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Versions: 00 01

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

                                                            Aldrin Issac
                                                               Bloomberg

                                                             Nabil Bitar
                                                                 Verizon

                                                              Sam Aldrin
                                                                  Huawei

Expires: April 10, 2014                                 October 10, 2013


                              TRILL-EVPN
                     draft-ietf-l2vpn-trill-evpn-01

Status of this Memo

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Copyright and License 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
   Provisions Relating to IETF Documents



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   (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 VPN (E-VPN) technology is used
   to interconnect TRILL [TRILL] networks over an MPLS/IP network, with
   two key characteristics: C-MAC address transparency on the hand-off
   point and control-plane isolation among the interconnected TRILL
   networks.

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. C-MAC Address Transparency on the Hand-off Point  . . . . .  4
     4.2. Control Plane Isolation among TRILL Networks  . . . . . . .  5
   5.  Solution Overview  . . . . . . . . . . . . . . . . . . . . . .  5
     5.1. TRILL Nickname Assignment . . . . . . . . . . . . . . . . .  6
     5.2.  TRILL Nickname Advertisement Route . . . . . . . . . . . .  7
     5.3. Frame Format  . . . . . . . . . . . . . . . . . . . . . . .  7
     5.4.  Unicast Forwarding . . . . . . . . . . . . . . . . . . . .  8
     5.5. Handling Multicast  . . . . . . . . . . . . . . . . . . . .  9
       5.5.1. Multicast Stitching with Per-Source Load Balancing  . . 10
       5.5.2. Multicast Stitching with Per-VLAN Load Balancing  . . . 10
       5.5.3. Multicast Stitching with Per-Flow Load Balancing  . . . 11
       5.5.4. Multicast Stitching with Per-Tree Load Balancing  . . . 11
   6.  OAM Considerations . . . . . . . . . . . . . . . . . . . . . . 12
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   10.  Intellectual Property Considerations  . . . . . . . . . . . . 12
   11.  Normative References  . . . . . . . . . . . . . . . . . . . . 12
   12.  Informative References  . . . . . . . . . . . . . . . . . . . 13



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   13.  Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . 13


















































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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. [TRILL] defines a solution for optimal forwarding of
   Ethernet frames with support for multipathing of unicast and
   multicast traffic, using IS-IS control-plane and associated tunneling
   encapsulation that includes a hop count. In this document, we discuss
   how Ethernet VPN (E-VPN) technology can be used to interconnect TRILL
   [TRILL] networks over an MPLS/IP network, while guaranteeing two key
   characteristics: C-MAC address transparency on the hand-off point and
   control-plane isolation among the interconnected TRILL networks. The
   resulting solution is referred to as TRILL-EVPN.

2.  Contributors

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

   Keyur Patel Cisco
   Tissa Senevirathne Cisco


3.  Terminology


   CE: Customer Edge
   C-MAC: Customer/Client MAC Address
   DHD: Dual-homed Device
   DHN: Dual-homed Network
   E-VPN: Ethernet VPN
   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
   TRILL: Transparent Interconnect of Lots of Links

4.  Requirements

4.1. C-MAC Address Transparency on the Hand-off Point

   [TRILL] addresses the problem of MAC address table scalability on



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   intermediate switching devices by introducing a tunneling technology
   and confining C-MAC address learning/forwarding to the edge of the
   TRILL network. When TRILL networks are interconnected over an MPLS/IP
   network, it is required to maintain C-MAC address transparency on the
   hand-off point and the edge (i.e. MES) of the MPLS network.
   Otherwise, the MPLS edge nodes may suffer from MAC address table
   space exhaustion given that they would need to learn the C-MAC
   addresses from all interconnected TRILL networks.

   TRILL-EVPN supports seamless interconnect with TRILL while
   guaranteeing C-MAC address transparency on the MES nodes.

4.2. Control Plane Isolation among TRILL Networks

   It is required to maintain control-plane isolation among the various
   TRILL networks being interconnected over the MPLS/IP network. This
   ensures the following characteristics:

   - scalability of the IS-IS control plane in large deployments. In
   TRILL, all nodes must calculate the shared multicast trees, so as the
   number of interconnected cloud networks scales, this places a burden
   on the RBridges, especially if roots are to be located in every site
   to ensure optimality of the data-path.

