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Versions: (draft-muks-trill-dci) 00 01 02

INTERNET-DRAFT                                            Mohammed Umair
Intended Status: Informational                  Kingston Smiler Selvaraj
                                                    Shaji Ravindranathan
                                                              IPInfusion
                                                               Lucy Yong
                                                     Donald Eastlake 3rd
                                                     Huawei Technologies
Expires: September 2, 2017                                 March 1, 2017


                 Data Center Interconnect using TRILL
                     <draft-ietf-trill-dci-02.txt>


Abstract

   This document describes a TRILL based Data Center Interconnect (DCI)
   solution. TRILL is used inside a data center for providing intra-data
   center switching optimally by utilizing multiple links. This draft
   described a way to use TRILL to extend a network across different
   data center via MPLS service provider network using Virtual TRILL
   Service/Switch Domain (VTSD) as described in draft [VTSD].

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
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   http://www.ietf.org/shadow.html

Copyright and License Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors. All rights reserved.



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   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  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Date Center Topology . . . . . . . . . . . . . . . . . . . . .  7
   3.  Requirements of DCI Protocol . . . . . . . . . . . . . . . . .  7
     3.1.  Multi-homing with all-active forwarding  . . . . . . . . .  8
     3.2.  Effectively scaling the bandwidth by adding more links . .  8
     3.3.  Auto-discovery of services . . . . . . . . . . . . . . . .  9
     3.4.  Delivering Layer 2 and Layer 3 services over the same
           interface  . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.5.  BUM traffic optimization . . . . . . . . . . . . . . . . .  9
     3.6.  Control plane learning of MAC  . . . . . . . . . . . . . . 10
     3.7.  Virtualisation and isolation of different instances  . . . 10
     3.8.  MAC mass-withdrawal  . . . . . . . . . . . . . . . . . . . 10
     3.9.  Significantly larger Name-Space in the Overlay (16M
           segments)  . . . . . . . . . . . . . . . . . . . . . . . . 10
     3.10.  Extensive OAM Capabilities  . . . . . . . . . . . . . . . 11
     3.11.  Supporting Ring topology in the Core Network  . . . . . . 11
   4.  TRILL DCI Operations . . . . . . . . . . . . . . . . . . . . . 11
     4.1. TRILL data center . . . . . . . . . . . . . . . . . . . . . 12
     4.2. Layer2 data center  . . . . . . . . . . . . . . . . . . . . 12
       4.2.1.  TRILL Access load-balancing  . . . . . . . . . . . . . 13
         4.2.1.1.  Appointed Forwarder Mechanism  . . . . . . . . . . 13
         4.2.1.2.  TRILL Active-Active Access . . . . . . . . . . . . 13
       4.2.2. TRILL Pseudowire load-balancing . . . . . . . . . . . . 14
   5. MPLS encapsulation and Loop free provider PSN/MPLS  . . . . . . 15
   6. Frame Processing  . . . . . . . . . . . . . . . . . . . . . . . 15
     6.1. Frame processing between data center T2 switch and TIR. . . 15
     6.2. Frame processing between TIR's  . . . . . . . . . . . . . . 16
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 17
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20



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1  Introduction

   The IETF Transparent Interconnection of Lots of Links (TRILL)
   protocol [RFC6325] [RFC7177] [RFC7780] provides transparent
   forwarding in multi-hop networks with arbitrary topology and link
   technologies using a header with a hop count and link-state routing.
   TRILL provides optimal pair-wise forwarding without configuration,
   safe forwarding even during periods of temporary loops, and support
   for multipathing of both unicast and multicast traffic. Devices
   implementing TRILL are called Routing Bridges(RBridges)or TRILL
   Switches.

   TRILL is used inside data centers for providing intra-data center
   switching optimally by utilizing multiple links. Though TRILL usually
   runs within a data center, there is a need to interconnect various
   data center sites to provide connectivity across data centers. This
   draft describes a solution to this problem by using VTSD (Virtual
   TRILL Switch Domain) as described in the draft [VTSD].

   The draft [VTSD] introduces a new terminology called VTSD (Virtual
   TRILL Switch Domain) and VPTS (Virtual Private TRILL Service).

   The (Virtual Private TRILL Service) VPTS is a L2 TRILL service, that
   emulates TRILL service across a Wide Area Network (WAN) over MPLS
   PWE3. VPTS is similar to what VPLS does for bridge domain.

