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Versions: (draft-perlman-trill-rbridge-protocol) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 6325

TRILL Working Group                                        Radia Perlman
INTERNET-DRAFT                                          Sun Microsystems
Intended status: Proposed Standard                           Silvano Gai
                                                           Nuova Systems
                                                          Dinesh G. Dutt
                                                                   Cisco
                                                     Donald Eastlake 3rd
                                                   Motorola Laboratories
Expires: January 2008                                          July 2007


                 Rbridges: Base Protocol Specification
                 --------- ---- -------- -------------
               <draft-ietf-trill-rbridge-protocol-05.txt>


Status of This Document

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Distribution of this document is unlimited. Comments should be sent
   to the TRILL working group mailing list.

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














R. Perlman, S. Gai, D. Dutt, D. Eastlake                        [Page 1]


INTERNET-DRAFT                                          RBridge Protocol


Abstract

   RBridges allow for optimal pair-wise forwarding with zero
   configuration, safe forwarding even during periods of temporary
   loops, and multipathing for both unicast and multicast traffic. They
   achieve these goals using IS-IS routing and encapsulation of traffic
   with a header that includes a hop count.

   RBridges are compatible with previous IEEE 802.1 bridges as well as
   current IPv4 and IPv6 routers and end nodes. They are as invisible to
   current IP routers as bridges are and, like routers, they terminate
   the bridge spanning tree protocol.

   The design supports VLANs, and, optionally, optimization of the
   distribution of multi-destination frames based on VLAN and IP derived
   multicast groups.  It also allows forwarding tables to be based on
   RBridge destinations (rather than end node destinations), which
   allows internal forwarding tables to be substantially smaller than in
   conventional bridge systems.



Acknowledgements

   Many people have contributed to this design, including, in alphabetic
   order, Alia Atlas, Caitlin Bestler, Stewart Bryant, James Carlson,
   Dino Farinacci, Don Fedyk, Eric Gray, Erik Nordmark, Sanjay Sane, and
   Joe Touch. We invite you to join the mailing list at
   http://www.postel.org/rbridge.























R. Perlman, S. Gai, D. Dutt, D. Eastlake                        [Page 2]


INTERNET-DRAFT                                          RBridge Protocol


Table of Contents

      Status of This Document....................................1

      Abstract...................................................2
      Acknowledgements...........................................2

      Table of Contents..........................................3

      Table of Contents Continued................................4

      Table of Contents Continued................................5

      1. Introduction............................................6
      1.1 Algorhyme V2, by Ray Perlner...........................7
      1.2 Conventions used in this document......................7

      2. RBridges................................................8
      2.1. RBridge Architecture..................................9
      2.2 RBridges and VLANs....................................11
      2.3 Forwarding of Different Frame Types...................12
      2.3.1 Known-Unicast.......................................12
      2.3.2 Multi-destination...................................12

      3. Details of the TRILL Header............................14
      3.1 TRILL Header Format...................................14
      3.2 Version / Pruning (V).................................14
      3.3 Multi-destination (M).................................15
      3.4 Hop Count.............................................15
      3.5 RBridge Nicknames.....................................16
      3.5.1 Egress RBridge Nickname.............................16
      3.5.2 Ingress RBridge Nickname............................17
      3.5.3 RBridge Nickname Allocation.........................17
      3.6 TRILL Header Options..................................18

      4. Other RBridge Design Details...........................20
      4.1 Ethernet Data Encapsulation...........................20
      4.1.1 VLAN Tag Information................................21
      4.1.2 Outer VLAN Info.....................................22
      4.1.3 Inner VLAN Info.....................................23
      4.1.4 Frame CheckSum (FCS)................................24
      4.2 Link State Protocol (IS-IS)...........................24
      4.2.1 IS-IS RBridge Identity..............................25
      4.2.2 Distinguishing IS-IS Instances......................25
      4.2.3 TRILL IS-IS Information.............................25
      4.2.3.1 Core IS-IS Information............................26
      4.2.3.2 Optional Per-VLAN IS-IS Instance Information......27
      4.2.4 Designated RBridge..................................27
      4.3 Distribution Trees....................................29
      4.3.1 Distribution Tree Calculation and Checks............30


R. Perlman, S. Gai, D. Dutt, D. Eastlake                        [Page 3]


INTERNET-DRAFT                                          RBridge Protocol


Table of Contents Continued

      4.3.2 Pruning the Distribution Tree.......................31
      4.3.3 Forwarding Using a Distribution Tree................32
      4.4 Forwarding Behavior...................................33
      4.4.1 Receipt of a Native Frame...........................33
      4.4.1.1 Native Unicast Case...............................33
      4.4.1.2 Native Multicast and Broadcast Frames.............34
      4.4.2 Receipt of a Non-Native (TRILL) Frame...............34
      4.4.2.1 TRILL IS-IS Frames................................35
      4.4.2.2 TRILL Data Frames.................................35
      4.4.2.2.1 Unicast TRILL Data Frames.......................35
      4.4.2.2.2 Multi-Destination TRILL Data Frames.............36
      4.4.3 Tree Distribution Optimization......................37
      4.5 IGMP, MLD, and MRD Learning...........................38
      4.6 Learning End Station Addresses........................38
      4.7 Shared VLAN Learning..................................40

      5. Pseudo Code............................................41
      5.1 802MUL Destination Frames.............................41
      5.1.1 Spanning Tree Protocol..............................43
      5.1.2 Media Multicast Frames..............................43
      5.1.3 802.1X Frames.......................................43
      5.1.4 802.1AB Frames......................................44
      5.1.5 GARP, GMRP, and GVRP................................44
      5.1.6 Other Bridge Frames.................................45
      5.2 Processing a Frame Received by an RBridge.............45
      5.2.1 Further Dispatch for IP Frames......................46
      5.2.2 Common Subroutines..................................46
      5.2.2.1 Learn Source MAC Address..........................47
      5.2.2.2 TRILL Data Frame Multi-destination Forwarding.....47
      5.2.2.3 TRILL Data Frame Outer VLAN Tag...................47
      5.2.3 TRILL Ethertype Frames..............................48
      5.2.3.1 TRILL IS-IS Frames................................48
      5.2.3.2 TRILL Data Frames.................................50
      5.2.4 Native Frame Receipt................................51
      5.2.5 IGMP and MLD Frames.................................53
      5.2.6 PIM and MRD Frames..................................53
      5.3 Frames Spontaneously Sourced..........................53
      5.3.1 IS-IS Frames Sourced................................53
      5.3.1.1 Core IS-IS Frames.................................54
      5.3.1.2 Per-VLAN IS-IS Frames.............................55
      5.3.2 Other Frames Sourced................................56

      6. Incremental Deployment Considerations..................57
      6.1 Incremental Deployment................................57
      6.2 Wiring Closet Topology................................58
      6.2.1 The RBridge Solution................................59
      6.2.2 The Spanning Tree Solution..........................60



R. Perlman, S. Gai, D. Dutt, D. Eastlake                        [Page 4]


INTERNET-DRAFT                                          RBridge Protocol


Table of Contents Continued

      6.2.3 The VLAN Solution...................................60
      6.2.4 Comparison of Solutions.............................61

      7. RBridge Addresses, Parameters, and Constants...........62

      8. Security Considerations................................63

      9. Assignment Considerations..............................64
      9.1 IANA Considerations...................................64
      9.2 IEEE 802 Assignment Considerations....................64

      10. Normative References..................................65
      11. Informative References................................65

      Appendix A: Revision History..............................67
      Changes from -03 to -04...................................67
      Changes from -04 to -05...................................68

      Disclaimer................................................70
      Additional IPR Provisions.................................70
      Authors' Addresses........................................70
      Expiration and File Name..................................71




























R. Perlman, S. Gai, D. Dutt, D. Eastlake                        [Page 5]


INTERNET-DRAFT                                          RBridge Protocol


1. Introduction

   In traditional IPv4 and IPv6 networks, each subnet has a unique
   prefix. Therefore, a node in multiple subnets has multiple IP
   addresses, typically one per interface. This also means that when an
   interface moves from one subnet to another, it changes its IP
   address. Administration of IP networks is complicated because IP
   routers require significant configuration and careful IP address
   management is required to avoid creating subnets that are sparsely
   populated and waste addresses.  IEEE 802.1 bridges avoid these
   problems by transparently gluing many physical links into what
   appears to IP to be a single LAN [802.1D].

   Bridge forwarding using the spanning tree protocol has some
   disadvantages:

   o  The spanning tree protocol blocks ports, limiting the number of
      forwarding links, and therefore creates bottlenecks by
      concentrating traffic onto selected links.

   o  The Ethernet header does not contain a hop count (or TTL) field
      and this is dangerous when there are temporary loops such as when
      spanning tree messages are lost or components such as repeaters
      are added.

   o  Forwarding is not pair-wise shortest path, but is instead whatever
      path remains after the spanning tree eliminates redundant paths.

