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Versions: (draft-hao-trill-irb) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 RFC 7956

TRILL Working Group                                              W. Hao
INTERNET-DRAFT                                                    Y. Li
Intended Status: Standard Track                                  Huawei
                                                                  A. Qu
                                                               MediaTec
                                                             M. Durrani
                                                                  Cisco
                                                         P. Sivamurugan
                                                            IP Infusion
Expires: January 4, 2017                                   July 4, 2016



                     TRILL Distributed Layer 3 Gateway
                        draft-ietf-trill-irb-14.txt

Abstract

   The base TRILL (Transparent Interconnection of Lots of Links)
   protocol provides optimal pair-wise data frame forwarding for layer
   2 intra-subnet traffic but not for layer 3 inter-subnet traffic. A
   centralized gateway solution is typically used for layer 3 inter-
   subnet traffic forwarding but has the following issues:

         1. Sub-optimum forwarding paths for inter-subnet traffic.

         2. A centralized gateway may need to support a very large
   number of gateway interfaces in a data center, one per tenant per
   data label used by that tenant, to provide interconnect
   functionality for all the layer 2 virtual networks in a TRILL campus.

         3. A traffic bottleneck at the gateway.

   This document specifies an optional TRILL distributed gateway
   solution that resolves these centralized gateway issues.

Status of this Memo

   This Internet-Draft is submitted 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."



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   The list of current Internet-Drafts can be accessed at
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Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors. All rights reserved.

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   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
      1.1. Document Organization................................... 3
   2. Conventions used in this document............................ 4
   3. Simplified Example and Problem Statement..................... 5
      3.1. Simplified Example...................................... 6
      3.2. Problem Statement Summary............................... 8
   4. Layer 3 Traffic Forwarding Model............................. 9
   5. Distributed Gateway Solution Details......................... 9
      5.1. Local Routing Information .............................. 10
      5.2. Local Routing Information Synchronization .............. 11
      5.3. Active-active Access ................................... 14
      5.4. Data Traffic Forwarding Process ........................ 14
   6. Distributed Layer 3 Gateway Process Example ................. 15
      6.1. Control plane process .................................. 16
      6.2. Data Plane Process ..................................... 17
   7. TRILL Protocol Extensions ................................... 18
      7.1. The Tenant Label and Gateway MAC APPsub-TLV ............ 19
      7.2. "SE" Flag in NickFlags APPsub-TLV ...................... 20
      7.3. The IPv4 Prefix APPsub-TLV ............................. 20
      7.4. The IPv6 Prefix APPsub-TLV ............................. 21


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   8. Security Considerations ..................................... 22
   9. Management Considerations ................................... 22
   10. IANA Considerations ........................................ 23
   11. Normative References ....................................... 23
   12. Informative References ..................................... 24
   Acknowledgments  ............................................... 25
   Authors' Addresses  ............................................ 25

1. Introduction

   The TRILL (Transparent Interconnection of Lots of Links) protocol
   [RFC6325] provides a solution for least cost transparent routing in
   multi-hop networks with arbitrary topologies and link technologies,
   using [IS-IS] [RFC7176] link-state routing and a hop count. TRILL
   switches are sometimes called RBridges (Routing Bridges).

   The base TRILL protocol provides optimal unicast forwarding for
   Layer 2 intra-subnet traffic but not for Layer 3 inter-subnet
   traffic, where subnet means different IP address prefix and
   typically a different Data Label (VLAN or FGL (Fine Grained Label)).
   In this document, a TRILL-based distributed Layer 3 gateway solution
   is specified that provides optimal unicast forwarding for Layer 3
   inter-subnet traffic. With distributed gateway support, an edge
   RBridge provides both routing based on Layer 2 identity (address and
   virtual network (VN, i.e., Data Label)) among end stations (ESs)
   that belong to same subnet and also provides routing based on Layer
   3 identity among ESs that belong to different subnets of the same
   routing domain. An edge RBridge supporting this feature needs to
   provide routing instances and Layer 3 gateway interfaces for locally
   connected ESs. Such routing instances provide IP address isolation
   between tenants. In the TRILL distributed Layer 3 gateway solution,
   inter-subnet traffic can be fully spread over edge RBridges, so
   there is no single bottleneck.

1.1. Document Organization

   This document is organized as follows: Section 3 gives a simplified
   example and also a more detailed problem statement. Section 4 gives
   the Layer 3 traffic forwarding model. Section 5 provides a
   distributed gateway solution overview. Section 6 gives a detailed
   distributed gateway solution example. And Section 7 describes the
   TRILL protocol extensions needed to support this distributed gateway
   solution.






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2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

   The terms and acronyms in [RFC6325] are used with the following
   additions:

         AGG: Aggregation switch.

         ARP: Address Resolution Protocol [RFC826].

         Campus: The name for a network using the TRILL protocol in the
   same sense that a ''bridged LAN'' is the name for a network using
   bridging. In TRILL, the word ''campus'' has no academic implication.

         COR: Core switch.

         Data Label: VLAN or FGL [RFC7172].

         DC: Data Center.

         Edge RBridge: An RBridges that connects to one or more End
   Stations without any intervening RBridges.

         FGL: Fine Grained Label [RFC7172].

         ES: End Station. A VM (Virtual Machine) or physical server,
   whose address is either the destination or source of a data frame.

         Gateway interface: A Layer 3 virtual interface that terminates
   layer 2 forwarding and forwards IP traffic to the destination using
   IP forwarding rules. Incoming traffic from a physical port on a
   gateway will be distributed to its virtual gateway interface based
   on Data Label (VLAN or FGL).

         Inner.MacDA: The inner MAC destination address in a TRILL Data
   packet [RFC6325].

         Inner.MacSA: The inner MAC source address in a TRILL Data
   packet [RFC6325].

         Inner.VLAN: The inner VLAN tag in a TRILL Data packet payload
   [RFC6325].

         L2: Layer 2.


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         L3: IP Layer 3.

