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Versions: (draft-sajassi-l2vpn-pbb-evpn) 00 01 02 03 04 05 06 07 08 09 10 RFC 7623

Internet Working Group                                       Ali Sajassi
Internet Draft                                               Samer Salam
Category: Standards Track                                   Sami Boutros
                                                                   Cisco

Florin Balus                                                 Nabil Bitar
Wim Henderickx                                                   Verizon
Alcatel-Lucent
                                                            Aldrin Isaac
Clarence Filsfils                                              Bloomberg
Dennis Cai
Cisco                                                        Lizhong Jin
                                                                     ZTE

Expires: December 20, 2012                                 June 20, 2012


                               PBB-EVPN
                      draft-ietf-l2vpn-pbb-evpn-03

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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Copyright and License Notice

   Copyright (c) 2012 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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   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Abstract

   This document discusses how Ethernet Provider Backbone Bridging
   [802.1ah] can be combined with E-VPN in order to reduce the number of
   BGP MAC advertisement routes by aggregating Customer/Client MAC (C-
   MAC) addresses via Provider Backbone MAC address (B-MAC), provide
   client MAC address mobility using C-MAC aggregation and B-MAC sub-
   netting, confine the scope of C-MAC learning to only active flows,
   offer per site policies and avoid C-MAC address flushing on topology
   changes. The combined solution is referred to as PBB-EVPN.

Conventions

   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.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  4
     4.1.  MAC Advertisement Route Scalability  . . . . . . . . . . .  5
     4.2.  C-MAC Mobility with MAC Summarization  . . . . . . . . . .  5
     4.3.  C-MAC Address Learning and Confinement . . . . . . . . . .  5
     4.4.  Per Site Policy Support  . . . . . . . . . . . . . . . . .  6
     4.5.  Avoiding C-MAC Address Flushing  . . . . . . . . . . . . .  6
   5.  Solution Overview  . . . . . . . . . . . . . . . . . . . . . .  6
   6.  BGP Encoding . . . . . . . . . . . . . . . . . . . . . . . . .  7
     6.1.  BGP MAC Advertisement Route  . . . . . . . . . . . . . . .  7
     6.2.  Ethernet Auto-Discovery Route  . . . . . . . . . . . . . .  7
     6.3.  Per VPN Route Targets  . . . . . . . . . . . . . . . . . .  7
     6.4.  MAC Mobility Extended Community  . . . . . . . . . . . . .  7
   7.  Operation  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     7.1.  MAC Address Distribution over Core . . . . . . . . . . . .  8
     7.2.  Device Multi-homing  . . . . . . . . . . . . . . . . . . .  8
       7.2.1 Flow-based Load-balancing  . . . . . . . . . . . . . . .  8



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         7.2.1.1  MES B-MAC Address Assignment  . . . . . . . . . . .  8
         7.2.1.2.  Automating B-MAC Address Assignment  . . . . . . . 10
         7.2.1.3  Split Horizon and Designated Forwarder Election . . 11
       7.2.2 I-SID Based Load-balancing . . . . . . . . . . . . . . . 11
         7.2.2.1 MES B-MAC Address Assignment . . . . . . . . . . . . 11
         7.2.2.2 Split Horizon and Designated Forwarder Election  . . 12
     7.3.  Network Multi-homing . . . . . . . . . . . . . . . . . . . 12
     7.4.  Frame Forwarding . . . . . . . . . . . . . . . . . . . . . 12
       7.4.1.  Unicast  . . . . . . . . . . . . . . . . . . . . . . . 12
       7.4.2.  Multicast/Broadcast  . . . . . . . . . . . . . . . . . 13
   8.  Minimizing ARP Broadcast . . . . . . . . . . . . . . . . . . . 13
   9. Seamless Interworking with IEEE 802.1aq/802.1Qbp  . . . . . . . 13
     9.1 B-MAC Address Assignment . . . . . . . . . . . . . . . . . . 14
     9.2  IEEE 802.1aq / 802.1Qbp B-MAC Advertisement Route . . . . . 14
     9.3 Operation: . . . . . . . . . . . . . . . . . . . . . . . . . 15
   10.  Solution Advantages . . . . . . . . . . . . . . . . . . . . . 15
     10.1.  MAC Advertisement Route Scalability . . . . . . . . . . . 15
     10.2.  C-MAC Mobility with MAC Sub-netting . . . . . . . . . . . 16
     10.3.  C-MAC Address Learning and Confinement  . . . . . . . . . 16
     10.4.  Seamless Interworking with TRILL and 802.1aq Access
            Networks  . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.5.  Per Site Policy Support . . . . . . . . . . . . . . . . . 17
     10.6.  Avoiding C-MAC Address Flushing . . . . . . . . . . . . . 17
   11.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . 18
   12.  Security Considerations . . . . . . . . . . . . . . . . . . . 18
   13.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
   14.  Intellectual Property Considerations  . . . . . . . . . . . . 18
   15.  Normative References  . . . . . . . . . . . . . . . . . . . . 18
   16.  Informative References  . . . . . . . . . . . . . . . . . . . 18
   17.  Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . 18





















