TRILL Active-Active Edge Using Multiple MAC Attachments
draft-ietf-trill-aa-multi-attach-03

The information below is for an old version of the document
Document Type Active Internet-Draft (trill WG)
Authors Mingui Zhang  , Radia Perlman  , Hongjun Zhai  , Muhammad Durrani  , Sujay Gupta 
Last updated 2015-07-31 (latest revision 2015-02-06)
Replaces draft-zhang-trill-aa-multi-attach
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Send notices to draft-ietf-trill-aa-multi-attach.shepherd@ietf.org, draft-ietf-trill-aa-multi-attach.ad@ietf.org, trill-chairs@ietf.org, d3e3e3@gmail.com, draft-ietf-trill-aa-multi-attach@ietf.org
IANA IANA review state IANA - Review Needed
INTERNET-DRAFT                                              Mingui Zhang
Intended Status: Proposed Standard                                Huawei
                                                           Radia Perlman
                                                                     EMC
                                                            Hongjun Zhai
                                                                     JIT
                                                        Muhammad Durrani
                                                                 Brocade
                                                             Sujay Gupta
                                                             IP Infusion
Expires: August 9, 2015                                 February 5, 2015

        TRILL Active-Active Edge Using Multiple MAC Attachments
                draft-ietf-trill-aa-multi-attach-03.txt

Abstract

   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 RFC 7379.

   This draft specifies a method by which member RBridges in an active-
   active edge RBridge group use their own nicknames as ingress RBridge
   nicknames to encapsulate frames from attached end systems. Thus,
   remote edge RBridges are required to keep multiple locations of one
   MAC address in one Data Label. Design goals of this specification are
   discussed in the document.

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
   http://www.ietf.org/1id-abstracts.html

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html
 

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Copyright and License Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Acronyms and Terminology  . . . . . . . . . . . . . . . . . . .  4
     2.1. Acronyms and Terms  . . . . . . . . . . . . . . . . . . . .  4
     2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . .  5
   3. Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4. Incremental Deployable Options  . . . . . . . . . . . . . . . .  6
     4.1. Detail of Option C  . . . . . . . . . . . . . . . . . . . .  7
     4.2. Extended RBridge Capability Flags APPsub-TLV  . . . . . . .  9
   5. Meeting the Design Goals  . . . . . . . . . . . . . . . . . . . 10
     5.1. No MAC Flip-Flopping (Normal Unicast Egress)  . . . . . . . 10
     5.2. Regular Unicast/Multicast Ingress . . . . . . . . . . . . . 10
     5.3. Correct Multicast Egress  . . . . . . . . . . . . . . . . . 11
       5.3.1. No Duplication (Single Exit Point)  . . . . . . . . . . 11
       5.3.2. No Echo (Split Horizon) . . . . . . . . . . . . . . . . 11
     5.4. No Black-hole or Triangular Forwarding  . . . . . . . . . . 12
     5.5. Load Balance Towards the AAE  . . . . . . . . . . . . . . . 13
     5.6. Scalability . . . . . . . . . . . . . . . . . . . . . . . . 13
   6. E-L1FS Backwards Compatibility  . . . . . . . . . . . . . . . . 13
   7. Security Considerations . . . . . . . . . . . . . . . . . . . . 14
   8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 14
     8.1. TRILL APPsub-TLVs . . . . . . . . . . . . . . . . . . . . . 14
     8.2. Extended RBridge Capabilities Registry  . . . . . . . . . . 14
     8.3 Active Active Flags  . . . . . . . . . . . . . . . . . . . . 14
   9. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
     10.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Appendix A. Scenarios for Split Horizon  . . . . . . . . . . . . . 17
   Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19

 

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1. Introduction

   As discussed in [RFC7379], in a TRILL Active-Active Edge (AAE)
   topology, a Local Active-Active Link Protocol (LAALP), for example, a
   Multi-Chassis Link Aggregation Group (MC-LAG), is used to connect
   multiple RBridges to multi-port Customer Equipment (CE), such as a
   switch, vSwitch or a multi-port end station. An endnode clump is
   attached in the case of switch or vSwitch. It is required that data
   traffic within a specific VLAN from this endnode clump (including the
   multi-port end station case) can be ingressed and egressed by any of
   these RBridges simultaneously. End systems in the clump can spread
   their traffic among these edge RBridges at the flow level. When a
   link fails, end systems keep using the remaining links in the LAALP
   without waiting for the convergence of TRILL, which provides
   resilience to link failures.