         ND: IPv6's Neighbor Discovery [RFC4861].

         ToR: Top of Rack.

         VN: Virtual Network. In a TRILL campus, a unique 12-bit VLAN
   ID or a 24-bit Fine Grained Label [RFC7172] identifies each virtual
   network.

         VRF: Virtual Routing and Forwarding. In IP-based computer
   networks, Virtual Routing and Forwarding (VRF) technology supports
   multiple instances of routing tables existing within the same router
   at the same time.

3. Simplified Example and Problem Statement

   There is normally a Data Label (VLAN or FGL) associated with each IP
   subnet. For traffic within a subnet, that is IP traffic to another
   end station in the same Data Label attached to the TRILL campus, the
   end station just ARPs for the MAC address of the destination end
   station's IP. It then uses this MAC address for traffic to that
   destination. TRILL routes the ingressed TRILL data packets to the
   destination's edge RBridge based on the egress nickname for that
   destination MAC address and Data Label. This is the regular TRILL
   base protocol [RFC6325] process.

   If two end stations of the same tenant are on different subnets and
   need to communicate with each other, their packets are typically
   forwarded to an IP Layer 3 gateway that performs L3 routing and, if
   necessary, changes the Data Label. Either a centralized layer 3
   gateway solution or the distributed layer 3 gateway solution
   specified in this document can be used for the inter-subnet traffic
   forwarding.

   Section 3.1 gives a simplified example in a TRILL campus with and
   without a distributed layer 3 gateway using VLAN Data Labels.
   Section 3.2 gives the detailed description of the problem without a
   distributed layer 3 gateway. The remainder of this document,
   particularly Section 5, describes the distributed gateway solution
   in detail.








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3.1. Simplified Example
                  -------                --------
                  | COR1|                | COR2 |
                  -------                --------
                     |                      |
                  -------                -------
                  |AGG1 |                |AGG2 |
                  -------                -------
                     |                      |
       -----------------------------------------------------
       |  -------------|------------------|----------------|
       |  |            |  |               |  |          |  |
     -------          -------           -------        -------
     | RB1 |          | RB2 |           | RB3 |        | RB4 |
     |TOR1 |          |TOR2 |           |TOR3 |        |TOR4 |
     -------          -------           -------        -------
      |    |           |    |            |    |         |    |
   -----  -----     -----  -----      -----  -----   -----  -----
   |ES1|  |ES2|     |ES3|  |ES4|      |ES5|  |ES6|   |ES7|  |ES8|
   -----  -----     -----  -----      -----  -----   -----  -----
                       Figure 1. A Typical TRILL DC Network

   Figure 1 depicts a TRILL Data Center Network where Top of Rack (ToR)
   switches are edge RBridges and the aggregation (AGG) and core (COR)
   switches are non-edge RBridges. ES1 to ES8 belong to one tenant
   network and the tenant has four subnets with each subnet
   corresponding to one VLAN (which indicates one individual layer 2
   virtual network). Each ES's IP address, VLAN and subnet are listed
   below:

   +----+----------------+-----------------+----------+
   | ES |   IP Address   |    Subnet       |  VLAN    |
   +----+----------------+-----------------+----------+
   | ES1| 192.0.2.2      | 192.0.2.0/24    |   10     |
   +----+----------------+-----------------+----------+
   | ES2| 198.51.100.2   | 198.51.100.0/24 |   11     |
   +----+----------------+-----------------+----------+
   | ES3| 192.0.2.3      | 192.0.2.0/24    |   10     |
   +----+----------------+-----------------+----------+
   | ES4| 198.51.100.3   | 198.51.100.0/24 |   11     |
   +----+----------------+-----------------+----------+
   | ES5| 203.0.113.2    | 203.0.113.0/25  |   12     |
   +----+----------------+-----------------+----------+
   | ES6| 203.0.113.130  | 203.0.113.128/25|   13     |
   +----+----------------+-----------------+----------+
   | ES7| 203.0.113.3    | 203.0.113.0/25  |   12     |
   +----+----------------+-----------------+----------+
   | ES8| 203.0.113.131  | 203.0.113.128/25|   13     |
   +----+----------------+-----------------+----------+




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   Assume a centralized gateway solution is used with both COR1 and
   COR2 acting as centralized gateways for redundancy in figure 1. COR1
   and COR2 each have four gateway interfaces for the four subnets in
   the tenant. In centralized layer 3 gateway solution, all traffic
   within the tenant between different VLANs must go through the
   centralized layer 3 gateway device of COR1 or COR2, even if the
   traffic is between two end stations connected to the same edge
   RBridge, because only the layer 3 gateway can change the VLAN
   labeling of the traffic.

   This is generally sub-optimal because the two end stations may be
   connected to the same ToR where L3 switching could have been
   performed locally. For example, in above Figure 1, the unicast IP
   traffic between ES1 and ES2 has to go through a centralized gateway
   of COR1 or COR2. It can't be locally routed between them on TOR1.
   However, if an edge RBridge has the distributed gateway capabilities
   specified in this document, then it can still perform optimum L2
   forwarding for intra-subnet traffic and, in addition, optimum L3
   forwarding for inter-subnet traffic, thus delivering optimum
   forwarding for unicast packets in all important cases.

   With a distributed layer 3 gateway, each edge RBridge acts as a
   default layer 3 gateway for local connecting ESs and has IP router
   capabilities to direct IP communications to other edge RBridges.
   Each edge RBridge only needs gateway interfaces for local connecting
   ESs, i.e., RB1 and RB2 need gateway interfaces only for VLAN 10 and
   VLAN 11 while RB3 and RB4 need gateway interfaces only for VLAN 12
   and VLAN 13. No device needs to maintain gateway interfaces for all
   VLANs in entire network. This will enhance the scalability in terms
   of number of tenants and subnets per tenant.

