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rfc:rfc7623

Internet Engineering Task Force (IETF) A. Sajassi, Ed. Request for Comments: 7623 S. Salam Category: Standards Track Cisco ISSN: 2070-1721 N. Bitar

                                                               Verizon
                                                              A. Isaac
                                                               Juniper
                                                         W. Henderickx
                                                        Alcatel-Lucent
                                                        September 2015
  Provider Backbone Bridging Combined with Ethernet VPN (PBB-EVPN)

Abstract

 This document discusses how Ethernet Provider Backbone Bridging (PBB)
 can be combined with Ethernet VPN (EVPN) in order to reduce the
 number of BGP MAC Advertisement routes by aggregating Customer/Client
 MAC (C-MAC) addresses via Provider Backbone MAC (B-MAC) address,
 provide client MAC address mobility using C-MAC aggregation, 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.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7623.

Sajassi, et al. Standards Track [Page 1] RFC 7623 PBB-EVPN September 2015

Copyright Notice

 Copyright (c) 2015 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
 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.

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................4
 3. Requirements ....................................................4
    3.1. MAC Advertisement Route Scalability ........................5
    3.2. C-MAC Mobility Independent of B-MAC Advertisements .........5
    3.3. C-MAC Address Learning and Confinement .....................5
    3.4. Per-Site Policy Support ....................................6
    3.5. No C-MAC Address Flushing for All-Active Multihoming .......6
 4. Solution Overview ...............................................6
 5. BGP Encoding ....................................................7
    5.1. Ethernet Auto-Discovery Route ..............................7
    5.2. MAC/IP Advertisement Route .................................7
    5.3. Inclusive Multicast Ethernet Tag Route .....................8
    5.4. Ethernet Segment Route .....................................8
    5.5. ESI Label Extended Community ...............................8
    5.6. ES-Import Route Target .....................................9
    5.7. MAC Mobility Extended Community ............................9
    5.8. Default Gateway Extended Community .........................9
 6. Operation .......................................................9
    6.1. MAC Address Distribution over Core .........................9
    6.2. Device Multihoming .........................................9
         6.2.1. Flow-Based Load-Balancing ...........................9
                6.2.1.1. PE B-MAC Address Assignment ...............10
                6.2.1.2. Automating B-MAC Address Assignment .......11
                6.2.1.3. Split Horizon and Designated
                         Forwarder Election ........................12
         6.2.2. Load-Balancing based on I-SID ......................12
                6.2.2.1. PE B-MAC Address Assignment ...............12
                6.2.2.2. Split Horizon and Designated
                         Forwarder Election ........................13
                6.2.2.3. Handling Failure Scenarios ................13

Sajassi, et al. Standards Track [Page 2] RFC 7623 PBB-EVPN September 2015

    6.3. Network Multihoming .......................................14
    6.4. Frame Forwarding ..........................................14
         6.4.1. Unicast ............................................15
         6.4.2. Multicast/Broadcast ................................15
    6.5. MPLS Encapsulation of PBB Frames ..........................16
 7. Minimizing ARP/ND Broadcast ....................................16
 8. Seamless Interworking with IEEE 802.1aq / 802.1Qbp .............17
    8.1. B-MAC Address Assignment ..................................17
    8.2. IEEE 802.1aq / 802.1Qbp B-MAC Address Advertisement .......17
    8.3. Operation: ................................................17
 9. Solution Advantages ............................................18
    9.1. MAC Advertisement Route Scalability .......................18
    9.2. C-MAC Mobility Independent of B-MAC Advertisements ........18
    9.3. C-MAC Address Learning and Confinement ....................19
    9.4. Seamless Interworking with 802.1aq Access Networks ........19
    9.5. Per-Site Policy Support ...................................20
    9.6. No C-MAC Address Flushing for All-Active Multihoming ......20
 10. Security Considerations .......................................20
 11. IANA Considerations ...........................................20
 12. References ....................................................21
    12.1. Normative References .....................................21
    12.2. Informative References ...................................21
 Acknowledgements ..................................................22
 Contributors ......................................................22
 Authors' Addresses ................................................23

1. Introduction

 [RFC7432] introduces a solution for multipoint Layer 2 Virtual
 Private Network (L2VPN) services, with advanced multihoming
 capabilities, using BGP for distributing customer/client MAC address
 reachability information over the core MPLS/IP network.  [PBB]
 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
 [RFC7080].
 In this document, we discuss how PBB can be combined with EVPN in
 order to: reduce the number of BGP MAC Advertisement routes by
 aggregating Customer/Client MAC (C-MAC) addresses via Provider
 Backbone MAC (B-MAC) address, provide client MAC address mobility
 using C-MAC aggregation, 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.