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1.  Introduction

   [E-VPN] introduces a solution for multipoint L2VPN services, with
   advanced multi-homing capabilities, using BGP for distributing
   customer/client MAC address reach-ability information over the core
   MPLS/IP network. [802.1ah] defines an architecture for Ethernet
   Provider Backbone Bridging (PBB), where MAC tunneling is employed to
   improve service instance and MAC address scalability in Ethernet as
   well as VPLS networks [PBB-VPLS].

   In this document, we discuss how PBB can be combined with E-VPN in
   order to: reduce the number of BGP MAC advertisement routes by
   aggregating Customer/Client MAC (C-MAC) addresses via Provider
   Backbone MAC address (B-MAC), provide client MAC address mobility
   using C-MAC aggregation and B-MAC sub-netting, confine the scope of
   C-MAC learning to only active flows, offer per site policies and
   avoid C-MAC address flushing on topology changes. The combined
   solution is referred to as PBB-EVPN.

2.  Contributors

   In addition to the authors listed above, the following individuals
   also contributed to this document.

   Keyur Patel, Cisco
   Sam Aldrin, Huawei

3.  Terminology

   BEB: Backbone Edge Bridge
   B-MAC: Backbone MAC Address
   CE: Customer Edge
   C-MAC: Customer/Client MAC Address
   DHD: Dual-homed Device
   DHN: Dual-homed Network
   LACP: Link Aggregation Control Protocol
   LSM: Label Switched Multicast
   MDT: Multicast Delivery Tree
   MES: MPLS Edge Switch
   MP2MP: Multipoint to Multipoint
   P2MP: Point to Multipoint
   P2P: Point to Point
   PoA: Point of Attachment
   PW: Pseudowire
   E-VPN: Ethernet VPN

4.  Requirements




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   The requirements for PBB-EVPN include all the requirements for E-VPN
   that were described in [EVPN-REQ], in addition to the following:

4.1.  MAC Advertisement Route Scalability

   In typical operation, an [E-VPN] MES sends a BGP MAC Advertisement
   Route per customer/client MAC (C-MAC) address. In certain
   applications, this poses scalability challenges, as is the case in
   virtualized data center environments where the number of virtual
   machines (VMs), and hence the number of C-MAC addresses, can be in
   the millions. In such scenarios, it is required to reduce the number
   of BGP MAC Advertisement routes by relying on a 'MAC summarization'
   scheme, as is provided by PBB. Note that the MAC summarization
   capability already built into E-VPN is not sufficient in those
   environments, as will be discussed next.

4.2.  C-MAC Mobility with MAC Summarization

   Certain applications, such as virtual machine mobility, require
   support for fast C-MAC address mobility. For these applications, it
   is not possible to use MAC address summarization in E-VPN, i.e.
   advertise reach-ability to a MAC address prefix. Rather, the exact
   virtual machine MAC address needs to be transmitted in BGP MAC
   Advertisement route. Otherwise, traffic would be forwarded to the
   wrong segment when a virtual machine moves from one Ethernet segment
   to another. This hinders the scalability benefits of summarization.

   It is required to support C-MAC address mobility, while retaining the
   scalability benefits of MAC summarization. This can be achieved by
   leveraging PBB technology, which defines a Backbone MAC (B-MAC)
   address space that is independent of the C-MAC address space, and
   aggregate C-MAC addresses via a B-MAC address and then apply
   summarization to B-MAC addresses.

