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TRILL: Pseudo-Nickname for Active-active Access
draft-ietf-trill-pseudonode-nickname-01

The information below is for an old version of the document.
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This is an older version of an Internet-Draft that was ultimately published as RFC 7781.
Authors Hongjun Zhai , Tissa Senevirathne , Radia Perlman , Mingui Zhang , Yizhou Li
Last updated 2014-09-05
Replaces draft-hu-trill-pseudonode-nickname
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draft-ietf-trill-pseudonode-nickname-01
TRILL Working Group                                              H. Zhai
Internet-Draft                                                       JIT
Intended Status: Standards Track                         T. Senevirathne
Expires: March 9, 2015                                     Cisco Systems
                                                              R. Perlman
                                                                     EMC
                                                                M. Zhang
                                                                   Y. Li
                                                                  Huawei
                                                       September 5, 2014

            TRILL: Pseudo-Nickname for Active-active Access 
                draft-ietf-trill-pseudonode-nickname-01

Abstract

   The IETF TRILL (TRansparent Interconnection of Lots of Links)
   protocol provides support for flow level multi-pathing for both
   unicast and multi-destination traffic in networks with arbitrary
   topology. Active-active access at the TRILL edge is the extension of
   these characteristics to end stations that are multiply connected to
   a TRILL campus. In this document, the edge RBridge (TRILL switch)
   group providing active-active access to such an end station can be
   represented as a Virtual RBridge. Based on the concept of Virtual
   RBridge along with its pseudo-nickname, this document facilitates the
   TRILL active-active access of such end stations.

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

 

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   The list of Internet-Draft Shadow Directories can be accessed at
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Copyright and License Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1. Terminology and Acronyms  . . . . . . . . . . . . . . . . .  5
   2. Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3. Virtual RBridge and its Pseudo-nickname . . . . . . . . . . . .  7
   4. Member RBridges Auto-Discovery  . . . . . . . . . . . . . . . .  8
     4.1. Discovering Member RBridge for an RBv . . . . . . . . . . .  9
     4.2. Selection of Pseudo-nickname for RBv  . . . . . . . . . . . 11
   5. Distribution Trees and Designated Forwarder . . . . . . . . . . 12
     5.1. Different Trees for Different Member RBridges . . . . . . . 13
     5.2. Designated Forwarder for Member RBridges  . . . . . . . . . 13
     5.3. Ingress Nickname Filtering  . . . . . . . . . . . . . . . . 16
   6. TRILL Traffic Processing  . . . . . . . . . . . . . . . . . . . 16
     6.1. Native Frames Ingressing  . . . . . . . . . . . . . . . . . 16
     6.2. Egressing TRILL Data Packets  . . . . . . . . . . . . . . . 17
       6.2.1. Unicast TRILL Data Packets  . . . . . . . . . . . . . . 17
       6.2.2. Multi-Destination TRILL Data Packets  . . . . . . . . . 18
   7. MAC Information Synchronization in Edge Group . . . . . . . . . 19
   8. Member Link Failure in RBv  . . . . . . . . . . . . . . . . . . 20
     8.1. Link Protection for Unicast Frame Egressing . . . . . . . . 20
   9. TLV Extensions for Edge RBridge Group . . . . . . . . . . . . . 21
     9.1. LAALP Membership (LM) Sub-TLV . . . . . . . . . . . . . . . 21
     9.2. PN-RBV sub-TLV  . . . . . . . . . . . . . . . . . . . . . . 22
     9.3. MAC-RI-LAALP Boundary APPsub-TLVs . . . . . . . . . . . . . 23
   10. OAM Packets  . . . . . . . . . . . . . . . . . . . . . . . . . 25
   11. Configuration Consistency  . . . . . . . . . . . . . . . . . . 25
 

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   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 26
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 26
   14. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 26
   15. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 26
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 27
     16.2. Informative References . . . . . . . . . . . . . . . . . . 28
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28

 

H. Zhai, et al                                                  [Page 3]
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1. Introduction

   The IETF TRILL protocol [RFC6325] provides optimal pair-wise data
   frame forwarding without configuration, safe forwarding even during
   periods of temporary loops, and support for multi-pathing of both
   unicast and multicast traffic. TRILL accomplishes this by using IS-IS
   [IS-IS] [RFC7176] link state routing and encapsulating traffic using
   a header that includes a hop count.  Devices that implement TRILL are
   called RBridges or TRILL switches.

   In the base TRILL protocol, an end node can be attached to the TRILL
   campus via a point-to-point link or a shared link such as a bridged
   LAN (Local Area Network). Although there might be more than one edge
   RBridge on a shared link, to avoid potential forwarding loops, one
   and only one of the edge RBridges is permitted to provide forwarding
   service for end station traffic in each VLAN (Virtual LAN). That
   RBridge is referred to as the Appointed Forwarder (AF) for the VLAN
   on the link [RFC6325] [RFC6439]. However, in some practical
   deployments, to increase the access bandwidth and reliability, an end
   station might be multiply connected to several edge RBridges and all
   of the uplinks are handled via a Local Active-Active Link Protocol
   (LAALP) such as a Multi-Chassis Link Aggregation (MC-LAG) bundle. In
   this case, it's required that traffic can be ingressed/egressed
   into/from the TRILL campus by any of the RBridges for each given
   VLAN. These RBridges constitutes an Active-Active Edge (AAE) RBridge
   group.

   Traffic with the same VLAN and source MAC address but belonging to
   different flows might be sent to different member RBridges of the AAE
   group, and then is ingressed into TRILL campus. When an Egress
   RBridge receives such TRILL data packets ingressed by different
   RBridges, it learns different VLAN and MAC address to nickname
   correspondences continuously when decapsulating the packets if it has
   data plane address learning enabled. This issue is known as the "MAC
   flip-flopping" issue, which makes most TRILL switches behave badly
   and causes the returning traffic to reach the destination via
   different paths resulting in persistent re-ordering of the frames. In
   addition to this issue, other issues such as duplication egressing
   and loop back of multi-destination frames may also disturb the end
   stations multiply connected to the member RBridges of an AAE group
   [AAProb].

   Edge RBridge groups, which can be represented as a Virtual RBridge
   (RBv) and assigned a pseudo-nickname, address the AAE issues of TRILL
   in this document.  A member RBridge of such a group uses a pseudo-
   nickname, instead of its own nickname, as the ingress RBridge
   nickname when ingressing frames received on attached LAALP links.

 

H. Zhai, et al                                                  [Page 4]
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   The main body of this document is organized as follows: Section 2
   gives an overview of the TRILL active-active access issues and the
   reason that a virtual RBridge (RBv) is used to resolve the issues.
   Section 3 gives the concept of virtual RBridge and its pseudo-
   nickname. Section 4 describes how edge RBridges can support an RBv
   automatically and get a pseudo-nickname for the RBv. Section 5
   discusses how to protect multi-destination traffic against disruption
   due to Reverse Forwarding Path (RPF) check failure, duplication and
   forwarding loop, etc. Section 6 covers the special processing of
   native frames and TRILL data packets at member RBridges of an RBv
   (also referred to as an Active-Active Edge (AAE) RBridge group);
   followed by Section 7, which describes the MAC information
   synchronization among the member RBridges of an RBv. Section 8
   discusses protection against downlink failure at a member RBridge;
   and Section 9 gives the necessary IS-IS code points and data
   structures for AAE RBridge group.