Sajassi, et al. Standards Track [Page 3] RFC 7623 PBB-EVPN September 2015

2. Terminology

 ARP: Address Resolution Protocol
 BEB: Backbone Edge Bridge
 B-MAC: Backbone MAC
 B-VID: Backbone VLAN ID
 CE: Customer Edge
 C-MAC: Customer/Client MAC
 ES: Ethernet Segment
 ESI: Ethernet Segment Identifier
 EVI: EVPN Instance
 EVPN: Ethernet VPN
 I-SID: Service Instance Identifier (24 bits and global within a PBB
        network see [RFC7080])
 LSP: Label Switched Path
 MP2MP: Multipoint to Multipoint
 MP2P: Multipoint to Point
 NA: Neighbor Advertisement
 ND: Neighbor Discovery
 P2MP: Point to Multipoint
 P2P: Point to Point
 PBB: Provider Backbone Bridge
 PE: Provider Edge
 RT: Route Target
 VPLS: Virtual Private LAN Service
 Single-Active Redundancy Mode: When only a single PE, among a group
 of PEs attached to an Ethernet segment, is allowed to forward traffic
 to/from that Ethernet segment, then the Ethernet segment is defined
 to be operating in Single-Active redundancy mode.
 All-Active Redundancy Mode: When all PEs attached to an Ethernet
 segment are allowed to forward traffic to/from that Ethernet segment,
 then the Ethernet segment is defined to be operating in All-Active
 redundancy mode.
 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 BCP 14 [RFC2119].

3. Requirements

 The requirements for PBB-EVPN include all the requirements for EVPN
 that were described in [RFC7209], in addition to the following:

Sajassi, et al. Standards Track [Page 4] RFC 7623 PBB-EVPN September 2015

3.1. MAC Advertisement Route Scalability

 In typical operation, an EVPN PE sends a BGP MAC Advertisement route
 per C-MAC address.  In certain applications, this poses scalability
 challenges, as is the case in data center interconnect (DCI)
 scenarios 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.

3.2. C-MAC Mobility Independent of B-MAC Advertisements

 Certain applications, such as virtual machine mobility, require
 support for fast C-MAC address mobility.  For these applications,
 when using EVPN, the 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 ES to another.  This means MAC address prefixes cannot be used in
 data center applications.
 In order to support C-MAC address mobility, while retaining the
 scalability benefits of MAC summarization, PBB technology is used.
 It defines a B-MAC address space that is independent of the C-MAC
 address space, and aggregates C-MAC addresses via a single B-MAC
 address.

3.3. C-MAC Address Learning and Confinement

 In EVPN, all the PE nodes participating in the same EVPN instance are
 exposed to all the C-MAC addresses learned by any one of these PE
 nodes because a C-MAC learned by one of the PE nodes is advertised in
 BGP to other PE nodes in that EVPN instance.  This is the case even
 if some of the PE nodes for that EVPN 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 PE, the
 device memory is still consumed by keeping record of the C-MAC
 addresses in the routing information base (RIB) table.  In network
 applications with millions of C-MAC addresses, this introduces a non-
 trivial waste of PE resources.  As such, it is required to confine
 the scope of visibility of C-MAC addresses to only those PE nodes
 that are actively involved in forwarding traffic to, or from, these
 addresses.

Sajassi, et al. Standards Track [Page 5] RFC 7623 PBB-EVPN September 2015

3.4. 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 PE nodes in the network
 can forward traffic to, or from, a given site.  Both EVPN and PBB-
 EVPN are capable of providing this granularity of policy control.  In
 the case where the policy needs to be at the granularity of per C-MAC
 address, then the C-MAC address should be learned in the control
 plane (in BGP) per [RFC7432].

3.5. No C-MAC Address Flushing for All-Active Multihoming

 Just as in [RFC7432], it is required to avoid C-MAC address flushing
 upon link, port, or node failure for All-Active multihomed segments.

4. Solution Overview

 The solution involves incorporating IEEE Backbone Edge Bridge (BEB)
 functionality on the EVPN PE nodes similar to PBB-VPLS, where BEB
 functionality is incorporated in the VPLS PE nodes.  The PE 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 EVPN PE, 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|
     +----+\    | PE1| |   IP/MPLS    | | PE3|   +----+
            \   +----+ |   Network    | +----+
             \         |              |
           AC2\ +----+ |              |
               \|    | |              |
                | PE2| |              |
                +----+ |              |
                  /\   +--------------+
                  ||
                  BEB
       <-802.1Q-> <------PBB over MPLS------> <-802.1Q->
                      Figure 1: PBB-EVPN Network

Sajassi, et al. Standards Track [Page 6] RFC 7623 PBB-EVPN September 2015

 The PE nodes perform the following functions:
  1. Learn customer/client MAC addresses (C-MACs) over the attachment

circuits in the data plane, per normal bridge operation.

