ISIDs instead of VLANs. At
        the PE GWs, an IP VPN VRF is configured for every DC tenant.
        Each "ISID ELAN" for Tenant 1 is seen as a logical Ethernet
        endpoint and is assigned an IP interface on the Tenant 1 VRF.
        Tenant 1 enterprise sites are connected to IP VPN PEs
        distributed across the WAN. IP VPN instances on PE GWs can be
        automatically discovered and connected to the WAN IP VPN using
        standard procedures [RFC4364].
     
     
     
     
     
     
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        In certain cases, the DC GW PEs are part of the IPVPN service
        provider network providing IPVPN services to the enterprise
        customers. In other cases, DC PEs are operated and managed by
        the DC/cloud provider and interconnect to multiple IPVPN
        service providers using inter-AS BGP/MPLS models A, B, or C
        [RFC4364]. The same discussion applies to the case of IPSec
        VPNs from a PBB ELAN termination perspective.
     
     
     
        If tenant sites are connected to the DC using WAN VPLS, the PE
        GWs need to implement the BEB function described in the PBB-
        VPLS PE model [PBB-VPLS] and the procedures from [PBB-Interop]
        to perform the required translation. Figure 7 describes the
        VPLS WAN scenario:
     
                      Customer sites connected over VPLS
     
                           ,--+-'.              ;-`.--.
                           (  PE  ) VPLS on PEs .  PE  )
                               '-----'              '-----'
                              |                    |
                      ,-------------------------------.
                      (      VPLS over IP/MPLS WAN     )
                      `---.'-----------------------`.-'
                       +--+--+                      +-+---+
                       |PE GW| <-- PBB-VPLS/BEB --> |PE GW|
             DC with PBB   +--+--+                      +--+--+
                Tenant 1      |                            |
                  view     PBB|ELAN11                   PBB|ELAN13
                         '':'''''''':'               '':'''''''':'
                      ,'.      ,'.                ,'.      ,'.
                     (VM ) .. (VM )              (VM ) .. (VM )
                      `-'      `-'                `-'      `-'
                         Compute Resources inside DC
     
                 Figure 7 Logical Service View with VPLS WAN
     
     
     
        One VSI is required at the PE GW for every DC ELAN domain.
        Same as in the IP VPN case, DC PE GWs may be fully integrated
        as part of the WAN provider network or using Inter-AS/Inter-
        provider models A,B or C.
     
     
     
     
     
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        The VPN connectivity may be provided by one or multiple PE
        GWs, depending on capacity need and/or the operational model
        used by the DC/cloud operator.
     
     
     
        If a VM group is serving Internet connected customers, the
        related ISID ELAN will be terminated into a routing context
        (global public instance or another VRF) connected to the
        Internet. Same as in the IP VPN case, the 24bit ISID will be
        represented as a logical Ethernet endpoint on the Internet
        routing context and an IP interface will be allocated to it.
        Same PE GW may be used to provide both VPN and Internet
        connectivity with the routing contexts separated internally
        using the IP VPN models.
     
     
     
     6.3.9. DC Interconnect
     
     
     
        L2 DC interconnect may be required to expand the ELAN domains
        for Management, VM Mobility or when a VM Group needs to be
        distributed across DCs.
     
     
     
        PBB may be used to provide ELAN extension across multiple DCs
        as depicted in Figure 8:
     
                      ,-------------------------------.
                      (           IP/MPLS WAN          )
                      `---.'------------------------`.'
                       +--+--+                      +-+---+
                       |PE GW| <----- PBB BCB ----> |PE GW|
             DC with PBB   +--+--+                      +--+--+
                Tenant 1      |                            |
                  view     PBB|ELAN11                   PBB|ELAN11
                         '':'''''''':'               '':'''''''':'
                      ,'.      ,'.                ,'.      ,'.
                     (Hvz) .. (Hvz)              (Hvz) .. (Hvz)
                      `-'      `-'                `-'      `-'
                         Compute Resources inside DC
     
                   Figure 8 PBB BCB providing VMotion ELAN
     
     
     
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        ELAN11 is expanded across DC to provide interconnect for the
        pool of server blades assigned to the same VMotion domain.
        This time Hypervisors are connected directly to ELAN11. The PE
        GW operates in this case as a PBB Backbone Core Bridge (BCB)
        combined with PBB-EVPN capabilities [PBB-EVPN]. The I-SID
        ELANs do not require any additional provisioning touches and
        do not consume additional MPLS resources on the PE GWs. Per I-
        SID auto-discovery and flood containment is provided by IS-
        IS/SPB [802.1aq] and BGP [PBB-EVPN].
     