   This document presents the design for RBridges (Routing Bridges),
   which combines the advantages of bridges and routers and which are
   poetically summarized below. While RBridge technology can be applied
   to a variety of link protocols, this specification concentrates on
   IEEE 802.3 links [802.3].



















R. Perlman, S. Gai, D. Dutt, D. Eastlake                        [Page 6]


INTERNET-DRAFT                                          RBridge Protocol


1.1 Algorhyme V2, by Ray Perlner

      I hope that we shall one day see
      A graph more lovely than a tree.

      A graph to boost efficiency
      While still configuration-free.

      A network where RBridges can
      Route packets to their target LAN.

      The paths they find, to our elation,
      Are least cost paths to destination!

      With packet hop count we now see,
      The network need not be loop-free!

      RBridges work transparently.
      Without a common spanning tree.



1.2 Conventions used in this document

   In general, TRILL refers to the protocol specified herein while
   RBridge refers to the devices which implement that protocol.  The
   second letter in Rbridge is case insensitive. Both Rbridge and
   RBridge are correct.

   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 [RFC2119].




















R. Perlman, S. Gai, D. Dutt, D. Eastlake                        [Page 7]


INTERNET-DRAFT                                          RBridge Protocol


2. RBridges

   The main idea is to have RBridges run a link state protocol amongst
   themselves. This enables them to have enough information to compute
   pairwise optimal paths for unicast, and to calculate distribution
   trees for delivery of frames either to unknown MAC destinations, or
   to multicast/broadcast groups.

   ECMP (Equal Cost MultiPath) may be supported, but it may introduce
   frame reordering. It is also possible, as it is with 802.1 bridges,
   for re-ordering to occur during changes in network topology.

   To mitigate temporary loop issues, RBridges forward based on a header
   with a hop count. Although the hop count discards looping frames,
   RBridges specify the next hop RBridge when forwarding unicast frames
   across a shared-media link, which avoids spawning additional copies
   of frames during a temporary loop.

   The first RBridge that a frame encounters in a campus, RB1,
   encapsulates the received frame with a TRILL header that specifies
   the last RBridge, RB2. RB1 is known as the "ingress RBridge" and RB2
   is known as the "egress RBridge".  To save room in the TRILL header,
   a dynamic nickname acquisition protocol is run among the RBridges to
   select a 2-byte nickname for each RBridge, unique within the campus,
   which is an abbreviation for the 6-byte IS-IS system ID of the
   RBridge.  The 2-byte nicknames are used to specify the ingress and
   egress RBridges in the TRILL header.

   RBridges run the IS-IS election protocol to elect one RBridge per
   link to be the "Designated RBridge" (DRB). Only the DRB on a link is
   allowed to act as the ingress RBridge, and encapsulate traffic
   received on that link, or to act as the egress RBridge and
   decapsulate traffic received from the campus and forward onto the
   link.

   If a link is actually a bridged LAN configured for VLANs, it is
   possible that the link might be partitioned with respect to some
   VLANs.  The default is to run a single DRB election on a link, with
   the IS-IS Hellos either with no VLAN tag (the default), or with the
   VLAN tag specifying the default VLAN for the link. If the RBridge is
   configured to support a set of k VLANs on the link, then the RBridge
   runs the IS-IS DRB election up to k times, each instance tagged with
   one of the VLANs in that set of VLANs depending on its configuration.
   Therefore there might be multiple DRBs on the link, but at most one
   on that link per VLAN. By configuration, the DRB for some VLANs may
   be set by copying the DRB status in the relevant RBridges from a
   different VLAN rather than by election.

   RBridges MUST learn the location of end nodes. The DRB on a link
   learns the location and layer 2 addresses of attached end nodes on


R. Perlman, S. Gai, D. Dutt, D. Eastlake                        [Page 8]


INTERNET-DRAFT                                          RBridge Protocol


   that link from the source address of frames, as bridges do (for
   example, see section 8.7 of [802.1Q]).  The DRB learns the layer 2
   address of distant end nodes, and the corresponding RBridge to which
   they are attached, by looking at the ingress RBridge nickname in the
   TRILL header and the source address in the inner frame header, of
   TRILL data frames that the DRB is decapsulating onto a link.  (See
   Section 4.6.)

   Additionally, a per-VLAN instance of IS-IS MAY be used by an RBridge
   which is DRB on a link to announce some or all of the attached end
   nodes on that link. The intention is that such an announcement would
   be used to announce end nodes that have explicitly enrolled, and so
   such information would be more authoritative than simply learning
   from data packets being decapsulated onto the link. Also, it can be
   more secure because not only might the enrollment be
   cryptographically authenticated, but IS-IS supports cryptographic
   authentication.  But even if a per-VLAN instance is used to announce
   attached end nodes, RBridges MUST still learn from decapsulating data
   packets unless configured not to do so. Conflicts are resolved using
   a confidence level reported with the address in the per-VLAN IS-IS
   data. (See Section 4.6.)

   Advertising end nodes using a per-VLAN instance of IS-IS is optional,
   as is learning from these announcements.



2.1. RBridge Architecture

      +----------------------------------------------------------+
      |                  Higher Layer Entities                   |
      +--+--------------+----------------------+--------------+--+
      |   \ TRILL Layer | RBridge Relay Entity | TRILL Layer /   |
      +----+------------+----------------------+------------+----+
      | Data Link Layer |                      | Data Link Layer |
      +-----------------+                      +-----------------+
      | Physical Layer  |                      | Physical  Layer |
      +-------+---------+                      +-------+---------+
              |                                        |
             P1                                       P2

                   Figure 1. Architecture of an RBridge

   Figure 1 shows an RBridge that contains:

   o  An Rbridge Relay Entity that interconnects two Rbridge ports;

   o  At least one port (two in the example);

   o  Higher Layer Entities, including at least the IS-IS protocol.


R. Perlman, S. Gai, D. Dutt, D. Eastlake                        [Page 9]


INTERNET-DRAFT                                          RBridge Protocol


   o  The TRILL Layer. An RBridge encapsulates incoming IEEE 802.3
      frames (in this document also referred to as Ethernet frames) with
      a TRILL header to forward them to other Rbridges.

   The layer 2 technology used to connect Rbridges may be either IEEE
   802.3 or some other technology such as PPP. This is possible since
   the functionality of an RBridge relay entity is layered on top of the
   layer 2 technologies.

   However, in accordance with the TRILL WG charter, the first edition
   of this document specifies only an IEEE 802.3 encapsulation [802.3].

   Figure 2 shows two RBridges RB1 and RB2 interconnected through an
   Ethernet cloud. There are no restrictions on what may compose the
   Ethernet cloud: point-to-point or shared media, hubs and 802.1
   bridges. The Ethernet cloud may support VLAN tagging or not.

                            ------------
                           /            \
              +-----+     /   Ethernet   \    +-----+
              | RB1 |----<                >---| RB2 |
              +-----+     \    Cloud     /    +-----+
                           \            /
                            ------------

                     Figure 2. Interconnected RBridges

   Figure 3 shows the format of a TRILL frame traveling through the
   Ethernet cloud from RB1 to RB2.

                   +--------------------------------+
                   |     Outer Ethernet Header      |
                   +--------------------------------+
                   |          TRILL Header          |
                   +--------------------------------+
                   |     Inner Ethernet Header      |
                   +--------------------------------+
                   |        Ethernet Payload        |
                   +--------------------------------+
                   |         Ethernet FCS           |
                   +--------------------------------+

              Figure 3. An Ethernet Encapsulated TRILL Frame

   In the case of other media different from Ethernet, the outer
   Ethernet header is replaced by the header specific to that media. For
   example, Figure 4 shows a TRILL encapsulation over PPP.





R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 10]


INTERNET-DRAFT                                          RBridge Protocol


                   +--------------------------------+
                   |           PPP Header           |
                   +--------------------------------+
                   |          TRILL Header          |
                   +--------------------------------+
                   |     Inner Ethernet Header      |
                   +--------------------------------+
                   |        Ethernet Payload        |
                   +--------------------------------+
                   |         Ethernet FCS           |
                   +--------------------------------+

                 Figure 4. A PPP Encapsulated TRILL Frame

   The outer header is link-specific and, although this document
   specifies only Ethernet links, other links are allowed.

   In both cases the Inner Ethernet Header and the Ethernet Payload are
   derived from the original frame though the frames are encapsulated
   with a TRILL header as they travel between RBridges for several
   reasons:

   1. to mitigate loop issues a hop count field is included;

   2. to prevent original source MAC learning in the core from frames in
      transit;

   3. to direct frames towards the egress RBridge.  This enables
      forwarding tables of RBridges to be sized with the number of
      RBridges rather than the total number of end nodes.

   When forwarding unicast frames between RBridges across a shared-
   media, the outer header contains the address of the next hop Rbridge,
   to avoid frame duplication. Having the outer header specify the
   transmitting RBridge as source address ensures that bridges inside
   the shared-media link will not get confused, as they might given
   multipathing, if they were to see the original source or ingress
   RBridge in the outer header.