  1. Learn remote C-MAC to B-MAC bindings in the data plane for traffic

received from the core per the bridging operation described in

    [PBB].
  1. Advertise local B-MAC address reachability information in BGP to

all other PE nodes in the same set of service instances. Note

    that every PE has a set of B-MAC addresses that uniquely
    identifies the device.  B-MAC address assignment is described in
    details in Section 6.2.2.
  1. Build a forwarding table from remote BGP advertisements received

associating remote B-MAC addresses with remote PE IP addresses and

    the associated MPLS label(s).

5. BGP Encoding

 PBB-EVPN leverages the same BGP routes and attributes defined in
 [RFC7432], adapted as described below.

5.1. Ethernet Auto-Discovery Route

 This route and all of its associated modes are not needed in PBB-EVPN
 because PBB encapsulation provides the required level of indirection
 for C-MAC addresses -- i.e., an ES can be represented by a B-MAC
 address for the purpose of data-plane learning/forwarding.
 The receiving PE knows that it need not wait for the receipt of the
 Ethernet A-D (auto-discovery) route for route resolution by means of
 the reserved ESI encoded in the MAC Advertisement route: the ESI
 values of 0 and MAX-ESI indicate that the receiving PE can resolve
 the path without an Ethernet A-D route.

5.2. MAC/IP Advertisement Route

 The EVPN MAC/IP Advertisement route is used to distribute B-MAC
 addresses of the PE nodes instead of the C-MAC addresses of end-
 stations/hosts.  This is because the C-MAC addresses are learned in
 the data plane for traffic arriving from the core.  The MAC
 Advertisement route is encoded as follows:
  1. The MAC address field contains the B-MAC address.
  1. The Ethernet Tag field is set to 0.

Sajassi, et al. Standards Track [Page 7] RFC 7623 PBB-EVPN September 2015

  1. The Ethernet Segment Identifier field must be set to either 0 (for

single-homed segments or multihomed segments with per-I-SID load-

    balancing) or to MAX-ESI (for multihomed segments with per-flow
    load-balancing).  All other values are not permitted.
  1. All other fields are set as defined in [RFC7432].
 This route is tagged with the RT corresponding to its EVI.  This EVI
 is analogous to a B-VID.

5.3. Inclusive Multicast Ethernet Tag Route

 This route is used for multicast pruning per I-SID.  It is used for
 auto-discovery of PEs participating in a given I-SID so that a
 multicast tunnel (MP2P, P2P, P2MP, or MP2MP LSP) can be set up for
 that I-SID.  [RFC7080] uses multicast pruning per I-SID based on
 [MMRP], which is a soft-state protocol.  The advantages of multicast
 pruning using this BGP route over [MMRP] are that a) it scales very
 well for a large number of PEs and b) it works with any type of LSP
 (MP2P, P2P, P2MP, or MP2MP); whereas, [MMRP] only works over P2P
 pseudowires.  The Inclusive Multicast Ethernet Tag route is encoded
 as follows:
  1. The Ethernet Tag field is set with the appropriate I-SID value.
  1. All other fields are set as defined in [RFC7432].
 This route is tagged with an RT.  This RT SHOULD be set to a value
 corresponding to its EVI (which is analogous to a B-VID).  The RT for
 this route MAY also be auto-derived from the corresponding Ethernet
 Tag (I-SID) based on the procedure specified in Section 5.1.2.1 of
 [OVERLAY].

5.4. Ethernet Segment Route

 This route is used for auto-discovery of PEs belonging to a given
 redundancy group (e.g., attached to a given ES) per [RFC7432].

5.5. ESI Label Extended Community

 This extended community is not used in PBB-EVPN.  In [RFC7432], this
 extended community is used along with the Ethernet A-D route to
 advertise an MPLS label for the purpose of split-horizon filtering.
 Since in PBB-EVPN, the split-horizon filtering is performed natively
 using B-MAC source address, there is no need for this extended
 community.

Sajassi, et al. Standards Track [Page 8] RFC 7623 PBB-EVPN September 2015

5.6. ES-Import Route Target

 This RT is used as defined in [RFC7432].

5.7. MAC Mobility Extended Community

 This extended community is defined in [RFC7432] and it is used with a
 MAC route (B-MAC route in case of PBB-EVPN).  The B-MAC route is
 tagged with the RT corresponding to its EVI (which is analogous to a
 B-VID).  When this extended community is used along with a B-MAC
 route in PBB-EVPN, it indicates that all C-MAC addresses associated
 with that B-MAC address across all corresponding I-SIDs must be
 flushed.
 When a PE first advertises a B-MAC, it MAY advertise it with this
 extended community where the sticky/static flag is set to 1 and the
 sequence number is set to zero.  In such cases where the PE wants to
 signal the stickiness of a B-MAC, then when a flush indication is
 needed, the PE advertises the B-MAC along with the MAC Mobility
 extended community where the sticky/static flag remains set and the
 sequence number is incremented.