     
     
     6.3.10. Interoperating with existing DC VLANs
     
     
     
        While green field deployments will definitely benefit from all
        the advantages described in the previous sections, in many
        other scenarios, existing DC VLAN environments will have to be
        gradually migrated to the new architecture. Figure 9 depicts
        an example of a possible migration scenario where both PBB and
        VLAN technologies are present:
     
                                 ,---------.
                               ,'  Inter-DC  `.
                              (L2VPN (PBB-VPLS)
                               `.or PBB-EVPN),'
                                 `-/------\-'
                              +---+-+   +-+---+
                              |PE GW|+-+|PE GW|
                            .-+-----+   +-----+:-.
                         .-'                      `-.
                       ,'                            `-:.
                     +          PBBN/SPB DC             \
                     |                                  +
                     :                                  ;
                       `-+------+   +------+  +--+----+-'
                         | ToR  |.. | ToR  |..|  ToR  |
                         +-+--+-+   +-+--+-+  +-+--+--+
                         .'PBB `.   .'    `.  .'VLAN`.
                    +--+-+    +-+-++     +-++-+    +-+--+
                    |VSw |    :VSw :     :VSw :    :VSw :
                    +----+    +----+     +----+    +----+
                        Figure 9 DC with PBB and VLANs
     
     
     
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        This example assumes that the two VSWs on the right do not
        support PBB but the ToRs do. The VSw on the left side are
        running PBB while the ones on the right side are still using
        VLANs. The left ToR is performing only Ethernet switching
        whereas the one on the right is translating from VLANs to
        ISIDs and performing PBB encapsulation using the BEB function
        [802.1ah] and [PBB-VPLS]. The ToR in the middle is performing
        both functions: core Ethernet tunneling for the PBB VSw and
        BEB function for the VLAN VSw.
     
     
     
        The SPB control plane is still used between the ToRs,
        providing the benefits described in the previous section. The
        VLAN VSw must use regular multi-homing functions to the ToRs:
        for example STP or Multi-chassis-LAG.
     
     
     
        DC VLANs may be also present initially on some of the legacy
        ToRs or Core SWs. PBB interoperability will be performed as
        follows:
     
     
     
             -If VLANs are used in the ToRs, PBB BEB function may be
             performed by the Core SW(s) where the ToR uplink is
             connected.
     
     
     
             -If VLANs are used in the Core SW, PBB BEB function may
             be performed by the PE GWs where the Core SW uplink is
             connected.
     
     
     
        It is possible that some DCs may run PBB or PBB-VLAN
        combination while others may still be running VLANs. An
        example of this interoperability scenario is described in
        Figure 10:
     
     
                      ,-------------------------------.
     
     
     
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                     (          IP/MPLS WAN            )
                      `------/-----------------\-------'
                         +--/--+             +--\--+
                         |PE GW|PBB-VPLS     |PE GW|VPLS
                       .'+-----+-'         .'+------+.
                      /           \       /           \
                      |            |      |            |
                      |   PBB DC   |      |  VLAN DC   |
                      \           /       \           /
                       +---+ +---+         +---+ +---+
                       |VSw|.|VSw|         |VSw|.|VSw|
                       +---+ +---+         +---+ +---+
               Figure 10    Interoperability to a VLAN-based DC
     
     
     
        Interoperability with existing VLAN DC is required for DC
        interconnect. The PE-GW in the PBB DC or the PE GW in the VLAN
        DC must implement PBB-VPLS PE model described in [PBB-VPLS].
        This interoperability scenario is addressed in detail in [PBB-
        Interop].
     
     
     
        Connectivity to existing VPN customer sites (IP VPN, VPLS,
        IPSec) or Internet does not require any additional procedures
        beyond the ones described in the VPN connectivity section. The
        PE GW in the DC VLAN will aggregate DC ELANs through IP
        interfaces assigned to VLAN logical endpoints whereas the PE
        GW in the PBB DC will assign IP interfaces to ISID logical
        endpoints.
     
     
     
        If EVPN is used to interconnect the two DCs, PBB-EVPN
        functions described in [PBB-EVPN] must be implemented in one
        of the PE-GWs.
     
     
     
     6.4. TRILL and L2VPN toolset
     
     
     
        TRILL and SPB control planes provide similar functions. IS-IS
        is the base protocol used in both specifications to provide
     
     
     
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        multi-pathing and fast convergence for core networking. [PBB-
        EVPN] describes how seamless Inter-DC connectivity can be
        provided over an MPLS/IP network for both TRILL [RFC6325] and
        SPB [802.1aq]/[802.1Qbp] networks.
     