1.1. Terminology and Acronyms

   This document uses the acronyms and terms defined in [RFC6325]
   [AAProb], and the following additional acronyms:

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

   FGL - Fine-Grained Labeling or Fine-Grained Labeled or Fine-Grained
   Label [RFC7172].

   AAE - Active-active Edge RBridge group, a group of edge RBridges to
   which at least one CE is multiply attached with an LAALP. AAE is also
   referred to as edge group or Virtual RBridge in this document.

   LAALP - Local Active-Active Link Protocol [AAProb].

   RBv - Virtual RBridge, an alias of active-active edge RBridge group
   in this document.

   vDRB - The Designated RBridge in an RBv. It is responsible for
   deciding on a pseudo-nickname for the RBv.

   OE flag - A flag used by the member RBridge of an LAALP to tell other
   edge RBridges whether it is willing to share an RBv with other LAALPs
   if they multiply attach to the same set of edge RBridges as it. When
   this flag for an LAALP is 1, it means that the LAALP needs to be
   served by an RBv by itself and is not willing to share, that is, it
   should Occupy an RBv Exclusively (OE).

 

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   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].

2. Overview

   To minimize impact during failures and maximize available access
   bandwidth, Customer Equipment (referred to as CE in this document)
   may be multiply connected to TRILL campus via multiple edge RBridges.
   Figure 1 shows such a typical deployment scenario, where CE1 attaches
   to RB1, RB2, ... RBk and treats all of the uplinks as an LAALP
   bundle. Then RB1, RB2, ... RBk constitute an Active-active Edge (AAE)
   RBridge group for CE1 in this LAALP. Even if a member RBridge or an
   uplink fails, CE1 can still get frame forwarding service from the
   TRILL campus if there are still member RBridges and uplinks available
   in the AAE group. Furthermore, CE1 can make flow-based load balancing
   across the available member links of the LAALP bundle in the AAE
   group when it communicates with other CEs across the TRILL campus
   [AAProb].

                  ----------------------
                 |                      |
                 |     TRILL Campus     |
                 |                      |
                  ----------------------
                      |       |    |
                +-----+       |    +--------+
                |             |             |
            +------+      +------+      +------+
            |(RB1) |      |(RB2) |      | (RBk)|
            +------+      +------+      +------+
              |..|          |..|          |..|
              |  +----+     |  |          |  |
              |   +---|-----|--|----------+  |
              | +-|---|-----+  +-----------+ |
              | | |   +------------------+ | |    
    LAALP1-->(| | |)                    (| | |) <--LAALPn
            +-------+    .  .  .       +-------+
            | CE1   |                  | CEn   |
            +-------+                  +-------+

        Figure 1  Active-Active Connection to TRILL Edge RBridges       

   By design, an LAALP (say LAALP1) does not forward packets received on
   one member port to other member ports. As a result, the TRILL Hello
   messages sent by one member RBridge (say RB1) via a port to CE1 will
   not be forwarded to other member RBridges by CE1. That is to say,
 

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   member RBridges will not see each other's Hellos via the LAALP. So
   every member RBridge of LAALP1 thinks of itself as appointed
   forwarder for all VLANs enabled on an LAALP1 link and can
   ingress/egress frames simultaneously in these VLANs. 

   The simultaneous flow-based ingressing/egressing may cause some
   problems. For example, simultaneous egressing of multi-destination
   traffic by multiple member RBridges will result in frame duplication
   at CE1 (see Section 3.1 of [AAProb]); simultaneous ingressing of
   frames originated by CE1 for different flows in the same VLAN will
   result in MAC address flip-flopping at remote egress RBridges that
   has data plane address learning enabled (see Section 3.3 of
   [AAProb]). The flip-flopping would in turn cause packet re-ordering
   in reverse traffic.

   Since edge RBridges learn Data Label and MAC address to nickname
   correspondences by default via decapsulating TRILL data packets (see
   Section 4.8.1 of [RFC6325] as updated by [RFC7172]), the MAC flip-
   flopping issue should be solved based on the assumption that the
   default learning is enabled at edge RBridges. So this document
   specifies Virtual RBridge, together with its pseudo-nickname, to fix
   these issues.

3. Virtual RBridge and its Pseudo-nickname

   A Virtual RBridge (RBv) represents a group of edge RBridges to which
   at least one CE is multiply attached using LAALP. More exactly, it
   represents a group of ports on the edge RBridges providing end
   station service and the service provided to the CE(s) on these ports,
   through which the CE(s) are multiply attached to TRILL campus using
   LAALP(s). Such end station service ports are called RBv ports; in
   contrast, other access ports at edge RBridges are called regular
   access ports in this document. RBv ports are always LAALP connecting
   ports, but not vice versa (see Section 4.1). For an edge RBridge, if
   one or more of its end station service ports are ports of an RBv,
   that RBridge is a member RBridge of that RBv.

   For the convenience of description, a Virtual RBridge is also
   referred to as an Active-Active Edge (AAE) group in this document. In
   the TRILL campus, an RBv is identified by its pseudo-nickname, which
   is different from any RBridge's regular nickname(s). An RBv has one
   and only one pseudo-nickname. Each member RBridge (say RB1, RB2 ...,
   RBk) of an RBv (say RBvn) advertises RBvn's pseudo-nickname using a
   Nickname sub-TLV in its TRILL IS-IS LSP (Link State PDU) [RFC7176]
   and SHOULD do so with maximum priority of use (0xFF), along with
   their regular nickname(s). (Maximum priority is recommended to avoid
   the disruption to AAE group that would occur if the nickname were
 

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   taken away by a higher priority RBridge.) Then, from these LSPs,
   other RBridges outside the AAE group know that RBvn is reachable
   through RB1 to RBk.

   A member RBridge (say RBi) loses its membership from RBvn when its
   last port of RBvn becomes unavailable due to failure, re-
   configuration, etc. Then RBi removes RBvn's pseudo-nickname from its
   LSP and distributes the updated LSP as usual. From those updated
   LSPs, other RBridges know that there is no path to RBvn through RBi
   now.

   When member RBridges receive native frames from their RBv ports and
   decide to ingress the frames into the TRILL campus, they use that
   RBv's pseudo-nickname instead of their own regular nicknames as the
   ingress nickname to encapsulate them into TRILL Data packets. So when
   these packets arrive at an egress RBridge, even if they are
   originated by the same end station in the same VLAN but ingressed by
   different member RBridges, no address flip-flopping is observed on
   the egress RBridge when decapsulating these packets. (When a member
   RBridge of an AAE group ingresses a frame from a non-RBv port, it
   still uses its own regular nickname as the ingress nickname.)

   Since RBv is not a physical node and no TRILL frames are forwarded
   between its ports via a LAALP, pseudo-node LSP(s) MUST NOT be created
   for an RBv. RBv cannot act as a root when constructing distribution
   trees for multi-destination traffic and its pseudo-nickname is
   ignored when determining the distribution tree root for TRILL campus
   [CMT]. So the tree root priority of RBv's nickname MUST be set to 0,
   and this nickname SHOULD NOT be listed in the "s" nicknames (see
   Section 2.5 of [RFC6325]) by the RBridge holding the highest priority
   tree root nickname.