   When each end station ARPs for their layer 3 gateway, that is, their
   IP router, the edge RBridge to which it is connected will respond
   with that RBridge's 'gateway MAC'. When the end station later sends
   IP traffic to the layer 3 gateway, which it does if the destination
   IP is outside of its subnet, the edge RBridge intercepts the IP
   packet because the destination MAC is its gateway MAC. That RBridge
   routes the IP packet using the routing instance associated with that
   tenant, handling it in one of three ways:

            (1) ES1 communicates with ES2. The destination IP is
   connected to the same edge RBridge, the RBridge of TOR1 can simply
   transmit the IP packet out the right edge port in the destination
   VLAN.

            (2) If the destination IP is located in an outside network,
   the edge RBridge encapsulates it as a TRILL Data packet and sends it


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   to the actual TRILL campus edge RBridge connecting to an external IP
   router.

            (3) ES1 communicates with ES4. The destination end station
   is connected to a different edge RBridge, the ingress RBridge TOR1
   uses TRILL encapsulation to route the IP packet to the correct
   egress RBridge TOR2, using the egress RBridge's gateway MAC and an
   Inner.VLAN identifying the tenant. Finally, the egress RBridge
   terminates the TRILL encapsulation and routes the IP packet to the
   destination end station based on the routing instance for that
   tenant.



3.2. Problem Statement Summary

   With Fine Grained Labeling [RFC7172], in theory, up to 16 million
   Layer 2 VN can be supported in a TRILL campus. To support inter-
   subnet traffic, a very large number of Layer 3 gateway interfaces
   could be needed on a centralized gateway, if each VN corresponds to
   a subnet and there are many tenant with many subnets per tenant. It
   is a big burden for the centralized gateway to support so many
   interfaces. In addition all inter-subnet traffic will go through a
   centralized gateway that may become the traffic bottleneck.

   The centralized gateway has the following issues:

            1. Sub-optimum forwarding paths for inter-subnet traffic
   due to the requirements to perform IP routing and possibly change
   Data Labels at a centralized gateway.

            2. The centralized gateway may need to support a very large
   number of gateway interfaces, in a data center one per tenant per
   data label used by that tenant, to provide interconnect
   functionality for all the layer 2 virtual networks in the TRILL
   campus.

            3. There may be a traffic bottleneck at the centralized
   gateway.

   A distributed gateway on edge RBridges addresses these issues.
   Through the distributed layer 3 gateway solution, the inter-subnet
   traffic is fully dispersed and is transmitted along optimal pair-
   wise forwarding paths, improving network efficiency.





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4. Layer 3 Traffic Forwarding Model

   +---------------------------------------------+
   |                                             |
   |      +-----------+         +-----------+    |
   |      | Tenant n  |---------|  VRF n    |    |
   |   +------------+ |     +------------+  |    |
   |   |  +-----+   | |     |            |  |    |
   |   |  | VN1 |   | |     |            |  |    |
   |   |  +-----+   | |     |    VRF 1   |  |    |
   |   |     ..     +-------+            |  |    |
   |   |  +-----+   | |     |            |  |    |
   |   |  | VNm |   | |     |            |  |    |
   |   |  +-----+   | |     |            |  |    |
   |   |  Tenant 1  |-+     |            |  |    |
   |   +------------+       |            |  |    |
   |   +------------+       +------------+       |
   |                                             |
   |               Edge RBridge                  |
   +---------------------------------------------+

   Figure 2. Edge RBridge Model as Distributed Gateway

   In a data center network, each tenant has one or more Layer 2
   virtual networks and, in normal cases, each tenant corresponds to
   one routing domain. Normally each Layer 2 virtual network uses a
   different Data Label and corresponds to one or more IP subnets.

   Each Layer 2 virtual network in a TRILL campus is identified by a
   unique 12-bit VLAN ID or 24-bit Fine Grained Label [RFC7172].
   Different routing domains may have overlapping address space but
   need distinct and separate routes. The end stations that belong to
   the same subnet communicate through L2 forwarding, end stations of
   the same tenant that belong to different subnets communicate through
   L3 routing.

   Figure 2 depicts the model where there are n VRFs corresponding to n
   tenants with each tenant having up to m segments/subnets (virtual
   network).

5. Distributed Gateway Solution Details

   With the TRILL distributed gateway solution, an edge RBridge
   continues to perform routing based on the Layer 2 MAC address for
   the ESs that are on the same subnet but performs IP routing for the
   ESs that are on the different subnets of the same tenant.

   As the IP address space in different routing domains can overlap,
   VRF instances need to be created on each edge RBridge to isolate the


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   IP forwarding process for different routing domains present on the
   edge RBridge. A tenant ID unique across the TRILL campus identifies
   each routing domain. The network operator MUST configure the tenant
   IDs on each edge RBridge for each routing domain consistently so
   that the same ID always refers to the same tenant. Otherwise data
   might be delivered to the wrong tenant. If a routing domain spreads
   over multiple edge RBridges, routing information for the routing
   domain is synchronized among these edge RBridges through the link
   state database to ensure reachability to all ESs in that routing
   domain. The routing information is, in effect, labeled with the
   Tenant ID to differentiate the routing domains.

   From the data plane perspective, all edge RBridges are connected to
   each other via one or more TRILL hops, however they are always just
   a single IP hop away. When an ingress RBridge receives inter-subnet
   IP traffic from a local ES whose destination MAC is the edge
   RBridge's gateway MAC, that RBridge will perform Ethernet header
   termination. The tenant involved is determined by the VLAN of the
   traffic and the port on which it arrives. The edge RBridge looks up
   in its IP routing table for that tenant how to route the traffic to
   the IP next hop. If the destination ES is connected to a remote edge
   RBridge, the remote RBridge will be the IP next hop for traffic
   forwarding. For such inter-subnet traffic, the ingress RBridge will
   rewrite the original Ethernet header with the ingress RBridge's
   gateway MAC address as the Inner.MacSA and the egress RBridge's
   gateway MAC address as the Inner.MacDA and then perform TRILL
   encapsulation to the remote RBridge's nickname setting the inner
   Data Label to indicate the tenant involved. TRILL then routes it to
   the remote edge RBridge through the TRILL campus.