     
     
        The main differences exist in the encapsulation and data plane
        forwarding. TRILL encapsulation [RFC6325] was designed
        initially for large enterprise and campus networks where 4k
        VLANs are sufficient. As a consequence the ELAN space in
        [RFC6325] is limited to 4K VLANs; however, this VLAN scale
        issue is being addressed in [Fine-Grained].
     
     
     
     7. L3VPN applicability to Cloud Networking
     
     
     
        This section discusses the role of IP VPN technology in
        addressing the L3 Virtualization challenges described in
        section 5.
     
     
     
        IP VPN technology defined in L3VPN working group may be used
        to provide L3 virtualization in support of multi-tenancy in
        the DC network as depicted in Figure 11.
     
                      ,-------------------------------.
                     (     IP VPNs over IP/MPLS WAN    )
                      `----.'------------------------`.'
                        ,--+-'.                      ;-`.--.
                   .....  VRF1 )......              .  VRF2 )
                      |    '-----'      |               '-----'
                      |     Tenant1     |ELAN12     Tenant1|
                  |ELAN11       ....|........          |ELAN13
                  '':'''''''':'       |        |     '':'''''''':'
               ,'.      ,'.      ,+.      ,+.     ,'.      ,'.
              (VM )....(VM )    (VM )... (VM )   (VM )....(VM )
               `-'      `-'      `-'      `-'     `-'      `-'
                Figure 11    Logical Service View with IP VPN
     
     
     
     
     
     
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        Tenant 1 might buy Cloud Services in different DC locations
        and choose to associate the VMs in 3 different groups, each
        mapped to a different ELAN: ELAN11, ELAN12 and ELAN13. L3
        interconnect between the ELANs belonging to tenant1 is
        provided using a BGP/MPLS IPVPN and associated VRF1 and VRF2,
        possibly located in different DCs. Each tenant that requires
        L3 virtualization will be allocated a different IP VPN
        instance. Using full fledge IP VPN for L3 Virtualization
        inside a DC presents the following advantages compared with
        existing DC technologies like Virtual Routing:
     
           - Interoperates with existing WAN VPN technology
     
           - Deployment tested, provides a full networking toolset
     
           - Scalable core routing: only one MP-BGP routing instance
             is required compared with one per customer/tenant in the
             Virtual Routing case
     
           - Service Auto-discovery: automatic discovery and route
             distribution between related service instances
     
           - Well defined and deployed Inter-Provider/Inter-AS models
     
           - Supports a variety of VRF-to-VRF tunneling options
             accommodating different operational models: MPLS
             [RFC4364], IP or GRE [RFC4797]
     
     
     
        To provide Cloud services to related customer IP VPN instances
        located in the WAN the following connectivity models may be
        employed:
     
           - DC IP VPN instance may participate directly in the WAN IP
             VPN
     
           - Inter-AS Options A, B or C models may be employed with
             applicability to both Intra and Inter-Provider use cases
             [RFC4364]
     
     
     
        VRF implementation could be done in the endsystem [endsystem]
     to facilitate endsystem to endsystem direct communication.
     
     
     
     
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        Table 5 summarizes the comparison between BGP/MPLS IPVPN
        functional elements and those of NVo3 [NV03-fmwk].
     
     
     
        Table 5: Functional comparison between BGP/MPLS IPVPN and NV03
        functional elements
     
     
     
         Nvo3 Function                  Matching BGP/MPLS-IPVPN Fun
        -------------------------------------------------------------
     
      Virtual Access Point (VAP)     Attachment Circuit (AC)
     
     
      Network Virtual Edge (NVE)         Provider Edge (PE)
     
     
        Virtual Network Instance (VNI)     Virtual Routing and
                                           Forwarding (VRF)
     
     
        Virtual Network Context (VN        A 20-bit MPLS label
        Context) identifier
     
        Overlay Module and tunneling       -MPLS over MPLS tunnels
     
                                           -MPLS over IP/GRE in an
                                           IP network
     
     
        Control Plane: TBD                 Control plane:
     
                                           - MP-BGP for VPN
                                           signaling /routing
     
                                           Core Routing:
     
                                           - IGP: OSPF/ISIS -(TE)
     
                                           Core Signaling:
     
                                         - RSVP or LDP for MPLS LSPs
     
     
     
     
        Depending on the implementation model, BGP/MPLS IPVPN can
        address some of the issues described in Section 5 and in
        [NVo3-problem-statement], but not all:
     
     
     
     
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             -Dynamic Provisioning as described in [NVo3-problem-
             statement] Section 2.1: This is not addressed today in
             the BGP/MPLS IPVPN solution, as it was not a requirement
             for that solution. However, a mechanism may be developed
             to perform such provisioning dynamically as compute
             resources are configured. Considerations must be given to
             the cases where VMs and the VRF, providing connectivity
             to these VMs, are co-located on the same end-system vs.
             being on different physical devices. It should be noted
             that BGP/MPLS IPVPN currently supports auto-discovery of
             PEs with instances of the same IPVPN, as a component of
             the dynamic provisioning of and IPVPN service.
     