   NOTE: In order to reduce the consumption of nicknames, especially in
   large TRILL campus with lots of RBridges and/or active-active
   accesses, when multiple CEs attach to the exact same set of edge
   RBridges via LAALPs, those edge RBridges should be considered as a
   single RBv with a pseudo-nickname.

4. Member RBridges Auto-Discovery

   Edge RBridges connected to a CE via an LAALP can automatically
   discover each other with minimal configuration through exchange of
   LAALP connection information.

   From the perspective of edge RBridges, a CE that connects to edge
   RBridges via an LAALP can be identified by the ID of the LAALP that
   is unique across the TRILL campus (for example, the MC-LAG System ID
 

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   [802.1AX]), which is referred to as LAALP ID in this document. On
   each of such edge RBridges, the access port to such a CE is
   associated with an LAALP ID for the CE. An LAALP is considered valid
   on an edge RBridge only if the RBridge still has operational down-
   link to that LAALP. For such an edge RBridge, it advertises a list of
   LAALP IDs for its valid local LAALPs to other edge RBridges via its
   TRILL IS-IS LSP(s). Based on the LAALP IDs advertised by other
   RBridges, each RBridge can know which edge RBridges could constitute
   an AAE group (See Section 4.1 for more details). Then one RBridge is
   elected from the group to allocate an available nickname (the pseudo-
   nickname) for the group (See Section 4.2 for more details).

4.1. Discovering Member RBridge for an RBv

   Take Figure 2 as an example, where CE1 and CE2 multiply attach to
   RB1, RB2 and RB3 via LAALP1 and LAALP2 respectively; CE3 and CE4
   attach to RB3 and RB4 via LAALP3 and LAALP4 respectively. Assume
   LAALP3 is configured to occupy a Virtual RBridge by itself.

                      ------------------------
                    /                          \
                   |       TRILL Campus         |
                    \                          /
                      ------------------------- 
                       |    |             |  |
               +-------+    |             |  +----------+
               |            |             |             |
           +-------+     +-------+      +-------+     +-------+
           |  RB1  |     |  RB2  |      |  RB3  |     |  RB4  |
           +-------+     +-------+      +-------+     +-------+
             |   |        |   |          | | | |       |     |
             |   +--------|--+ | +-------|-+ | +-------|---+ |
             | +----------+  | | |       |   |         |   | |
             | | +-----------|-|-|-------+   | +-------+   | |
             | | |           | | |           | |           | |
    LAALP1->(| | |) LAALP2->(| | |) LAALP3->(| |) LAALP4->(| |)
           +-------+      +-------+     +-------+      +-------+
           |  CE1  |      |  CE2  |     |  CE3  |      |  CE4  |
           +-------+      +-------+     +-------+      +-------+

               Figure 2  Different LAALPs to TRILL Campus               

   RB1 and RB2 advertise {LAALP1, LAALP2} in the LAALP Membership sub-
   TLV (see Section 9.1 for more details) via their TRILL IS-IS LSPs
   respectively; RB3 announces {LAALP1, LAALP2, LAALP3, LAALP}; and RB4
   announces {LAALP3, LAALP4}, respectively.

   An edge RBridge is called an LAALP related RBridge if it has at least
 

H. Zhai, et al                                                  [Page 9]
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   one LAALP configured on an access port. On receipt of the LAALP
   Membership sub-TLVs, RBn ignores them if it is not an LAALP related
   RBridge; otherwise, RBn SHOULD use the LAALP information contained in
   the sub-TLVs, along with its own LAALP Membership sub-TLVs to decide
   which RBv(s) it should join and which edge RBridges constitute each
   of such RBvs. Based on the information received, each of the 4
   RBridges knows the following information:

              LAALP ID   OE-flag    Set of edge RBridges
              ---------   --------   ---------------------
              LAALP1      0          {RB1, RB2, RB3}
              LAALP2      0          {RB1, RB2, RB3}
              LAALP3      1          {RB3, RB4}
              LAALP4      0          {RB3, RB4}

   Where the OE-flag indicates whether an LAALP is willing to share an
   RBv with other LAALPs if they multiply attach to exact the same set
   of edge RBridges as it. For an LAALP (for example LAALP3), if its OE-
   flag is one, it means that LAALP3 does not want to share, so it MUST
   Occupy an RBv Exclusively (OE).

   Otherwise, the LAALP (for example LAALP1) will share an RBv with
   other LAALPs if possible. By default, this flag is set zero. For an
   LAALP, this flag is considered 1 only if any edge RBridge advertises
   it as one (see Section 9.1). 

   In the above table, there might be some LAALPs that attach to a
   single RBridge due to mis-configuration or link failure, etc. Those
   LAALPs are considered as invalid entries. Then each of the LAALP
   related edge RBridges performs the following algorithm to decide
   which valid LAALPs can be served by an RBv.

   Step 1: Take all the valid LAALPs that have their OE-flags set to 1
   out of the table and create an RBv per such LAALP.

   Step 2: Sort the valid LAALPs left in the table in descending order
   based on the number of RBridges in their associated set of multi-
   homed RBridges. In the case that several LAALPs have same number of
   RBridges, these LAALPs are then ordered in ascending order in the
   proper places of the table based on their LAALP IDs considered as
   unsigned integers. (for example, in the above table, both LAALP1 and
   LAALP2 have 3 member RBridges, assuming LAALP1 ID is smaller than
   LAALP2 ID, so LAALP1 is followed by LAALP2 in the ordered table.)

   Step 3: Take the first valid LAALP (say LAALP_i) with the maximum set
   of RBridges, say S_i, out of the table and create a new RBv (Say
   RBv_i) for it.

 

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   Step 4: Walk through the remaining valid LAALPs in the table one by
   one, pick up all the valid LAALPs that their sets of multi-homed
   RBridges contain exactly the same RBridges as that of LAALP_i and
   take them out of the table.  Then appoint RBv_i as the servicing RBv
   for those LAALPs.

   Step 5: Repeat Step 3-4 for the left LAALPs until all the valid
   entries in the table has be associated with an RBv.

   After performing the above steps, all the 4 RBridges know that LAALP3
   is served by an RBv, say RBv1, which has RB3 and RB4 as member
   RBrdges; LAALP1 and LAALP2 are served by another RBv, say RBv2, which
   has RB1, RB2 and RB3 as member RBridges; and LAALP4 is served by
   RBv3, which has RB3 and RB4 as member RBridges, shown as follows:

         RBv    Serving LAALPs       Member RBridges
         -----  -------------------  ---------------
         RBv1   {LAALP3}             {RB3, RB4}
         RBv2   {LAALP1, LAALP2}     {RB1, RB2, RB3}
         RBv3   {LAALP4}             {RB3, RB4}

   In each RBv, one of the member RBridges is elected as the DRB
   (Designated RBridge) of the RBv. Then this RBridge picks up an
   available nickname as the pseudo-nickname for the RBv and announces
   it to all other member RBridges of the RBv via its TRILL IS-IS LSPs
   (refer to Section 9.2 for the relative extended sub-TLVs).