5.8. Default Gateway Extended Community

 This extended community is not used in PBB-EVPN.

6. Operation

 This section discusses the operation of PBB-EVPN, specifically in
 areas where it differs from [RFC7432].

6.1. MAC Address Distribution over Core

 In PBB-EVPN, host MAC addresses (i.e., C-MAC addresses) need not be
 distributed in BGP.  Rather, every PE independently learns the C-MAC
 addresses in the data plane via normal bridging operation.  Every PE
 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.

6.2. Device Multihoming

6.2.1. Flow-Based Load-Balancing

 This section describes the procedures for supporting device
 multihoming in an All-Active redundancy mode (i.e., flow-based load-
 balancing).

Sajassi, et al. Standards Track [Page 9] RFC 7623 PBB-EVPN September 2015

6.2.1.1. PE B-MAC Address Assignment

 In [PBB], 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 PE nodes must be examined carefully as it has implications on the
 proper operation of multihoming.  In particular, for the scenario
 where a CE is multihomed to a number of PE nodes with All-Active
 redundancy mode, a given C-MAC address would be reachable via
 multiple PE nodes concurrently.  Given that any given remote PE will
 bind the C-MAC address to a single B-MAC address, then the various PE
 nodes connected to the same CE must share the same B-MAC address.
 Otherwise, the MAC address table of the remote PE nodes will keep
 oscillating between the B-MAC addresses of the various PE devices.
 For example, consider the network of Figure 1, and assume that PE1
 has B-MAC address BM1 and PE2 has B-MAC address BM2.  Also, assume
 that both links from CE1 to the PE nodes are part of the same
 Ethernet link aggregation group.  If BM1 is not equal to BM2, the
 consequence is that the MAC address table on PE3 will keep
 oscillating such that the C-MAC address M1 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
 multihomed to the same set of PE nodes, then it is required for all
 the PE 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 PE.
                             +---------+
              +-------+  PE1 | IP/MPLS |
             /               |         |
          CE1                | Network |     PEr
         M1  \               |         |
              +-------+  PE2 |         |
              /-------+      |         |
             /               |         |
          CE2                |         |
        M2   \               |         |
              \              |         |
               +------+  PE3 +---------+
                  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 PE1/PE2 and PE2/PE3,
 respectively.  Assume that BM1 is the B-MAC used for the site

Sajassi, et al. Standards Track [Page 10] RFC 7623 PBB-EVPN September 2015

 corresponding to CE1.  Similarly, BM2 is the B-MAC used for the site
 corresponding to CE2.  On PE1, a single B-MAC address (BM1) is
 required for the site corresponding to CE1.  On PE2, two B-MAC
 addresses (BM1 and BM2) are required, one per site.  Whereas on PE3,
 a single B-MAC address (BM2) is required for the site corresponding
 to CE2.  All three PE nodes would advertise their respective B-MAC
 addresses in BGP using the MAC Advertisement routes defined in
 [RFC7432].  The remote PE, PEr, would learn via BGP that BM1 is
 reachable via PE1 and PE2, whereas BM2 is reachable via both PE2 and
 PE3.  Furthermore, PEr establishes, via the PBB bridge learning
 procedure, that C-MAC M1 is reachable via BM1, and C-MAC M2 is
 reachable via BM2.  As a result, PEr can load-balance traffic
 destined to M1 between PE1 and PE2, as well as traffic destined to M2
 between both PE2 and PE3.  In the case of a failure that causes, for
 example, CE1 to be isolated from PE1, the latter can withdraw the
 route it has advertised for BM1.  This way, PEr would update its path
 list for BM1 and will send all traffic destined to M1 over to PE2
 only.

6.2.1.2. Automating B-MAC Address Assignment

 The PE B-MAC address used for single-homed or Single-Active sites can
 be automatically derived from the hardware (using for example the
 backplane's address and/or PE's reserved MAC pool ).  However, the
 B-MAC address used for All-Active sites must be coordinated among the
 redundancy group members.  To automate the assignment of this latter
 address, the PE can derive this B-MAC address from the MAC address
 portion of the CE's Link Aggregation Control Protocol (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 PE nodes connected to the same All-
 Active CE use the same value for the B-MAC address.
 Note that with this automatic provisioning of the B-MAC address
 associated with All-Active CEs, it is not possible to support the
 uncommon scenario where a CE has multiple link bundles within the
 same LACP session towards the PE 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 PE, either manually or
 automatically (as an outcome of CE auto-discovery), the PE MUST
 transmit a MAC Advertisement route for the B-MAC address with a
 downstream assigned MPLS label that uniquely identifies that address

Sajassi, et al. Standards Track [Page 11] RFC 7623 PBB-EVPN September 2015

 on the advertising PE.  The route is tagged with the RTs of the
 associated EVIs as described above.