   - fault domain localization, where link or node failures in one site
   do not trigger SPF re-computations in remote sites.

   Interconnect solutions which extend the IS-IS control-plane over the
   MPLS network, as an overlay, do not meet this requirement. TRILL-EVPN
   provides control-plane isolation between interconnected TRILL
   networks by terminating the TRILL IS-IS at the MPLS edge nodes.

5.  Solution Overview

   TRILL-EVPN enables seamless connectivity of TRILL networks over an
   MPLS/IP core while ensuring control-plane separation among these
   networks, and maintaining C-MAC address transparency on the MES
   nodes.

   Every TRILL network that is connected to the MPLS core runs an
   independent instance of the IS-IS control-plane. Each MES
   participates in the TRILL IS-IS control plane of its local site. The
   MES peers, in IS-IS protocol, with the RBridges internal to the site,
   but does not terminate the TRILL data-plane encapsulation. So, from a
   control-plane viewpoint, the MES appears as an edge RBridge; whereas,
   from a data-plane viewpoint, the MES appears as a core RBridge to the
   TRILL network. The MES nodes encapsulate TRILL frames with MPLS in
   the imposition path, and de-capsulate them in the disposition path.



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                           +--------------+
                           |              |
           +---------+     |     MPLS     |    +---------+
   +----+  |         |   +----+        +----+  |         |  +----+
   |RB1 |--|         |   |MES1|        |MES2|  |         |--| RB3|
   +----+  |  TRILL  |---|    |        |    |--|  TRILL  |  +----+
   +----+  |         |   +----+        +----+  |         |  +----+
   |RB2 |--|         |     |   Backbone   |    |         |--| RB4|
   +----+  +---------+     +--------------+    +---------+  +----+

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


   |<-------------------------  TRILL -------------------------->|  DP
                           |<----MPLS----->|

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

   Figure 1: Interconnecting TRILL Networks with TRILL-EVPN

5.1. TRILL Nickname Assignment

   In TRILL, edge RBridges build forwarding tables that associate remote
   C-MAC addresses with remote edge RBridge nicknames via data-path
   learning (except if the optional ESADI function is in use). When
   different TRILL networks are interconnected over an MPLS/IP network
   using a seamless hand-off, the edge RBridges (corresponding to the
   ingress and egress RBridges of particular traffic flows) may very
   well reside in different TRILL networks. Therefore, in order to
   guarantee correct connectivity, the TRILL Nicknames must be globally
   unique across all the interconnected TRILL islands in a given EVI.
   This can be achieved, for instance, by using a hierarchical Nickname
   assignment paradigm, and encoding a Site ID in the high-order bits of
   the Nickname:

   Nickname = [Site ID : Rbridge ID ]

   The Site ID uniquely identifies a TRILL network, whereas the RBridge
   ID portion of the Nickname has local significance to a TRILL site,
   and can be reused in different sites to designate different RBridges.
   However, the fully qualified Nickname is globally unique in the
   entire domain of interconnected TRILL networks for a given EVI.

   It is worth noting here that this hierarchical Nickname encoding
   scheme guarantees that Nickname collisions do not occur between
   different TRILL islands. Therefore, there is no need to define TRILL
   Nickname collision detection/resolution mechanisms to operate across



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   separate TRILL islands interconnected via TRILL-EVPN.

   Another point to note is that there are proposals to achieve per-site
   Nickname significance; however, these proposals either require C-MAC
   learning on the border RBridge (i.e. violate the C-MAC address
   transparency requirement), or require a completely new encapsulation
   and associated data-path for TRILL [TRILL-MULTILEVEL].