4.2. Selection of Pseudo-nickname for RBv

   As described in Section 3, in the TRILL campus, an RBv is identified
   by its pseudo-nickname. In an AAE group (i.e., RBv), one member
   RBridge is elected for the duty to select a pseudo-nickname for this
   RBv; this RBridge is called Designated RBridge of the RBv (vDRB) in
   this document. The winner is the RBridge with the largest IS-IS
   System ID considered as an unsigned integer, in the group. Then based
   on its TRILL IS-IS link state database and the potential pseudo-
   nickname(s) reported in the LAALP Membership sub-TLVs by other member
   RBridges of this RBv (see Section 9.1 for more details), the vDRB
   selects an available nickname as the pseudo-nickname for this RBv and
   advertizes it to the other RBridges via its TRILL IS-IS LSP(s) (see
   Section 9.2). Except as provided below, the selection of a nickname
   to use as the pseudo-nickname follows the usual TRILL rules given in
   [RFC6325] as updated by [RFC7180bis]. On receipt of the pseudo-
   nickname advertised by the vDRB, all the other RBridges of that group
   associate it with the LAALPs served by the RBv, and then download the
   association to their data plane fast path logic.

   To reduce the traffic disruption caused by nickname changing, if
 

H. Zhai, et al                                                 [Page 11]
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   possible, vDRB SHOULD attempt to reuse the pseudo-nickname recently
   used by the group when selecting nickname for the RBv. To help the
   vDRB to do so, each LAALP related RBridge advertises a re-using
   pseudo-nickname for each of its LAALPs in its LAALP Membership sub-
   TLV if it has used such a pseudo-nickname for that LAALP recently.
   Although it is up to the implementation of the vDRB as to how to
   treat the re-using pseudo-nicknames, the following is suggested:

   o  If there are multiple available re-using pseudo-nicknames that are
      reported by all the member RBridges of some LAALPs in this RBv,
      the available one that is reported by most of such LAALPs is
      chosen as the pseudo-nickname for this RBv. If a tie exists, the
      re-using pseudo-nickname with the smallest value considered as an
      unsigned integer is chosen.

   o  If only one re-using pseudo-nickname is reported, it SHOULD be
      chosen if available.

   If there is no available re-using pseudo-nickname reported, the vDRB
   selects a nickname by its usual method.

   Then the selected pseudo-nickname is announced by the vDRB to other
   member RBridges of this RBv in the PN-RBv sub-TLV (see Section 9.2)
   via its TRILL IS-IS LSP(s). After receiving the pseudo-nickname,
   other RBridges of that RBv associate the nickname with their ports of
   that RBv and download the association to their data plane fast path
   logic.

5. Distribution Trees and Designated Forwarder

   In an AAE group (i.e., an RBv), as each of the member RBridges thinks
   it is the appointed forwarder for VLAN x, without changes made for
   active-active connection support, they would all ingress/egress
   frames into/from TRILL campus for all VLANs. For multi-destination
   frames, more than one member RBridges ingressing them may cause some
   of the resulting TRILL Data packets to be discarded due to failure of
   Reverse Path Forwarding (RPF) Check on other RBridges; for a multi-
   destination traffic, more than one RBridges egressing it may cause
   local CE(s) receiving duplication frames [AAProb]. Furthermore, in an
   AAE group, a multi-destination frame sent by a CE (say CEi) may be
   ingressed into TRILL campus by one member RBridge, then another
   member RBridge will receive it from TRILL campus and egress it to
   CEi, which will result in loop back of frame for CEi. 

   In the following sub-sections, the first two issues are discussed in
   Section 5.1 and Section 5.2, respectively; the third one is discussed
   in Section 5.3.
 

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5.1. Different Trees for Different Member RBridges

   In TRILL, RBridges use distribution trees to forward multi-
   destination frames (although under some circumstances they can be
   unicast as specified in [RFC7172]). RPF Check along with other
   checking is used to avoid temporary multicast loops during topology
   changes (Section 4.5.2 of [RFC6325]). RPF check mechanism only
   accepts a multi-destination frame ingressed by an RBridge RBi and
   forwarded on a distribution tree Tx if it arrives at another RBridge
   RBn on an expected port. If arriving on other ports, the frame MUST
   be dropped. To avoid address flip-flopping on remote RBridges, member
   RBridges use RBv's pseudo-nickname instead of their regular nicknames
   as ingress nickname to ingress native frames, including multicast
   frames. From the view of other RBridges, these frames appear as if
   they were ingressed by the RBv. When multicast frames of different
   flows are ingressed by different member RBridges of an RBv and
   forwarded along the same distribution tree, they may arrive at RBn on
   different ports. Some of them will violate the RFC check principle at
   RBn and be dropped, which may result in traffic disruption.

   In an RBv, if different member RBridge uses different distribution
   trees to ingress multi-destination frames, the RFC check violation
   issue can be fixed. Coordinated Multicast Trees (CMT) proposes such
   an approach, and makes use of the Affinity sub-TLV defined in
   [RFC7176] to tell other RBridges which trees a member RBridge (say
   RBi) may choose when ingressing multi-destination frames, then all
   RBridges in the TRILL campus calculate RFC check information for RBi
   on those trees [CMT].

   In this document, the approach proposed in [CMT] is used to fix the
   RFC check violation issue, please refer to [CMT] for more details of
   the approach.

5.2. Designated Forwarder for Member RBridges

   Take Figure 3 as an example, where CE1 and CE2 are served by an RBv,
   which has RB1 and RB2 as member RBridges. In VLAN x, the three CEs
   can communicate with each other.

 

H. Zhai, et al                                                 [Page 13]
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                    ---------------------
                  /                       \
                 |       TRILL Campus      |
                  \                       /
                   -----------------------
                       |             |
                  +----+             +------+
                  |                         |
             +---------+                +--------+
             |   RB1   |                |   RB2  |
             | oooooooo|oooooooooooooooo|ooooo   | 
             +o--------+    RBv         +-----o--+ 
               o|oooo|oooooooooooooooooooo|o|o  | 
                | +--|--------------------+ |   |  
                | |  +---------+ +----------+   |  
               (| |)<-LAALP1  (| |)<-LAALP2     |
            +-------+       +-------+      +-------+ 
            |  CE1  |       |  CE2  |      |  CE3  | 
            +-------+       +-------+      +-------+

       Figure 3  A Topology with Multi-homed and Single-homed CEs       

   When a remote RBridge (say RBn) sends a multi-destination TRILL Data
   packet in VLAN x (or the FGL that VLAN x maps to if the packet is an
   FGL one), both RB1 and RB2 will receive it. As each of them thinks it
   is the appointed forwarder for VLAN x, without changes made for
   active-active connection support, they would both forward the frame
   to CE1/CE2. As a result, CE1/CE2 would receive duplication copies of
   the frame through this RBv.

   In another case, assume CE3 is single-homed to RB2. When it transmits
   a native multi-destination frame onto link CE3-RB2 in VLAN x, the
   frame can be locally replicated to the ports to CE1/CE2, and also
   encapsulated into TRILL Data packet and ingressed into TRILL campus.
   When the packet arrives at RB1 across the TRILL campus, it will be
   egressed to CE1/CE2 by RB1. Then CE1/CE2 receives duplicate copies
   from RB1 and RB2.