4.3.  C-MAC Address Learning and Confinement

   In E-VPN, all the MES nodes participating in the same E-VPN instance
   are exposed to all the C-MAC addresses learnt by any one of these MES
   nodes because a C-MAC learned by one of the MES nodes is advertise in
   BGP to other MES nodes in that E-VPN instance. This is the case even
   if some of the MES nodes for that E-VPN instance are not involved in
   forwarding traffic to, or from, these C-MAC addresses. Even if an
   implementation does not install hardware forwarding entries for C-MAC
   addresses that are not part of active traffic flows on that MES, the
   device memory is still consumed by keeping record of the C-MAC
   addresses in the routing table (RIB). In network applications with
   millions of C-MAC addresses, this introduces a non-trivial waste of
   MES resources. As such, it is required to confine the scope of



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   visibility of C-MAC addresses only to those MES nodes that are
   actively involved in forwarding traffic to, or from, these addresses.

4.4.  Per Site Policy Support

   In many applications, it is required to be able to enforce
   connectivity policy rules at the granularity of a site (or segment).
   This includes the ability to control which MES nodes in the network
   can forward traffic to, or from, a given site. PBB-EVPN is capable of
   providing this granularity of policy control. In the case where per
   C-MAC address granularity is required, the EVI can always continue to
   operate in E-VPN mode.

4.5.  Avoiding C-MAC Address Flushing

   It is required to avoid C-MAC address flushing upon link, port or
   node failure for multi-homed devices and networks. This is in order
   to speed up re-convergence upon failure.

5.  Solution Overview

   The solution involves incorporating IEEE 802.1ah Backbone Edge Bridge
   (BEB) functionality on the E-VPN MES nodes similar to PBB-VPLS, where
   BEB functionality is incorporated in the VPLS PE nodes. The MES
   devices would then receive 802.1Q Ethernet frames from their
   attachment circuits, encapsulate them in the PBB header and forward
   the frames over the IP/MPLS core. On the egress E-VPN MES, the PBB
   header is removed following the MPLS disposition, and the original
   802.1Q Ethernet frame is delivered to the customer equipment.
                   BEB   +--------------+  BEB
                   ||    |              |  ||
                   \/    |              |  \/
       +----+ AC1 +----+ |              | +----+   +----+
       | CE1|-----|    | |              | |    |---| CE2|
       +----+\    |MES1| |   IP/MPLS    | |MES3|   +----+
              \   +----+ |   Network    | +----+
               \         |              |
             AC2\ +----+ |              |
                 \|    | |              |
                  |MES2| |              |
                  +----+ |              |
                    /\   +--------------+
                    ||
                    BEB
         <-802.1Q-> <------PBB over MPLS------> <-802.1Q->

   Figure 1: PBB-EVPN Network




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   The MES nodes perform the following functions:- Learn customer/client
   MAC addresses (C-MACs) over the attachment circuits in the data-
   plane, per normal bridge operation.

   - Learn remote C-MAC to B-MAC bindings in the data-plane from traffic
   ingress from the core per [802.1ah] bridging operation.

   - Advertise local B-MAC address reach-ability information in BGP to
   all other MES nodes in the same set of service instances. Note that
   every MES has a set of local B-MAC addresses that uniquely identify
   the device. More on the MES addressing in section 5.

   - Build a forwarding table from remote BGP advertisements received
   associating remote B-MAC addresses with remote MES IP addresses and
   the associated MPLS label(s).

6.  BGP Encoding

   PBB-EVPN leverages the same BGP Routes and Attributes defined in [E-
   VPN], adapted as follows:

6.1.  BGP MAC Advertisement Route

   The E-VPN MAC Advertisement Route is used to distribute B-MAC
   addresses of the MES nodes instead of the C-MAC addresses of end-
   stations/hosts. This is because the C-MAC addresses are learnt in the
   data-plane for traffic arriving from the core. The MAC Advertisement
   Route is encoded as follows:

   - The MAC address field contains the B-MAC address.
   - The Ethernet Tag field is set to 0.

   The route is tagged with the RT corresponding to the EVI associated
   with the B-MAC address.

   All other fields are set as defined in [E-VPN].

6.2.  Ethernet Auto-Discovery Route

   This route and all of its associated modes are not needed in PBB-
   EVPN.

6.3.  Per VPN Route Targets

   PBB-EVPN uses the same set of route targets defined in [E-VPN]. The
   future revision of this document will describe new RT types.

6.4.  MAC Mobility Extended Community



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   This extended community is a new transitive extended community. It
   may be advertised along with the MAC Advertisement route. When used
   in PBB-EVPN, it indicates that the C-MAC forwarding tables for the I-
   SIDs associated with the RT tagging the MAC Advertisement route must
   be flushed. This extended community is encoded in 8-bytes as follows:

   - Type (1 byte) = Pending IANA assignment.
   - Sub-Type (1 byte) = Pending IANA assignment.
   - Reserved (2 bytes)
   - Counter (4 bytes)

   Note that all other BGP messages and/or attributes are used as
   defined in [E-VPN].