   Since a frame from each endnode can be ingressed by any RBridge in
   the AAE group, a remote edge RBridge may observe multiple attachment
   points (i.e., egress RBridges) for this endnode identified by its MAC
   address and Data Label (VLAN or Fine Grained Label (FGL)). This issue
   is known as the "MAC flip-flopping". Three potential solutions arise
   to address this issue: 

      1) AAE member RBridges use a pseudo-nickname, instead of their
      own, as the ingress nickname for end systems attached to the
      LAALP. [PN] falls within this category.

      2) AAE member RBridges split work among themselves as to which one
      will be responsible for which MAC addresses. A member RBridge will
      encapsulate the frame using its own nickname if it is responsible
      for the source MAC address. Otherwise, if the frame is known
      unicast, it encapsulates the frame using the nickname of the
      responsible RBridge; if the frame is multi-destination, it needs
      to tunnel the native frame to its responsible RBridge for
      encapsulation, for example using [ChannelTunnel].

      3) AAE member RBridges keep using their own nicknames. Remote edge
      RBridges are required to keep multiple points of attachment per
      MAC address and Data Label attached to the AAE. 

   The purpose of this document is to specify an approach based on
   solution 3. Although it focuses on exploring solution 3, the major
   design goals discussed here are common for all three AAE solutions.
   The use of any of these solutions in an AAE group does not prohibit
   the use of other solutions in other AAE groups in the same TRILL
   campus. For example, the specification in this draft and the
   specification in [PN] could be simultaneously deployed for different
   AAE groups in the same campus.
 

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   The main body of the document is organized as follows. Section 2
   lists the acronyms and terminologies. Section 3 gives the overview
   model. Section 4 provides options for incremental deployment. Section
   5 describes how this approach meets the design goals. The Sections
   after Section 5 cover security, IANA, and some backwards
   compatibility considerations.

2. Acronyms and Terminology

2.1. Acronyms and Terms

   AAE: Active-Active Edge

   Campus: a TRILL network consisting of TRILL switches, links, and
   possibly bridges bounded by end stations and IP routers. For TRILL,
   there is no "academic" implication in the name "campus"

   CE : Customer Equipment (end station or bridge). The device can be
   either physical or virtual equipment.

   Data Label: VLAN or FGL

   DRNI: Distributed Resilient Network Interconnect. A link aggregation
   specified in [802.1AX] that can provide an LAALP between from 1 to 3
   CEs and 2 or 3 RBridges.

   Edge RBridge: An RBridge providing end station service on one or more
   of its ports.

   ESADI: End Station Address Distribution Information [RFC7357]

   FGL: Fine Grained Label [RFC7172]

   IS-IS: Intermediate System to Intermediate System [ISIS]

   LAALP: As in [RFC7379], Local Active-Active Link Protocol. Any
   protocol similar to MC-LAG (or DRNI) that runs in a distributed
   fashions on a CE, the links from that CE to a set of edge group
   RBridges, and on those RBridges.

   MC-LAG: Multi-Chassis LAG. Proprietary extensions of Link Aggregation
   [802.1AX] that can provide an LAALP between one CE and 2 or more
   RBridges.

   RBridge: A device implementing the TRILL protocol.

   TRILL: TRansparent Interconnection of Lots of Links or Tunneled
   Routing in the Link Layer [RFC6325] [RFC7177].
 

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   TRILL switch: An alternative name for an RBridge.

   vSwitch: A virtual switch such as a hypervisor that also simulates a
   bridge.

2.2. Terminology

   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].

   Familiarity with [RFC6325], [RFC6439] and [RFC7177] is assumed in
   this document. 

3. Overview

                               +-----+
                               | RB4 |
                    +----------+-----+----------+
                    |                           |
                    |                           |
                    |       Rest of campus      |
                    |                           |
                    |                           |
                    +-+-----+--+-----+--+-----+-+
                      | RB1 |  | RB2 |  | RB3 |
                      +-----\  +-----+  /-----+
                              \   |   /
                                \ | /
                                 |||LAALP1
                                 |||
                                +---+
                                | B |
                                +---+
                             H1 H2 H3 H4: VLAN 10

      Figure 3.1: An example topology for TRILL Active-Active Edge

   Figure 3.1 shows an example network for TRILL Active-Active Edge. In
   this figure, endnodes (H1, H2, H3 and H4) are attached to a bridge B
   that communicates with multiple RBridges (RB1, RB2 and RB3) via the
   LAALP. Suppose RB4 is a 'remote' RBridge not in the AAE group in the
   TRILL campus. This connection model is also applicable to the
   virtualized environment where the physical bridge can be replaced
   with a vSwitch while those bare metal hosts are replaced with virtual
   machines (VM).  

   For a frame received from its attached endnode clumps, a member
 

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   RBridge of the AAE group conforming to this document always
   encapsulates that frame using its own nickname as the ingress
   nickname no matter whether it's unicast or multicast.