   In this document, Designated Forwarder (DF) for a VLAN is introduced
   to avoid the duplicate copies. The basic idea of DF is to elect one
   RBridge per VLAN from an RBv to egress multi-destination TRILL Data
   traffic and replicate locally-received multi-destination native
   frames to the CEs served by the RBv.

   Note that DF has an effect only on the egressing/replicating of
   multi-destination traffic, no effect on the ingressing of frames or
   forwarding/egressing of unicast frames. Furthermore, DF check is
   performed only for RBv ports, not on regular access ports.
 

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   Each RBridge in an RBv elects a DF using same algorithm which
   guarantees the same RBridge elected as DF per VLAN.

   Assuming there are m LAALPs and k member RBridges in an RBv; each
   LAALP is referred to as LAALPi where 0 <= i < m, and each RBridge is
   referred to as RBj where 0 <= j < k-1, DF election algorithm per VLAN
   is as follows:

   Step 1: For LAALPi, sort all the RBridges in numerically ascending
   order based on (System IDj | LAALPi) mod k, where "System IDj" is the
   IS-IS System ID of RBj, "|" means concatenation, and LAALPi is the
   LAALP ID for LAALPi. In the case that some RBridges get the same
   result of the mod, these RBridges are sorted in numerically ascending
   order in the proper places of the result in the list by their System
   IDs.

   Step 2: Each RBridge in the numerically sorted list is assigned a
   monotonically increasing number j, such that increasing number j
   corresponding to its position in the sorted list, i.e., the first
   RBridge (the first one with the smallest (System ID | LAALP ID) mod
   k) is assigned zero and the last is assigned k-1.

   Step 3: For VLAN ID n, choose the RBridge whose number equals (n mod
   k) as DF.

   Step 4: Repeat Step 1-3 for the remaining LAALPs until there is a DF
   per VLAN per LAALP in the RBv.

   For a multi-destination native frame of VLAN x received, if RBi is an
   LAALP attached RBridge, in addition to local replication of the frame
   to regular access ports as per [RFC6325] (and [RFC7172] for FGL), it
   should also locally replicate the frame to the following RBv ports:

   1) RBv ports associated with the same pseudo-nickname as that of the
      incoming port, no matter whether RBi is the DF for the frame's
      VLAN on the outgoing ports;

   2) RBv ports on which RBi is the DF for the frame's VLAN while they
      are associated with different pseudo-nickname(s) to that of the
      incoming port.

   Furthermore, the frame MUST NOT be replicated back to the incoming
   port. For non-LAALP related RBridges or for non-RBv ports on an LAALP
   related RBridge, local replication is performed as per [RFC6325].

   For a multi-destination TRILL Data packet received, RBi MUST NOT
   egress it out of the RBv ports where it is not DF for the frame's
   Inner.VLAN (or for the VLAN corresponding to the Inner.Label if the
 

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   packet is an FGL one). Otherwise, whether or not egressing it out of
   such ports is further subject to the filtering check result of the
   frame's ingress nickname on these ports (see Section 5.3).

5.3. Ingress Nickname Filtering

   As shown in Figure 3, CE1 may send a multicast traffic in VLAN x to
   TRILL campus via a member RBridge (say RB1). The traffic is then
   TRILL-encapsulated by RB1 and delivered through TRILL campus to
   multi-destination receivers. RB2 may receive the traffic, and egress
   it back to CE1 if it is the DF for VLAN x on the port to LAALP1. Then
   the traffic loops back to CE1 (see Section 3.2 of [AAProb]).

   To fix the above issue, an ingress nickname filtering check is
   required by this document. The idea of this check is to check the
   ingress nickname of a multi-destination TRILL Data packet before
   egressing a copy of it out of an RBv port. If the ingress nickname
   matches the pseudo-nickname of the RBv (associated with the port),
   the filtering check should fail and the copy MUST NOT be egressed out
   of that RBv port. Otherwise, the copy is egressed out of that port if
   it has also passed other checks, such as the appointed forwarder
   check in Section 4.6.2.5 of [RFC6325] and the DF check in Section
   5.2.

   Note that this ingress nickname filtering check has no effect on the
   multi-destination native frames received on access ports and
   replicated to other local ports (including RBv ports), since there is
   no ingress nickname associated with such frames. Furthermore, for the
   RBridge regular access ports, there is no pseudo-nickname associated
   with them; so no ingress nickname filtering check is required on
   those ports.

   More details of data packet processing on RBv ports are given in the
   next section.

6. TRILL Traffic Processing

   This section provides more details of native frame and TRILL Data
   packet processing as it relates to the RBv's pseudo-nickname.

6.1. Native Frames Ingressing

   When RB1 receives a unicast native frame from one of its ports that
   has end-station service enabled, it processes the frame as described
   in Section 4.6.1.1 of [RFC6325] with the following exception.

   o  If the port is an RBv port, RB1 uses the RBv's pseudo-nickname,
 

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      instead of one of its regular nickname(s) as the ingress nickname
      when doing TRILL encapsulation on the frame.

   When RB1 receives a native multi-destination (Broadcast, Unknown
   unicast or Multicast) frame from one of its access ports (including
   regular access ports and RBv ports), it processes the frame as
   described in Section 4.6.1.2 of [RFC6325] with the following
   exceptions.

   o  If the incoming port is an RBv port, RB1 uses the RBv's pseudo-
      nickname, instead of one of its regular nickname(s) as the ingress
      nickname when doing TRILL encapsulation on the frame.

   o  For the copies of the frame replicated locally to RBv ports, there
      are two cases as follows:

      -  If the outgoing port(s) is associated with the same pseudo-
         nickname as that of the incoming port, the copies are forwarded
         out of that outgoing port(s) after passing the appointed
         forwarder check for the frame's VLAN. That is to say, the
         copies are processed on such port(s) as Section 4.6.1.2 of
         [RFC6325].

      -  Else, the Designated Forwarder (DF) check is further made on
         the outgoing ports for the frame's VLAN after the appointed
         forwarder check. The copies are not output through the ports
         that failed the DF check (i.e., RB1 is not DF for the frame's
         VLAN on the ports); otherwise, the copies are forwarded out of
         the ports that pass the DF check (see Section 5.2).

   For such a frame received, the MAC address information learned by
   observing it, together with the LAALP ID of the incoming port SHOULD
   be shared with other member RBridges in the group (see Section 7).

6.2. Egressing TRILL Data Packets

   This section describes egress processing of the TRILL Data packets
   received on an RBv member RBridge (say RBn). Section 6.2.1 describes
   the egress processing of unicast TRILL Data packets and Section 6.2.2
   specifies the multi-destination TRILL Data packets egressing.

6.2.1. Unicast TRILL Data Packets

   When receiving a unicast TRILL data packet, RBn checks the egress
   nickname in the TRILL header of the packet.  If the egress nickname
   is one of RBn's regular nicknames, the packet is processed as defined
   in Section 4.6.2.4 of [RFC6325].

 

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   If the egress nickname is the pseudo-nickname of one local RBv, RBn
   is responsible for learning the source MAC address, unless the data
   plane learning has been disabled. The learned {Inner.MacSA, Data
   Label, ingress nickname} triplet SHOULD be shared within the AAE
   group (See Section 7).