7.  Operation

   This section discusses the operation of PBB-EVPN, specifically in
   areas where it differs from [E-VPN].

7.1.  MAC Address Distribution over Core

   In PBB-EVPN, host MAC addresses (i.e. C-MAC addresses) need not be
   distributed in BGP. Rather, every MES independently learns the C-MAC
   addresses in the data-plane via normal bridging operation. Every MES
   has a set of one or more unicast B-MAC addresses associated with it,
   and those are the addresses distributed over the core in MAC
   Advertisement routes.

7.2.  Device Multi-homing

7.2.1 Flow-based Load-balancing

   This section describes the procedures for supporting device multi-
   homing in an all-active redundancy model with flow-based load-
   balancing.

7.2.1.1  MES B-MAC Address Assignment

   In [802.1ah] every BEB is uniquely identified by one or more B-MAC
   addresses. These addresses are usually locally administered by the
   Service Provider. For PBB-EVPN, the choice of B-MAC address(es) for
   the MES nodes must be examined carefully as it has implications on
   the proper operation of multi-homing. In particular, for the scenario
   where a CE is multi-homed to a number of MES nodes with all-active
   redundancy and flow-based load-balancing, a given C-MAC address would
   be reachable via multiple MES nodes concurrently. Given that any
   given remote MES will bind the C-MAC address to a single B-MAC
   address, then the various MES nodes connected to the same CE must



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   share the same B-MAC address. Otherwise, the MAC address table of the
   remote MES nodes will keep oscillating between the B-MAC addresses of
   the various MES devices. For example, consider the network of Figure
   1, and assume that MES1 has B-MAC BM1 and MES2 has B-MAC BM2. Also,
   assume that both links from CE1 to the MES nodes are part of an all-
   active multi-chassis Ethernet link aggregation group. If BM1 is not
   equal to BM2, the consequence is that the MAC address table on MES3
   will keep oscillating such that the C-MAC address CM of CE1 would
   flip-flop between BM1 or BM2, depending on the load-balancing
   decision on CE1 for traffic destined to the core.

   Considering that there could be multiple sites (e.g. CEs) that are
   multi-homed to the same set of MES nodes, then it is required for all
   the MES devices in a Redundancy Group to have a unique B-MAC address
   per site. This way, it is possible to achieve fast convergence in the
   case where a link or port failure impacts the attachment circuit
   connecting a single site to a given MES.

                               +---------+
                +-------+ MES1 | IP/MPLS |
               /               |         |
            CE1                | Network |    MESr
           M1  \               |         |
                +-------+ MES2 |         |
                /-------+      |         |
               /               |         |
            CE2                |         |
          M2   \               |         |
                \              |         |
                 +------+ MES3 +---------+

   Figure 2: B-MAC Address Assignment

   In the example network shown in Figure 2 above, two sites
   corresponding to CE1 and CE2 are dual-homed to MES1/MES2 and
   MES2/MES3, respectively. Assume that BM1 is the B-MAC used for the
   site corresponding to CE1. Similarly, BM2 is the B-MAC used for the
   site corresponding to CE2. On MES1, a single B-MAC address (BM1) is
   required for the site corresponding to CE1. On MES2, two B-MAC
   addresses (BM1 and BM2) are required, one per site. Whereas on MES3,
   a single B-MAC address (BM2) is required for the site corresponding
   to CE2. All three MES nodes would advertise their respective B-MAC
   addresses in BGP using the MAC Advertisement routes defined in [E-
   VPN]. The remote MES, MESr, would learn via BGP that BM1 is reachable
   via MES1 and MES2, whereas BM2 is reachable via both MES2 and MES3.
   Furthermore, MESr establishes via the normal bridge learning that C-
   MAC M1 is reachable via BM1, and C-MAC M2 is reachable via BM2. As a
   result, MESr can load-balance traffic destined to M1 between MES1 and



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   MES2, as well as traffic destined to M2 between both MES2 and MES3.
   In the case of a failure that causes, for example, CE1 to be isolated
   from MES1, the latter can withdraw the route it has advertised for
   BM1. This way, MESr would update its path list for BM1, and will send
   all traffic destined to M1 over to MES2 only.