   When that remote edge RBridge receives the traffic, it will
   decapsulate the TRILL data packet and see that the inner destination
   MAC is its gateway MAC.  It then terminates the inner Ethernet
   encapsulation and looks up the destination IP in the RBridge's IP
   forwarding table for the tenant indicated by the inner Data Label to
   route it to the destination ES.

   Through this method, TRILL with distributed gateways provides
   optimum pair-wise data routing for inter-subnet traffic.

5.1. Local Routing Information

   An ES can be locally connected to an edge RBridges through a layer 2
   network (such as a point-to-point Ethernet link or a bridged LAN) or
   externally connected through a layer 3 IP network.




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   If the ES is connected to an edge RBridge through a Layer 2 network,
   then the edge RBridge acts as a Layer 3 Gateway for the ES. A
   gateway interface is established on the edge RBridge for the
   connecting ES. Because the ESs in a subnet may be spread over
   multiple edge RBridges, in each of these edge RBridges which
   establishes its gateway interface for the subnet the edge RBridges
   SHOULD share the same gateway MAC and gateway IP address
   configuration. Sharing the configuration and insuring configuration
   consistency can be done by local configuration and netconf/Yang
   models.

   With distributed gateway, the edge RBridge to which an end station
   is connected appears to be the local IP router on its link. As in
   any IP network, before the end station starts to send inter-subnet
   traffic, it acquires its gateway's MAC through the ARP/ND process.
   Local connecting edge RBridges that support this distributed gateway
   feature always respond with the gateway MAC address when receiving
   ARP/ND requests for the gateway IP. Through the ARP/ND process, the
   edge RBridge can learn the IP and MAC correspondence of a local ES
   connected to the edge RBridge by Layer 2 and then generate local IP
   routing entries for that ES in the corresponding routing domain.

   An IP router connected to an edge RBridge looks to TRILL like an ES.
   If a router/ES is located in an external IP network, normally it
   provides access to one or more IP prefixes. The router/ES SHOULD run
   an IP routing protocol with the connecting TRILL edge RBridge. The
   edge RBridge will learn the IP prefixes behind the router/ES through
   that IP routing protocol, then the RBridge will generate local IP
   routing entries in the corresponding routing domain. If such a
   routing protocol is not run with the edge RBridge, then only the IP
   prefixes behind the router/ES that are explicitly configured on the
   edge RBridge will be accessible.

5.2. Local Routing Information Synchronization

   When a routing instance is created on an edge RBridge, the tenant ID,
   tenant Data Label (VLAN or FGL), tenant gateway MAC that correspond
   to that instance are configured and MUST be globally advertised (see
   Section 7.1). The Tenant ID uniquely identifies that tenant
   throughout the campus. The tenant Data Label identifies that tenant
   at the edge RBridge. The tenant gateway MAC MAY identify that tenant
   or all tenants or some subset of tenants at the edge RBridge.

   When an ingress RBridge performs inter-subnet traffic TRILL
   encapsulation, the ingress RBridge uses the Data Label advertised by
   the egress RBridge as the inner VLAN or FGL and uses the tenant
   gateway MAC advertised by the egress RBridge as the Inner.MacDA. The


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   egress RBridge relies on this tenant Data Label to find the local
   VRF instance for the IP forwarding process when receiving inter-
   subnet traffic from the TRILL campus. (The role of tenant Data Label
   is akin to an MPLS VPN Label in an MPLS IP/MPLS VPN network.) Tenant
   Data Labels are independently allocated on each edge RBridge for
   each routing domain. An edge RBridge can use an access Data Label
   from a routing domain to act as the inter-subnet Data Label, or the
   edge RBridge can use a Data Label different from any access Data
   Labels to be a tenant Data Label. It is implementation dependent and
   there is no restriction on this assignment of Data Labels.

   The tenant gateway MAC differentiates inter-subnet Layer 3 traffic
   from intra-subnet Layer 2 traffic on the egress RBridge. Each tenant
   on a RBridge can use a different gateway MAC or same tenant gateway
   MAC for inter-subnet traffic purposes. This is also implementation
   dependent and there is no restriction on it.

   When a local IP prefix is learned in a routing instance on an edge
   RBridge, the edge RBridge should advertise the IP prefix information
   for the routing instance so that other edge RBridges will generate
   IP routing entries. If the ESs in a VN are spread over multiple
   RBridges, these RBridges MUST advertise each local connecting end
   station's IP address in the VN to other RBridges. If the ESs in a VN
   are only connected to one edge RBridge, that RBridge only needs to
   advertise the subnet corresponding to the VN to other RBridges using
   host routes. A tenant ID unique across the TRILL campus is also
   carried in the advertisement to differentiate IP prefixes between
   different tenants, because the IP address space of different tenants
   can overlap (see Sections 7.3 and 7.4).

   If a tenant is deleted on an edge RBridge RB1, RB1 updates the local
   tenant Data Label, tenant gateway MAC, and related IP prefixes
   information it is advertising to include only the rest of the
   tenants. It may take some time for the updating to reach all other
   RBridges, so during this period of time there may be transient route
   inconsistency among the edge RBridges. If there is traffic in flight
   during this time, it will be dropped at the egress RBridge due to
   local tenant deletion. When a stable state is reached, the traffic
   to the deleted tenant will be dropped by the ingress RBridge.
   Therefore the transient routes consistency won't cause issues other
   than wasting some network bandwidth.

   If there is a new tenant which is created and a previously used tenant
   Data Label is assigned to the new tenant immediately, it may cause a
   security policy violation for the traffic in flight, because when
   the egress RBridge receives traffic from the old tenant, it will
   forward it in the new tenant's routing instance and deliver it to


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   the wrong destination. So a tenant Data Label MUST NOT be re-
   allocated until a reasonable amount of time, for example twice the
   IS-IS Holding Time generally in use in the TRILL campus, has passed
   to allow any traffic in flight to be discarded.