             -VM Mobility as also defined in [NVo3-problem-statement]
             section 2.2: VM mobility is supported in [endsystem] when
             the NVE, being a VRF, is co-located with the VM(s) to
             which the VRF provides connectivity. However, further
             enhancements must provide support for VM mobility in
             other cases.
     
             -IP table sizes in edge routers as also described in
             [NVo3-problem-statement] Section 2.3: As opposed to an
             802.1q based core Ethernet network, tenant VM addresses
             are only learned at a PBB edge. If the VsW implements PBB
             edge functionality and the ToR implements PBB-EVPN or
             PBB-VPLS, then the vsW will learn the MAC addresses of
             other VMs and devices in the same LAN, but the ToR will
             also learn the MAC addresses of Backbone bridges that
             will be on the order of number of servers not VMs,
             conserving MAC FDB entries on the ToR. This is because
             there are two layers of overlay, one at the VsW for PBB,
             and one at the ToR for VPLS or E-VPN, on a core IP/MPLS
             network.
     
             -VLAN limitation as also described in [NV03-proble-
             statement] Section 2.7: The number of service instances
             that can supported is 16 Millions.
     
     
     
     8. VM Mobility with E-VPN
     
     8.1. Layer 2 Extension Solution
     
     
     This document illustrates a solution for the layer 2 extension
     
     
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     based on E-VPNs [E-VPN]. That is, the L2 sites that contain VMs
     of a given L2-based Community User Group (CUG) or Virtual Network
     (VN) are interconnected together using E-VPN. Thus, a given E-VPN
     corresponds/associated with a single L2-based VN. An L2-based VN
     is associated with a single E-VPN Ethernet Tag Identifier.
     
     
     This section provides a brief overview of how E-VPN is used as
     the solution for the "layer 2 extension problem". Details of E-
     VPN operations can be found in [E-VPN].
     
     
     A single L2 site could be as large as the whole network within a
     single data center, in which case the Data Center Border Routers
     (DCBRs) of that data center, in addition to acting as IP routers
     for the L2-based VNs present in the data center, also act as PEs.
     In this scenario, E-VPN is used to handle VM migration between
     servers in different data centers.
     
     
     A single L2 site could be as small as a single ToR with the
     server connected to it, in which case the ToR acts as a PE. In
     this scenario, E-VPN is used to handle VM migration between
     servers that are either in the same or in different data centers.
     Note that in this scenario this document assumes that DCBRs, in
     addition to acting as IP routers for the L2-based VNs present in
     their data center, also participate in the E-VPN procedures,
     acting as BGP Route Reflectors for the E-VPN routes originated by
     the ToRs acting as PEs.
     
     
     In the case where E-VPN is used to interconnect L2 sites in
     different data centers, the network that interconnects DCBRs of
     these data centers could provide either (a) only Ethernet or
     IP/MPLS connectivity service among these DCBRs, or (b) may offer
     the E-VPN service. In the former case DCBRs exchange E-VPN routes
     among themselves relying only on the Ethernet or IP/MPLS
     connectivity service provided by the network that interconnects
     these DCBRs. The network does not directly participate in the
     exchange of these E-VPN routes. In the latter case the routers at
     the edge of the network maybe either co-located with DCBRs, or
     
     
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     may establish E-VPN peering with DCBRs.  Either way, in this case
     the network facilitates exchange of E-VPN routes among DCBRs (as
     in this case DCBRs would not need to exchange E-VPN routes
     directly with each other).
     
     
     Please note that for the purpose of solving the layer 2 extension
     problem the propagation scope of E-VPN routes for a given L2-
     based VN is constrained by the scope of the PEs connected to the
     L2 sites that presently contain VMs of that VN. This scope is
     controlled by the Route Target of the E-VPN routes. Controlling
     propagation scope could be further facilitated by using Route
     Target Constrain [RFC4684].
     
     
     Use of E-VPN ensures that traffic among members of the same L2-
     based VN is optimally forwarded, irrespective of whether members
     of that VN are within the same or in different data centers. This
     follows from the observation that E-VPN inherently enables
     (disaggregated) forwarding at the granularity of the MAC address
     of the VM.
     