   For single-homed sites, it is possible to assign a unique B-MAC
   address per site, or have all the single-homed sites connected to a
   given MES share a single B-MAC address. The advantage of the first
   model over the second model is the ability to avoid C-MAC destination
   address lookup on the disposition PE (even though source C-MAC
   learning is still required in the data-plane). Also, by assigning the
   B-MAC addresses from a contiguous range, it is possible to advertise
   a single B-MAC subnet for all single-homed sites, thereby rendering
   the number of MAC advertisement routes required at par with the
   second model.

   In summary, every MES may use a unicast B-MAC address shared by all
   single-homed CEs or a unicast B-MAC address per single-homed CE and,
   in addition, a unicast B-MAC address per dual-homed CE. In the latter
   case, the B-MAC address MUST be the same for all MES nodes in a
   Redundancy Group connected to the same CE.

7.2.1.2.  Automating B-MAC Address Assignment

   The MES B-MAC address used for single-homed sites can be
   automatically derived from the hardware (using for e.g. the
   backplane's address). However, the B-MAC address used for multi-homed
   sites must be coordinated among the RG members. To automate the
   assignment of this latter address, the MES can derive this B-MAC
   address from the MAC Address portion of the CE's LACP System
   Identifier by flipping the 'Locally Administered' bit of the CE's
   address. This guarantees the uniqueness of the B-MAC address within
   the network, and ensures that all MES nodes connected to the same
   multi-homed CE use the same value for the B-MAC address.

   Note that with this automatic provisioning of the B-MAC address
   associated with multi-homed CEs, it is not possible to support the
   uncommon scenario where a CE has multiple bundles towards the MES
   nodes, and the service involves hair-pinning traffic from one bundle
   to another. This is because the split-horizon filtering relies on B-
   MAC addresses rather than Site-ID Labels (as will be described in the
   next section). The operator must explicitly configure the B-MAC
   address for this fairly uncommon service scenario.

   Whenever a B-MAC address is provisioned on the MES, either manually
   or automatically (as an outcome of CE auto-discovery), the MES MUST
   transmit an MAC Advertisement Route for the B-MAC address with a



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   downstream assigned MPLS label that uniquely identifies that address
   on the advertising MES. The route is tagged with the RTs of the
   associated EVIs as described above.

7.2.1.3  Split Horizon and Designated Forwarder Election

   [E-VPN] relies on access split horizon, where the Ethernet Segment
   Label is used for egress filtering on the attachment circuit in order
   to prevent forwarding loops. In PBB-EVPN, the B-MAC source address
   can be used for the same purpose, as it uniquely identifies the
   originating site of a given frame. As such, Segment Labels are not
   used in PBB-EVPN, and the egress split-horizon filtering is done
   based on the B-MAC source address. It is worth noting here that
   [802.1ah] defines this B-MAC address based filtering function as part
   of the I-Component options, hence no new functions are required to
   support split-horizon beyond what is already defined in [802.1ah].
   Given that the Segment label is not used in PBB-EVPN, the MES sets
   the Label field in the Ethernet Segment Route to 0.

   The Designated Forwarder election procedures are defined in [I-D-
   Segment-Route].

7.2.2 I-SID Based Load-balancing

   This section describes the procedures for supporting device multi-
   homing in an all-active redundancy model with per-ISID load-
   balancing.

7.2.2.1 MES B-MAC Address Assignment

   In the case where per-ISID load-balancing is desired among the MES
   nodes in a given redundancy group, multiple unicast B-MAC addresses
   are allocated per multi-homed Ethernet Segment: Each MES connected to
   the multi-homed segment is assigned a unique B-MAC. Every MES then
   advertises its B-MAC address using the BGP MAC advertisement route.

   A remote MES initially floods traffic to a destination C-MAC address,
   located in a given multi-homed Ethernet Segment, to all the MES nodes
   connected to that segment. Then, when reply traffic arrives at the
   remote MES, it learns (in the data-path) the B-MAC address and
   associated next-hop MES to use for said C-MAC address. When a MES
   connected to a multi-homed Ethernet Segment loses connectivity to the
   segment, due to link or port failure, it withdraws the B-MAC route
   previously advertised for that segment. This causes the remote MES
   nodes to flush all C-MAC addresses associated with the B-MAC in
   question. This is done across all I-SIDs that are mapped to the EVI
   of the withdrawn MAC route.




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7.2.2.2 Split Horizon and Designated Forwarder Election The procedures
   are similar to the flow-based load-balancing case, with the only
   difference being that the DF filtering must be applied to unicast as
   well as multicast traffic, and in both core-to-segment as well as
   segment-to-core directions.