6.2.1.3. Split Horizon and Designated Forwarder Election

 [RFC7432] relies on split-horizon filtering for a multi-homed ES,
 where the ES 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, ES 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
 [PBB] 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 filtering beyond what is already defined in
 [PBB].
 The Designated Forwarder (DF) election procedures are defined in
 [RFC7432].

6.2.2. Load-Balancing based on I-SID

 This section describes the procedures for supporting device
 multihoming in a Single-Active redundancy mode with per-I-SID load-
 balancing.

6.2.2.1. PE B-MAC Address Assignment

 In the case where per-I-SID load-balancing is desired among the PE
 nodes in a given redundancy group, multiple unicast B-MAC addresses
 are allocated per multihomed ES: Each PE connected to the multihomed
 segment is assigned a unique B-MAC.  Every PE then advertises its
 B-MAC address using the BGP MAC Advertisement route.  In this mode of
 operation, two B-MAC address-assignment models are possible:
  1. The PE may use a shared B-MAC address for all its single-homed

segments and/or all its multi-homed Single-Active segments (e.g.,

    segments operating in per-I-SID load-balancing mode).
  1. The PE may use a dedicated B-MAC address for each ES operating

with per-I-SID load-balancing mode.

 A PE implementation MAY choose to support either the shared B-MAC
 address model or the dedicated B-MAC address model without causing
 any interoperability issues.  The advantage of the dedicated B-MAC
 over the shared B-MAC address for multi-homed Single-Active segments,
 is that when C-MAC flushing is needed, fewer C-MAC addresses are
 impacted.  Furthermore, it gives the disposition PE the ability to

Sajassi, et al. Standards Track [Page 12] RFC 7623 PBB-EVPN September 2015

 avoid C-MAC destination address lookup even though source C-MAC
 learning is still required in the data plane.  Its disadvantage is
 that there are additional B-MAC advertisements in BGP.
 A remote PE initially floods traffic to a destination C-MAC address,
 located in a given multihomed ES, to all the PE nodes configured with
 that I-SID.  Then, when reply traffic arrives at the remote PE, it
 learns (in the data path) the B-MAC address and associated next-hop
 PE to use for said C-MAC address.

6.2.2.2. 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.

6.2.2.3. Handling Failure Scenarios

 When a PE connected to a multihomed ES loses connectivity to the
 segment, due to link or port failure, it needs to notify the remote
 PEs to trigger C-MAC address flushing.  This can be achieved in one
 of two ways, depending on the B-MAC assignment model:
  1. If the PE uses a shared B-MAC address for multiple Ethernet

segments, then the C-MAC flushing is signaled by means of having

    the failed PE re-advertise the MAC Advertisement route for the
    associated B-MAC, tagged with the MAC Mobility extended community
    attribute.  The value of the Counter field in that attribute must
    be incremented prior to advertisement.  This causes the remote PE
    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.
  1. If the PE uses a dedicated B-MAC address for each ES operating

under per-I-SID load-balancing mode, the failed PE simply

    withdraws the B-MAC route previously advertised for that segment.
    This causes the remote PE 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.
 When a PE connected to a multihomed ES fails (i.e., node failure) or
 when the PE becomes completely isolated from the EVPN network, the
 remote PEs will start purging the MAC Advertisement routes that were
 advertised by the failed PE.  This is done either as an outcome of
 the remote PEs detecting that the BGP session to the failed PE has
 gone down, or by having a Route Reflector withdrawing all the routes
 that were advertised by the failed PE.  The remote PEs, in this case,

Sajassi, et al. Standards Track [Page 13] RFC 7623 PBB-EVPN September 2015

 will perform C-MAC address flushing as an outcome of the MAC
 Advertisement route withdrawals.
 For all failure scenarios (link/port failure, node failure, and PE
 node isolation), when the fault condition clears, the recovered PE
 re-advertises the associated ES route to other members of its
 redundancy group.  This triggers the backup PE(s) in the redundancy
 group to block the I-SIDs for which the recovered PE is a DF.  When a
 backup PE blocks the I-SIDs, it triggers a C-MAC address flush
 notification to the remote PEs by re-advertising the MAC
 Advertisement route for the associated B-MAC, with the MAC Mobility
 extended community attribute.  The value of the Counter field in that
 attribute must be incremented prior to advertisement.  This causes
 the remote PE 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/re-advertised MAC route.