   The remote RBridge RB4 will see multiple attachments for each MAC
   from one of the end-nodes. Although this could cause problems if RB4
   is learning remote end station attachments from the data plane, we
   specify a solution below ("Option C").

4. Incremental Deployable Options

   Three options are listed below to handle incremental deployment
   scenarios. Among them, Option C can be incrementally implemented
   throughout a TRILL campus with common existing TRILL fast path
   hardware. Further details on Option C are given in Section 4.1.

   -- Option A

      A new capability announcement would appear in LSPs: "I can cope
      with data plane learning of multiple attachments for an endnode".
      This mode of operation is generally not supported by existing
      TRILL fast path hardware. Only if all edge RBridges to which the
      group has data connectivity and that are interested in any of the
      Data Labels in which the AAE is interested announce this
      capability can the AAE group safely use this approach. If all such
      RBridges do not announce this "Option A" capability, then a
      fallback would be needed such as reverting from active-active to
      active-standby operation or isolating the RBridge that would need
      to support this capability and do not support it. Further details
      for Options A are beyond the scope of this document except that in
      Section 4.2 a bit is reserved to indicate support for Option A
      because a remote RBridge supporting Option A is compatible with an
      AAE group using Option C.

   -- Option B

      Each edge RBridge in the AAE group ingresses frames from any LAALP
      into a specific TRILL topology [TRILL-MT]. In this way, the
      topology ID is used as the discriminator of different locations of
      a specific MAC address at the remote RBridge. TRILL could reserve
      a list of topology IDs to be dedicated to AAE. A variety of
      fallbacks might be needed for RBridges that do not support multi-
      topology or do not support a needed topology. Further details for
      this Options B are beyond the scope of this document.

   -- Option C

      As pointed out in Section 4.2.6 of [RFC6325] and Section 5.3 of
 

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      [RFC7357], one MAC address may be persistently claimed to be
      attached to multiple RBridges within the same Data Label in the
      TRILL ESADI-LSPs. For Option C, AAE member RBridges make use of
      the TRILL ESADI protocol to distribute multiple attachments of a
      MAC address. Remote RBridges SHOULD disable the data plane MAC
      learning for such multi-attached MAC addresses from TRILL Data
      packet decapsulation unless they also support Option A. The
      ability to configure an RBridge to disable data plane learning is
      provided by the base TRILL protocol [RFC6325].

4.1. Detail of Option C

   With Option C, an RBridge in an AAE group MUST advertise all Data
   Labels enabled for all its attached LAALPs and participate in ESADI
   for those Data Labels. Receiver edge RBridges MUST avoid flip-flop
   errors in MAC learned from the TRILL Data packet decapsulation for
   the originating RBridge within these Data Labels. It's RECOMMENDED
   that the receiver edge RBridge disable the data plane MAC learning
   from TRILL Data packet decapsulation within those advertised Data
   Labels for the originating RBridge unless the receiver RBridge also
   supports Option A. However, alternative implementations MAY be used
   to produce the same expected behavior. A promising way is to make use
   of the confidence level mechanism [RFC6325]. For example, let the
   receiver edge RBridge give a prevailing confidence value (e.g., 0x21)
   to the first MAC attachment learned from the data plane over others
   from the TRILL Data packet decapsulation. So the receiver edge
   RBridge will stick to this MAC attachment until it is overridden by
   one learned from the ESADI protocol [RFC7357]. The MAC attachment
   learned from ESADI is set to have higher confidence value (e.g.,
   0x80) to override any alternative learning from the decapsulation of
   received TRILL Data packets [RFC6325]. 

   The advertisement of enabled Data Labels for an LAALP can be realized
   by allocating one reserved flag from the Interested VLANs and
   Spanning Tree Roots Sub-TLV (Section 2.3.6 of [RFC7176]) and one
   reserved flag from the Interested Labels and Spanning Tree Roots Sub-
   TLV (Section 2.3.8 of [RFC7176]). When this flag is set to 1, the
   originating IS (RBridge) is advertising Data Labels for LAALPs rather
   than plain LAN links. (See Section 8.3)

   Whenever a MAC from the LAALP of this AAE is learned through ingress
   or configuration, it MUST be advertised via the ESADI protocol
   [RFC7357]. In its TRILL ESADI-LSPs, the originating RBridge needs to
   include the identifier of this AAE. Remote RBridges need to know all
   nicknames of RBridges in this AAE. This is achieved by listening to
   the "AA LAALP Group RBridges" TRILL APPsub-TLV defined in Section
   5.3.2. The MAC Reachability TLVs [RFC6165] are composed in a way that
   each TLV only contains MAC addresses of end-nodes attached to a
 

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   single LAALP. Each such TLV is enclosed in a TRILL APPsub-TLV defined
   as follows.