2.2 RBridges and VLANs

   A VLAN is a way to partition end nodes into different communities
   [802.1Q]. The usual method of determining which community a frame
   belongs to is based on the port from which it is received although
   end stations can insert this information in a frame. Use of VLANs
   requires configuration. Rbridges can be configured to provide
   essentially the same VLAN support as IEEE 802.1Q compliant bridges.



R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 11]


INTERNET-DRAFT                                          RBridge Protocol


   IEEE 802.1Q bridges have the capability of supporting multiple VLANs
   over a single link by inserting/removing a VLAN tag into the frame.
   Some end nodes have the same capability.

   The VLAN tag is structured according to IEEE 802.1Q. As shown in
   Figure 3, there are two places where such tags may be present in a
   TRILL-encapsulated frame which is sent over an IEEE 802.3 link: one
   in the outer header (outer VLAN) and one in the inner header (inner
   VLAN). Inner and Outer VLANs are further discussed in Section 4.1.

   RBridges enforce delivery of a frame originating in a particular
   inner VLAN only to other links in the same inner VLAN.



2.3 Forwarding of Different Frame Types

   There are several types of frames which RBridges forward slightly
   differently. They are here classified into two main categories:
   known-unicast and multi-destination.



2.3.1 Known-Unicast

   These frames have an inner MAC Destination Address (Inner.MacDA) that
   is unicast and the egress RBridge for that destination MAC address
   location is known to the ingress RBridge.



2.3.2 Multi-destination

   These are frames that must be delivered to multiple destinations.

   They are as follows:

   1. frames for unknown unicast destinations: the Inner.MacDA is
      unicast, but the ingress RBridge does not know its location;

   2. frames for layer 2 multicast addresses derived from IP multicast
      addresses: the Inner.MacDA is multicast, from the set of layer 2
      multicast addresses derived from IPv4 [RFC1112] or IPv6 [RFC2464]
      multicast addresses; these frames are handled somewhat differently
      in different subcases:

      2.1 IGMP [RFC3376] and MLD [RFC2710] multicast group membership
          reports.;

      2.2 IGMP [RFC3376] and MLD [RFC2710] queries and MRD [4286]


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 12]


INTERNET-DRAFT                                          RBridge Protocol


          announcement messages;

      2.3 other IP derived layer 2 multicast frames;

   3. frames for layer 2 multicast addresses not derived from IP
      multicast addresses: the Inner.MacDA is multicast, and not from
      the set of layer 2 multicast addresses derived from IPv4 or IPv6
      multicast addresses;

   4. frames for the layer 2 broadcast addresses: the Inner.MacDA is
      broadcast.

   RBridges build distribution trees (see Section 4.3) and use these
   trees for forwarding multi-destination frames.






































R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 13]


INTERNET-DRAFT                                          RBridge Protocol


3. Details of the TRILL Header

   The section provides a textual and diagrammatic description of the
   TRILL header. Section 4 below provides other RBridge design details,
   and Section 5 give pseudo-code.



3.1 TRILL Header Format

   The TRILL header is shown in Figure 5 and is independent of the data
   link layer used. When that layer is IEEE 802.3, it is prefixed with
   the 16-bit TRILL Ethertype and is 64 bit aligned.

                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   |   V   |M|Op-Length| Hop Count |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Egress RBridge Nickname     |  Ingress RBridge Nickname     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 5. TRILL Headers

   o  V (Version / pruning): 4-bit. See Section 3.2.

   o  M (Multi-destination): 1-bit. See Section 3.3.

   o  Op-Length (Options Length): 5-bit. See Section 3.6.

   o  Hop Count: 6-bit unsigned integer. See Section 3.4.

   o  Egress RBridge Nickname: 16-bit address. See Section 3.5.1.

   o  Ingress RBridge Nickname: 16-bit address. See Section 3.5.2.



3.2 Version / Pruning (V)

   According to IEEE's Ethertype format guidelines, a single Ethertype
   is granted to a protocol and it is the protocol's responsibility to
   structure the format of the protocol header so as to support future
   revisions to the protocol. In adhering to this guideline, there is a
   two bit Version field in the TRILL header. Version is zero for TRILL
   as specified in this document. An RBridge that sees a message with a
   version value it does not understand MUST silently discard the
   message because it may not be able to parse it.

   It is also useful to distinguish TRILL frames that have been analyzed
   as to optimized tree distribution pruning particularly with regard to
   IP derived multicast. If the Version is zero, the bottom two bits of


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 14]


INTERNET-DRAFT                                          RBridge Protocol


   V indicate this status as further discussed in Section 4.4.3.

   The Version is the top or most significant two bits of the V field in
   Figure 5 while the pruning status is the bottom two bits for Version
   zero. To avoid having to state two tests when the values of these
   fields are being checked and to avoid having to state two assignments
   when the values of these fields are being set, they are concatenated
   and treated as one field called Variation and referred to by "V" in
   the rest of this document. In other words, V = ( 4 * Version ) +
   pruning status.



3.3 Multi-destination (M)

   The Multi-destination bit (see Section 2.3.2) indicates whether the
   frame is to be delivered to a single destination station or a class
   of destination end stations. It specifies the meaning of the egress
   RBridge nickname field as follows:

   o  M = 0 (FALSE) - the frame is unicast data or core TRILL IS-IS; the
      egress RBridge nickname contains the nickname of the egress
      Rbridge for a TRILL unicast data frame and is zero for a core
      instance TRILL IS-IS frame;

   o  M = 1 (TRUE) - the egress RBridge nickname field contains the
      nickname of the RBridge that is the root of the distribution tree.
      This tree is selected by the ingress RBridge for a TRILL data
      frame or the source RBridge for a per VLAN TRILL IS-IS frame.



3.4 Hop Count

   A 6-bit unsigned integer. Each RBridge that is about to forward a
   frame to another RBridge MUST check this field and discard the frame
   if this field is zero. If this field is non-zero, it MUST be
   decremented in the forwarded frame.

   For known unicast frames, the ingress RBridge (or source RBridge for
   a control frame) MUST set the Hop Count to at least the number of
   RBridge hops it expects to the egress RBridge and SHOULD set it in
   excess of that number to allow for alternate routing later in the
   path.

   For multi-destination frames, to minimize potential problems with
   temporary loops when forwarding, the Hop Count SHOULD be set by the
   ingress RBridge (or source RBridge for a control frame) to the
   expected number of hops to the most distant RBridge. To accomplish
   this, RBridge RBn calculates, for each branch of the distribution


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 15]


INTERNET-DRAFT                                          RBridge Protocol


   tree rooted at RBi, the maximum number of hops in that branch. When
   forwarding a multi-destination frame onto a branch, transit RBridge
   RBm MAY decrease the hop count by more than 1 to set the hop count to
   be no more than necessary to reach all destinations in that branch of
   the RBi tree.

   Although the RBridge MAY decrease the hop count by more than 1, the
   RBridge MUST decrease the hop count by at least 1, and discard the
   packet if the hop count becomes 0.



3.5 RBridge Nicknames

   Nicknames are 16-bit dynamically assigned abbreviations for each
   RBridge's 48-bit IS-IS System ID (see Section 4.2.1) to achieve a
   more compact encoding. This assignment allows specifying up to 64K
   RBridges. The value zero is reserved to indicate that a nickname is
   not specified and the value 0xFFFF is reserve for future
   specification.  RBridges piggyback a nickname acquisition protocol on
   the link state protocol (see Section 3.5.3) to acquire a nickname
   unique within the campus.



3.5.1 Egress RBridge Nickname

   There are three cases for the contents of this field, depending on
   the M-bit (see Section 3.3) and the Inner.MacDA (see Section 4.1). It
   is filled in by the ingress RBridge for data frames and by the source
   RBridge for control frames.

   o  For known-unicast data frames M = 0, the Inner.MacDA is not All-
      RBridge, and the egress RBridge nickname field specifies the
      egress RBridge i.e. it specifies the RBridge that needs to remove
      the TRILL header from the data frame.

   o  For multi-destination data frames, M = 1, and the egress RBridge
      nickname field contains the nickname of the root RBridge of the
      distribution tree selected to be used to forward the frame.  The
      root MUST NOT be changed by transit RBridges.

   o  For core instance TRILL IS-IS frames M = 0, Inner.MacDA == All-
      Rbridge, and egress RBridge nickname field is not used. Such
      frames may be sent before nicknames have been established and are
      only sent one hop.  The Egress RBridge Nickname MUST be set to
      zero by the source RBridge for such frames and is ignored by other
      RBridges.




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3.5.2 Ingress RBridge Nickname

   The ingress RBridge nickname contains the nickname of the ingress
   RBridge for data frames (Inner.MacDA != All-Rbridges) and for per
   VLAN TRILL IS-IS frames (Inner.MacDA == All-Rbridges and an VLAN tag
   is present).

   For core TRILL IS-IS frames (Inner.MacDA == All-Rbridges and no inner
   VLAN tag is present) this field is not used and MUST be set to zero
   by the source RBridge for the control frame and ignored by other
   RBridges.