   When the ARP entry in an edge RBridge for an ES times out, it will
   trigger an edge RBridge LSP advertisement to other edge RBridges
   with the corresponding IP routing entry deleted. If the ES is an IP
   router, the edge RBridge also notifies other edge RBridges that they
   must delete the routing entries corresponding to the IP prefixes
   accessible through that IP router. During the IP prefix deleting
   process, if there is traffic in flight, the traffic will be
   discarded at the egress RBridge because there is no local IP routing
   entry to the destination.

   If an edge RBridge changes its tenant gateway MAC, it will trigger
   an edge RBridge LSP advertisement to other edge RBridges giving the
   new gateway MAC to be used as Inner.MacDA for future traffic
   destined to the edge RBridge. During the gateway MAC changing
   process, if there is traffic in flight using the old gateway MAC as
   Inner.MacDA, the traffic will be discarded or be forwarded as layer
   2 intra-subnet traffic on the edge RBridge. If the inter-subnet
   tenant Data Label is a unique Data Label that is different from any
   access Data Labels, when the edge RBridge receives the traffic whose
   Inner.MacDA is different from local tenant gateway MAC, the traffic
   will be discarded. If the edge RBridge uses one of the access Data
   Labels as an inter-subnet tenant Data Label, the traffic will be
   forwarded as layer 2 intra-subnet traffic unless a special traffic
   filtering policy is enforced on the edge RBridge.

   If there are multiple nicknames owned by an edge RBridge, the edge
   RBridge also can specify one nickname as the egress nickname for
   inter-subnet traffic forwarding. A NickFlags APPsub-TLV with the SE-
   flag set can be used for this purpose. If the edge RBridge doesn't
   specify a nickname for this purpose, the ingress RBridge can use any
   one of the nicknames owned by the egress as the egress nickname for
   inter-subnet traffic forwarding.

   TRILL E-L1FS FS-LSP [RFC7780] APPsub-TLVs are used for IP routing
   information synchronization in each routing domain among edge
   RBridges. Based on the synchronized information from other edge
   RBridges, each edge RBridge generates routing entries in each
   routing domain for remote IP addresses and subnets.

   Through this solution, the intra-subnet forwarding function and
   inter-subnet IP routing functions are integrated and network
   management and deployment is simplified.


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5.3. Active-active Access

   TRILL active-active service provides end stations with flow level
   load balance and resilience against link failures at the edge of
   TRILL campuses as described in [RFC7379].

   If an ES is connected to two TRILL RBridges, say RB1 and RB2, in
   active-active mode, RB1 and RB2 MUST both be configured to act as a
   distributed layer 3 gateway for the ES in order to use a distributed
   gateway. RB1 and RB2 each learn the ES's IP address through the
   ARP/ND process and then they announce the IP address to the TRILL
   campus independently. The remote ingress RBridge will generate an IP
   routing entry corresponding with the IP address with two IP next
   hops of RB1 and RB2. When the ingress RBridge receives inter-subnet
   traffic from a local access network, the ingress RBridge selects RB1
   or RB2 as the IP next hop based on least cost or, if costs are equal,
   the local load balancing algorithm. Then the traffic will be
   transmitted to the selected next hop destination RB1 or RB2 through
   the TRILL campus.

5.4. Data Traffic Forwarding Process

   After a Layer 2 connected ES1 in VLAN-x acquires its gateway's MAC,
   it can start inter-subnet data traffic transmission to ES2 in VLAN-y.

   When the edge RBridge attached to ES1 receives inter-subnet traffic
   from ES1, that RBridge performs Layer 2 header termination, then,
   using the local VRF corresponding to VLAN-x, it performs the IP
   routing process in that VRF.

   If destination ES2 is attached to the same edge RBridge, the traffic
   will be locally forwarded to ES2 by that RBridge. Compared to the
   centralized gateway solution, the forwarding path is optimal and a
   traffic detour through the centralized gateway is avoided.

   If ES2 is attached to a remote edge RBridge, the remote edge RBridge
   is IP next hop and the inter-subnet traffic is forwarded to the IP
   next hop through TRILL encapsulation. If there are multiple equal
   cost shortest paths between ingress RBridge and egress RBridge, all
   these paths can be used for inter-subnet traffic forwarding, so load
   spreading can be achieved for inter-subnet traffic.

   When the remote RBridge receives the inter-subnet TRILL encapsulated
   traffic, the RBridge decapsulates the TRILL encapsulation and check
   the Inner.MacDA. If that MAC address is the local gateway MAC
   corresponding to the inner Label (VLAN or FGL), the inner Label will
   be used to find the corresponding local VRF, then the IP routing


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   process in that VRF will be performed, and the traffic will be
   locally forwarded to the destination ES2.

   In summary, this solution avoids traffic detours through a central
   gateway, both inter-subnet and intra-subnet traffic can be forwarded
   along pair-wise shortest paths, and network bandwidth is conserved.



6. Distributed Layer 3 Gateway Process Example

   This section gives a detailed description of a distributed layer 3
   gateway solution example for IPv4 and IPv6.

   ---------             ---------
   |  RB3  |             |  RB4  |
   ---------             ---------
   #   *                     #  *
   #   **************************
   ###########################  *
   #                            *
   #                            *
   #                            *
   ---------              ---------
   |  RB1  |              |  RB2  |
   ---------              ---------
      |                       |
    -----                   -----
    |ES1|                   |ES2|
    -----                   -----
   Figure 3. Distributed gateway scenario

   In figure 3, RB1 and RB2 support the distribution gateway function,
   ES1 connects to RB1, ES2 connects to RB2. ES1 and ES2 belong to
   Tenant1, but are in different subnets.