6.3. Network Multihoming

 When an Ethernet network is multihomed to a set of PE nodes running
 PBB-EVPN, Single-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 PE 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 just like a Single-Active multihomed device
 scenario (but unlike an All-Active multihomed device scenario where
 DF filtering is limited to multi-destination frames in the core-to-
 access direction).  Similar to a Single-Active multihomed device
 scenario, with load-balancing based on I-SID, a unique B-MAC address
 is assigned to each of the PE nodes connected to the multihomed
 network (segment).

6.4. Frame Forwarding

 The frame-forwarding functions are divided in between the Bridge
 Module, which hosts the [PBB] 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.

Sajassi, et al. Standards Track [Page 14] RFC 7623 PBB-EVPN September 2015

6.4.1. Unicast

 Known unicast traffic received from the Attachment Circuit (AC) will
 be PBB-encapsulated by the PE 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 an EVPN label associated with the B-MAC
 destination address.  If per flow load-balancing over ECMPs in the
 MPLS core is required, then a flow label is added below the label
 associated with the B-MAC address in the label stack.
 For unknown unicast traffic, the PE forwards these frames over the
 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.

6.4.2. Multicast/Broadcast

 Multi-destination frames received from the AC will be PBB-
 encapsulated by the PE 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 [PBB].  The
 resulting frame is then forwarded over the MPLS core using one of the
 following two options:
 Option 1: the MPLS Forwarder can perform ingress replication over a
    set of MP2P or P2P tunnel LSPs.  The frame is encapsulated with a
    tunnel LSP label and the EVPN ingress replication label advertised
    in the Inclusive Multicast Ethernet Tag [RFC7432].
 Option 2: the MPLS Forwarder can use P2MP tunnel LSP per the
    procedures defined in [RFC7432].  This includes either the use of
    Inclusive or Aggregate Inclusive trees.  Furthermore, the MPLS
    Forwarder can use MP2MP tunnel LSP if Inclusive trees are used.
 Note that the same procedures for advertising and handling the
 Inclusive Multicast Ethernet Tag defined in [RFC7432] apply here.

Sajassi, et al. Standards Track [Page 15] RFC 7623 PBB-EVPN September 2015

6.5. MPLS Encapsulation of PBB Frames

 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:
                         +------------------+
                         | IP/MPLS Header   |
                         +------------------+
                         | PBB Header       |
                         +------------------+
                         | Ethernet Header  |
                         +------------------+
                         | Ethernet Payload |
                         +------------------+
                         | Ethernet FCS     |
                         +------------------+
                 Figure 3: PBB over MPLS Encapsulation

7. Minimizing ARP/ND Broadcast

 The PE nodes MAY implement an ARP/ND-proxy function in order to
 minimize the volume of ARP/ND traffic that is broadcasted over the
 MPLS network.  In case of ARP proxy, this is achieved by having each
 PE node snoop on ARP request and response messages received over the
 access interfaces or the MPLS core.  The PE builds a cache of IP/MAC
 address bindings from these snooped messages.  The PE then uses this
 cache to respond to ARP requests ingress on access ports and target
 hosts that are in remote sites.  If the PE 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 P2MP LSPs.  In case of ND proxy, this is achieved
 similar to the above but with ND/NA messages per [RFC4389].

Sajassi, et al. Standards Track [Page 16] RFC 7623 PBB-EVPN September 2015

8. Seamless Interworking with IEEE 802.1aq / 802.1Qbp

                         +--------------+
                         |              |
         +---------+     |     MPLS     |    +---------+
 +----+  |         |   +----+        +----+  |         |  +----+
 |SW1 |--|         |   | PE1|        | PE2|  |         |--| 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 4: Interconnecting 802.1aq / 802.1Qbp Networks with PBB-EVPN

8.1. B-MAC Address Assignment

 The B-MAC addresses need to be globally unique across all networks
 including PBB-EVPN and IEEE 802.1aq / 802.1Qbp networks.  The B-MAC
 addresses used for single-homed and Single-Active Ethernet segments
 should be unique because they are typically auto-derived from the
 PE's pools of reserved MAC addresses that are unique.  The B-MAC
 addresses used for All-Active Ethernet segments should also be unique
 given that each network operator typically has its own assigned
 Organizationally Unique Identifier (OUI) and thus can assign its own
 unique MAC addresses.

8.2. IEEE 802.1aq / 802.1Qbp B-MAC Address Advertisement

 B-MAC addresses associated with 802.1aq / 802.1Qbp switches are
 advertised using the EVPN MAC/IP route advertisement already defined
 in [RFC7432].