5.2.  TRILL Nickname Advertisement Route

   A new BGP route is defined to support the interconnection of TRILL
   networks over TRILL-EVPN: the TRILL Nickname Advertisement' route,
   encoded as follows:

   +---------------------------------------+
   | RD (8 octets)                         |
   +---------------------------------------+
   |Ethernet Segment Identifier (10 octets)|
   +---------------------------------------+
   | Ethernet Tag ID (4 octets)            |
   +---------------------------------------+
   | Nickname Length (1 octet)             |
   +---------------------------------------+
   | RBridge Nickname (2 octets)           |
   +---------------------------------------+
   | MPLS Label (1 octet)                  |
   +---------------------------------------+

   Figure 2: TRILL Nickname Advertisement Route

   The MES uses this route to advertise the reachability of TRILL
   RBridge nicknames to other MES nodes in the EVI. The MPLS label
   advertised in this route is allocated on a per EVI basis and serves
   the purpose of identifying to the disposition MES that the MPLS-
   encapsulated packet holds an MPLS encapsulated TRILL frame.

5.3. Frame Format

   The encapsulation for the transport of TRILL frames over MPLS is
   encoded as shown in the figure below:











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

   Figure 3: TRILL over MPLS Encapsulation

   It is worth noting here that while it is possible to transport
   Ethernet encapsulated TRILL frames over MPLS, that approach
   unnecessarily wastes 16 bytes per packet. That approach further
   requires either the use of well-known MAC addresses or having the MES
   nodes advertise in BGP their device MAC addresses, in order to
   resolve the TRILL next-hop L2 adjacency. To that end, it is simpler
   and more efficient to transport TRILL natively over MPLS, and this is
   the reason why a new BGP route for TRILL Nickname advertisement is
   defined.

5.4.  Unicast Forwarding

   Every MES advertises in BGP the Nicknames of all RBridges local to
   its site in the TRILL Nickname Advertisement routes. Furthermore, the
   MES advertises in IS-IS, to the local island, the Rbridge nicknames
   of all remote switches in all the other TRILL islands that the MES
   has learned via BGP. This is required since TRILL [RFC6325] currently
   does not define the concept of default routes. However, if the
   concept of default routes is added to TRILL, then the MES can
   advertise itself as a border RBridge, and all the other Rbridges in
   the TRILL network would install a default route pointing to the MES.
   The default route would be used for all unknown destination
   Nicknames. This eliminates the need to redistribute Nicknames learnt
   via BGP into TRILL IS-IS.

   Note that by having multiple MES nodes (connected to the same TRILL
   island) advertise routes to the same RBridge nickname, with equal BGP
   Local_Pref attribute, it is possible to perform active/active load-
   balancing to/from the MPLS core.

   When a MES receives an Ethernet-encapsulated TRILL frame from the
   access side, it removes the Ethernet encapsulation (i.e. outer MAC
   header), and performs a lookup on the egress RBridge nickname in the
   TRILL header to identify the next-hop. If the lookup yields that the



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   next hop is a remote MES, the local MES would then encapsulate the
   TRILL frame with appropriate MPLS label stack. The label stack
   comprises of the VPN label (advertised by the remote MES), 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 TRILL frame with a single
   label: the VPN label. The value of the label indicates to the
   disposition MES that this is a TRILL packet, so the label is popped,
   the TTL field (in the TRILL header) is reinitialized and normal TRILL
   processing is employed from this point onwards.

5.5. Handling Multicast

   Each TRILL network independently builds its shared multicast trees.
   The number of these trees need not match in the different
   interconnected TRILL islands. In the MPLS/IP network, multiple
   options are available for the delivery of multicast traffic:

   - Ingress replication
   - LSM with Inclusive trees
   - LSM with Aggregate Inclusive trees
   - LSM with Selective trees
   - LSM with Aggregate Selective trees

   When LSM is used, the trees may be either P2MP or MP2MP.

   The MES nodes are responsible for stitching the TRILL multicast
   trees, on the access side, to the ingress replication tunnels or LSM
   trees in the MPLS/IP core. The stitching must ensure that the
   following characteristics are maintained at all times:

   1. Avoiding Packet Duplication: In the case where the TRILL network
   is multi-homed to multiple MES nodes, if all of the MES nodes forward
   the same multicast frame, then packet duplication would arise. This
   applies to both multicast traffic from site to core as well as from
   core to site.