   Then the packet is de-capsulated to its native form. The Inner.MacDA
   and Data Label are looked up in RBn's local forwarding tables, and
   one of the three following cases may occur. RBn uses the first case
   that applies and ignores the remaining cases:

   o  If the destination end station identified by the Inner.MacDA and
      Data Label is on a local link, the native frame is sent onto that
      link with the VLAN from the Inner.VLAN or VLAN corresponding to
      the Inner.Label if the packet is FGL.

   o  Else if RBn can reach the destination through another member
      RBridge RBk, it tunnels the native frame to RBk by re-
      encapsulating it into a unicast TRILL Data packet and sends it to
      RBk. RBn uses RBk's regular nickname, instead of the pseudo-
      nickname as the egress nickname for the re-encapsulation, and the
      ingress nickname remains unchanged (Section 2.4.2.1 of
      [RFC7180bis]). If the hop count value of the packet is too small
      for it to reach RBk safely, RBn SHOULD increase that value
      properly in doing the re-encapsulation. (NOTE: When receiving that
      re-encapsulated TRILL Data packet, as the egress nickname of the
      packet is RBk's regular nickname rather than the pseudo-nickname
      of a local RBv, RBk will process it as Section 4.6.2.4 of
      [RFC6325], and will not re-forward it to another RBridge.)

   o  Else, RBn does not know how to reach the destination; it sends the
      native frame out of all the local ports on which it is appointed
      forwarder for the Inner.VLAN (or appointed forwarder for the VLAN
      into which the Inner.Label maps for FGL TRILL Data packet
      [RFC7172]).

6.2.2. Multi-Destination TRILL Data Packets

   When RB1 receives a multi-destination TRILL Data Packet, it checks
   and processes the packet as described in Section 4.6.2.5 of [RFC6325]
   with the following exception.

   o  On each RBv port where RBn is the appointed forwarder for the
      packet's Inner.VLAN (or for the VLAN to which the packet's
      Inner.Label maps if it is an FGL TRILL Data packet), the
      Designated Forwarder check (see Section 5.2) and the Ingress
      Nickname Filtering check (see Section 5.3) are further performed.
      For such an RBv port, if either the DF check or the filtering
 

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      check fails, the frame MUST NOT be egressed out of that port. That
      is to say, 1) if the port is associated with the same pseudo-
      nickname as the ingress nickname of the packet, the packet SHOULD
      be discarded; or 2) if RBn is not the DF for the packet's
      Inner.VLAN (or VLAN the packet's Inner.Label maps to) on the port,
      the packet SHOULD also be discarded; otherwise, it can be egressed
      out of the port.

7. MAC Information Synchronization in Edge Group

   An edge RBridge, say RB1 in LAALP1, may have learned a MAC address
   and Data Label to nickname correspondence for a remote host h1 when
   h1 sends a packet to CE1. The returning traffic from CE1 may go to
   any other member RBridge of LAALP1, for example RB2. RB2 may not have
   that correspondence stored. Therefore it has to do the flooding for
   unknown unicast. Such flooding is unnecessary since the returning
   traffic is almost always expected and RB1 had learned the address
   correspondence. To avoid the unnecessary flooding, RB1 SHOULD share
   the correspondence with other RBridges of LAALP1. RB1 synchronizes
   the correspondence by using MAC-RI sub-TLV [RFC6165] in its ESADI-
   LSPs [RFC7357].

   On the other hand, RB2 has learned the MAC&VLAN of CE1 when CE1 sends
   a frame to h1 through RB2. The returning traffic from h1 may go to
   RB1. RB1 may not have CE1's MAC&VLAN stored even though it is in the
   same LAALP for CE1 as RB2. Therefore it has to flood the traffic out
   of all its access ports where it is appointed forwarder for the VLAN
   (see Section 6.2.1). Such flooding is unnecessary since the returning
   traffic is almost always expected and RB2 had learned the CE1's
   MAC&VLAN information. To avoid that unnecessary flooding, RB2 SHOULD
   share the MAC and VLAN (or MAC and FGL if the egress port is an FGL
   port [RFC7172]) with other RBridges of LAALP1. RB2 synchronizes the
   MAC and Data Label by enclosing the relative MAC-RI TLV with a pair
   of boundary TRILL APPsub-TLVs for LAALP1 (see Section 9.3) in its
   ESADI-LSP [RFC7357]. After receiving the enclosed MAC-RI TLVs, the
   member RBridges of LAALP1 (i.e., LAALP1 related RBridges) treat the
   MAC and Data Label as if it learned them locally on its member port
   of LAALP1; the LAALP1 unrelated RBridges just ignore LAALP1's
   information contained in the boundary APPsub-TLVs and treat the MAC
   and Data Label as specified in [RFC7357]. Furthermore, in order to
   make the the LAALP1 unrelated RBridges know that the MAC/Data Label
   is reachable through the RBv that provides service to LAALP1, the
   Topology-id/Nickname field of the MAC-RI TLV SHOULD carry the pseudo-
   nickname of the RBv rather than zero or one of the originating
   RBridge's (i.e., RB2's) regular nicknames.

 

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8. Member Link Failure in RBv

   As shown in Figure 4, suppose the link RB1-CE1 fails. Although a new
   RBv will be formed by RB2 and RB3 to provide active-active service
   for LAALP1 (see Section 5), the unicast traffic to CE1 might be still
   forwarded to RB1 before the remote RBridge learns CE1 is attached to
   the new RBv. That traffic might be disrupted by the link failure.
   Section 8.1 discusses the failure protection in this scenario.

   However, for multi-destination TRILL Data packets, since they can
   reach all member RBridges of the new RBv and be egressed to CE1 by
   either RB2 or RB3 (i.e., the new DF for the traffic's Inner.VLAN or
   the VLAN the packet's Inner.Label maps to in the new RBv), special
   actions to protect against down-link failure for such multi-
   desination packets is not needed.

                   ------------------    
                 /                    \  
                |     TRILL Campus     | 
                 \                    / 
                  --------------------  
                      |     |     |         
                  +---+     |     +----+    
                  |         |          |    
              +------+     +------+   +------+
              | RB1  |     | RB2  |   | RB3  |
              ooooooo|ooooo|oooooo|ooo|ooooo | 
             o+------+ RBv +------+   +-----o+  
              o|oooo|ooooooo|oooo|ooooo|oo|o 
               |    |       |  +-|-----+  |    
              \|/+--|-------+  | +------+ |  
             - B |  +----------|------+ | |  
              /|\| +-----------+      | | |
              (| | |)<--LAALP1       (| | |)<--LAALP2
             +-------+              +-------+
             |  CE1  |              |  CE2  |
             +-------+              +-------+
   B - Failed Link or Link bundle

       Figure 4  A Topology with Multi-homed and Single-homed CEs       

8.1. Link Protection for Unicast Frame Egressing

   When the link CE1-RB1 fails, RB1 loses its direct connection to CE1.
   The MAC entry through the failed link to CE1 is removed from RB1's
   local forwarding table immediately. Another MAC entry learned from
   another member RBridge of LAALP1 (for example RB2, since it is still
   a member RBridge of LAALP1) is installed into RB1's forwarding table
 

H. Zhai, et al                                                 [Page 20]
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   (see Section 9.3).  In that new entry, RB2 (identified by one of its
   regular nicknames) is the egress RBridge for CE1's MAC address. Then
   when a TRILL Data packet to CE1 is delivered to RB1, it can be
   tunneled to RB2 after being re-encapsulated (ingress nickname remains
   unchanged and egress nickname is replaced by RB2's regular nickname)
   based on the above installed MAC entry (see bullet 2 in Section
   6.2.1). Then RB2 receives the frame and egresses it to CE1.