3.5.3 RBridge Nickname Allocation

   The nickname allocation protocol is piggybacked on the core TRILL IS-
   IS instance as follows:

   o  The nickname being used by an RBridge is carried in an IS-IS TLV
      (type-length-value data element) along with a priority of use
      value.  Each RBridge chooses its own nickname.

   o  The nickname value MAY be configured. An RBridge that has been
      configured with a nickname value will have priority for that
      nickname value over all Rbridges with non-configured nicknames.

   o  The nickname values zero and 0xFFFF are reserved and may not be
      selected or configured.

   o  The priority of use field reported with a nickname is an unsigned
      8-bit value, where the most significant bit (0x80) indicates that
      the nickname value was configured. The bottom 7 bits have the
      default value 0x40, but MAY be configured to be some other value.
      Additionally, an RBridge MAY increase the priority (once) after
      holding the nickname for some amount of time, to prevent a newly
      arriving RBridge that has not yet seen all the LSPs, from usurping
      its nickname, unless the new RBridge has been configured with the
      nickname value and the RBridge using that nickname value was not
      manually configured with that nickname value. The most significant
      bit of the priority MUST NOT be set unless the nickname value was
      configured.

   o  Each RBridge is also responsible for ensuring that its nickname is
      unique.  If RB1 chooses nickname x, and RB1 discovers, through
      receipt of RB2's LSP, that RB2 has also chosen x, then the RBridge
      with the numerically higher priority keeps the nickname, or if
      there is a tie with priority, the RBridge with the numerically
      higher System ID keeps the nickname, and the other RBridge MUST
      choose a new nickname.


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   o  If two RBridge campuses merge then transient nickname collisions
      are possible. As soon as each RBridge receives the link state
      frames from the other RBridges, the RBridges that need to change
      nicknames choose new nicknames that do not, to the best of their
      knowledge, collide with any existing nicknames.

   To minimize the probability of nickname collisions, each RBridge
   chooses its nickname by randomly hashing some of its parameters.
   There is no reason for all Rbridges to use the same algorithm for
   choosing nicknames.

   Once an RBridge has successfully acquired a nickname it SHOULD store
   it in non-volatile memory and attempt to reuse it in the case of a
   reboot.

   To minimize the probability of a new RBridge usurping a nickname
   already in use, an RBridge SHOULD wait to acquire the link state
   database from a neighbor before it announces its own nickname.

   In IS-IS [ISO10589] a shared link is modeled as a pseudonode.
   Pseudonodes never act as ingress or egress RBridges and are never
   treated as distribution tree roots. Thus they do not need and do not
   have nicknames.



3.6 TRILL Header Options

   The TRILL Protocol includes an option capability in the TRILL Header.
   The Op-Length header field gives the length of the options in units
   of 4 bytes which allows up to 124 bytes of options area.  If Op-
   Length is zero there are no options present; else, the options follow
   immediately after the Ingress Rbridge Nickname field.

   All Rbridges MUST be able to skip the number of 4-byte chunks
   indicated by the Op-Length field in order to find the inner frame,
   since RBridges must be able to find the destination MAC destination
   address and VLAN tag in the inner frame.  (Transit RBridges need such
   information to filter IP multicast and VLANs, etc. Egress Rbridges
   need to find the inner frame to correctly decapsulate and dispose of
   the inner frame.)

   All transit Rbridges that do not implement any options MUST
   transparently copy the options area in frames they forward.

   Options will be further specified in later documents and are expected
   to include provisions for hop-by-hop and ingress-to-egress options as
   well as critical and non-critical options. A critical option is one
   which must be understood to safely process a frame.  A non-critical
   options can be safely ignored.


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   Warning: Most RBridges are expected to be implemented to optimize the
   simplest and most common cases of frame forwarding and processing.
   The inclusion of any options may, and the inclusion of complex or
   lengthy options almost certainly will, cause frame processing using a
   "slow path" with markedly inferior performance to "fast path"
   processing. Limited slow path throughput may cause some of such
   frames to be lost.













































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4. Other RBridge Design Details

   Section 3 above describes the TRILL Headers while this Section
   provides a textual and diagrammatic description of other RBridge
   design details. Section 5 below provides pseudo-code.



4.1 Ethernet Data Encapsulation

   TRILL data frames in transit on Ethernet links are encapsulated with
   an outer Ethernet header (see Figure 3). This outer header looks, to
   a bridge on the path between two RBridges, like the header of a
   regular Ethernet frame and therefore bridges forward the frame
   without requiring any modification. To enable RBridges to distinguish
   TRILL frames, a new Ethertype = TRILL (to be assigned) is used in the
   outer header.

   Figure 7 details a data frame with an outer VLAN tag traveling on the
   Ethernet cloud of Figure 2 from RB1 to RB2. This encapsulation has
   the advantage, in the absence of TRILL options, of aligning the
   original Ethernet frame at a 64 bit boundary.

   When a TRILL data frame is carried over an Ethernet cloud it has
   three pairs of addresses:

   o  Outer Ethernet Header: Outer Destination MAC Address and Outer
      Source MAC Address: These addresses are used to specify the next
      hop RBridge, and the transmitting RBridge, respectively, over a
      shared Ethernet cloud.

   o  TRILL Header: Egress (RB2) Nickname and Ingress (RB1) Nickname.
      These specify the nickname values of the egress and ingress
      RBridges, respectively, for data frames.

   o  Inner Ethernet Header: Inner Destination MAC Address and Inner
      Source MAC Address: These addresses are as transmitted by the
      original end node, specifying, respectively, the destination and
      source of the inner frame.

   It also potentially has two VLAN tags that can carry two different
   VLAN Identifiers and also include priority.










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   Outer Ethernet Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |             Outer Destination MAC Address  (RB2)              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Outer Destination MAC Address | Outer Source MAC Address      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                Outer Source MAC Address  (RB1)                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Ethertype = IEEE 802.1Q       |  Outer.VLAN Tag Information   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   TRILL Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Ethertype = TRILL             |   V   |M|Op-Length| Hop Count |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Egress (RB2) Nickname      |    Ingress (RB1) Nickname     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Inner Ethernet Header:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               Inner Destination MAC Address                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Inner Destination MAC Address |  Inner Source MAC Address     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                    Inner Source MAC Address                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Ethertype = IEEE 802.1Q       |  Inner.VLAN Tag Information   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Payload:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                 Original Ethernet Payload                     |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Frame CheckSum:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  New FCS (Frame CheckSum)                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 7. TRILL Data Encapsulation over Ethernet



4.1.1 VLAN Tag Information

   The information in a "VLAN Tag", also known as a "Q-tag", is more
   than just a VLAN ID. It always includes a priority field as shown in
   Figure 8. In fact, the "VLAN ID" may be zero, indicating the no VLAN
   is specified, just priority, although such a tag is properly called a
   "priority tag" rather than a "VLAN Tag" [802.1Q].




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INTERNET-DRAFT                                          RBridge Protocol


     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
     | Priority  | C |               VID (VLAN ID)                   |
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

                     Figure 8. VLAN Q-Tag Information

   As recommended in [802.1Q] Rbridges SHOULD be implemented so as to
   allow use of the full range of VIDs from 1 through 0xFFE. VID zero is
   the null VLAN identifier and indicates that no VLAN is specified
   while VID 0xFFF is reserved.  Rbridges MAY support a smaller number
   of simultaneously active VLAN IDs than the total number of different
   VLAN IDs they allow.

   The "C" bit shown in Figure 8 is the CFI or Canonical Format
   Indicator bit. It refers to the format of the associated source and
   destination addresses.  The CFI is not used with IEEE 802.3. In
   TRILL, it MUST be set to zero and is ignored by receivers.

   As specified in [802.1Q], the priority field contains an unsigned
   value from 0 through 7 where 1 indicates the lowest priority, 7 the
   highest priority, and the default priority zero is considered to be
   higher than priority 1 but lower than priority 2. Devices, including
   RBridges, are not required to implement 8 priority levels so frames
   with different priority levels may be treated as if they had the same
   priority. Differing priorities can cause frame re-ordering.

   The Q-Tag Ethertype is 0x8100.



4.1.2 Outer VLAN Info

   The "Outer VLAN Info" field carries the outer VLAN tag and may or may
   not be present. If present, it specifies a priority and may be
   required to specify a VLAN to enable connectivity between two
   RBridges through an Ethernet cloud that supports VLANs. Once two
   RBridges have established connectivity on an outer VLAN, they become
   adjacent and they start to operate as if connected by a direct link.

   For example, a network manager may configure VLAN 4 for RBridges RB1
   and RB2 to communicate (the outer VID contains the value 4). VLAN 3
   may be assigned for RB2 and RB3 to communicate (the outer VID
   contains the value 3). In this case RB2 becomes adjacent to both RB1
   (on VLAN 4) and RB3 (on VLAN 3), but RB1 and RB3 are not adjacent
   (since they have no common VLAN).