7.3.  Network Multi-homing

   When an Ethernet network is multi-homed to a set of MES nodes running
   PBB-EVPN, an all-active redundancy model can be supported with per
   service instance (i.e. I-SID) load-balancing. In this model, DF
   election is performed to ensure that a single MES node in the
   redundancy group is responsible for forwarding traffic associated
   with a given I-SID. This guarantees that no forwarding loops are
   created. Filtering based on DF state applies to both unicast and
   multicast traffic, and in both access-to-core as well as core-to-
   access directions (unlike the multi-homed device scenario where DF
   filtering is limited to multi-destination frames in the core-to-
   access direction). Similar to the multi-homed device scenario, with
   I-SID based load-balancing, a unique B-MAC address is assigned to
   each of the MES nodes connected to the multi-homed network (Segment).

7.4.  Frame Forwarding

   The frame forwarding functions are divided in between the Bridge
   Module, which hosts the [802.1ah] Backbone Edge Bridge (BEB)
   functionality, and the MPLS Forwarder which handles the MPLS
   imposition/disposition. The details of frame forwarding for unicast
   and multi-destination frames are discussed next.

7.4.1.  Unicast

   Known unicast traffic received from the AC will be PBB-encapsulated
   by the MES using the B-MAC source address corresponding to the
   originating site. The unicast B-MAC destination address is determined
   based on a lookup of the C-MAC destination address (the binding of
   the two is done via transparent learning of reverse traffic). The
   resulting frame is then encapsulated with an LSP tunnel label and the
   MPLS label which uniquely identifies the B-MAC destination address on
   the egress MES. If per flow load-balancing over ECMPs in the MPLS
   core is required, then a flow label is added as the end of stack
   label.

   For unknown unicast traffic, the MES forwards these frames over MPLS
   core. When these frames are to be forwarded, then the same set of
   options used for forwarding multicast/broadcast frames (as described
   in next section) are used.




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7.4.2.  Multicast/Broadcast

   Multi-destination frames received from the AC will be PBB-
   encapsulated by the MES using the B-MAC source address corresponding
   to the originating site. The multicast B-MAC destination address is
   selected based on the value of the I-SID as defined in [802.1ah]. The
   resulting frame is then forwarded over the MPLS core using one out of
   the following two options:

   Option 1: the MPLS Forwarder can perform ingress replication over a
   set of MP2P tunnel LSPs. The frame is encapsulated with a tunnel LSP
   label and the E-VPN ingress replication label advertised in the
   Inclusive Multicast Route.

   Option 2: the MPLS Forwarder can use P2MP tunnel LSP per the
   procedures defined in [E-VPN]. This includes either the use of
   Inclusive or Aggregate Inclusive trees.

   Note that the same procedures for advertising and handling the
   Inclusive Multicast Route defined in [E-VPN] apply here.

8.  Minimizing ARP Broadcast

   The MES nodes implement an ARP-proxy function in order to minimize
   the volume of ARP traffic that is broadcasted over the MPLS network.
   This is achieved by having each MES node snoop on ARP request and
   response messages received over the access interfaces or the MPLS
   core. The MES builds a cache of IP / MAC address bindings from these
   snooped messages. The MES then uses this cache to respond to ARP
   requests ingress on access ports and targeting hosts that are in
   remote sites. If the MES finds a match for the IP address in its ARP
   cache, it responds back to the requesting host and drops the request.
   Otherwise, if it does not find a match, then the request is flooded
   over the MPLS network using either ingress replication or LSM.


9. Seamless Interworking with IEEE 802.1aq/802.1Qbp














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                           +--------------+
                           |              |
           +---------+     |     MPLS     |    +---------+
   +----+  |         |   +----+        +----+  |         |  +----+
   |SW1 |--|         |   |MES1|        |MES2|  |         |--| SW3|
   +----+  | 802.1aq |---|    |        |    |--| 802.1aq |  +----+
   +----+  |  .1Qbp  |   +----+        +----+  |  .1Qbp  |  +----+
   |SW2 |--|         |     |   Backbone   |    |         |--| SW4|
   +----+  +---------+     +--------------+    +---------+  +----+

   |<------ IS-IS -------->|<-----BGP----->|<------ IS-IS ------>|  CP


   |<-------------------------   PBB  -------------------------->|  DP
                           |<----MPLS----->|

   Legend: CP = Control Plane View
           DP = Data Plane View

   Figure 7: Interconnecting 802.1aq/802.1Qbp Networks with PBB-EVPN

9.1 B-MAC Address Assignment

   For the same reasons cited in the TRILL section, the B-MAC addresses
   need to be globally unique across all the IEEE 802.1aq / 802.1Qbp
   networks. The same hierarchical address assignment scheme depicted
   above is proposed for B-MAC addresses as well.