     
     Optimal forwarding among VMs of a given L2-based VN that are
     within the same data center requires propagating VM MAC
     addresses, and comes at the cost of disaggregated forwarding
     within a given data center. However, such disaggregated
     forwarding is not necessary between data centers if a given L2-
     based VN spans multiple data centers. For example, when a given
     ToR acts as a PE, this ToR has to maintain MAC advertisement
     routes only to the VMs within its own data center (and
     furthermore, only to the VMs that belong to the L2-based VNs
     whose site(s) are connected to that ToR), and then point a
     "default" MAC route to one of the DCBRs of that data center.  In
     this scenario a DCBR of a given data center, when it receives MAC
     advertisement routes from DCBR(s) in other data centers, does not
     re-advertise these routes to the PEs within its own data center,
     but just advertises a single "default" MAC advertisement route to
     these PEs.
     
     When a given VM moves to a new L2 site, if in the new site this
     
     
     
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     VM is the only VM from its L2-based VN, then the PEs connected to
     the new site need to be provisioned with the E-VPN Instances
     (EVI) of the E-VPN associated with this L2-based VN. Likewise, if
     after the move the old site no longer has any VMs that are in the
     same L2 bas the VM that moved, the PEs connected to the old site
     need be de-provisioned with the EVI of the E-VPN.  Procedures to
     accomplish this are outside the scope of this document.
     
     8.2. VM Default Gateway Solutions
     
     
     Once a VM moves to a new L2 site, solving the VM Default Gateway
     problem would require PEs connected to that L2 site to apply IP
     forwarding to the inter-L2VN/inter-subnet traffic originated from
     that VM. That implies that (a) PEs should be capable of
     performing both MAC-based and IP-based forwarding (although IP-
     based forwarding functionality could be limited to just
     forwarding either based on IP host routes, or based on the IP
     default route), and (b) PEs should be able to distinguish between
     intra-L2VN/intra-subnet and inter-L2VN/inter-subnet traffic
     originated by that VM (in order to apply MAC-based forwarding to
     the former and IP-based forwarding to the latter).
     
     As a VM moves to a new L2 site, the default gateway IP address of
     the VM may not change. Further, the ARP cache of the VM may not
     time out. Thus, the destination MAC address in the inter-
     L2VN/inter-subnet traffic originated by that VM would not change
     as the VM moves to the new site. Given that, how would PEs
     connected to the new L2 site be able to recognize inter-
     L2VN/inter-subnet traffic originated by that VM? The following
     describes two possible solutions.
     
     Both of the solutions assume that for inter-L2VN/inter-subnet
     traffic between a VM and its peers outside of VM's own data
     center, one or more DCBRs of that data center act as fully
     functional default gateways for that traffic.
     
     8.2.1. VM Default Gateway Solution 1
     
     
     The first solution relies on the use of an anycast default
     gateway IP address and an anycast default gateway MAC address.
     
     
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     If DCBRs act as PEs for an E-VPN corresponding to a given L2-
     based VN, then these anycast addresses are configured on these
     DCBRs. Likewise, if ToRs act as PEs, then these anycast addresses
     are configured on these ToRs. All VMs of that L2-based VN are
     (auto)configured with the (anycast) IP address of the default
     gateway. This ensures that a particular DCBR (or ToR), acting as
     a PE, can always apply IP forwarding to the packets sent by a VM
     to the (anycast) default gateway MAC address. It also ensures
     that such DCBR (or ToR) can respond to the ARP Request generated
     by a VM for the default gateway (anycast) IP address.
     
     Note that with this approach when originating E-VPN MAC
     advertisement routes for the MAC address of the default gateways
     of a given L2-based VN, all these routes MUST indicate that this
     MAC address belongs to the same Ethernet Segment Identifier
     (ESI).
     
     8.2.2. VM Default Gateway Solution 2
     
     
     The second solution does not require configuration of the anycast
     default gateway IP and MAC address on the PEs.
     
     Each DCBR (or each ToR) that acts as a default gateway for a
     given L2-based VN advertises in the E-VPN control plane its
     default gateway IP and MAC address using the MAC advertisement
     route, and indicates that such route is associated with the
     default gateway. The MAC advertisement route MUST be advertised
     as per procedures in [E-VPN]. The MAC address in such an
     advertisement MUST be set to the default gateway MAC address of
     the DCBR (or ToR). The IP address in such an advertisement MUST
     be set to the default gateway IP address of the DCBR (or ToR). To
     indicate that such a route is associated with a default gateway,
     the route MUST carry the "Default Gateway" community.
     