   The Designated RBridge election (see Section 4.2.4) can be run by RB1
   on a given port multiple times, up to once for each VLAN that RB1 is
   configured to support on that port.  RB1 MAY be separately configured
   with a Designated RBridge priority for each VLAN/port pair that it


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INTERNET-DRAFT                                          RBridge Protocol


   supports and may see different adjacencies for different VLANs.
   Therefore, RB1 may get elected DRB for some VLANs on a port, and not
   for others. The IS-IS Hello messages on a port MUST be transmitted
   with the VLAN ID in the "Outer.VLAN Info" field set to the VLAN for
   which the election is being run.

   The priority field in the Outer VLAN Info is set on an outgoing TRILL
   frame to a copy of the priority field in the Inner VLAN Info for data
   frames or to 7, the highest priority, for TRILL IS-IS frames.



4.1.3 Inner VLAN Info

   The "Inner VLAN Info" field contains the VLAN information associated
   with the original native frame when it was ingressed or the VLAN
   information associated with a per VLAN IS-IS message when that
   message was created.  When a TRILL frame with Inner VLAN Info
   arrives, that Inner VLAN Info is not changed.

   When a native (non-TRILL) frame arrives, the priority and VLAN in the
   Inner VLAN Info are determined as specified in [802.1Q] (see [802.1Q]
   Section 6.7). A high level informative summary of how this VLAN Info
   is determined, omitting some details, is given in the bulleted items
   below:

   o  When an untagged native frame arrives, a zero configuration
      RBridges associates the default priority, zero, and the VLAN ID 1
      with it. It actually sets the VLAN for the untagged frame to be
      the "port VLAN ID" associated with that port. The port VLAN ID
      (PVID) defaults to VLAN ID 1 but may be configured to be any other
      VLAN ID. An Rbridge may also be configured on a per port basis to
      discard such frames or to associate a different priority with
      them.  Determination of the configured port VLAN IDs may also be
      made dependent on the Ethertype or NSAP (referred to in 802.1 as
      the Protocol) of the arriving frame.

   o  When a priority tagged native frame arrives, a zero configuration
      RBridge associates the port VLAN ID, which defaults to 1, and the
      priority provided in the frame with it. An Rbridge may be
      configured on a per port basis to discard such frames or to
      associate them with a different VLAN ID as described in the point
      above.  It may also be configured to map the priority provided in
      the frame by specifying, for each of the eight possible priorities
      that might be frame, what actual priority will be associated with
      the frame by the RBridge.

   o  When a Q-tagged native frame arrives, a zero configuration RBridge
      associates with it the VID and priority in the Q-tag.  An RBridge
      may be configured on a per port per VLAN basis to discard such


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      frames. It may also be configured on a per port basis to map the
      priority as specified above for priority tagged frames.

   In 802.1, the process of assigning a priority to a frame including
   mapping a priority provided in the frame to another priority, is
   referred to as priority "regeneration".

   Thus, in TRILL, the Inner VLAN Tag always specifies a VLAN ID.  This
   Inner VLAN ID is required at every ingress Rbridge as one element in
   determining the appropriate egress Rbridge for a known unicast frame
   and is required at the ingress and every transit Rbridge for multi-
   destination frames to correctly prune the distribution tree.

   Note that the VLAN ID 0xFFF is reserved and MUST NOT be used.
   Rbridges MUST discard any frame they receive which is tagged as being
   in VLAN 0xFFF.



4.1.4 Frame CheckSum (FCS)

   Each frame has a single Frame CheckSum (FCS) that is computed to
   cover the entire  frame. It is calculated before transmission and
   checked on receipt. Any frame for which the FCS fails is discarded.
   The FCS is generally recalculated on every hop due to changes such as
   the decrementing of the hop count.



4.2 Link State Protocol (IS-IS)

   TRILL uses IS-IS as the routing protocol, since it has the following
   advantages:

   o  it runs directly over layer 2, so therefore may be run with zero
      configuration (no IP addresses need to be assigned);

   o  it is easy to extend by defining new TLV (type-length-value)
      encoded data elements for carrying TRILL information;

   IS-IS has three types of packets; LSPs (Link State PDUs), Hellos (for
   finding neighbors and running the Designated RBridge election
   protocol), and SNPs (sequence numbers packets, for acknowledging one
   or more LSPs).








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4.2.1 IS-IS RBridge Identity

   Each RBridge has a unique 6-byte IS-IS System ID, which may be
   derived from any of the RBridge's unique MAC addresses.



4.2.2 Distinguishing IS-IS Instances

   TRILL implements separate IS-IS instances from the one used by layer
   3, that is, different from the one used by IP routers.  TRILL IS-IS
   messages are distinguished from layer 3 IS-IS messages because TRILL
   IS-IS frames have a TRILL header and use a distinct, constant Area
   Address that would never appear as a real layer 3 IS-IS area address.
   This Area Address is the value zero. All TRILL IS-IS frames have the
   Inner.MacDA == All-Rbridges.

   Within TRILL, there is a mandatory core IS-IS across all Rbridges in
   the campus and optional per VLAN instances between the RBridges on
   each supported VLAN. They are distinguished by the presence of an
   inner VLAN tag in the per VLAN instance frames and the absence of
   such a tag in the core instances frames.

   All Rbridges must participate in the core IS-IS instance.  Core IS-IS
   instance frames are never forwarded by an RBridge but are
   decapsulated and locally processed. (Such processing may cause the
   RBridge to emit additional core IS-IS instance frames.)

   RBridges that are the Designated RBridge for a link having an end
   station in a particular VLAN MAY participate in the per VLAN IS-IS
   instance for that VLAN. But all transit RBridges MUST properly
   forward per VLAN IS-IS instance frames. Because of this forwarding,
   it appears to a per VLAN IS-IS instance at an RBridge that it is
   directly connected by a shared link to all other RBridges in the
   campus running that per VLAN IS-IS instance.  Egress RBridges that do
   not implement the per VLAN IS-IS instance for that VLAN do not
   decapsulate or locally process any per VLAN IS-IS frames they
   receive.



4.2.3 TRILL IS-IS Information

   The information in the IS-IS link state for the mandatory core and
   optional per-VLAN TRILL IS-IS instances is listed below.  The
   actually encoding of this information and the IS-IS Type values for
   any new IS-IS TLV data elements will be specified in a separate
   document.




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INTERNET-DRAFT                                          RBridge Protocol


4.2.3.1 Core IS-IS Information

   The information contained in the LSP of RBridge RBn for the mandatory
   core IS-IS instance is as follows:

   1. The IS-IS System IDs of RBridges which are neighbors of RBridge
      RBn, and the cost of the link to each of those neighbors.

   2. The nickname of RBridge RBn (2 bytes) and the unsigned 8-bit
      priority for RBn to have that nickname (see Section 3.5.3);

   3. The TRILL Header variations supported by RBridge RBn (16 bits).

   4. A flag RequestTree indicating whether RBridges MUST calculate a
      tree rooted at RBn (default RequestTree = TRUE).

   5. The list of RBridge nicknames that RBn might select for a
      distribution tree when RBn injects a multi-destination frame into
      the campus. The purpose of this field is so that RBridges can
      efficiently build receipt filters to avoid multicast loops (see
      Section 4,3,1).

   6. The list of VLAN IDs of VLANs directly connected to RBn for links
      on which RBn is DRB. (Note: an RBridge may advertise that it is
      connected to additional VLANs in order to receive additional
      information to support certain VLAN based features beyond the
      scope of this specification as discussed in Section 4.7.) In
      addition, the LSP contains the following information on a per VLAN
      basis.

      6.1 Multicast Router attached: This is two bits of information per
         VLAN that indicate whether there is an IPv4 and/or IPv6
         multicast router attached to the Rbridge on that VLAN. An
         RBridge which does not do IP multicast control snooping MUST
         set both of these bits (see Section 4.4.3).  This information
         is used because IGMP [RFC3376] and MLD [RFC2710] Membership
         Reports MUST be transmitted to all links with IP multicast
         routers, and SHOULD NOT be transmitted to links without such
         routers. Also, all frames for IP-derived multicast addresses
         MUST be transmitted to all links with IP multicast routers
         (within a VLAN), in addition to links from which an IP node has
         explicitly asked to join the group the frame is for.

      6.2 Optionally, Layer 2 addresses derived from IPv4 IGMP or IPv6
         MLD notification messages received from attached end nodes on
         each VLAN, indicating the location of listeners for these
         multicast addresses (see Section 4.4.3)

      6.3 Optionally, RBn MAY announce the set of IDs of Root bridges
         for links for which RBn is DRB for that VLAN. This is to


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         quickly detect cases where two layer 2 clouds accidentally get
         merged, and where there might otherwise temporarily be two DRBs
         for the same VLAN on the same link. (See Section 4.2.4.)

   7. Optionally, the list of VLAN groups, where each VLAN group is a
      list of VLAN IDs, with the first VLAN ID listed in a group is the
      "primary" and the others are "secondary". This is solely to detect
      misconfiguration of features outside the scope of this document.
      RBridges that do not support features such as "shared VLAN
      learning" ignore this field (see Section 4.7).