   The VTSD [Virtual Trill Switch Domain] is similar to VSI (layer 2
   bridge) in VPLS model, but this acts as a TRILL RBridge. VTSD is a
   superset of VSI and must support all the functionality provided by
   the VSI as defined in [RFC4026]. Along with VSI functionality, the
   VTSD must be capable of supporting TRILL protocols and form TRILL
   adjacency.  The VTSD must be capable of performing all the operations
   that a standard TRILL Switch can do.

   Pseudo Wire Emulation Edge-to-Edge (PWE3) is a mechanism that
   emulates the essential attributes of a service such as Ethernet over
   a Packet Switched Network (PSN).  The required functions of PWs
   include encapsulating service-specific PDUs arriving at an ingress
   port, and carrying them across a path or tunnel, managing their
   timing and order, and any other operations required to emulate the
   behavior and characteristics of the service as faithfully as
   possible.

   The PEs may be connected by an MPLS Label Switched Path (LSP)
   infrastructure, which provides the benefits of MPLS technology.  The
   PEs may also be connected by an IP network, in which case IP/GRE
   (Generic Routing Encapsulation) tunneling or other IP tunneling can
   be used to provide PSN functionality.  The detailed procedures in



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   this document are specified only for MPLS LSPs as PSN.  However,
   these procedures are designed to be extensible to use IP tunnels as
   PSN, which is outside the scope of this document.

1.1  Terminology



      Acronyms used in this document include the following:

            AC                 - Attachment Circuit [RFC4664]


            Access Port        - A TRILL switch port configured with
                                 the "end station service disable" bit
                                 off, as described in
                                 Section 4.9.1 of [RFC6325].
                                 All AC's, VTSD ports
                                 connected to CE's, should configured
                                 as TRILL Access Ports.

            AF                 - Appointed Forwarder [RFC6325]
                                 and [RFC6439bis].

            BUM                - Broadcast, Unknown destination Unicast
                                 and Multicast

            Data Label         - VLAN or FGL

            DCI                - Data Center Interconnect

            ECMP               - Equal Cost Multi Pathing

            FGL                - Fine-Grained Labeling [RFC7172]

            IS-IS              - Intermediate System to Intermediate
                                 System [IS-IS]

            L2                 - Layer 2

            LAN                - Local Area Network

            Link               - The means by which adjacent TRILL
                                 switches or VTSD are connected.
                                 May be a bridged LAN.

            MC-LAG             - Multi-Chassis Link Aggregation




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            MPLS               - Multi-Protocol Label Switching

            PE                 - Provider Edge Device

            PSN                - Packet Switched Network

            PW                 - Pseudowire [RFC4664]

            RBridge            - An alternative name for TRILL Switch

            TIR                - TRILL Intermediate Router
                                (Devices where Pseudowire starts and
                                 Terminates)

            TRILL              - Transparent Interconnection of Lots
                                 of Links OR Tunneled Routing in the
                                 Link Layer [RFC6325]

            TRILL Site         - A part of a TRILL campus that
                                 contains at least one RBridge.

            TRILL switch       - A device implementing the TRILL
                                 protocol. An alternative name
                                 for an RBridge.

            Trunk port         - A TRILL switch port configured with
                                 the "end station service disable"
                                 bit on, as described in
                                 Section 4.9.1 of [RFC6325].
                                 All pseudowires should
                                 be configured as TRILL Trunk port.

            VLAN               - Virtual Local Area Network

            VPLS               - Virtual Private LAN Service

            VPTS               - Virtual Private TRILL Service

            VSI                - Virtual Service Instance [RFC4664]

            VTSI               - Virtual TRILL Service Instance

            VTSD               - Virtual TRILL Switch Domain OR
                                 Virtual TRILL Service Domain
                                 A Virtual RBridge that segregates
                                 one tenant's TRILL database as well
                                 as traffic from the other.