   After the failure recovery, RB1 learns that it can reach CE1 via link
   CE1-RB1 again by observing CE1's native frames or from the MAC
   information synchronization by member RBridge(s) of LAALP1 described
   in Section 7, then it restores the MAC entry to its previous one and
   downloads it to its data plane fast path logic.

9. TLV Extensions for Edge RBridge Group

9.1. LAALP Membership (LM) Sub-TLV

   This Sub-TLV is used by an edge RBridge to announce its associated
   LAALP information. It is defined as a sub-TLV of the Router
   Capability TLV (#242) and the Multi-Topology-Aware Capability (MT-
   CAP) TLV (#144). It has the following format:

         +-+-+-+-+-+-+-+-+
         |  Type= LAALPM |  (1 byte)
         +-+-+-+-+-+-+-+-+
         |  Length       |  (1 byte)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
         |  LAALP RECORD(1)                          |  (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
         .                                           .
         .                                           .
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
         |  LAALP RECORD(n)                          |  (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

            Figure 5  LAALP Membership Advertisement Sub-TLV            

   where each LAALP RECORD has the following form:

 

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         +--+-+-+-+-+-+-+-+
         |OE|     RESV    |                  (1 byte)
         +--+-+-+-+-+-+-+-+
         |  Size          |
         +--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |  Re-using Pseudo-nickname      |  (2 bytes)
         +--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
         |  LAALP ID                                  |  (variable)
         +--+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   o  LAALPM (1 byte): Defines the type of this sub-TLV, #TBD.

   o  Length (1 byte): the sum of the lengths of the LAALP RECORDs. 

   o  OE (1 bit): an flag indicating whether or not the LAALP wants to
      occupy an RBv by itself; 1 for occupying by itself (or Occupying
      Exclusively (OE)). By default, it is set to 0 on transmit. This
      bit is used for edge RBridge group auto-discovery (see Section
      4.1). For any one LAALP, the values of this flag might conflict in
      the LSPs advertised by different member RBridges of that LAALP. In
      that case, the flag for that LAALP is considered as 1.

   o  RESV (7 bits): Transmitted as zero and ignored on receipt.

   o  Size (1 byte): Size of remaining part of LAALP RECORD (2 plus
      length of the LAALP ID).

   o  Re-using Pseudo-nickname (2 bytes): Suggested pseudo-nickname of
      the AAE group serving the LAALP. If the LAALP is not served by any
      AAE group, this field MUST be set to zero. It is used by the
      originating RBridge to help the vDRB to reuse pseudo-nickname of
      an AAE group (see Section 4.2).

   o  LAALP ID (variable): The ID of the LAALP. If the LAALP is an MC-
      LAG, it is the 8 byte ID as specified in Section 5.3.2 in
      [802.1AX].

   On receipt of such a sub-TLV, if RBn is not an LAALP related edge
   RBridge, it ignores the sub-TLV; otherwise, it parses the sub-TLV.
   When new LAALPs are found or old ones are withdrawn compared to its
   old copy, and they are also configured on RBn, it triggers RBn to
   perform the "Member RBridges Auto-Discovery" approach described in
   Section 4.1.

9.2. PN-RBV sub-TLV

   PN-RBv sub-TLV is used by a Designated RBridge of a Virtual RBridge
   (vDRB) to dictate the Pseudo-nickname for the LAALPs served by the
 

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   RBv. It is defined as a sub-TLV the Router Capability TLV (#242) and
   the Multi-Topology-Aware Capability (MT-CAP) TLV (#144). It has the
   following format:

         +-+-+-+-+-+-+-+-+
         | Type= PN_RBv  |  (1 byte)
         +-+-+-+-+-+-+-+-+
         | Length        |  (1 byte)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | RBv's Pseudo-Nickname         |  (2 bytes)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         | LAALP ID Size |  (1 byte)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
         | LAALP ID (1)                                |  (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
         .                                             .
         .                                             .
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+
         | LAALP ID (n)                                |  (variable)
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+...+-+

   o  PN_RBv (1 byte): Defines the type of this sub-TLV, #TBD.

   o  Length (1 byte): 3+n*k bytes, where there are n LAALP IDs, each of
      size k bytes.

   o  RBv's Pseudo-Nickname (2 bytes): The appointed pseudo-nickname for
      the RBv that serves for the LAALPs listed in the following fields.

   o  LAALP ID Size (1 byte): The size of each of the following LAALP
      IDs in this sub-TLV. 8 if the LAALPs listed are MC-LAGs

   o  LAALP ID (LAAP ID Size bytes): The ID of the LAALP.

   This sub-TLV may occur multiple times with the same RBv pseudo-
   nickname with the meaning that all of the LAALPs listed are
   identified by that pseudo-nickname. For example, if there are LAALP
   IDs of different length, then the LAALP IDs of each size would have
   to be listed in a separate sub-TLV.

   On receipt of such a sub-TLV, if RBn is not an LAALP related edge
   RBridge, it ignores the sub-TLV. Otherwise, if RBn is also a member
   RBridge of the RBv identified by the list of LAALPs, it associates
   the pseudo-nickname with the ports of these LAALPs and downloads the
   association onto data plane fast path logic.

9.3. MAC-RI-LAALP Boundary APPsub-TLVs

 

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   In this document, two APPsub-TLVs are used as boundary APPsub-TLVs
   for edge RBridge to enclose the MAC-RI TLV(s) containing the MAC
   address information leant form local port of an LAALP when this
   RBridge wants to share the information with other edge RBridges. They
   are defined as TRILL APPsub-TLVs [RFC7357]. The MAC-RI-LAALP-INFO-
   START APPsub-TLV has the following format: 

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type =MAC-RI-LAALP-INFO-START | (2 byte)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Length                        | (2 byte)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-...+-+-+-+-+-+-+
      | LAALP ID                                 | (variable)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-...+-+-+-+-+-+-+

   o  MAC-RI-LAALP-INFO-START (2 bytes): Defines the type of this
      APPsub-TLV, #TBD.

   o  Length (2 bytes): the size of the following LAALP ID. 8 if the
      LAALP listed is an MAC-LAG.

   o  LAALP ID (variable): The ID of the LAALP (for example, for an MC-
      LAG the ID as specified in Section 5.3.2 in [802.1AX]). This ID
      identifies the LAALP for all MAC addresses contained in following
      MAC-RI TLVs until an MAC-RI-LAALP-INFO-END APPsub-TLV is
      encountered.