     Each PE that receives this route and imports it as per procedures
     of[E-VPN] MUST create MAC forwarding state that enables it to
     apply IP forwarding to the packets destined to the MAC address
     carried in the route. The MES that receives this E-VPN route
     follows procedures in Section 12 of [E-VPN] when replying to ARP
     Requests that it receives if such Requests are for the IP address
     
     
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     in the received E-VPN route.
     
     
     
     9. Solutions and Considerations for other DC challenges
     
     
     
     9.1. Addressing IP/ARP explosion
     
     
     
        This section will be updated in the next revision.
     
     
     
     9.2. Optimal traffic forwarding
     
     
     
        IP networks, built using links-state protocols such as OSPF or
        ISIS and BGP provide optimal traffic forwarding through the
        use of equal cost multiple path (ECMP) and ECMP traffic load-
        balancing, and the use of traffic engineering tools based on
        BGP and/or MPLS-TE as applicable. In the Layer2 case, SPB or
        TRILL based protocols provide for load-balancing across
        parallel paths or equal cost paths between two nodes. Traffic
        follows the shortest path. For multicast, data plane
        replication at layer2 or layer3 happens in the data plane
        albeit with different attributes after multicast trees are
        built via a control plane and/or snooping. In the presence of
        VM mobility, optimal forwarding relates to avoiding
        triangulation and providing for optimum forwarding between any
        two VMs. Solutions that provide for routing in presence of VM
        mobility are described in [VM-Mobility].
     
     
     
     9.3. VM Mobility
     
     
     
        IP VPN technology may be used to support DC Interconnect for
        different functions like VM Mobility and Cloud Management. A
        description of VM Mobility between server blades located in
        different IP subnets using extensions to existing MP-BGP and
        IP VPN procedure is described in [VM-Mobility]. Support for VM
     
     
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        mobility is also described in [endystems]. Other solutions can
        exist as well. What is needed is a solution that provides for
        fast convergence toward the steady state whereby communication
        among any two VMs can take place on the shortest path or most
        optimum path, transit triangulation time is minimized, traffic
        black-holing is avoided, and impact on routing scale for both
        IPv4 and IPv6 is controllable or minimized.
     
     
     
     9.4. Dynamic provisioning of network services
     
     
     
        The need for fast dynamic provisioning of virtual network
        services is described in [NVo3-problem-statement] to match the
        elasticity and mobility in compute and storage resource
        allocation. Such dynamic provisioning was not part of initial
        L2VPN or L3VPN work except for some work to provide for
        dynamic bandwidth access [VPN-RSVP-TE]. In current L2VPN and
        L3VPN targeted deployments, the customer equipment connected
        to a VPN PE is static in location. Thus, the logical
        forwarding instance on the connected PE (e.g., IPVPN VRF, VSI
        or EVI) and the attachment circuit to that instance as well
        any routing and forwarding policies within that instance are
        provisioned via network management systems upon a service
        order at a much larger time scale than needed in this case. In
        dynamic data centers, services (e.g., VRF, attachment circuit)
        need to be established and torn down at a much smaller time
        scale to match the dynamicity of compute resources connected
        via these services. Mechanisms to provide for such timely
        dynamic provisioning at a scale are needed.
     
     
     
        In addition, CEs in traditional L3VPN deployments are routers
        able to exchange signaling and routing protocol information
        with the PE, providing for the dynamic exchange of routing
        information and liveliness check between the CEs and the PEs.
        In NVo3, the CE equivalent is a TS that may be a virtualized
        or a physical CE with the same capabilities as the traditional
        CE in L3VPN deployments. However, in some other cases, VMs
        providing compute rather than network services may connect
        directly to the NVE providing Lyaer3 forwarding service
        (equivalent to a PE). In that case, control plane mechanisms
        that enable fast and dynamic connectivity of a VM to an NVE
     
     
     
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        and reachability exchange among NVEs providing connectivity
        among VMs in the same NV must be provided.
     