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            VTSD-AP            - A VTSD TRILL Access port can be a
                                 AC or a logical port connected with
                                 CE's. it can be a combination of
                                 physical port and Data Label.
                                 OR just Physical port connected to
                                 CE's


2.  Date Center Topology

   The reference topology used in this document is a 3 tier traditional
   topology.  Although other topologies may be utilized within the data
   center, most of such L2 based data centers may be modeled as a 3 tier
   traditional topology. The reference topology is illustrated in Figure
   1. To keep terminologies simple and uniform, in this document these
   layers will be referred to as the Tier-1, Tier-2 and Tier-3 "tiers",
   and the switches in these layers will be termed as T1SW, T2SW etc.
   For simplicity reasons, the entire data center topology will not be
   mentioned in the further sections. Only the relevant nodes will be
   shown identified by this nomenclature.

                +------+  +------+
                |      |  |      |
                | T1SW1|--| T1SW2|           Tier-1
                |      |  |      |
                +------+  +------+
                  |  |      |  |
        +---------+  |      |  +----------+
        | +-------+--+------+--+-------+  |
        | |       |  |      |  |       |  |
      +----+     +----+    +----+     +----+
      |    |     |    |    |    |     |    |
      |T2SW|-----|T2SW|    |T2SW|-----|T2SW| Tier-2
      |    |     |    |    |    |     |    |
      +----+     +----+    +----+     +----+
         |         |          |         |
         |         |          |         |
         | +-----+ |          | +-----+ |
         +-|T3SW |-+          +-|T3SW |-+    Tier-3
           +-----+              +-----+
            | | |                | | |
        <- Servers ->        <- Servers ->


       Figure 1: Typical data center network topology

3.  Requirements of DCI Protocol




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   This section describes in detail the primary requirements of a data
   center interconnect (DCI) solution.

3.1.  Multi-homing with all-active forwarding

   One of the primary requirements of a data center DCI layer is to
   efficiently use all the links in the network by spreading load across
   them. There are two types of links in the DCI layer. The links that
   provides connectivity to the data center and the links that provides
   connectivity to other data center via backbone network. The DCI layer
   should use both of these link types optimally in an all-active
   forwarding manner. Typically the links towards the data center will
   have multiple connectivity towards the peer for providing redundancy
   in the network.  TRILL supports multiple active parallel links
   between the TRILL RBridges / traditional L2 bridges. For providing
   active load-balance for traffic from layer2 data center TRILL uses
   the Appointed Forwarder mechanism.

   The Appointed forwarder mechanism defined in [RFC6439bis] provides a
   way to actively forward end station traffic by a RBridge, so that
   native traffic in each VLAN is handled by at most one RBridge. By
   default, the DRB (Designated RBridge) on a link is in-charge of
   native traffic for all VLANs on the link.  The DRB may, if it wishes,
   act as Appointed Forwarder for any VLAN and it may appoint other
   RBridges that have ports on the link as Appointed Forwarder for one
   or more VLANs with any one of the mechanism described in
   [RFC6439bis].

   An RBridge on a multi-access link forms adjacency [RFC7177] with
   other RBridges if the VLAN's configured/enabled between them are
   common. For example there are four RBridges attached to multi-access
   link, say RB1, RB2, RB3 and RB4. RB1 and RB2 are configured with
   single VLAN "VLAN 2", whereas RB3 and RB4 are configured with "VLAN
   3". Assume that there are no Native VLAN's present on any of the
   RBridges connected to thw multi-access link. If TRILL Hellos are sent
   with VLAN Tag enabled on the interface, RB3 and RB4 drops the hellos
   of RB1 and RB2 (since they are not configured for VLAN 2). Similarly
   RB1 and RB2 drops the Hellos of RB3 and RB4. This results in RB1 and
   RB2 not forming adjacency with RB3 and RB4. RB1 and RB2 after
   electing DRB and forming adjacency between them, will decide about
   VLAN 2 AF. Similarly RB3 and RB4 decide about the VLAN 3 AF.

3.2.  Effectively scaling the bandwidth by adding more links

   As more and more services are deployed over the cloud, there is a
   clear requirement for easily scaling the bandwidth in the network
   without disturbing the existing running services. One of the ways to
   scale the bandwidth is to add a link (either physical or logical)



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   across the devices which require higher bandwidth rate. The same
   requirement is applicable in the DCI layer for interfaces towards the
   backbone network and towards the data center.

   TRILL protocol itself, by design, inherently takes care of this by
   optimally utilizing multiple links. As PWE3 interface, which provides
   connectivity to different data center is also part of TRILL network,
   it is possible to dynamically scale the bandwidth in the backbone
   network / DCI interface by adding more PWE3 to the VTSD instance.