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type = AA-LAALP-GROUP-MAC     | (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Length                        | (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | LAALP ID Size |                 (1 byte)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+
      | LAALP ID                        (k bytes)       | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+
      | MAC-Reachability TLV            (7 + 6*n bytes) |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+

   o  Type: AA LAALP Grouped MAC (TRILL APPsub-TLV type tbd1) 

   o  Length: The MAC-Reachability TLV [RFC6165] is contained in the
      value field as a sub-TLV. The total number of bytes contained in
      the value field is given by k+8+6*n.

   o  LAALP ID Size: The length k of the LAALP ID in bytes.

   o  LAALP ID: The ID of the LAALP that is k bytes long. Here, it also
      serves as the identifier of the AAE. If the LAALP is an MC-LAG (or
      DRNI), it is the 8 byte ID as specified in Clause 6.3.2 in
      [802.1AX].

   o  MAC-Reachability sub-TLV: The AA-LAALP-GROUP-MAC APPsub-TLV value
      contains the MAC-Reachability TLV as a sub-TLV. As specified in
      Section 2.2 in [RFC7356], the type and length fields of the MAC-
      Reachability TLV are encoded as unsigned 16 bit integers. The one
      octet unsigned Confidence along with these TLVs SHOULD be set to
      prevail over those MAC addresses learned from TRILL Data
      decapsulation by remote edge RBridges.

   This AA-LAALP-GROUP-MAC APPsub-TLV MUST be included in a TRILL
   GENINFO TLV [RFC7357] in the ESADI-LSP. There may be more than one
   occurrence of such TRILL APPsub-TLV in one ESADI-LSP fragment.

   For those MAC addresses contained in an AA-LAALP-GROUP-MAC APPsub-
   TLV, this document applies. Otherwise, [RFC7357] applies. For
   example, an AAE member RBridge continues to enclose MAC addresses
   learned from TRILL Data packet decapsulation in MAC-Reachability TLV
   as per [RFC6165] and advertise them using the ESADI protocol. 

   When the remote RBridge learns MAC addresses contained in the AA-
   LAALP-GROUP-MAC APPsub-TLV via the ESADI protocol [RFC7357], it sends
 

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   the packets destined to these MAC addresses to the closest one (the
   one to which the remote RBridge has the least cost forwarding path)
   of those RBridges in the AAE identified by the LAALP ID in the AA-
   LAALP-GROUP-MAC APPsub-TLV. If there are multiple equal least cost
   member RBridges, the ingress RBridge is required to select a unique
   one in a pseudo-random way as specified in Section 5.3 of [RFC7357].

   When another RBridge in the same AAE group receives an ESADI-LSP with
   the AA-LAALP-GROUP-MAC APPsub-TLV, it also learns MAC addresses of
   those end-nodes served by the corresponding LAALP. These MAC
   addresses SHOULD be learned as if those end-nodes are locally
   attached to this RBridge itself.

   An AAE member RBridge MUST use the AA-LAALP-GROUP-MAC APPsub-TLV to
   advertise in ESADI the MAC addresses learned from a plain local link
   (a non LAALP link) with Data Labels that happen to be covered by the
   Data Labels of any attached LAALP. The reason is that MAC learning
   from TRILL Data packet decapsulation within these Data Labels at the
   remote edge RBridge has normally been disabled for this RBridge.

4.2. Extended RBridge Capability Flags APPsub-TLV

   The following Extended RBridge Capability Flags APPsub-TLV will be
   included in an E-L1FS FS-LSP fragment zero [RFC7180bis] as an APPsub-
   TLV of the TRILL GENINFO-TLV.

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type = EXTENDED-RBRIDGE-CAP   | (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Length                        | (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Topology                      | (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |E|H|     Reserved                                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Reserved (continued)                                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  Type: Extended RBridge Capability (TRILL APPsub-TLV type tbd2) 

   o  Length: Set to 8.

   o  Topology: Indicates the topology to which the capabilities apply.
      When this field is set to zero, this implies that the capabilities
      apply to all topologies or topologies are not in use [TRILL-MT].

   o  E: Bit 0 of the capability bits. When this bit is set, it
      indicates the originating IS acts as specified in Option C above.
 

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   o  H: Bit 1 of the capability bits. When this bit is set, it
      indicates that the originating IS keeps multiple MAC attachments
      learned from TRILL Data packet decapsulation with fast path
      hardware, that is, it acts as specified in Option A above.

   o  Reserved: Flags extending from bit 2 through bit 63 of the
      capability fits reserved for future use. These MUST be sent as
      zero and ignored on receipt.