     
     
     9.5. Considerations for Layer2 and Layer3 VPNS on End-systems
     
     
     
        With the advent of computing power on end-systems providing VM
        services, and to provide for more efficient communication
        among VMs minimizing middle boxes in the path, there is a
        strong requirement for enabling Layer2 and Layer3 VN
        forwarding on these servers. Layer2 VN forwarding today is
        supported via vSW implementations and is often limited to
        intra data centers. Evolving proprietary technologies such as
        vxlan and provide for L2 service transport over an IP network.
        If Layer2 and Layer3 VN forwarding solutions on end-systems
        are to leverage existing L2VPN and L3VPN solutions,
        considerations should be given to new PE models and
        specifically to decoupling of forwarding from control plane
        functions across different systems to best utilize compute
        resources of end-systems and provide for scale. [endystems] is
        one of the solutions being adopted for implementation of
        BGP/MPLS VPNs in a DC end-system environment. In that case,
        the end-system uses XMPP to exchange labeled IP VPN routes
        with a route server that supports MP-BGP labeled IPVPN route
        exchange with tradition VPN Route Reflectors and PEs. [sdn-
        control] proposes a more generic model for PE functionality
        decomposed across forwarding end-systems and control plane
        systems that control the forwarding function on these end-
        systems and interact with other systems such as other similar
        control systems, PEs and Route reflectors. These efforts
        targeting new PE models that best fit a scalable multi-tenant
        environment may also require extensions of existing protocols
        or definition of new ones.
     
     
     
     10. Operator Considerations
     
        To be filled in a later version of this document.
     
     
     
     
     
     
     
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     11. Security Considerations
     
        No new security issues are introduced beyond those described
        already in the related L2VPN and L3VPN solutions drafts and
        RFCs in relation to the VPN technologies themselves when the
        deployment model and PE model remain the same. Allowing for
        dynamic provisioning of VPN services within a DC must ensure
        that tenant network privacy is preserved. In addition, when
        provisioning, dynamically or statically, VPN services for a
        tenant across domain boundaries, the tenant privacy must be
        preserved. Dynamic provisioning must include communication of
        a secure channel and ensure that the service is provided to an
        authorized tenant and connected to the right tenant service.
        In addition, changing the PE model by separating the
        forwarding plane and control plane must consider and address
        security implications.
     
     
     
     12. IANA Considerations
     
     
     
        IANA does not need to take any action for this draft.
     
     
     
     13. References
     
     13.1. Normative References
     
        [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.
     
        [RFC4761] Kompella, K. and Rekhter, Y. (Editors), "Virtual
                  Private LAN Service (VPLS) Using BGP for Auto-
                  Discovery and Signaling", RFC 4761, January 2007.
     
        [RFC4762] Lasserre, M. and Kompella, V. (Editors), "Virtual
                  Private LAN Service (VPLS) Using Label Distribution
                  Protocol (LDP) Signaling", RFC 4762, January 2007.
     
        [PBB-VPLS] Balus, F. et al. "Extensions to VPLS PE model for
                  Provider Backbone Bridging", draft-ietf-l2vpn-pbb-
                  vpls-pe-model-07.txt (work in progress), June 2013.
     
     
     
     
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        [PBB-Interop] Sajassi, A. et al. "VPLS Interoperability with
                  Provider Backbone Bridging", draft-ietf-l2vpn-pbb-
                  vpls-interop-05.txt (work in progress), July 2013.
     
        [802.1ah] IEEE 802.1ah "Virtual Bridged Local Area Networks,
                  Amendment 6: Provider Backbone Bridges", Approved
                  Standard June 12th, 2008.
     
        [802.1aq] IEEE Draft P802.1aq/D4.3 "Virtual Bridged Local Area
                  Networks, Amendment: Shortest Path Bridging", Work
                  in Progress, September 21, 2011.
     
        [RFC6325] Perlman, et al., "Routing Bridges (Rbridges): Base
                  Protocol Specification", RFC 6325, July 2011.
     
        [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual
                  Private Networks (VPNs)", RFC 4364, February 2006.
     
        [RFC4797] Rosen, E. and Y. Rekhter, "Use of Provider Edge to
                  Provider Edge (PE-PE) Generic Routing encapsulation
                  (GRE) or IP in BGP/MPLS IP Virtual Private
                  Networks", RFC 4797, January 2007.
     
     13.2. Informative References
     
        [RFC4026] Andersson, L. et Al., "Provider Provisioned Virtual
                  Private Network (VPN) Terminology", RFC 4026, May
                  2005.
     
        [802.1Qbp] IEEE Draft P802.1Qbp/D0.1 "Virtual Bridged Local
                  Area Networks, Amendment: Equal Cost Multiple Paths
                  (ECMP)", Work in Progress, October 13, 2011.
     
        [802.1Qbg] IEEE Draft P802.1Qbg/D1.8 "Virtual Bridged Local
                  Area Networks, Amendment: Edge Virtual Bridging",
                  Work in Progress, October 17, 2011.
     
        [EVPN]    Raggarwa, R. et al. "BGP MPLS based Ethernet VPN",
                  draft-ietf-l2vpn-evpn-04.txt (work in
                  progress), July 2013.
     