3.3.  Auto-discovery of services

   Auto-discovery of services is one of the primary requirements of data
   center so DCI services will be provisioned with minimal configuration
   effort. Currently the TRILL protocol doesn't have any mechanism to
   discover peer VTSD / TIR nodes. Addressing this question in TRILL is
   left to a future document.

3.4.  Delivering Layer 2 and Layer 3 services over the same interface

   It is desirable to provide a mechanism to advertise both layer 2 and
   layer 3 forwarding information (Route (IP prefix) in case of L3 and
   MAC in case of L2) to the peer nodes across the data centers. The
   control plane way of distributing the forwarding information provides
   multiple benefits in terms of scale, performance and security.
   [ARP/ND-Optimization] and [RFC7961] provides mechanism to distribute
   both MAC and IP information over TRILL network.

3.5.  BUM traffic optimization

   A key design consideration in a DCI network is handling BUM
   (Broadcast, Unknown Unicast and Multicast) traffic. If the BUM
   packets are handled as in the traditional layer 2 network (by
   forwarding to all the ports which are part of the same broadcast
   domain), this will create excessive overhead in the network. TRILL
   takes care of this issue using the distribution tree and pruning
   mechanism.

   Any unknown unicast, multicast or broadcast frames inside VTSD should
   be processed or forwarded through any one of the distribution tree's
   path. If any multi-destination frame is received from the wrong
   pseudowire at a VTSD, the TRILL protocol running in VTSD should
   perform a RPF check as specified in [RFC7780] and drops the packet.

   Pruning (VLAN (or FGL) and multicast pruning) mechanism of
   Distribution Tree as specified in [RFC6325] and [RFC7780] can also be
   used for forwarding of multi-destination data frames on the branches
   that are not pruned.



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   Also the ARP/ND-proxy and control plane MAC address learning
   mechanism mentioned in Sections 3.4 and 3.6 will help the
   VTSD/RBridges in the network to learn the unicast MAC address from
   ARP/ND packets. This reduces the unknown unicast flow.

3.6.  Control plane learning of MAC

   Learning MAC addresses in the data plane brings the scaling
   limitations of the devices to the DCI layer. Hence the protocol that
   provides DCI should provide control plane learning to overcome the
   data plane learning limitation. Mac address learning through ESADI
   (End Station Address Distribution Information Protocol) is described
   in [RFC7357] and requires no changes to the protocol. However the
   following optional extensions can be provided for controlling the MAC
   learning mechanism.


    a) Way to disable remote MAC Addresses learning through data
    plane and
    b) Control over the number of MAC Addresses to be advertised
    to the remote VTSD's.


   The mechanism to provide these optional extensions is out side the
   scope of this document.

3.7.  Virtualisation and isolation of different instances

   VTSD provides a way to isolate the TRILL link state databases and the
   forwarding information between different TRILL sites.  As VPTS is
   similar to VPLS, the mac address and the nickname learnt on a
   particular VPTS is isolated from other VPTS instance in the system.

3.8.  MAC mass-withdrawal

   It is desirable in the data center to have a mechanism to flush a set
   of MAC addresses from the network, in the event of node failures in
   the network. This Mass MAC-Address withdrawal may also be applicable
   when there is any movement in the End-stations.  Mass MAC-Address
   withdrawal is specified in draft [Address-Flush] and requires no
   changes to the protocol.

3.9.  Significantly larger Name-Space in the Overlay (16M segments)

   Layer2 DCI technologies can be used to provide overlay connectivity
   between Top of Rack switches over an IP underlay. When a DCI protocol
   is used as an overlay, there is a clear requirement to have a larger
   namespace to provide services to different customers. TRILL FGL



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   [RFC7172] provides 2^24 data labels to isolate different TRILL
   services.

3.10.  Extensive OAM Capabilities

   It is desirable to provide extensive OAM support in the data center
   network for fault indication, fault localization, performance
   information and diagnostic functions. TRILL already provides
   extensive support for OAM capabilities as specified in [RFC7174] and
   [RFC7175]. These mechanisms can be used for fault indication,
   localization and performance information.