8.3. Operation:

 When a PE 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 PE, the local PE would then encapsulate the PBB frame in MPLS.
 The label stack comprises of the VPN label (advertised by the remote

Sajassi, et al. Standards Track [Page 17] RFC 7623 PBB-EVPN September 2015

 PE), followed by an LSP/IGP label.  From that point onwards, regular
 MPLS forwarding is applied.
 On the disposition PE, assuming penultimate-hop-popping is employed,
 the PE receives the MPLS-encapsulated PBB frame with a single label:
 the VPN label.  The value of the label indicates to the disposition
 PE 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.

9. 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.

9.1. MAC Advertisement Route Scalability

 In PBB-EVPN, the number of MAC Advertisement routes is a function of
 the number of Ethernet segments (e.g., sites) rather than the number
 of hosts/servers.  This is because the B-MAC addresses of the PEs,
 rather than C-MAC addresses (of hosts/servers), are being advertised
 in BGP.  As discussed above, there's a one-to-one mapping between
 All-Active multihomed segments and their associated B-MAC addresses;
 there can be either a one-to-one or many-to-one mapping between
 Single-Active multihomed segments and their associated B-MAC
 addresses; and finally there is a many-to-one mapping between single-
 home sites and their associated B-MAC addresses on a given PE.  This
 means a single B-MAC is associated with one or more segments where
 each segment can be associated with many C-MAC addresses.  As a
 result, the volume of MAC Advertisement routes in PBB-EVPN may be
 multiple orders of magnitude less than EVPN.

9.2. C-MAC Mobility Independent of B-MAC Advertisements

 As described above, in PBB-EVPN, a single B-MAC address can aggregate
 many C-MAC addresses.  Given that B-MAC addresses are associated with
 segments attached to a PE or to the PE itself, their locations are
 fixed and thus not impacted what so ever by C-MAC mobility.
 Therefore, C-MAC mobility does not affect B-MAC addresses (e.g., any
 re-advertisements of them).  This is because the association of C-MAC
 address to B-MAC address is learned in the data-plane and C-MAC
 addresses are not advertised in BGP.  Aggregation via B-MAC addresses
 in PBB-EVPN performs much better than EVPN.

Sajassi, et al. Standards Track [Page 18] RFC 7623 PBB-EVPN September 2015

 To illustrate how this compares to EVPN, consider the following
 example:
    If a PE running EVPN advertises reachability for N MAC addresses
    via a particular segment, and then 50% of the MAC addresses in
    that segment move to other segments (e.g., due to virtual machine
    mobility), then N/2 additional MAC Advertisement routes need to be
    sent for the MAC addresses that have moved.  With PBB-EVPN, on the
    other hand, the B-MAC addresses that are statically associated
    with PE nodes 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 in PBB-EVPN.

9.3. C-MAC Address Learning and Confinement

 In PBB-EVPN, C-MAC address reachability information is built via
 data-plane learning.  As such, PE 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, PE nodes will not maintain any
 record of them in the control-plane routing table.

9.4. Seamless Interworking with 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.
                             +--------------+
                             |              |
             +---------+     |     MPLS     |    +---------+
     +----+  |         |   +----+        +----+  |         |  +----+
     | CE |--|         |   | PE1|        | PE2|  |         |--| CE |
     +----+  | 802.1aq |---|    |        |    |--|  MPLS   |  +----+
     +----+  |         |   +----+        +----+  |         |  +----+
     | CE |--|         |     |   Backbone   |    |         |--| CE |
     +----+  +---------+     +--------------+    +---------+  +----+
                Figure 5: Interoperability with 802.1aq
 If the MPLS backbone network employs EVPN, then the 802.1aq data-
 plane encapsulation must be terminated on PE1 or the edge device
 connecting to PE1.  Either way, all the PE 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 PE1.  If PBB-EVPN is also

Sajassi, et al. Standards Track [Page 19] RFC 7623 PBB-EVPN September 2015

 extended over the MPLS access network on the right, then C-MAC
 addresses would be transparent to PE2 as well.

9.5. Per-Site Policy Support

 In PBB-EVPN, the per-site policy can be supported via B-MAC addresses
 via assigning a unique B-MAC address for every site/segment
 (typically multihomed but can also be single-homed).  Given that the
 B-MAC addresses are sent in BGP MAC/IP route advertisement, it is
 possible to define per-site (i.e., B-MAC) forwarding policies
 including policies for E-TREE service.