   The Extended RBridge Capability Flags TRILL APPsub-TLV is used to
   notify other RBridges whether the originating IS supports the
   capability indicated by the E and H bits. For example, if E bit is
   set, it indicates the originating IS will act as defined in Option C.
   That is, it will disable the MAC learning from TRILL Data packet
   decapsulation within Data Labels advertised by AAE RBridges while
   waiting for the TRILL ESADI-LSPs to distribute the {MAC, Nickname,
   Data Label} association. Meanwhile, this RBridge is able to act as an
   AAE RBridge. It's required to advertise MAC addresses learned from
   local LAALPs in TRILL ESADI-LSPs using the AA-LAALP-GROUP-MAC APPsub-
   TLV defined in Section 4.1. If the RBridge in an AAE group as
   specified herein observe a remote RBridge interested in one or more
   of that AAE group's Data Labels and the remote RBridge does not
   support, as indicated by its extended capabilities, either Option A
   or Option C, then the AAE group MUST fall back to active-standby
   mode.

   Capability specification for Option B is out the scope of this
   document.

5. Meeting the Design Goals

   How this specification meets the major design goals of AAE is
   explored in this section. 

5.1. No MAC Flip-Flopping (Normal Unicast Egress)

   Since all RBridges talking with the AAE RBridges in the campus are
   able to see multiple locations for one MAC address in ESADI
   [RFC7357], a MAC address learned from one AAE member will not be
   overwritten by the same MAC address learned from another AAE member.
   Although multiple entries for this MAC address will be created, for
   return traffic the remote RBridge is required to adhere to a unique
   one of the locations (see Section 4.1) for each MAC address rather
   than keep flip-flopping among them.

5.2. Regular Unicast/Multicast Ingress

   LAALP guarantees that each frame will be sent upward to the AAE via
 

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   exactly one uplink. RBridges in the AAE can simply follow the process
   per [RFC6325] to ingress the frame. For example, each RBridge uses
   its own nickname as the ingress nickname to encapsulate the frame. In
   such a scenario, each RBridge takes for granted that it is the
   Appointed Forwarder for the VLANs enabled on the uplink of the LAALP.

5.3. Correct Multicast Egress

   A fundamental design goal of AAE is that there must be no duplication
   or forwarding loop.

5.3.1. No Duplication (Single Exit Point)

   When multi-destination TRILL Data packets for a specific Data Label
   are received from the campus, it's important that exactly one RBridge
   out of the AAE group let through each multi-destination packet so no
   duplication will happen. The LAALP will have defined its selection
   function (using hashing or election algorithm) to designated a
   forwarder for a multi-destination frame. Since AAE member RBridges
   support the LAALP, they are able to utilize that selection function
   to determine the single exit point. If the output of the selection
   function points to the port attached to the receiver RBridge itself
   (i.e., the packet should be egressed out of this node), it MUST
   egress this packet for that AAE group. Otherwise, the packet MUST NOT
   be egressed for that AAE group. (It is output or not as specified in
   [RFC6325] updated by [RFC7172] for ports that lead to non-AAE links.)

5.3.2. No Echo (Split Horizon)

   When a multi-destination frame originated from an LAALP is ingressed
   by an RBridge of an AAE group, distributed to the TRILL network and
   then received by another RBridge in the same AAE group, it is
   important that this RBridge does not egress this frame back to this
   LAALP. Otherwise, it will cause a forwarding loop (echo). The well
   known 'split horizon' technique can be used to eliminate the echo
   issue.

   RBridges in the AAE group need to split horizon based on the ingress
   RBridge nickname plus the VLAN of the TRILL Data packet. They need to
   set up per port filtering lists consists of the tuple of <ingress
   nickname, VLAN>. Packets with information matching with any entry of
   the filtering list MUST NOT be egressed out of that port. The
   information of such filters is obtained by listening to the following
   "LAALP Group RBridges" APPsub-TLV included in the TRILL GENINFO TLV
   in FS-LSPs [RFC7180bis].

 

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      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type = AA-LAALP-GROUP-RBRIDGES| (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Length                        | (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Sender Nickname               | (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | LAALP ID Size |                 (1 byte)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+
      | LAALP ID                        (k bytes)       | 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+-+

   o  Type: AA LAALP Grouped RBridges (TRILL APPsub-TLV type tbd3)

   o  Length: 3+k

   o  Sender Nickname: The nickname the originating IS will use as the
      ingress nickname. This field is useful because the originating IS
      might own multiple nicknames. 

   o  LAALP ID Size: The length k of the LAALP ID in bytes.

   o  LAALP ID: The ID of the LAALP which is k bytes long. If the LAALP
      is an MC-LAG or DRNI, it is the 8-byte ID specified in Clause
      6.3.2 in [802.1AX].