   For IPv4, the IP address, VLAN, and subnet information of ES1 and
   ES2 are as follows:


   +----+---------+------------------+------------------+----------+
   | ES | Tenant  |   IP Address     |  Subnet          |  VLAN    |
   +----+---------+------------------+------------------+----------+
   | ES1| Tenant1 |   192.0.2.2      |  192.0.2.0/24    |   10     |
   +----+---------+------------------+------------------+----------+
   | ES2| Tenant1 |   198.51.100.2   |  198.51.100.0/24 |   20     |
   +----+---------+------------------+------------------+----------+
                           Figure 4a. IPv4 ES information


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   For IPv6, the IP address, VLAN, and subnet information of ES1 and
   ES2 are as follows:


   +----+---------+------------------+------------------+----------+
   | ES | Tenant  | IP Address       | Subnet           |  VLAN    |
   +----+---------+------------------+------------------+----------+
   | ES1| Tenant1 | 2001:db8:0:1::2  |2001:db8:0:1::0/64|   10     |
   +----+---------+------------------+------------------+----------+
   | ES2| Tenant1 | 2001:db8:0:2::2  |2001:db8:0:2::0/64|   20     |
   +----+---------+------------------+------------------+----------+

                           Figure 4b. IPv6 ES information

   The nickname, VRF, tenant Label, tenant gateway MAC for Tenant1 on
   RB1 and RB2 are as follows:
   +----+---------+----------+-------+--------------+--------------+
   | RB | Nickname|  Tenant  | VRF   | Tenant Label |  Gateway MAC |
   +----+---------+----------+-------+--------------+--------------+
   | RB1|  nick1  |  Tenant1 | VRF1  |    100       |    MAC1      |
   +----+---------+----------+-------+--------------+--------------+
   | RB2|  nick2  |  Tenant1 | VRF2  |    100       |    MAC2      |
   +----+---------+----------+-------+--------------+--------------+
                         Figure 5. RBridge information

6.1. Control plane process

   RB1 advertises the following local routing information to the
   campus:     TRILL

            Tenant ID: 1

            Tenant gateway MAC: MAC1

            Tenant Label for Tenant1: VLAN 100.

            IPv4 prefix for Tenant1: 192.0.2.0/24

            IPv6 prefix for Tenant1: 2001:db8:0:1::0/64

   RB2 announces the following local routing information to TRILL
   campus:

            Tenant ID: 1

            Tenant gateway MAC: MAC2


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            Tenant Label for Tenant1: VLAN 100.

            IPv4 prefix for Tenant1: 198.51.100.0/24

            IPv6 prefix for Tenant1: 2001:db8:0:2::0/64


   Relying on the routing information from RB2, remote routing entries
   on RB1 are generated as follows:

   +------------------+-------------+--------------+----------------+
   |  Prefix/Mask     | Inner.MacDA | Inner VLAN   | Egress Nickname|
   +------------------+-------------+--------------+----------------+
   |198.51.100.0/24   |    MAC2     |    100       |     nick2      |
   +------------------+-------------+--------------+----------------+
   |2001:db8:0:2::0/64|    MAC2     |    100       |     nick2      |
   +------------------+-------------+--------------+----------------+
             Figure 6. Tenant 1 remote routing table on RB1

   Similarly, relying on the routing information from RB1, remote
   routing entries on RB2 are generated as follows:

   +------------------+-------------+--------------+----------------+
   |   Prefix/Mask    | Inner.MacDA | Inner VLAN   | Egress Nickname|
   +------------------+-------------+--------------+----------------+
   |  192.0.2.0/24    |     MAC1    |    100       |     nick1      |
   +------------------+-------------+--------------+----------------+
   |2001:db8:0:1::0/64|     MAC1    |    100       |     nick1      |
   +------------------+-------------+--------------+----------------+
             Figure 7. Tenant 1 remote routing table on RB2

6.2. Data Plane Process

   Assuming ES1 sends unicast inter-subnet traffic to ES2, the traffic
   forwarding process is as follows:

   1. ES1 sends unicast inter-subnet traffic to RB1 with RB1's

    gateway's MAC as the destination MAC and VLAN as VLAN 10.

   2. Ingress RBridge (RB1) forwarding process:

    RB1 checks the destination MAC, if the destination MAC equals the
    local gateway MAC, the gateway function will terminate the Layer 2
    header and perform L3 routing.



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    RB1 looks up IP routing table information by destination IP and
    Tenant ID to get IP next hop information, which includes the egress
    RBridge's gateway MAC (MAC2), tenant Label (VLAN 100) and egress
    nickname (nick2). Using this information, RB1 will perform inner
    Ethernet header encapsulation and TRILL encapsulation. RB1 will use
    MAC2 as the Inner.MacDA, MAC1 (RB1's own gateway MAC) as the
    Inner.MacSA, VLAN 100 as the Inner.VLAN, nick2 as the egress
    nickname and nick1 as the ingress nickname.

    RB1 looks up TRILL forwarding information by egress nickname and
    sends the traffic to the TRILL next hop as per [RFC6325]. The
    traffic will be sent to RB3 or RB4 as a result of load balancing.

    Assuming the traffic is forwarded to RB3, the following occurs:

   3. Transit RBridge (RB3) forwarding process:

    RB3 looks up TRILL forwarding information by egress nickname and
    forwards the traffic to RB2 as per [RFC6325].

   4. Egress RBridge forwarding process:

    As the egress nickname is RB2's own nickname, RB2 performs TRILL
    decapsulation. Then it checks the Inner.MacDA and, because that MAC
    is equal to the local gateway MAC, performs inner Ethernet header
    termination. Using the inner VLAN, RB2 finds the local
    corresponding VRF and looks up the packets destination IP address
    in the VRF's IP routing table. The traffic is then be locally
    forwarded to ES2 with VLAN 20.