   MAC-RI-LAALP-INFO-END APPsub-TLV is defined as follows:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type = MAC-RI-LAALP-INFO-END  | (2 byte)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Length                        | (2 byte)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   o  MAC-RI-LAALP-INFO-END (2 bytes): Defines the type of this sub-TLV,
      #TBD.

   o  Length (2 bytes): 0.

   This pair of APPsub-TLVs can be carried multiple times in an ESADI
   LSP and in multiple ESADI LSPs. When an LAALP related edge RBridge
   (say RBn) wants to share with other edge RBridges the MAC addresses
   learned on its local ports of different LAALPs, it uses one or more
   pairs of such APPsub-TLVs for each of such LAALPs in its ESADI-LSPs.
   Each encloses the MAC-RI TLVs containing the MAC addresses learned
   from a specific LAALP. Furthermore, if the LAALP is served by a local
   RBv, the value of Topology ID/Nickname field in the relative MAC-RI
 

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   TLVs SHOULD be the pseudo-nickname of the RBv rather than one of the
   RBn's regular nickname or zero. Then on receipt of such a MAC-RI TLV,
   remote RBridges know that the contained MAC addresses are reachable
   through the RBv.

   On receipt of such boundary APPsub-TLVs, when the edge RBridge is not
   an LAALP related one or cannot recognize such sub-TLVs, it ignores
   them and continues to parse the enclosed MAC-RI TLVs per [RFC7357].
   Otherwise, the recipient parses the boundary APPsub-TLVs, and

   1) If the edge RBridge is configured with the contained LAALP and the
      LAALP is also enabled locally, it treats all the MAC addresses,
      contained in the following MC-RI TLVs enclosed by the
      corresponding pair of boundary APPsub-TLVs, as if they were
      learned from its local port of that LAALP;

   2) Else, it ignores these boundary APPsub-TLVs and continues to parse
      the following MAC-RI TLVs per [RFC7357] until another pair of
      boundary APPsub-TLVs is encountered.

10. OAM Packets

   Attention must be paid when generating OAM packets.  To ensure the
   response messages can return to the originating member RBridge of an
   RBv, pseudo-nickname cannot be used as ingress nickname in TRILL OAM
   messages, except in the response to an OAM message that has that
   RBv's pseudo-nickname as egress nickname. For example, assume RB1 is
   a member RBridge of RBvi, RB1 cannot use RBvi's pseudo-nickname as
   the ingress nickname when originating OAM messages; otherwise the
   responses to the messages may be delivered to another member RBridge
   of RBvi rather than RB1. But when RB1 responds to the OAM message
   with RBvi's pseudo-nickname as egress nickname, it can use that
   pseudo-nickname as ingress nickname in the response message.

   Since RBridges cannot use OAM messages for the learning of MAC
   addresses (Section 3.2.1 of [RFC7174]), it will not lead to MAC
   address flip-flopping at a remote RBridge even though RB1 uses its
   regular nicknames as ingress nicknames in its TRILL OAM messages
   while uses RBvi's pseudo-nickname in its TRILL Data packets.

11. Configuration Consistency

   It is important that the VLAN membership of all the RBridge ports in
   an LAALP MUST be the same.  Any inconsistencies in VLAN membership
   may result in packet loss or non-shortest paths.

   Take Figure 1 for example, suppose RB1 configures VLAN1 and VLAN2 for
 

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   the link CE1-RB1, while RB2 only configures VLAN1 for the CE1-RB2
   link.  Both RB1 and RB2 use the same ingress nickname RBv for all
   frames originating from CE1.  Hence, a remote RBridge RBx will learn
   that CE1's MAC address in VLAN2 is originating from RBv.  As a
   result, on the returning path, remote RBridge RBx may deliver VLAN2
   traffic to RB2. However, RB2 does not have VLAN2 configured on CE1-
   RB2 link and hence the frame may be dropped or has to be redirected
   to RB1 if RB2 knows RB1 can reach CE1 in VLAN2.

   Furthermore, it is important that if any VLAN in an LAALP is being
   mapped by edge RBridges to an FGL [RFC7172], that the mapping MUST be
   same for all edge RBridge ports in the LAALP. Otherwise, for example,
   unicast FGL TRILL Data packets from remote RBridges may get mapped
   into different VLANs depending on which edge RBridge receives and
   egresses them.

12. Security Considerations

   This draft does not introduce any extra security risks. For general
   TRILL Security Considerations, see [RFC6325]. For ESADI Security
   Considerations, see [RFC7357].

13. IANA Considerations

   IANA is requested to allocate code points for the 4 sub-TLVs defined
   in Section 9.

14. Acknowledgments

   We would like to thank Mingjiang Chen for his contributions to this
   document.  Additionally, we would like to thank Erik Nordmark, Les
   Ginsberg, Ayan Banerjee, Dinesh Dutt, Anoop Ghanwani, Janardhanan
   Pathang, Jon Hudson and Fangwei Hu for their good questions and
   comments.

15. Contributing Authors

 

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   Weiguo Hao
   Huawei Technologies
   101 Software Avenue,
   Nanjing 210012
   China

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

   Donald E. Eastlake, III
   Huawei Technologies
   155 Beaver Street
   Milford, MA 01757 USA

   Phone: +1-508-333-2270
   Email: d3e3e3@gmail.com

16. References

16.1. Normative References

   [CMT]      T. Senevirathne, J. Pathangi, and J. Hudson, "Coordinated
              Multicast Trees (CMT) for TRILL", draft-ietf-trill-cmt-
              01.txt Work in Progress, April 2014.

   [RFC1195]  R. Callon, "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, December 1990.

   [RFC2119]  S. Bradner, "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]  R. Perlman,  D. Eastlake,  D. Dutt, S. Gai, and A.
              Ghanwani, "Routing Bridges (RBridges): Base Protocol
              Specification", RFC 6325, July 2011. 

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

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

   [RFC7357]  Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.
 

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              Stokes, "Transparent Interconnection of Lots of Links
              (TRILL): End Station Address Distribution Information
              (ESADI) Protocol", RFC 7357, September 2014.

   [FS-LSP]   draft-ietf-isis-fs-lsp, work in progress.

   [rfc7180bis]  draft-perlman-trill-clear-correct, work in progress.

   [802.1AX]  IEEE, "IEEE Standard for Local and Metropolitan Area/
              networks Link Aggregation", 802.1AX-2008, 1 January 2008.

16.2. Informative References

   [AAProb]   Y. Li, W. Hao, R. Perlman, J. Hudson and H. Zhai, "Problem
              Statement and Goals for Active-Active TRILL Edge", draft-
              ietf-trill-active-active-connection-prob-04, June 2014.

Authors' Addresses

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

   Email: honjun.zhai@tom.com

   Tissa Senevirathne
   Cisco Systems
   375 East Tasman Drive
   San Jose, CA  95134
   USA
        
   Phone: +1-408-853-2291
   Email: tsenevir@cisco.com

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

   Email: Radia@alum.mit.edu

 

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   Mingui Zhang
   Huawei Technologies
   Huawei Building, No.156 Beiqing Rd.
   Beijing, Beijing  100095
   China

   Email: zhangmingui@huawei.com

   Yizhou Li
   Huawei Technologies
   101 Software Avenue,
   Nanjing 210012
   China 

   Phone: +86-25-56625409
   Email: liyizhou@huawei.com

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