   All enabled VLANs MUST be consistent on all ports connected to an
   LAALP. So the enabled VLANs need not be included in the AA-LAALP-
   GROUP-RBRIDGES TRILL APPsub-TLV. They can be locally obtained from
   the port attached to that LAALP.

   Through parsing AA-LAALP-GROUP-RBRIDGES TRILL APPsub-TLVs, the
   receiver RBridge discovers all other RBridges connected to the same
   LAALP. The Sender Nickname of the originating IS will be added into
   the filtering list of the port attached to the LAALP. For example,
   RB3 in Figure 3.1 will set up a filtering list looks like {<RB1,
   VLAN10>, <RB2, VLAN10>} on its port attached to LAALP1. According to
   split horizon, TRILL Data packets within VLAN10 ingressed by RB1 or
   RB2 will not be egressed out of this port.

   When there are multiple LAALPs connected to the same RBridge, these
   LAALPs may have overlap VLANs. Customer may need hosts within these
   overlap VLANs to communicate with each other. In Appendix A, several
   scenarios are given to explain how hosts communicate within the
   overlap VLANs and how split horizon happens.

5.4. No Black-hole or Triangular Forwarding

 

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   If a sub-link of the LAALP fails while remote RBridges continue to
   send packets towards the failed port, a black-hole happens. If the
   AAE member RBridge with that failed port starts to redirect the
   packets to other member RBridges for delivery, triangular forwarding
   occurs.

   The member RBridge attached to the failed sub-link can make use of
   the ESADI protocol to flush those failure affected MAC addresses as
   defined in Section 5.2 of [RFC7357]. After doing that, no packets
   will be sent towards the failed port, hence no black-hole will
   happen. Nor will the member RBridge need to redirect packets to other
   member RBridges, which may otherwise lead to triangular forwarding.

5.5. Load Balance Towards the AAE

   Since a remote RBridge can see multiple attachments of one MAC
   address in ESADI, this remote RBridge can choose to spread the
   traffic towards the AAE members on a per flow basis. Each of them is
   able to act as the egress point. In doing this, the forwarding paths
   need not be limited to the least cost Equal Cost Multiple Paths from
   the ingress RBridge to the AAE RBridges. The traffic load from the
   remote RBridge towards the AAE RBridges can be balanced based on a
   pseudo-random selection method (see Section 4.1).

   Note that the load balance method adopted at a remote ingress RBridge
   is not to replace the load balance mechanism of LAALP. These two load
   spreading mechanisms should take effect separately.

5.6. Scalability

   With option A, multiple attachments need to be recorded for a MAC
   address learned from AAE RBridges. More entries may be consumed in
   the MAC learning table. However, MAC addresses attached to an LAALP
   are usually only a small part of all MAC addresses in the whole TRILL
   campus. As a result, the extra space required by the multi-attached
   MAC addresses can usually be accommodated by RBridges unused MAC
   table space. 

   With option C, remote RBridges will keep the multiple attachments of
   a MAC address in the ESADI link state databases that are usually
   maintained by software. While in the MAC table that is normally
   implemented in hardware, an RBridge still establishes only one entry
   for each MAC address.

6. E-L1FS Backwards Compatibility

   The Extended TLVs defined in Section 4 and 5 are to be used in an
   Extended Level 1 Flooding Scope ( E-L1FS [RFC7356] [RFC7180bis]) PDU.
 

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   For those RBridges that do not support E-L1FS, the EXTENDED-RBRIDGE-
   CAP TRILL APPsub-TLV will not be sent out either and and MAC multi-
   attach active-active is not supported. 

7. Security Considerations

   Authenticity for contents transported in IS-IS PDUs is enforced using
   regular IS-IS security mechanism [ISIS][RFC5310]. 

   For security considerations pertain to extensions transported by
   TRILL ESADI, see the Security Considerations section in [RFC7357].

   For general TRILL security considerations, see [RFC6325].

8. IANA Considerations

8.1. TRILL APPsub-TLVs

   IANA is requested to allocate three new types under the TRILL GENINFO
   TLV [RFC7357] for the TRILL APPsub-TLVs defined in Section 4.1, 4.2
   and 5.3.2 of this document. The following entries are added to the
   "TRILL APPsub-TLV Types under IS-IS TLV 251 Application Identifier 1"
   Registry on the TRILL Parameters IANA web page. 