7. TRILL Protocol Extensions

   If an edge RBridge RB1 participates in the distributed gateway
   function, it announces its tenant gateway MAC and tenant Data Label
   to the TRILL campus through the tenant Label and gateway MAC APPsub-
   TLV, it should announce its local IPv4 and IPv6 prefixes through the
   IPv4 Prefix APPsub-TLV and the IPv6 Prefix APPsub-TLV respectively.
   If RB1 has multiple nicknames, it can announce one nickname for
   distributed gateway use using Nickname Flags APPsub-TLV with "SE"
   Flag set to one.

   The remote ingress RBridges belonging to the same routing domain use
   this information to generate IP routing entries in that routing
   domain. These RBridges use the nickname, tenant gateway MAC, and
   tenant Label of RB1 to perform inter-subnet traffic TRILL
   encapsulation when they receive inter-subnet traffic from a local ES.
   The nickname is used as the egress nickname, the tenant gateway MAC


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   is used as the Inner.MacDA, and the tenant Data Label is used as the
   Inner.Label. The following APPsub-TLVs MUST be included in a TRILL
   GENINFO TLV in E-L1FS FS-LSPs [RFC7780].

7.1. The Tenant Label and Gateway MAC APPsub-TLV

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Type                        | (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Length                      | (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Tenant ID   (4 bytes)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Resv1 |     Label1            | (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Resv2 |     Label2            | (2 bytes)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+....-+-+-+-+-+-+-+-+-+-+
   |            Tenant Gateway Mac   (6 bytes)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+....-+-+-+-+-+-+-+-+-+-+


   o Type: Set to TENANT- GWMAC-LABEL sub-TLV type (TBD1). Two bytes,
    because this APPsub-TLV appears in an extended TLV [RFC7356].

   o Length: If Label1 field is used to represent a VLAN, the value of
    the length field is 12. If Label1 and Label2 field are used to
    represent an FGL, the value of the length field is 14.

   o Tenant ID: This identifies a tenant ID unique across the TRILL
    campus.

   o Resv1: 4 bits that MUST be sent as zero and ignored on receipt.

   o Label1: If the value of the length field is 12, it identifies a
    tenant Label corresponding to a VLAN ID. If the value of the length
    field is 14, it identifies the higher 12 bits of a tenant Label
    corresponding to a FGL.

   o Resv2: 4 bits that MUST be sent as zero and ignored on receipt.
    Only present if the length field is 14.

   o Label2: This field has the lower 12 bits of tenant Label
    corresponding to a FGL. Only present if the length field is 14.

   o Tenant Gateway MAC: This identifies the local gateway MAC
    corresponding to the tenant ID. The remote ingress RBridges uses
    the Gateway MAC as Inner.MacDA. The advertising TRILL RBridge uses



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    the gateway MAC to differentiate layer 2 intra-subnet traffic and
    layer 3 inter-subnet traffic in the egress direction.

7.2. "SE" Flag in NickFlags APPsub-TLV

   The NickFlags APPsub-TLV is specified in [RFC7780] where the IN flag
   is described. The SE Flag is assigned as follows:
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      |   Nickname                                    |
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      |IN|SE|         RESV                            |
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                               NICKFLAG RECORD



   o SE. If the SE flag is one, it indicates that the advertising
    RBridge suggests the nickname SHOULD be used as the Inter-Subnet
    Egress nickname for inter-subnet traffic forwarding. If flag is
    zero, that nickname SHOULD NOT be used for that purpose. The SE
    flag is ignored if the NickFlags APPsub-TLV is advertised by an
    RBridge that does not own the Nickname.



7.3. The IPv4 Prefix APPsub-TLV
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |   Type                        |                    (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |   Total Length                |                    (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |                     Tenant ID                    | (4 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |PrefixLength(1)|                                    (1 byte)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |                     Prefix (1)                   | (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |     .....     |                                    (1 byte)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |                    .....                         | (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |PrefixLength(N)|                                    (1 byte)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |                     Prefix (N)                   | (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+


   o Type: Set to IPV4-PREFIX sub-TLV type (TBD2). Two bytes, because
    this APPsub-TLV appears in an extended TLV [RFC7356].


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   o Total Length: This 2-byte unsigned integer indicates the total
    length of the Tenant ID, the Prefix Length, and the Prefix fields
    in octets. A value of 0 indicates that no IPv4 prefix is being
    advertised.

   o Tenant ID: This identifies a tenant ID unique across the TRILL
    campus.

   o Prefix Length: The Prefix Length field indicates the length in bits
    of the IPv4 address prefix.  A length of zero indicates a prefix
    that matches all IPv4 addresses (with prefix, itself, of zero
    octets).

   o Prefix: The Prefix field contains an IPv4 address prefix, followed
    by enough trailing bits to make the end of the field fall on an
    octet boundary. Note that the value of the trailing bits is
    irrelevant. For example, if the Prefix Length is 12, indicating 12
    bits, then the Prefix is 2 octets and the low order 4 bits of the
    Prefix are irrelevant.

7.4. The IPv6 Prefix APPsub-TLV
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |   Type                        |                    (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |   Total Length                |                    (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |                     Tenant ID                    | (4 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |PrefixLength(1)|                                    (1 byte)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |                     Prefix (1)                   | (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |     .....       |                                  (1 byte)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |                    .....                         | (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |PrefixLength(N)|                                    (1 byte)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+
         |                     Prefix (N)                   | (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...-+-+-+-+-+-+-+-+


   o Type: Set to IPV6-PREFIX sub-TLV type (TBD3). Two bytes, because
    this APPsub-TLV appears in an extended TLV [RFC7356].

   o Total Length: This 2-byte unsigned integer indicates the total
    length of the Tenant ID, the Prefix Length, and the Prefix fields
    in octets. A value of 0 indicates that no IPv6 prefix is being
    advertised.


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   o Tenant ID: This identifies a tenant ID unique across the TRILL
    campus.

   o Prefix Length: The Prefix Length field indicates the length in bits
    of the IPv6 address prefix.  A length of zero indicates a prefix
    that matches all IPv6 addresses (with prefix, itself, of zero
    octets).

   o Prefix: The Prefix field contains an IPv6 address prefix, followed
    by enough trailing bits to make the end of the field fall on an
    octet boundary. Note that the value of the trailing bits is
    irrelevant. For example, if the Prefix Length is 100, indicating
    100 bits, then the Prefix is 13 octets and the low order 4 bits of
    the Prefix are irrelevant.