9.2  IEEE 802.1aq / 802.1Qbp B-MAC Advertisement Route

   B-MAC addresses associated with 802.1aq / 802.1Qbp switches are
   advertised using the BGP MAC Advertisement route already defined in
   [E-VPN].

   The encapsulation for the transport of PBB frames over MPLS is
   similar to that of classical Ethernet, albeit with the additional PBB
   header, as shown in the figure below:














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   +------------------+
   | IP/MPLS Header   |
   +------------------+
   | PBB Header       |
   +------------------+
   | Ethernet Header  |
   +------------------+
   | Ethernet Payload |
   +------------------+
   | Ethernet FCS     |
   +------------------+

   Figure 8: PBB over MPLS Encapsulation

9.3 Operation:

   When a MES receives a PBB-encapsulated Ethernet frame from the access
   side, it performs a lookup on the B-MAC destination address to
   identify the next hop. If the lookup yields that the next hop is a
   remote MES, the local MES would then encapsulate the PBB frame in
   MPLS. The label stack comprises of the VPN label (advertised by the
   remote PE), followed by an LSP/IGP label. From that point onwards,
   regular MPLS forwarding is applied.

   On the disposition MES, assuming penultimate-hop-popping is employed,
   the MES receives the MPLS-encapsulated PBB frame with a single label:
   the VPN label. The value of the label indicates to the disposition
   MES that this is a PBB frame, so the label is popped, the TTL field
   (in the 802.1Qbp F-Tag) is reinitialized and normal PBB processing is
   employed from this point onwards.

10.  Solution Advantages

   In this section, we discuss the advantages of the PBB-EVPN solution
   in the context of the requirements set forth in section 3 above.

10.1.  MAC Advertisement Route Scalability

   In PBB-EVPN the number of MAC Advertisement Routes is a function of
   the number of segments (sites), rather than the number of
   hosts/servers. This is because the B-MAC addresses of the MESes,
   rather than C-MAC addresses (of hosts/servers) are being advertised
   in BGP. And, as discussed above, there's a one-to-one mapping between
   multi-homed segments and B-MAC addresses, whereas there's a one-to-
   one or many-to-one mapping between single-homed segments and B-MAC
   addresses for a given MES. As a result, the volume of MAC
   Advertisement Routes in PBB-EVPN is multiple orders of magnitude less
   than E-VPN.



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10.2.  C-MAC Mobility with MAC Sub-netting

   In PBB-EVPN, if a MES allocates its B-MAC addresses from a contiguous
   range, then it can advertise a MAC prefix rather than individual 48-
   bit addresses. It should be noted that B-MAC addresses can easily be
   assigned from a contiguous range because MES nodes are within the
   provider administrative domain; however, CE devices and hosts are
   typically not within the provider administrative domain. The
   advantage of such MAC address sub-netting can be maintained even as
   C-MAC addresses move from one Ethernet segment to another. This is
   because the C-MAC address to B-MAC address association is learnt in
   the data-plane and C-MAC addresses are not advertised in BGP. To
   illustrate how this compares to E-VPN, consider the following
   example:

   If a MES running E-VPN advertises reachability for a MAC subnet that
   spans N addresses via a particular segment, and then 50% of the MAC
   addresses in that subnet move to other segments (e.g. due to virtual
   machine mobility), then in the worst case, N/2 additional MAC
   Advertisement routes need to be sent for the MAC addresses that have
   moved. This defeats the purpose of the sub-netting. With PBB-EVPN, on
   the other hand, the sub-netting applies to the B-MAC addresses which
   are statically associated with MES nodes and are not subject to
   mobility. As C-MAC addresses move from one segment to another, the
   binding of C-MAC to B-MAC addresses is updated via data-plane
   learning.

10.3.  C-MAC Address Learning and Confinement

   In PBB-EVPN, C-MAC address reachability information is built via
   data-plane learning. As such, MES nodes not participating in active
   conversations involving a particular C-MAC address will purge that
   address from their forwarding tables. Furthermore, since C-MAC
   addresses are not distributed in BGP, MES nodes will not maintain any
   record of them in control-plane routing table.

10.4.  Seamless Interworking with TRILL and 802.1aq Access Networks

   Consider the scenario where two access networks, one running MPLS and
   the other running 802.1aq, are interconnected via an MPLS backbone
   network. The figure below shows such an example network.