   Using this information each RBridge can compute the optimal pair-wise
   forwarding for known-unicast traffic (the Forwarding Database) and
   the distribution trees for multi-destination traffic.

   The distribution of multi-destination frames (see Sections 4.3 and
   4.4.3) SHOULD also be pruned according to the list of VLAN IDs
   connected to each RBridge and for IP based multicast optimization
   (see Section 4.3.2).  If RBn is forwarding a multi-destination frame
   tagged with VLAN A, RBn SHOULD NOT forward it onto branches of the
   distribution tree that have no downstream VLAN A links.



4.2.3.2 Optional Per-VLAN IS-IS Instance Information

   The information in the LSP for the optional per VLAN TRILL IS-IS
   instances is the list of local end station MAC addresses known to the
   originating RBridge and for each such address a one byte unsigned
   "confidence" rating in the range 0-254 (see Section 4.6).



4.2.4 Designated RBridge

   IS-IS elects one RBridge for each link / VLAN pair to be the
   Designated RBridge (DRB), i.e. to have special duties. The Designated
   RBridge:

   o  learns and may advertise the identities of attached end nodes;

   o  encapsulates and forwards frames that originate on that link to
      the rest of the campus;

   o  decapsulates and forwards frames received from other RBridges onto
      that link;

   o  learns and caches (ingress RBridge, source MAC address) from
      frames it is decapsulating onto the link;



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   It is incorrect to have multiple RBridges being Designated RBridge on
   the same link at the same time, unless they are Designated for
   different VLANs. Multiple DRBs could temporarily happen if a
   partitioned bridged LAN became connected with a bridge or repeater.
   The situation resolves once the better priority RBridge's IS-IS Hello
   is received by the other RBridges on the link. However, it is
   desirable to have this situation resolve as quickly as possible,
   because if there are multiple DRBs, RB1 and RB2, RB1 might
   encapsulate and forward into the campus frames that R2B forwarded
   onto that link from the campus.

   BPDUs (Bridge Protocol Data Units) are messages that are transmitted
   and received even in preforwarding state (listening and learning
   states). If RBridges listen to BPDUs, and if the LANs for which RB1
   was Designated RBridge, and for which RB2 was Designated RBridge get
   joined, then either RB1 or RB2 can detect that the bridge Root has
   changed identity.

   A conservative solution would be to invoke something like a
   preforwarding state, in which the RBridge that detects that the
   identity of the root bridge has changed stops forwarding native
   frames to or from the link until it is sure the IS-IS link election
   would have completed. But the IS-IS election could get slowed down
   due to bridges in preforwarding state, and it would be undesirable to
   disrupt traffic to and from the link just because the root ID has
   changed.

   An alternative solution is to have RBridges participate in the
   spanning tree election, with higher priority for becoming root
   (actually, lowest numerical priority value) than any of the 802.1
   bridges, and with the same priority as for becoming Designated
   RBridge on the link. Then an RBridge is Designated RBridge if and
   only if it is the spanning tree Root. Note that RBridges MUST NOT
   merge spanning trees from different ports.  If two ports of RB1, p1,
   and p2, are connected to the same bridged LAN, RB1 will receive the
   IS-IS Hello message it transmitted on p1 on p2, and likewise, when it
   transmits an IS-IS Hello message on p2, it will receive it on p1. The
   IS-IS Hello must contain a port identifier, unique for each of RB1's
   ports, and if RB1 receives its own Hellos on a different port, then
   RB1 becomes DRB for at most one of those (connected) ports.

   So for example, RB1 sends BPDUs on each of its ports, with itself as
   Root (with highest, i.e., numerically lowest priority), 0 cost from
   Root, and the port ID. There are several possible cases:

   o  RB1 is the highest priority RBridge on the bridged LAN, in which
      case it becomes spanning tree Root and Designated RBridge.

   o  RB1 receives a BPDU from itself (because two of its ports are on
      the same shared medium without any bridges between). In this case,


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      the numerically lowest port remains in spanning tree forwarding
      state, and the other port(s) go into spanning tree blocking state.

   o  RB1 receives a BPDU from someone else with higher priority
      (numerically lower priority|ID), in which case RB1 is not Root,
      and not Designated RBridge. It is possible this is due to a bridge
      being configured with the lowest priority, and then if RB1
      declines being Designated RBridge, the LAN becomes orphaned from
      the campus.  We must treat this case as a misconfiguration of
      bridges, and the LAN becomes orphaned until the misconfiguration
      is corrected, but an RBridge could in theory eventually discover
      it is not receiving any IS-IS Hellos, and become Designated
      RBridge even though it is not spanning tree Root.

   RBridges MAY participate in the bridge spanning tree protocol as
   described above, and become Designated RBridge if and only if they
   are spanning tree root.

   If an RBridge RB1 does not participate in the bridge spanning tree
   then it SHOULD listen to bridge spanning tree messages, and if the
   root bridge ID changes from B1 to B2 on VLAN X, then RB1 SHOULD look
   at link state packets from other RBridges to see if any other
   RBridges report connectivity to VLAN X, bridge B2. If this is the
   case, then RB1 SHOULD delay before forwarding traffic to or from the
   link with new root bridge B2 until the IS-IS Designated Router
   election protocol has a chance to complete.

   If an RBridge participates in spanning tree, a port MUST NOT block
   TRILL Ethertype frames from being received or transmitted when it is
   in spanning tree blocked state, although this will stop the receipt
   and transmission of native (non-TRILL) data frames.



4.3 Distribution Trees

   RBridges use distribution trees to forward multi-destination frames
   (see Section 2.3.2). Distribution Trees are bidirectional. A single
   distribution tree is logically enough for the entire campus. The
   TRILL WG decided that the computation of additional distribution
   trees was warranted because:

   1. using a tree rooted at the ingress RBridge optimizes the
      distribution path and (almost always) the cost of delivery when
      the number of destination links is a subset of the total number of
      links, as is the case with VLANs and IP multicasts;

   2. for unknown unicast destinations, using a tree rooted at the
      ingress RBridge minimizes out-of-order delivery because, in the
      case where a flow starts before the location of the destination is


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      known by the RBridges, the path to the destination is the same as
      the shortest path to the destination.

   A distribution tree rooted in the ingress RBridge is not always the
   best choice:

   1. In some cases, a different tradeoff might be wanted in terms of
      the expense of computing many trees vs. optimality of traffic
      distribution (so fewer trees would be desired).

   2. It might be desirable to allow choosing a different distribution
      tree than the one rooted at the ingress RBridge for some frames in
      order to allow multipathing of multicast traffic injected by a
      particular RBridge.

   RBridges MUST calculate at least one distribution tree, and by
   default SHOULD compute one distribution tree for every Rbridge.
   However, to scale in the presence of a large number of RBridges in a
   campus, some RBridges MAY be configured to not be the root of a
   distribution tree. Each RBridge RBi announces whether RBridges MUST
   compute a tree rooted at RBi via the RequestTree flag in its IS-IS
   instance LSP. The default is RequestTree == TRUE, but management
   configuration MAY reduce the number of trees.

   If all Rbridges have their RequestTree == FALSE, then each RBridge
   MUST calculate a tree rooted at the RBridge with lowest ID.

   If RBi is a tree root, then any RBridge RBn that needs to send multi-
   destination traffic MAY select the RBi-tree by specifying RBi as the
   egress Nickname in the TRILL header. However, RBn MUST announce, in
   its LSP, an intention to use RBi as a tree root if RBn ever chooses
   the RBi-tree.  All the other RBridges MUST comply with the decision
   of the RBridge RBn.

   In IS-IS a shared link is modeled as a pseudonode. The RBridge acting
   as designed RBridge for a shared link MUST set RequestTree = FALSE in
   the pseudonode LSP.



4.3.1 Distribution Tree Calculation and Checks

   RBridges do not use the spanning tree protocol to calculate
   distribution trees. Instead, distribution trees are calculated based
   on the link state information, selecting a particular RBridge as the
   root.

   Calculation of a tree rooted at RBi is done independently by each
   RBridge RBn by performing the SPF (Shortest Path First) calculation
   with RBi as the root without requiring any additional exchange of


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   information.

   When a node RBn has two or more minimal equal cost paths toward the
   Root RBi a deterministic tie-breaker is needed to guarantee that all
   Rbridges calculate the same distribution tree. This is obtained by
   selecting the path that goes to the parent that has the lower IS-IS
   System ID.

   Each RBridge RBn keeps a set of adjacencies (port, neighbor pair) for
   each distribution tree. One of these adjacencies is toward the root
   RBi and the others are toward the leaves. Once the adjacencies are
   chosen, it is irrelevant which ones are towards the root RBi, and
   which are away from RBi. Let's suppose that RBn has calculated that
   adjacencies a, c, and f are in the RBi tree. A multi-destination
   frame for the distribution tree RBi is received only from one of the
   adjacencies a, c, or f (otherwise is discarded) and forwarded to the
   other two adjacencies.