      Type       Name                     Reference
      ---------  ----                     ---------
      tbd1[252]  AA-LAALP-GROUP-MAC       [This document]
      tbd2[253]  EXTENDED-RBRIDGE-CAP     [This document]
      tbd3[254]  AA-LAALP-GROUP-RBRIDGES  [This document]

8.2. Extended RBridge Capabilities Registry

   IANA is requested to create a registry under the TRILL Parameters
   registry as follows:

   Name: Extended RBridge Capabilities

   Registration Procedure: Expert Review

   Reference: [this document]

      Bit   Mnemonic  Description       Reference
      ----  --------  -----------       ---------
      0     E         Option C Support  [this document]
      1     H         Option A Support  [this document]
      2-63  -         Unassigned

8.3 Active Active Flags
 

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   IANA is requested to allocate two flag bits, with mnemonic "AA", as
   follows:

   One flag bit appears in the "Interested VLANs and Spanning Tree Roots
   Sub-TLV".

      Bit    Mnemonic  Description                      Reference
      ----   --------  -----------                      ---------
      0      M4        IPv4 Multicast Router Attached   [RFC7176]
      1      M6        IPv6 Multicast Router Attached   [RFC7176]
      2      -         Unassigned
      3      ES        ESADI Participation              [RFC7357]
      4-15   -         (used for a VLAN ID)             [RFC7176]
      16     AA        Enabled VLANs for Active-Active  [This document]
      17-19  -         Unassigned
      20-31  -         (used for a VLAN ID)             [RFC7176]

   One flag bit appears in the "Interested Labels and Spanning Tree
   Roots Sub-TLV".

      Bit    Mnemonic  Description                      Reference
      ---    --------  -----------                      ---------
      0      M4        IPv4 Multicast Router Attached   [RFC7176]
      1      M6        IPv6 Multicast Router Attached   [RFC7176]
      2      BM        Bit Map                          [RFC7176]
      3      ES        ESADI Participation              [RFC7357]
      4      AA        FGLs for Active-Active           [This document]
      5-7    -         Unassigned

9. Acknowledgements

   Authors would like to thank the comments and suggestions from Andrew
   Qu, Donald Eastlake, Erik Nordmark, Fangwei Hu, Liang Xia, Weiguo
   Hao, Yizhou Li and Mukhtiar Shaikh.

10. References 

10.1. Normative References

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

   [RFC6165] Banerjee, A. and D. Ward, "Extensions to IS-IS for Layer-2
             Systems", RFC 6165, April 2011.

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

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   [RFC6439] Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F. Hu,
             "Routing Bridges (RBridges): Appointed Forwarders", RFC
             6439, November 2011.

   [RFC7172] D. Eastlake 3rd and M. Zhang and P. Agarwal and R. Perlman
             and D. Dutt, "Transparent Interconnection of Lots of Links
             (TRILL): Fine-Grained Labeling", RFC 7172, May 2014.

   [RFC7176] D. Eastlake 3rd and T. Senevirathne and A. Ghanwani and D.
             Dutt and A. Banerjee, "Transparent Interconnection of Lots
             of Links (TRILL) Use of IS-IS", RFC7176, May 2014. 

   [RFC7177] D. Eastlake 3rd and R. Perlman and A. Ghanwani and H. Yang
             and V. Manral, "Transparent Interconnection of Lots of
             Links (TRILL): Adjacency", RFC 7177, May 2014.

   [RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
             Scope Link State PDUs (LSPs)", RFC 7356, September 2014.

   [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, September 2014.

   [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.

   [RFC7180bis] D. Eastlake, M. Zhang, et al, "TRILL: Clarifications,
             Corrections, and Updates", draft-eastlake-trill-rfc7180bis,
             work in progress.

   [802.1AX] IEEE, "IEEE Standard for Local and metropolitan area
             networks / Link Aggregation", 802.1AX-2014, 24 December
             2014.

10.2. Informative References

   [PN]      H. Zhai, T. Senevirathne, et al, "TRILL: Pseudo-Nickname
             for Active-active Access", draft-ietf-trill-pseudonode-
             nickname, work in progress.

   [ChannelTunnel] Eastlake, D. and Y. Li, "TRILL: RBridge Channel
             Tunnel Protocol", draft-ietf-trill-channel-tunnel, work in
             progress.

   [TRILL-MT] D. Eastlake, M. Zhang, A. Banerjee, V. Manral, "TRILL:
 

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             Multi-Topology", draft-eastlake-trill-multi-topology, work
             in progress.

   [ISIS]    ISO, "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.