3.11.  Supporting Ring topology in the Core Network

   In most cases, the backbone network that provides connectivity to the
   data center is deployed as a ring topology to provide fault
   tolerance. It is highly desirable to provide a similar kind of
   service with the DCI protocol. Most of the existing DCI technologies
   like VPLS doesn't provide this support due to split horizon rule
   running inside the backbone network.

   In case of VTSD, as TRILL takes care of forming loop-free topology,
   there is no need to run split horizon in the backbone network. This
   paves the way for traffic to move from one PW to another PW and eases
   the formation of service over ring topology in the core, without
   having any mesh or hub-spoke connections.

4.  TRILL DCI Operations

   The below diagram represents a high level overview of TRILL DCI. In
   the below diagram there are two data centers as DataCenter1 and
   DataCenter2. DataCenter1 has two core routers (which are also part of
   the backbone network) as TIR1 and TIR2. Similarly DataCenter2 has
   only one core router as TIR3. These TIR devices are connected via the
   backbone network using PSN Tunnels. Pseudowires are configured across
   these devices.

   Operations of VTSD is described in draft [VTSD]. There are multiple
   attachment circuit interfaces which are configured from T2SW to TIR1
   and TIR2. The T2SW can be part of Layer2 network (Layer2 data center)
   or TRILL network (TRILL data center).










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            |<-------------- Emulated Service ---------------->|
            |                                                  |
            |          |<------- Pseudo Wire ------>|          |
            |          |                            |          |
            |          |    |<-- PSN Tunnels-->|    |          |
            |          V    V                  V    V          |
            V    AC    +----+                  +----+     AC   V
      +-----+    |     |TIR1|==================|    |     |    +-----+
      |     |----------|....|..PW1..(active)...|....|     |    |     |
      |     |_        _|T1SW|==================|    |     |    |     |
      |     | \      / +----+                  |TIR3|     |    |     |
      |     |  \    /                          |    |     |    |T2SW |
      |     |   \  /                           |    |----------|     |
      |T2SW |    \/                            |    |          |     |
      |     |    /\                            |T1SW|          |     |
      |     |   /  \   +----+                  |    |          +-----+
      |     |_ /    \_ |TIR2|==================|    |
      |     |----------|....|..PW2..(active)...|....|
      +-----+    |     |T1SW|==================|    |
                 AC    +----+                  +----+
      <-----DataCenter1------>                 <-----DataCenter2------>

               Figure 1: Data Center DCI




4.1. TRILL data center

   In this case, the VTSD or TIR will form TRILL adjacencies with other
   VTSDs present in its peer VPTS neighbor, and also with the RBridges
   present in the TRILL sites (here it is T2SW).  As the entire network
   runs the TRILL protocol (from data center1 to data center2), TRILL
   will take care of efficiently using the multiple attachment circuit
   interfaces and PWE3 interfaces. Load balancing of frames between
   Tier-2 switch and VTSD will be taken care by the TRILL protocol
   running inside the RBridges (Tier-2 Switch) and VTSD (Tier-1 Switch)
   as described in draft [VTSD].

4.2. Layer2 data center

   In case of layer2 data center, as Tier-2 switches are Layer-2
   Ethernet switches, an Attachment Circuit should work as a normal
   TRILL Access port. As the data center is not running the TRILL
   protocol, the mechanism to provide active load balancing for
   Attachment Circuits differs from the TRILL data center. The
   subsequent sections describe in detail the operation of TRILL access
   load-balancing in a layer2 data center.



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4.2.1.  TRILL Access load-balancing

   This section describes the mechanism to provide active load balancing
   across Tier1 and Tier2 switch. There are two ways to provide load
   balancing.


 a) Using the Appointed Forwarder mechanism [RFC6439bis]
    (load-balancing based on VLAN), and
 b) Using TRILL Active-Active Access mechanism [RFC7379]
    (similar to MC-LAG solution).


4.2.1.1.  Appointed Forwarder Mechanism

   The Appointed Forwarder mechanism defined in [RFC6439bis] provides a
   way for actively forwarding the traffic by a RBridge, with the intent
   that native traffic in each VLAN be handled by at most one RBridge.
   By default, the DRB (Designated RBridge) on a link is in-charge of
   native traffic for all VLANs on the link.  The DRB may, if it wishes,
   act as Appointed Forwarder for any VLAN and it may appoint other
   RBridges that have ports on the link as Appointed Forwarder for one
   or more VLANs. The DRB may appoint other RBridges on the link with
   any one of the mechanism described in [RFC6439bis]. Based on the type
   of attachment circuit (port-based or VLAN based), the DRB chooses the
   appointed forwarder RBridges/VTSDs, which can distribute the traffic
   based on the VLANs.