   To further avoid temporary multicast loops during topology changes,
   RBridges MUST do a sanity check that a multi-destination frame
   arrives on the expected link. This call the Reverse Path Forwarding
   Check and is done as follows. When RBn calculates the RBi tree, for
   each adjacency in the RBi tree, RBn lists the possible ingress
   RBridge nicknames on that adjacency. The only ingress RBridges that
   appear on any of the adjacencies are RBridges that have explicitly
   stated, in their LSP, that they may select RBi as a distribution
   tree. If a multi-destination frame is received on a particular
   adjacency, marked as the RBi-tree, then RBn MUST NOT forward it if
   the ingress RBridge is not listed in the allowed list of ingress
   RBridges for that adjacency for that tree.



4.3.2 Pruning the Distribution Tree

   Each distribution tree SHOULD be pruned per VLAN eliminating branches
   that have no potential receivers downstream. Multi-destination frames
   SHOULD only be forwarded on branches that are not pruned.

   Further pruning SHOULD be done in the case of IGMP [RFC3376], MLD
   [RFC2710], and MRD [RFC4286] messages, where these are to be
   delivered only to ports with IP Multicast routers. In the case of a
   multicast derived from an IP multicast, these multicast data frames
   are delivered only to links that have registered listeners, plus
   links which have IP Multicast routers.

   Let's assume that RBridge RBn knows that adjacencies (a, c, and f)
   are in the RBi-distribution tree.  RBn marks pruning information for
   each of the adjacencies in the RBi-tree. For each adjacency and for
   each tree, RBn marks:


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   o  the set of VLANs reachable downstream, and for each one of those,
      a flag indicating whether there are IPv4 or IPv6 multicast routers
      downstream, and

   o  the set of layer 2 multicast addresses derived from IP multicast
      groups for which there are receivers downstream.



4.3.3 Forwarding Using a Distribution Tree

   Forwarding a multi-destination data frame is done as follows:

   o  The RBridge RBn receives a multi-destination frame with inner VLAN
      A and the TRILL header indicates the selected tree is the RBi-
      tree;

   o  if the adjacency from which the frame was received is not one of
      the adjacencies in the RBi-tree for the specified ingress RBridge,
      the frame is dropped (see Section 4.3.1);

   o  else if the frame is an IGMP or MLD announcement message or and
      MRD query message then the frame is forwarded onto adjacencies in
      the RBi-tree that indicate there are downstream VLAN A IPv4 or
      IPv6 multicast routers respectively (for more information see
      Section 4.4);

   o  else if the frame is for a layer 2 multicast address derived from
      an IP multicast group then the frame is forwarded onto adjacencies
      in the RBi-tree that indicate there are downstream VLAN A IP
      multicast routers, as well as adjacencies that indicate there are
      downstream VLAN A receivers for that group address (see Section
      4.4);

   o  else (the inner frame is for an unknown destination or layer 2
      multicast not derived from IP multicast or broadcast) the frame is
      forwarded onto an adjacency if and only if that adjacency is in
      the RBi-tree, and marked as reaching VLAN A links.

   For each link for which RBn is Designated RBridge, RBn additionally
   checks to see if it should decapsulate the frame and send it to the
   link, or process the frame.

   The per-VLAN instance of IS-IS frames will be delivered only to
   RBridges which are Designated RBridges for that VLAN. Per-VLAN TRILL
   IS-IS messages look, to transit RBridges, like any multicast data
   packet tagged with an inner VLAN tag. Such packets will be multicast
   throughout the campus, like any other multicast data packets, on the
   distribution tree chose by the RBridge which injected the per-VLAN
   IS-IS message, and pruned according to the inner VLAN tag so that it


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   is received by all the RBridges who are DRB for a link in that VLAN.



4.4 Forwarding Behavior

   This section describes RBridge behavior for a variety of received
   frames, including how they are forwarded when appropriate.



4.4.1 Receipt of a Native Frame

   An RBridge can tell that it has received a native frame because it
   does not have a TRILL Ethertype.

   The ingress Rbridge RB1 determines the VLAN ID according to the same
   rules as 802.1 bridges do (see Section 4.1.3). Once the VLAN is
   established, if RB1 is not the Designated RBridge (DRB) for the link
   from which the frame was received for that VLAN, it is discarded. If
   it is DRB, then it is forwarded according to 4.4.1.1 if the frame is
   unicast, and 4.4.1.2 if it is multicast or broadcast.



4.4.1.1 Native Unicast Case

   If the destination MAC address of the native frame is a unicast
   address, the following steps are performed.

   The layer 2 destination address D is looked up in the Encapsulation
   Database for that VLAN to find the egress RBridge RBm, or discover
   that D is unknown.

   If D is known, with egress RBm, then RB1 converts the native frame to
   a TRILL data frame with outer MAC addresses from RB1 unicast to the
   next hop RBridge towards RBm and a TRILL header with V = 0 and M = 0,
   the ingress nickname for itself, and the egress nickname for RBm.

   If D is unknown, RB1 converts the native frame to a TRILL data frame
   with outer MAC addresses of RB1 as source and the All-Rbridges
   multicast address as destination and a TRILL header with the
   variation field V = 1 (indicating that VLAN pruning is known to be
   the only pruning appropriate during tree distribution), the multi-
   destination bit M = 1, the ingress nickname for itself, and the
   egress nickname for the root of the distribution tree it wants to
   use.  The default is for RB1 to write its own nickname into the
   egress nickname field. However, RB1 MAY choose a different
   distribution tree if either RB1 has not elected to be a tree root, or
   if RB1 has been configured to path-split multicast. In that case RB1


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   MUST select a tree by specifying an RBridge that has elected to be a
   tree root. Also, RB1 MUST select a tree that RB1 has announced (in
   RB1's own LSP) to be one of the ones that RB1 MAY choose as a
   distribution tree. (see Section 4.3.1)



4.4.1.2 Native Multicast and Broadcast Frames

   If the destination address of a native frame is the broadcast address
   or a multicast address other than All-Rbridges, the frame is
   processed as described below. A native (non-TRILL) frame sent to the
   All-Rbridges address is erroneous and is discarded.

   If the frame is an IGMP [RFC3376], MLD [RFC2710], or MRD [RFC4286]
   message, then RB1 SHOULD analyze the frame, learn any group
   membership or IP multicast router presence indicated, and announce
   that information for the appropriate VLAN in its IS-IS link state
   (see Section 4.5).

   For all such frames, RB1 also chooses a distribution tree,
   encapsulates, and forwards the frame on the pruned distribution tree.
   In the encapsulation, M = 1, V is set to 1 if the Inner.MacDA is not
   an IP derived multicast address and to the appropriate value (see
   section 4.4.2.2.2) if it is an IP derived multicast address, the
   Outer.MacSA is set to that of the port on which the frame is being
   transmitted and the Outer.MacDA is normally the All-Rbridges
   multicast address; however, if for any particular port there is only
   one next hop RBridge, the frame MAY be sent with the unicast
   Outer.MacDA of the target RBridge. Using a unicast Outer.MacDA is of
   no benefit on a point-to-point link but may result in substantial
   savings if the link is actually a complex bridged LAN.



4.4.2 Receipt of a Non-Native (TRILL) Frame

   Non-native frames are indicated by a TRILL outer Ethertype. Such
   frames will be received with an Outer.MacDA that is unicast or that
   is the All-RBridges multicast address. TRILL frames with any other
   Outer.MacDA are erroneous and are discarded except that a TRILL frame
   with the broadcast Outer.MacDA MAY be treated as if the Outer.MacDA
   was the All-Rbridges multicast address. TRILL frames received by an
   RBridge on a port are processed regardless of that RBridge's DRB
   status for that port.

   If the Outer.MacDA is a unicast address, the frame is discarded
   unless that address is the address of the receiving Rbridge.  (Such
   discarded frames are most likely addressed to another RBridge on a
   multi-access link and that other Rbridge will handle them.)  After


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   this check, further processing of TRILL frames is independent of the
   Outer.MacDA.

   If the V field in the TRILL Header is greater than 3, the frame is
   discarded. The Inner.MacDA is then tested. If it is the All-Rbridges
   multicast address, processing proceeds as in Section 4.4.2.1 below.
   If it is any other address, processing proceeds as in Section
   4.4.2.2.



4.4.2.1 TRILL IS-IS Frames

   If there is no Inner VLAN tag, it is a core instance TRILL IS-IS
   frame and is processed by the core IS-IS instance on RBn and is not
   forwarded. Note that in this instance, nicknames may not yet have
   been established and the ingress and egress nickname fields are
   ignored.

   If there is an Inner VLAN tag, it is a per VLAN instance TRILL IS-IS
   frame. If M == 0 or V != 1, the frame is discarded.  The egress
   nickname will designate an appropriate distribution tree. in this
   case, the frame is forwarded as described in Section 4.4.2.2.2. In
   addition, if the forwarding Rbridge is a DRB for a link in the
   specified VLAN, the inner frame is decapsulated and provided to the
   local per VLAN IS-IS instance for that VLAN.