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                               +--------------+
                               |              |
               +---------+     |     MPLS     |    +---------+
       +----+  |         |   +----+        +----+  |         |  +----+
       | CE |--|         |   |MES1|        |MES2|  |         |--| CE |
       +----+  | 802.1aq |---|    |        |    |--|  MPLS   |  +----+
       +----+  |         |   +----+        +----+  |         |  +----+
       | CE |--|         |     |   Backbone   |    |         |--| CE |
       +----+  +---------+     +--------------+    +---------+  +----+

   Figure 9: Interoperability with 802.1aq

   If the MPLS backbone network employs E-VPN, then the 802.1aq data-
   plane encapsulation must be terminated on MES1 or the edge device
   connecting to MES1. Either way, all the MES nodes that are part of
   the associated service instances will be exposed to all the C-MAC
   addresses of all hosts/servers connected to the access networks.
   However, if the MPLS backbone network employs PBB-EVPN, then the
   802.1aq encapsulation can be extended over the MPLS backbone, thereby
   maintaining C-MAC address transparency on MES1. If PBB-EVPN is also
   extended over the MPLS access network on the right, then C-MAC
   addresses would be transparent to MES2 as well.

   Interoperability with TRILL access network will be described in
   future revision of this draft.

10.5.  Per Site Policy Support

   In PBB-EVPN, a unique B-MAC address can be associated with every site
   (single-homed or multi-homed). Given that the B-MAC addresses are
   sent in BGP MAC Advertisement routes, it is possible to define per
   site (i.e. B-MAC) forwarding policies including policies for E-TREE
   service.

10.6.  Avoiding C-MAC Address Flushing

   With PBB-EVPN, it is possible to avoid C-MAC address flushing upon
   topology change affecting a multi-homed device. To illustrate this,
   consider the example network of Figure 1. Both MES1 and MES2
   advertize the same B-MAC address (BM1) to MES3. MES3 then learns the
   C-MAC addresses of the servers/hosts behind CE1 via data-plane
   learning. If AC1 fails, then MES3 does not need to flush any of the
   C-MAC addresses learnt and associated with BM1. This is because MES1
   will withdraw the MAC Advertisement routes associated with BM1,
   thereby leading MES3 to have a single adjacency (to MES2) for this B-
   MAC address. Therefore, the topology change is communicated to MES3
   and no C-MAC address flushing is required.




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11.  Acknowledgements

   TBD.

12.  Security Considerations

   There are no additional security aspects beyond those of VPLS/H-VPLS
   that need to be discussed here.

13.  IANA Considerations

   This document requires IANA to assign a new SAFI value for L2VPN_MAC
   SAFI.

14.  Intellectual Property Considerations

   This document is being submitted for use in IETF standards
   discussions.

15.  Normative References

   [802.1ah] "Virtual Bridged Local Area Networks Amendment 7: Provider
              Backbone Bridges", IEEE Std. 802.1ah-2008, August 2008.

16.  Informative References

   [PBB-VPLS] Sajassi et al., "VPLS Interoperability with Provider
              Backbone Bridges", draft-ietf-l2vpn-vpls-pbb-interop-
              02.txt, work in progress, July, 2011.

   [EVPN-REQ] Sajassi et al., "Requirements for Ethernet VPN (E-VPN)",
              draft-sajassi-raggarwa-l2vpn-evpn-req-01.txt, work in
              progress, July, 2011.

   [E-VPN] Aggarwal et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
              l2vpn-evpn-00.txt, work in progress, February, 2012.



17.  Authors' Addresses

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





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


   Sami Boutros
   Cisco
   170 West Tasman Drive
   San Jose, CA  95134, US
   Email: sboutros@cisco.com


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


   Aldrin Isaac
   Bloomberg
   Email: aisaac71@bloomberg.net


   Florin Balus
   Alcatel-Lucent
   701 E. Middlefield Road
   Mountain View, CA, USA 94043
   Email: florin.balus@alcatel-lucent.com


   Wim Henderickx
   Alcatel-Lucent
   Email: wim.henderickx@alcatel-lucent.be


   Clarence Filsfils
   Cisco
   Email: cfilsfil@cisco.com


   Dennis Cai
   Cisco
   Email: dcai@cisco.com


   Lizhong Jin
   ZTE Corporation



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   889, Bibo Road
   Shanghai, 201203, China
   Email: lizhong.jin@zte.com.cn
















































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