        [PBB-EVPN] Sajassi, A. et al. "PBB-EVPN", draft-ietf-l2vpn-
                  pbb-evpn-05.txt (work in progress), July 2013.
     
     
     
     
     
     
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        [VM-Mobility] Raggarwa, R. et al. "Data Center Mobility based
                  on BGP/MPLS, IP Routing and NHRP", draft-raggarwa-
                  data-center-mobility-05.txt (work in progress), June
                  2013.
     
        [RFC4719] Aggarwal, R. et al., "Transport of Ethernet over
                  Layer 2 Tunneling Protocol Version 3 (L2TPv3)", RFC
                  4719, November 2006.
     
        [MVPN]    Rosen, E. and Raggarwa, R. "Multicast in MPLS/BGP IP
                  VPN", RFC 6513, February 2012.
     
        [ARPproxy] Carl-Mitchell, S. and Quarterman, S., "Using ARP to
                  implement transparent subnet gateways", RFC 1027,
                  October 1987.
     
        [MYERS] Myers, A., Ng, E. and Zhang, H., "Rethinking the
                  Service Model: Scaling Ethernet to a Million Nodes",
                  http://www.cs.cmu.edu/~acm/papers/myers-
                  hotnetsIII.pdf.
     
        [Fine-Grained] Eastlake, D. et Al., "RBridges: Fine-Grained
                  Labeling", draft-eastlake-trill-rbridge-fine-
                  labeling-02.txt (work in progress), October 2011.
     
        [Nvo3-problem-statement] Narten, T., et al., "Problem
                  Statement: Overlays for Network Virtualization",
                  draft-ietf-nvo3-overlay-problem-statement-04.txt
                  (work in progress), July 2013.
     
        [Nvo3-fmwk] Lasserre, M., et al., "Framework for DC Network
                  Virtualization", draft-ietf-nvo3-framework-03.txt
                  (work in progress), July 2013.
     
        [Nvo3-cp-reqts] Kreeger, L., et al., "Network Virtualization
                  Overlay Control Protocol Requirements", draft-
                  kreeger-nvo3-overlay-cp-04.txt (work in progress),
                  June 2013.
     
        [Nvo3-dp-reqts] Bitar, N., Lasserre, M., et al., "NVO3 Data
                  Plane Requirements", draft-ietf-nvo3-dataplane-
                  requirements-01.txt (work in progress), July
                  2013.
     
     
     
     
     
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        [endsystem] Marques, P., wt al., "BGP-signaled end-system
        IP/VPNs",   draft-ietf-l3vpn-end-system-01.txt (work in
        progress), April 2013.
     
     
     
     
     
     
     14. Acknowledgments
     
        In addition to the authors the following people have
        contributed to this document:
     
        Javier Benitez, Colt
     
        Dimitrios Stiliadis, Alcatel-Lucent
     
        Samer Salam, Cisco
     
        Yakov Rekhter, Juniper
     
     Authors' Addresses
     
        Nabil Bitar
        Verizon
        40 Sylvan Road
        Waltham, MA 02145
        Email: nabil.bitar@verizon.com
     
        Florin Balus
        Alcatel-Lucent
        777 E. Middlefield Road
        Mountain View, CA, USA 94043
        Email: florin.balus@alcatel-lucent.com
     
        Marc Lasserre
        Alcatel-Lucent
        Email: marc.lasserre@alcatel-lucent.com
     
     
     
     
     
     
     
     
     
     
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        Wim Henderickx
        Alcatel-Lucent
        Email: wim.henderickx@alcatel-lucent.com
     
        Ali Sajassi
        Cisco
        170 West Tasman Drive
        San Jose, CA 95134, USA
        Email: sajassi@cisco.com
     
        Luyuan Fang
        Cisco
        111 Wood Avenue South
        Iselin, NJ 08830
        Email: lufang@cisco.com
     
        Yuichi Ikejiri
        NTT Communications
        1-1-6, Uchisaiwai-cho, Chiyoda-ku
        Tokyo, 100-8019 Japan
        Email: y.ikejiri@ntt.com
     
     
        Mircea Pisica
        BT
        Telecomlaan 9
        Brussels 1831, Belgium
        Email: mircea.pisica@bt.com
     
        John E. Drake
        Juniper Networks
        Email: jnadeau@juniper.net
     
        Lucy Yong
        Huawei Technologies (USA)
        5340 Legacy Drive
        Plano, TX75025
        Email: lucy.yong@huawei.com
     
        Susan Hares
        ADARA
        Email: shares@ndzh.com
     
     
     
     
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