4.2.1.1.1. Port-based AC operations.

   In this case, the VTSDs in TIR1 and TIR2 will form TRILL adjacency
   via AC ports. If the attachment circuit port can carry N number of
   end-station service VLANs, then TIR1 and TIR2's VTSDs can equally
   distribute them using AF Mechanism of TRILL.

4.2.1.1.2. VLAN-based AC operations.

   Likewise in Port-based AC, in this case also the VTSDs in TIR1 and
   TIR2 will form TRILL adjacency via AC ports. Since only one VLAN end-
   station service is enabled per VTSD, only one TIR's VTSD can become
   AF for that VLAN. Hence native traffic can be processed by any one of
   the AC.

4.2.1.2.  TRILL Active-Active Access

   TRILL Active-Active Access is specified in [RFC7781], [RFC7379],
   [Centralized-replication], and [RFC7782] . Mechanisms specified in
   these drafts can be utilized effectively to provide TRILL Active-



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   Active Access.

4.2.2. TRILL Pseudowire load-balancing

   TRILL supports multiple parallel adjacencies between neighbor
   RBridges. Appendix C of [RFC6325] and section 3.5 of [RFC7177]
   describes this in detail. Multipathing across such parallel
   connections can be done for unicast TRILL Data traffic on a per-flow
   basis, but is restricted for multi-destination traffic. VTSD should
   also support this functionality.

   TRILL DCI Pseudowires which belong to the same VTSD instance in a TIR
   and connect to same remote TIR are referred to as parallel
   pseudowires. These parallel pseudowires corresponds to a single link
   inside VTSD.

   Here all pseudowires should be capable of carrying traffic.



           |<-------------- Emulated Service ------------------>|
           |                                                    |
           |           |<------- Pseudo Wire ------>|           |
           |           |                            |           |
           |           |     |<-- PSN Tunnels-->|    |          |
           |           V     V                  V    V          |
           V    AC     +-----+        PW1       +-----+   AC    V
     +------+    |     |VTSD1|==================|VTSD1|   |   +-------+
     |      |----------|     |                  |     |-------|       |
     |T2SW  |          | T1SW|==================| T1SW|       | T2SW  |
     |      |          +-----+       PW2        +-----+       |       |
     +------+                                                 +-------+
     <-----DataCenter1------>                   <-----DataCenter2------>

                Figure 2: Parallel pseudowires with TRILL DCI






   In above Figure 2, PW1 and PW2 are parallel pseudowires, as these
   pseudowires belongs to same VTSD and provides a connectivity across
   same TIRs.

   This mechanism provides a way for actively increasing and optimally
   utilizing the bandwidth in the backbone network without affecting the
   existing traffic.



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5. MPLS encapsulation and Loop free provider PSN/MPLS

   TRILL use of MPLS encapsulation over pseudowire is specified in
   [RFC7173], and requires no changes in the frame format.

   TRILL DCI doesn't require a Split Horizon mechanism in the backbone
   PSN network, as TRILL takes care of Loop free topology using
   Distribution Trees. Any multi-destination frame will traverse a
   distribution tree path. All distribution trees are calculated based
   on TRILL base protocol standard [RFC6325] as updated by [RFC7780].

6. Frame Processing

   This section specifies frame processing from data center T2 switch
   and TIR's

6.1. Frame processing between data center T2 switch and TIR.

   In a multi-homed topology, where in a data center switch (T2SW) is
   connected to two TIRs, the AF mechanism described in section 4.2.1.1
   will be used to decide which TIR/VTSD will carry the traffic for a
   particular VLAN. This is applicable to the case wherein the data
   center switch is connected to a PE/TIR device via multiple layer 2
   interfaces to increase the bandwidth.