9.6. No C-MAC Address Flushing for All-Active Multihoming

 Just as in [RFC7432], with PBB-EVPN, it is possible to avoid C-MAC
 address flushing upon topology change affecting an All-Active
 multihomed segment.  To illustrate this, consider the example network
 of Figure 1.  Both PE1 and PE2 advertise the same B-MAC address (BM1)
 to PE3.  PE3 then learns the C-MAC addresses of the servers/hosts
 behind CE1 via data-plane learning.  If AC1 fails, then PE3 does not
 need to flush any of the C-MAC addresses learned and associated with
 BM1.  This is because PE1 will withdraw the MAC Advertisement routes
 associated with BM1, thereby leading PE3 to have a single adjacency
 (to PE2) for this B-MAC address.  Therefore, the topology change is
 communicated to PE3 and no C-MAC address flushing is required.

10. Security Considerations

 All the security considerations in [RFC7432] apply directly to this
 document because this document leverages the control plane described
 in [RFC7432] and their associated procedures -- although not the
 complete set but rather a subset.
 This document does not introduce any new security considerations
 beyond that of [RFC7432] and [RFC4761] because advertisements and
 processing of B-MAC addresses follow that of [RFC7432] and processing
 of C-MAC addresses follow that of [RFC4761] -- i.e, B-MAC addresses
 are learned in the control plane and C-MAC addresses are learned in
 data plane.

11. IANA Considerations

 There are no additional IANA considerations for PBB-EVPN beyond what
 is already described in [RFC7432].

Sajassi, et al. Standards Track [Page 20] RFC 7623 PBB-EVPN September 2015

12. References

12.1. Normative References

 [PBB]      IEEE, "IEEE Standard for Local and metropolitan area
            networks - Media Access Control (MAC) Bridges and Virtual
            Bridged Local Area Networks", Clauses 25 and 26, IEEE Std
            802.1Q, DOI 10.1109/IEEESTD.2011.6009146.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC7432]  Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
            Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
            Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
            2015, <http://www.rfc-editor.org/info/rfc7432>.

12.2. Informative References

 [MMRP]     IEEE, "IEEE Standard for Local and metropolitan area
            networks - Media Access Control (MAC) Bridges and Virtual
            Bridged Local Area Networks", Clause 10, IEEE Std 802.1Q,
            DOI 10.1109/IEEESTD.2011.6009146.
 [OVERLAY]  Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Isaac, A.,
            Uttaro, J., Henderickx, W., Shekhar, R., Salam, S., Patel,
            K., Rao, D., and S. Thoria, "A Network Virtualization
            Overlay Solution using EVPN",
            draft-ietf-bess-evpn-overlay-01, February 2015.
 [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
            Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
            2006, <http://www.rfc-editor.org/info/rfc4389>.
 [RFC4761]  Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private
            LAN Service (VPLS) Using BGP for Auto-Discovery and
            Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
            <http://www.rfc-editor.org/info/rfc4761>.
 [RFC7080]  Sajassi, A., Salam, S., Bitar, N., and F. Balus, "Virtual
            Private LAN Service (VPLS) Interoperability with Provider
            Backbone Bridges", RFC 7080, DOI 10.17487/RFC7080,
            December 2013, <http://www.rfc-editor.org/info/rfc7080>.

Sajassi, et al. Standards Track [Page 21] RFC 7623 PBB-EVPN September 2015

 [RFC7209]  Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N.,
            Henderickx, W., and A. Isaac, "Requirements for Ethernet
            VPN (EVPN)", RFC 7209, DOI 10.17487/RFC7209, May 2014,
            <http://www.rfc-editor.org/info/rfc7209>.

Acknowledgements

 The authors would like to thank Jose Liste and Patrice Brissette for
 their reviews and comments of this document.  We would also like to
 thank Giles Heron for several rounds of reviews and providing
 valuable inputs to get this document ready for IESG submission.

Contributors

 In addition to the authors listed, the following individuals also
 contributed to this document.
 Lizhong Jin, ZTE
 Sami Boutros, Cisco
 Dennis Cai, Cisco
 Keyur Patel, Cisco
 Sam Aldrin, Huawei
 Himanshu Shah, Ciena
 Jorge Rabadan, ALU

Sajassi, et al. Standards Track [Page 22] RFC 7623 PBB-EVPN September 2015

Authors' Addresses

 Ali Sajassi, editor
 Cisco
 170 West Tasman Drive
 San Jose, CA  95134
 United States
 Email: sajassi@cisco.com
 Samer Salam
 Cisco
 595 Burrard Street, Suite # 2123
 Vancouver, BC V7X 1J1
 Canada
 Email: ssalam@cisco.com
 Nabil Bitar
 Verizon Communications
 Email: nabil.n.bitar@verizon.com
 Aldrin Isaac
 Juniper
 Email: aisaac@juniper.net
 Wim Henderickx
 Alcatel-Lucent
 Email: wim.henderickx@alcatel-lucent.com

Sajassi, et al. Standards Track [Page 23]

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