   2. Avoiding Forwarding Loops: In the case of TRILL network multi-
   homing, the solution must ensure that a multicast frame forwarded by
   a given MES to the MPLS core is not forwarded back by another MES (in
   the same TRILL network) to the TRILL network of origin. The same
   applies for traffic in the core to site direction.

   3. Pacifying TRILL RPF Checks: For multicast traffic originating from
   a different TRILL network, the RPF checks must be performed against
   the disposition MES (i.e. the MES on which the traffic ingress into



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   the destination TRILL network).

   There are two approaches by which the above operation can be
   guaranteed: one offers per-source load-balancing while the other
   offers per-flow load-balancing.

5.5.1. Multicast Stitching with Per-Source Load Balancing

   The MES nodes, connected to a multi-homed TRILL network, perform BGP
   DF election to decide which MES is responsible for forwarding
   multicast traffic from a given source RBridge. An MES would only
   forward multicast traffic from source RBridges for which it is the
   DF, in both the site to core as well as core to site directions. This
   solves both the issue of avoiding packet duplication as well as the
   issue of avoiding forwarding loops.

   In addition, the MES node advertises in IS-IS the nicknames of remote
   RBridges, learnt in BGP, for which it is the elected DF. This allows
   all RBridges in the local TRILL network to build the correct RPF
   state for these remote RBridge nicknames. Note that this results in
   all unicast traffic to a given remote RBridge being forwarded to the
   DF MES only (i.e. load-balancing of unicast traffic would not be
   possible in the site to core direction).

   Alternatively, all MES nodes in a redundancy group can advertise the
   nicknames of all remote RBridges learnt in BGP. In addition, each MES
   advertises the Affinity sub-TLV, defined in [TRILL-CMT], on behalf of
   each of the remote RBridges for which it is the elected DF. This
   ensures that the RPF check state is set up correctly in the TRILL
   network, while allowing load-balancing of unicast traffic among the
   MES nodes.

   In this approach, all MES nodes in a given redundancy group can
   forward and receive traffic on all TRILL trees.

5.5.2. Multicast Stitching with Per-VLAN Load Balancing

   The MES nodes, connected to a multi-homed TRILL network, perform BGP
   DF election to decide which MES node is responsible for forwarding
   multicast traffic associated with a given VLAN. An MES would forward
   multicast traffic for a given VLAN only when it is the DF for this
   VLAN. This forwarding rule applies in both the site to core as well
   as core to site directions.

   In addition, the MES nodes in the redundancy group partition among
   themselves the set of TRILL multicast trees so that each MES only
   sends traffic on a unique set of trees. This can be done using the RP
   Election Protocol as discussed in [TRILL-MULTILEVEL]. Alternatively,



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   the BGP DF election could be used for that. Each MES, then,
   advertises to the local TRILL network a Default Affinity sub-TLV, per
   [TRILL-MULTILEVEL], listing the trees that it will be using for
   multicast traffic originating from remote RBridges.

   In this approach, each MES node in given TRILL network receives
   traffic from all TRILL trees but forwards traffic on only a dedicated
   subset of trees. Hence, the TRILL network must have at least as many
   multicast trees as the number of directly attached MES nodes.

5.5.3. Multicast Stitching with Per-Flow Load Balancing

   This approach is similar to the per-VLAN load-balancing approach
   described above, with the difference being that the MES nodes perform
   the BGP DF election on a per-flow basis. The flow is identified by an
   N-Tuple comprising of Layer 2 and Layer 3 addresses in addition to
   Layer 4 ports. This can be done by treating the N-Tuple as a numeric
   value, and performing, for e.g., a modulo hash function against the
   number of PEs in the redundancy group in order to identify the index
   of the PE that is the DF for a given N-Tuple.

   In this approach, each MES node in given TRILL network receives
   traffic from all TRILL trees but forwards traffic on only a dedicated
   subset of trees. Hence, the TRILL network must have at least as many
   multicast trees as the number of directly attached MES nodes.