   As a frame gets ingressed into a TIR (or any one of the TIR, when the
   T2SW switches are connected to multiple TIR's) after passing the AF
   check, the TIR encapsulates the frame with TRILL and MPLS headers and
   forwards the frame on a pseudowire. If parallel pseudowires are
   present, the TRILL protocol running in VTSD will select any one of
   the pseudowires and forward the TRILL Data packet over it. Multi-
   destination packets will be forwarded on a distribution tree's path
   [RFC7780]

   Even if any of the paths or links fails between T2SW switch and TIR's
   or between TIR's, frames can be always be forwarded to any of
   available UP links or paths through other links/pseudowires. This is
   one of the key advantage provided by TRILL DCI mechanism.

   If multiple equal paths are available, TRILL will distribute traffic
   among all the paths.

   Also VTSD doesn't depend on the routing or signaling protocol that is
   running between TIRs, provided there is a PSN tunnel available with
   proper encapsulation mechanism.

   Any multi-destination frames, when ingressed to TIR's, will traverse
   one of the distribution trees, with strong RPF Checks. The Hop count



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   field in TRILL Header will avoid loops or duplication of traffic.

6.2. Frame processing between TIR's

   When a frame arrives from T2SW switch to a VTSD inside TIR, the TRILL
   protocol will forward the frames to the proper pseudowire. When
   multiple paths/pseudowires are available between the TIR's then, the
   shortest path calculated by TRILL protocol will be used. If multiple
   paths are of equal cost, then TRILL protocol will do ECMP load
   spreading. If any multi-destination frame gets received by the VTSD
   through a pseudowire, TRILL will do an RPF check.

   When a frame arrives from peer TIR/VTSD through a pseudowire, the
   MPLS header will be de-capsulated and further action will be taken
   depending on the egress nickname field of TRILL header. If egress
   nickname is the nickname of this VTSD, MAC address table and AF
   lookup will be performed and the frame will be forwarded by
   decapsulating the TRILL header. If egress nickname belongs to some
   other VTSD, frame will be forwarded on a pseudowire connected to that
   VTSD by encapsulating with an MPLS header.































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7.  Security Considerations

   This document does not change the TRILL protocol and thus has minimal
   security effects.

   See [RFC6325] for general TRILL Security Considerations.



8.  IANA Considerations

   This document requires no IANA actions.

   RFC Editor: Please delete this section before publication

9.  References

9.1.  Normative References

   [IS-IS]   "Intermediate system to Intermediate system routeing
              information exchange protocol for use in conjunction with
              the Protocol for providing the Connectionless-mode Network
              Service (ISO 8473)", ISO/IEC 10589:2002, 2002".


   [RFC6325]  Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
              Ghanwani, "Routing Bridges (RBridges): Base Protocol
              Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,
              <http://www.rfc-editor.org/info/rfc6325>.

   [RFC7172]  Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
              D. Dutt, "Transparent Interconnection of Lots of Links
              (TRILL): Fine-Grained Labeling", RFC 7172, DOI
              10.17487/RFC7172, May 2014, <http://www.rfc-
              editor.org/info/rfc7172>.

   [RFC7173]  Yong, L., Eastlake 3rd, D., Aldrin, S., and J. Hudson,
              "Transparent Interconnection of Lots of Links (TRILL)
              Transport Using Pseudowires", RFC 7173, DOI
              10.17487/RFC7173, May 2014, <http://www.rfc-
              editor.org/info/rfc7173>.

   [RFC7174]  Salam, S., Senevirathne, T., Aldrin, S., and D. Eastlake
              3rd, "Transparent Interconnection of Lots of Links (TRILL)
              Operations, Administration, and Maintenance (OAM)
              Framework", RFC 7174, DOI 10.17487/RFC7174, May 2014,
              <http://www.rfc-editor.org/info/rfc7174>.




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   [RFC7175]  Manral, V., Eastlake 3rd, D., Ward, D., and A. Banerjee,
              "Transparent Interconnection of Lots of Links (TRILL):
              Bidirectional Forwarding Detection (BFD) Support",
              RFC 7175, DOI 10.17487/RFC7175, May 2014, <http://www.rfc-
              editor.org/info/rfc7175>.

   [RFC7177]  Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and
              V. Manral, "Transparent Interconnection of Lots of Links
              (TRILL): Adjacency", RFC 7177, DOI 10.17487/RFC7177, May
              2014, <http://www.rfc-editor.org/info/rfc7177>.