8. Security Considerations

   Correct configuration of the edge RBridges participating is
   important to assure that data is not delivered to the wrong tenant,
   which would violate security constrains. IS-IS security [RFC5310]
   can be used to secure the information advertised by the edge
   RBridges in LSPs and FS-LSPs.

   See Section 5.2 for constraints on re-use of a tenant ID and on
   tenant gateway MAC change to avoid the mishandling of data in flight.
   It can be made more difficult for an adversary to guess a tenant ID
   that is in use by selecting tenant IDs in a pseudo-random fashion
   [RFC4086].

   Particularly sensitive data should be encrypted end-to-end, that is,
   from the source end station to the destination end station. Since
   the TRILL campus is, for the most part, transparent to end station
   traffic, such end stations are free to use whatever end-to-end
   security protocol they would like.

   For general TRILL Security Considerations, see [RFC6325].

9. Management Considerations

   The configuration at each RBridge to support the distributed Layer 3
   gateway feature is visible to all other RBridges in the campus in
   the link state database. OAM facilities for TRILL are primarily
   specified in [RFC7455] and [RFC7456].






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10. IANA Considerations

   IANA is requested to assign three APPsub-TLV type numbers from the
   range less than 255 and update the "TRILL APPsub-TLV Types under IS-
   IS TLV 251 Application Identifier 1" registry as follows:

      Type    Name               References

      ----   ----------------   ------------

      TBD1   TENANT-GWMAC-LABEL [this document]

      TBD2   IPV4-PREFIX        [this document]

      TBD3   IPV6-PREFIX        [this document]

   IANA is requested to assign a flag bit in the NickFlags APPsub-TLV
   as described in Section 7.2 and update the ''Nick Flags'' registry,
   created by [RFC7780], as follows:

       Bit   Mnemonic   Description          Reference

      -----  --------  -------------------  -----------

        1       SE     Inter-Subnet Egress  [this document]

11. Normative References

   [IS-IS] - ISO/IEC, "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.

   [RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, April 1997.

   [RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and
   A.Ghanwani, "Routing Bridges (RBridges): Base Protocol
   Specification", RFC 6325, July 2011.

   [RFC7172] - Eastlake, D., M. Zhang, P. Agarwal, R. Perlman, D. Dutt,
   "TRILL (Transparent Interconnection of Lots of Links): Fine-Grained
   Labeling", RFC7172, May 2014.

   [RFC7176] - Eastlake, D., T. Senevirathne, A. Ghanwani, D. Dutt and
   A. Banerjee" Transparent Interconnection of Lots of Links (TRILL) Use
   of IS-IS", RFC7176, May 2014.


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   [RFC7356] - Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
   Scope Link State PDUs (LSPs)", RFC 7356, September 2014,
   <http://www.rfc-editor.org/info/rfc7356>.

   [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>.

12. Informative References

   [RFC826] - Plummer, D., "Ethernet Address Resolution Protocol: Or
   Converting Network Protocol Addresses to 48.bit Ethernet Address for
   Transmission on Ethernet Hardware", STD 37, RFC 826, November 1982,
   <http://www.rfc-editor.org/info/rfc826>.

   [RFC4086] - Eastlake 3rd, D., Schiller, J., and S. Crocker,
   "Randomness Requirements for Security", BCP 106, RFC 4086, DOI
   10.17487/RFC4086, June 2005, <http://www.rfc-editor.org/info/rfc4086>.

   [RFC4861] - Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
   "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, September
   2007, <http://www.rfc-editor.org/info/rfc4861>.

   [RFC5310] - Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
   and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC 5310,
   February 2009.

   [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,
   October 2014, <http://www.rfc-editor.org/info/rfc7379>.

   [RFC7455] - Senevirathne, T., Finn, N., Salam, S., Kumar, D.,
   Eastlake 3rd, D., Aldrin, S., and Y. Li, "Transparent Interconnection
   of Lots of Links (TRILL): Fault Management", RFC 7455, DOI
   10.17487/RFC7455, March 2015, <http://www.rfc-
   editor.org/info/rfc7455>.

   [RFC7456] - Mizrahi, T., Senevirathne, T., Salam, S., Kumar, D., and
   D. Eastlake 3rd, "Loss and Delay Measurement in Transparent
   Interconnection of Lots of Links (TRILL)", RFC 7456, DOI
   10.17487/RFC7456, March 2015, <http://www.rfc-
   editor.org/info/rfc7456>.




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Acknowledgments

   The authors wish to acknowledge the important contributions of
   Donald Eastlake, Gayle Noble, Muhammed Umair, Susan Hares, Guangrui
   Wu, Zhenbin Li, Zhibo Hu, Liang Xia, Scott Bradner, Stephen Farrell,
   Shawn Emery, Ben Campbell, Russ White, Kathleen Moriarty, Suresh
   Krishnan, Mirja Kuhlewind, and Francis Dupont.

Authors' Addresses

       Weiguo Hao
       Huawei Technologies
       101 Software Avenue,
       Nanjing 210012, China

       Phone: +86-25-56623144
       Email: haoweiguo@huawei.com


       Yizhou Li
       Huawei Technologies
       101 Software Avenue,
       Nanjing 210012, China

       Phone: +86-25-56625375
       Email: liyizhou@huawei.com


       Andrew Qu
       MediaTec
       Email: laodulaodu@gmail.com


       Muhammad Durrani
       Cisco
       Email: mdurrani@cisco.com


       Ponkarthick Sivamurugan
       Address: IP Infusion,
       RMZ Centennial
       Mahadevapura Post


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       Bangalore - 560048
       Email: Ponkarthick.sivamurugan@ipinfusion.com













































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