5.5.4. Multicast Stitching with Per-Tree Load Balancing

   The MES nodes, connected to a multi-homed TRILL network, perform BGP
   DF election to decide which MES node is responsible for forwarding
   multicast traffic associated with a given TRILL multicast tree. An
   MES would forward multicast traffic with a given destination RBridge
   nickname only when it is the DF for this nickname. This forwarding
   rule applies in both the site to core as well as core to site
   directions. The outcome of the BGP DF election is then used to drive
   TRILL IS-IS advertisements: the MES advertises to the local TRILL
   network a Default Affinity sub-TLV, per [TRILL-MULTILEVEL], listing
   the trees for which it is the elected DF.

   Note that on the egress MES, the destination RBridge Nickname in
   multicast frames identifies the multicast tree of the remote TRILL
   network from which the frame originated. If the TRILL tree
   identifiers are not coordinated between sites, then the egress
   Nickname has no meaning in the directly attached (destination) TRILL
   network. So, the MES needs to select a new tree (after the MPLS
   disposition) based on a hash function, and rewrite the frame with
   this new destination Nickname before forwarding the traffic. This may
   be necessary in certain deployments to ensure complete decoupling



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   between the TRILL sites connected to the MPLS core. On the other
   hand, if the TRILL tree identifiers are coordinated between sites,
   then the MES doesn't have to rewrite the destination nickname in the
   TRILL header, after the MPLS disposition.

   In this approach, each MES node in a given redundancy group forwards
   and receives traffic on a disjoint set of TRILL trees. At a minimum,
   the TRILL network must have as many multicast trees as the number of
   directly attached MES nodes.

6.  OAM Considerations

   When TRILL networks are interconnected over MPLS networks, the IS-IS
   control plane is not extended across the MPLS network. As described
   in earlier sections, this will provide advantage in scaling the TRILL
   networks without any issues when changes happen within different
   TRILL networks.

   TRILL OAM could be performed in TRILL networks, within the framework
   defined in [TRILL-OAM-FWRK]. When TRILL networks are interconnected,
   TRILL OAM frames just like TRILL data frames are transparently sent
   over the MPLS network. There are no changes required to perform TRILL
   OAM operations. MPLS OAM operations could be performed as defined in
   [MPLS-OAM] to ensure the working of MPLS network interconnecting the
   TRILL networks.


7.  Acknowledgements

   The authors would like to thank Sami Boutros and Dennis Cai for their
   valuable comments.

8.  Security Considerations

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

9.  IANA Considerations

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

10.  Intellectual Property Considerations

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

11.  Normative References



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   [TRILL] Perlman et al., "Routing Bridges (RBridges): Base Protocol
              Specification", RFC 6325, July, 2011.

12.  Informative References


   [EVPN-REQ] Sajassi et al., "Requirements for Ethernet VPN (E-VPN)",
              draft-ietf-l2vpn-evpn-req-04.txt, work in progress, July,
              2013.

   [E-VPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
              l2vpn-evpn-04.txt, work in progress, July, 2013.

   [TRILL-CMT] Senevirathne et al., "Coordinated Multicast Trees for
              TRILL", draft-tissa-trill-cmt-01.txt, work in progress,
              January 2012.

   [TRILL-MULTILEVEL] Senevirathne et al., "Default Nickname Based
              Approach for Multilevel TRILL", draft-tissa-trill-
              multilevel-02.txt, work in progress, February 2012.

    [TRILL-OAM-FWRK] Salam et al., "TRILL OAM Framework", draft-ietf-
   trill-oam-framework-03, September, 2013.

    [MPLS-OAM] Kompella & Swallow, "Detecting MPLS Data Plane Failures",
   RFC 4379, February, 2006.

13.  Authors' Addresses

   Ali Sajassi
   Cisco
   Email: sajassi@cisco.com


   Samer Salam
   Cisco
   Email: ssalam@cisco.com


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


   Aldrin Isaac
   Bloomberg
   Email: aisaac71@bloomberg.net




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   Sam Aldrin
   Huawei
   Email: sam.aldrin@gmail.com
















































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