   [RFC7780]  Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
              Ghanwani, A., and S. Gupta, "Transparent Interconnection
              of Lots of Links (TRILL): Clarifications, Corrections, and
              Updates", RFC 7780, DOI 10.17487/RFC7780, February 2016,
              <http://www.rfc-editor.org/info/rfc7780>.

   [RFC7781]  Zhai, H., Senevirathne, T., Perlman, R., Zhang, M., and Y.
              Li, "Transparent Interconnection of Lots of Links (TRILL):
              Pseudo-Nickname for Active-Active Access", RFC 7781, DOI
              10.17487/RFC7781, February 2016, <http://www.rfc-
              editor.org/info/rfc7781>.

   [RFC7782]  Zhang, M., Perlman, R., Zhai, H., Durrani, M., and S.
              Gupta, "Transparent Interconnection of Lots of Links
              (TRILL) Active-Active Edge Using Multiple MAC
              Attachments", RFC 7782, DOI 10.17487/RFC7782, February
              2016, <http://www.rfc-editor.org/info/rfc7782>.

   [RFC7961]  Eastlake 3rd, D. and L. Yizhou, "Transparent
              Interconnection of Lots of Links (TRILL): Interface
              Addresses APPsub-TLV", RFC 7961, DOI 10.17487/RFC7961,
              August 2016, <http://www.rfc-editor.org/info/rfc7961>.



   [VTSD]      Umair, M., Smiler, K., Eastlake, D., Yong, L.,
               "TRILL Transparent Transport over MPLS"
               draft-ietf-trill-transport-over-mpls, work in
               progress.


   [RFC6439bis]  Eastlake, D., et al., "TRILL: Appointed Forwarders",
              draft-ietf-trill-rfc6439bis, work in progress.


   [ARP/ND-Optimization]  Li, Y., Eastlake, D., et al., "TRILL: ARP/ND
              Optimization", draft-ietf-trill-arp-optimization, work in



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              progress.


   [Centralized-replication]  Hao, W., Li, Y., et al., "Centralized
              Replication for BUM traffic in active-active edge
              connection", draft-ietf-trill-centralized-replication,
              work in progress.



9.2.  Informative References

   [RFC4026]  Andersson, L. and T. Madsen, "Provider Provisioned Virtual
              Private Network (VPN) Terminology", RFC 4026, DOI
              10.17487/RFC4026, March 2005, <http://www.rfc-
              editor.org/info/rfc4026>.

   [RFC4664]  Andersson, L., Ed., and E. Rosen, Ed., "Framework for
              Layer 2 Virtual Private Networks (L2VPNs)", RFC 4664, DOI
              10.17487/RFC4664, September 2006, <http://www.rfc-
              editor.org/info/rfc4664>.

   [RFC7357]  Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.
              Stokes, "Transparent Interconnection of Lots of Links
              (TRILL): End Station Address Distribution Information
              (ESADI) Protocol", RFC 7357, DOI 10.17487/RFC7357,
              September 2014, <http://www.rfc-editor.org/info/rfc7357>.

   [RFC7379]  Li, Y., Hao, W., Perlman, R., Hudson, J., and H. Zhai,
              "Problem Statement and Goals for Active-Active Connection
              at the Transparent Interconnection of Lots of Links
              (TRILL) Edge", RFC 7379, DOI 10.17487/RFC7379, October
              2014, <http://www.rfc-editor.org/info/rfc7379>.


















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Authors' Addresses


   Mohammed Umair
   IPInfusion
   RMZ Centennial
   Mahadevapura Post
   Bangalore - 560048 India
   EMail: mohammed.umair2@gmail.com


   Kingston Smiler Selvaraj
   IPInfusion
   RMZ Centennial
   Mahadevapura Post
   Bangalore - 560048 India
   EMail: kingstonsmiler@gmail.com


   Shaji Ravindranathan
   IPInfusion
   3965 Freedom Circle, Suite 200
   Santa Clara, CA 95054 USA
   EMail: srnathan2014@gmail.com


   Lucy Yong
   Huawei Technologies
   5340 Legacy Drive
   Plano, TX  75024
   USA
   Phone: +1-469-227-5837
   EMail: lucy.yong@huawei.com


   Donald E. Eastlake 3rd
   Huawei Technologies
   155 Beaver Street
   Milford, MA  01757
   USA
   Phone: +1-508-333-2270
   EMail: d3e3e3@gmail.com









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