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

Appendix A. Scenarios for Split Horizon

    +------------------+   +------------------+   +------------------+
    |        RB1       |   |        RB2       |   |        RB3       |
    +------------------+   +------------------+   +------------------+
    L1       L2       L3   L1       L2       L3   L1       L2       L3
    VL10~20  VL15~25  VL15 VL10~20  VL15~25  VL15 VL10~20  VL15~25  VL15
    LAALP1   LAALP2   LAN  LAALP1   LAALP2   LAN  LAALP1   LAALP2   LAN
    B1       B2       B10  B1       B2       B20  B1       B2       B30

        Figure A.1: An example topology to explain split horizon

   Suppose RB1, RB2 and RB3 are the Active-Active group connecting
   LAALP1 and LAALP2. LAALP1 and LAALP2 are connected to B1 and B2 at
   their other ends. Suppose all these RBridges use port L1 to connect
   LAALP1 while they use port L2 to connect LAALP2. Assume all three L1
   enable VLAN 10~20 while all three L2 enable VLAN 15~25. So that there
   is an overlap of VLAN 15~20. The customer needs hosts in these
   overlap VLANs to communicate with each other. That is, hosts attached
   to B1 in VLAN 15~20 need to communicate with hosts attached to B2 in
   VLAN 15~20. Assume the remote plain RBridge RB4 also has hosts
   attached in VLAN 15~20 which need to communicate with those hosts in
   these VLANs attached to B1 and B2.

   Two major requirements:

   1. Frames ingressed from RB1-L1-VLAN 15~20 MUST NOT be egressed out
   of ports RB2-L1 and RB3-L1. At the same time,

   2. frames coming from B1-VLAN 15~20 should reach B2-VLAN 15~20.

   RB3 stores the information for split horizon on its ports L1 and L2.
   On L1: {<ingress_nickname_RB1, VLAN 10~20>, <ingress_nickname_RB2,
   VLAN 10~20>} and on L2: {<ingress_nickname_RB1, VLAN 15~25>,
   <ingress_nickname_RB2, VLAN 15~25>}.

 

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   Five clarification scenarios:

   a. Suppose RB2/RB3 receives a TRILL multi-destination data packet
      with VLAN 15 and ingress nickname RB1. RB3 is the single exit
      point (selected out according to the hashing function of LAALP)
      for this packet. On ports L1 and L2, RB3 has covered
      <ingress_nickname_RB1, VLAN 15>, so that RB3 will not egress this
      packet out of either L1 or L2. Here, _split horizon_ happens.

      Beforehand, RB1 obtains a native frame on port L1 from B1 in VLAN
      15. RB1 judges it should be forwarded as a multi-destination
      packet across the TRILL campus. Also, RB1 replicates this frame
      without TRILL encapsulation and sends it out of port L2, so that
      B2 will get this frame.

   b. Suppose RB2/RB3 receives a TRILL multi-destination data packet
      with VLAN 15 and ingress nickname RB4. RB3 is the single exit
      point. On ports L1 and L2, since RB3 has not stored any tuple with
      ingress_ nickname_RB4, RB3 will decapsulate the packet and egress
      it out of both ports L1 and L2. So both B1 and B2 will receive the
      frame.

   c. Suppose there is a plain LAN link port L3 on RB1, RB2 and RB3,
      connecting to B10, B20 and B30 respectively. These L3 ports happen
      to be configured with VLAN 15. On port L3, RB2 and RB3 stores no
      information of split horizon for AAE (since this port has not been
      configured to be in any LAALP). They will egress the packet
      ingressed from RB1-L1 in VLAN 15.

   d. If a packet is ingressed from RB1-L1 or RB1-L2 with VLAN 15, port
      RB1-L3 will not egress packets with ingress-nickname-RB1. RB1
      needs to replicate this frame without encapsulation and sends it
      out of port L3. This kind of 'bounce' behavior for multi-
      destination frames is just as specified in paragraph 2 of Section
      4.6.1.2 of [RFC6325].

   e. If a packet is ingressed from RB1-L3, since RB1-L1 and RB1-L2
      cannot egress packets with VLAN 15 and ingress-nickname-RB1, RB1
      needs to replicate this frame without encapsulation and sends it
      out of port L1 and L2. (Also see paragraph 2 of Section 4.6.1.2 of
      [RFC6325].)

 

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Author's Addresses

   Mingui Zhang
   Huawei Technologies
   No.156 Beiqing Rd. Haidian District,
   Beijing 100095 P.R. China
        
   EMail: zhangmingui@huawei.com

   Radia Perlman
   EMC
   2010 256th Avenue NE, #200
   Bellevue, WA 98007 USA

   EMail: radia@alum.mit.edu

   Hongjun Zhai
   Jinling Institute of Technology
   99 Hongjing Avenue, Jiangning District
   Nanjing, Jiangsu 211169  China

   EMail: honjun.zhai@tom.com

   Muhammad Durrani
   Brocade
   130 Holger Way
   San Jose, CA 95134

   EMail: mdurrani@brocade.com

   Sujay Gupta
   IP Infusion, 
   RMZ Centennial
   Mahadevapura Post
   Bangalore - 560048
   India

   EMail: sujay.gupta@ipinfusion.com

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