4.4.2.2 TRILL Data Frames

   The port on which the frame was received is first checked and the
   frame discarded unless there is an IS-IS adjacency on that port.

   The Inner.MacDA is then checked. If it is unicast, processing
   continues as described in Section 4.4.2.2.1, otherwise processing
   continues as described in Section 4.4.2.2.2.



4.4.2.2.1 Unicast TRILL Data Frames

   If M == 1 the frame is discarded.

   Generally, the hop count is decremented by one and the frame
   forwarded to the next hop RBridge towards the egress RBridge, using
   the Forwarding Database, unless the hop count was reduced to zero, in
   which case the frame is discarded.

   On the other hand, if the egress RBridge indicated is the RBridge


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   performing the processing (RBn), the frame being forwarded is
   reconverted to native form. This frame is then either sent onto the
   link containing the destination or locally processed if the RBridge
   itself is the destination.



4.4.2.2.2 Multi-Destination TRILL Data Frames

   If M == 0, the frame is discarded.

   The Outer.MacSA is then checked and the frame discarded if it is not
   a tree adjacency for the tree indicated by the egress RBridge
   nickname or the RPF check fails (see Section 4.3.1).

   The frame is then forwarded down the tree specified by the egress
   RBridge nickname pruned as follows:

   V = 3, the tree SHOULD be pruned on VLAN and to branches with
          downstream IPv4 multicast routers if the Inner.MacDA is IPv4
          derived multicast or downstream IPv6 multicast routers if the
          Inner.MacDA is IPv6 derived multicast.

   V = 2, the tree SHOULD be pruned on VLAN and to branches with
          downstream IPv4 multicast routers or with IPv4 multicast
          listeners from which the Inner.MacDA would be derived and
          similarly for iPv6.

   V = 1, the tree SHOULD be pruned on VLAN only. It is either
          broadcast, a non-IP derived multicast, or an IP derived
          multicast derived from an IP address for which multicast group
          membership reports are not issued (see Section 4.4.3).

   V = 0, the tree SHOULD be pruned on VLAN but the native frame has not
          been fully analyzed from the point of view of multicast
          optimization. The processing RBridge SHOULD complete this
          analysis, set V to some value from 1 through 3, and use that
          pruning. However, if it chooses not to do this analysis, it
          can it can either do no multicast optimization or do a more
          limited optimization, for example based only on the
          Inner.MacDA.

   In the forwarded frame, the Outer.MacSA is set to that of the port on
   which the frame is being transmitted and the Outer.MacDA is normally
   the All-Rbridges multicast address; however, if for any particular
   port there is only one next hop RBridge, the frame MAY be sent with a
   unicast Outer.MacDA. Using a unicast Outer.MacDA is of no benefit on
   a point-to-point link but may result in substantial savings if the
   link is actually a complex bridged LAN.



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4.4.3 Tree Distribution Optimization

   RBridges MUST determine the VLAN associated with all native frames
   and properly enforce VLAN rules on the emission of native frames at
   egress RBridges according to how they are configured. They SHOULD
   also prune the distribtion tree of multi-destination frames according
   to VLAN.  But, since they are not required to do such pruning, they
   may receive TRILL data frames that should have been pruned earlier in
   the tree distribiton. They silently discard such frames. A campus may
   contain some Rbridges that prune on VLAN and some which do not.

   The situation is more complex for multicast. RBridges SHOULD analyze
   IP derived multicast frames, learn and announce listeners and IP
   multicast routers for such frames as discussed in Section 4.5 below.
   And they SHOULD prune the distribution of IP derived multicast frames
   based on such learning and announcements. But, as with VLANs, they
   are not required to prune and, unlike VLANs, they are not required to
   learn. A campus may contain a fixture of Rbridges with different
   levels of IP derived multicast optimization. An RBridge may receive
   IP derived multicast frames that should have been pruned earlier in
   the tree distribiton. They silently discard such frames.

   An RBridge that does not examine IP derived native multicast frames
   that it ingresses MUST advertise that it has IPv4 and IPv6 IP
   multicast routers attached for all the VLANs for which it is a DRB.
   It need not advertise any IP derived multicast listeners.  This will
   cause all IP derived multicast traffic to be sent to this RBridge for
   those VLANs. It then egresses that traffic onto the links for which
   it is DRB where the VLAN of the traffic matches the VLAN for which it
   is DRB on that link. This may cause the suppression of certain IGMP
   membership report messages from end stations but that is not
   significant as any multicast traffic such reports would be requesting
   will be sent to such end stations under these circumstances.

   When an IP derived multicast frame is fully examined at ingress, the
   V field of the TRILL header is set to indicate the pruning which
   should apply (see Section 4.4.2.2.2). If this analysis is not
   performed at ingress, V will be zero in the TRILL data frame. Transit
   RBridges may distribute such a multi-destination frame without
   pruning, or perform full or partial analysis of the frame, possibly
   set V, and forward based on such analysis.

   See also "Considerations for Internet Group Management Protocol
   (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches"
   [RFC4541].







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4.5 IGMP, MLD, and MRD Learning

   RBridges SHOULD learn, based on seeing IGMP [RFC3376], MLD [RFC2710],
   and MRD [RFC4286] frames, which multicast messages should be
   forwarded onto which links.

   An IGMP or MLD membership report received in native form from a link
   indicates a multicast group listener for that group on that link. An
   IGMP or MLD query or an MRD advertisement received in native form
   from a link indicates the presence of an IP multicast router on that
   link.

   IP multicast group membership reports have to be sent throughout the
   campus to all IP multicast routers, distinguishing IPv4 and IPv6. All
   multicast traffic must also be sent to all IP multicast routers for
   the same version of IP.

   IP multicast data SHOULD only be sent on links where there is either
   an IP multicast router for that IP type (IPv4 or IPv6) or an IP
   multicast group listener for that IP type and IP multicast derived
   MAC address.

   RBridges do not need to announce themselves as listeners to the All-
   Snoopers multicast group, used for MRD reports, because the IP
   multicast address for that group is in the range where frames sent to
   such addresses must be broadcast.

   See also "Considerations for Internet Group Management Protocol
   (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches"
   [RFC4541].



4.6 Learning End Station Addresses

   RBridges have to learn the MAC addresses and VLANs of their locally
   attached end stations for link/VLAN pairs for which they are the
   Designated RBridge so they can

   o  forward the native form of incoming TRILL data frames onto the
      correct link and

   o  decide for an incoming native unicast frame from a link, where the
      RBridge is the DRB, whether the frame is

      -  known to have been destined for another end station on the same
         link, so the RBridge need do nothing, or

      -  know to be destined for another end station on another local
         link where the RBridge is DRB so it can be directly forwarded


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         in native form or

      -  neither of the above, so the frame has to be converted to a
         TRILL data frame and forwarded.

   RBridges have to learn the MAC addresses of remote end stations and
   the remote RBridge that is the DRB for each such remote end station
   that are on the same VLAN or VLANs they are. That way, when they need
   to forward a locally received native unicast frame, after converting
   it to a TRILL data frame, they can frequently unicast it
   appropriately rather than always having to flood it.

   There are three ways an RBridge can learn end station addresses as
   follows:

   1. From the observation of data, learning the { source MAC, VLAN,
      port } triplet of received native frames and the { source MAC,
      VLAN, remote RBridge nickname } triplet of data frames that it
      decapsulates.

   2. By running a per VLAN IS-IS instance which receives remote
      information and transmits local information.

   3. By management configuration.

   RBridges MUST implement capability 1 above and MUST use it unless
   configured, for one or more particular VLANs and or ports, to not
   learn from either received local native frames or from decapsulated
   TRILL data frames or both.

   RBridges MAY implement capability 2 above. If implemented, such a per
   VLAN IS-IS instance is run only when the RBridge is configured to do
   so on a per VLAN basis.

   Entries in the table of learned MAC addresses and ancillary
   information also have a one byte unsigned confidence level associated
   with each entry. Such information learned from the observation of
   data has a confidence of 1 unless configured to have a different
   confidence.  Such information received via IS-IS is accompanied by a
   confidence level in the range 0 to 254. Such information configured
   by management defaults to a confidence level of 255 but may be
   configured to have another value.

   When a new learned address and related information are to be entered
   into the local database there are several possibilities:

   o  If this is a new address, the information is entered accompanied
      by the confidence level.

   o  If there is already an entry for this address with the same


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      accompanying information, the confidence level in the local
      database is set to the maximum of its existing confidence level
      and the confidence level with which it is being learned.

   o  If there is already an entry for this address with different
      information, the learned information is ignored unless it is being
      learned with higher or equal priority than the database entry.



4.7 Shared VLAN Learning

   Although outside the scope of this specification, there are some
   features in which a set of VLANs is considered to be a group, where
   one of the VLANs is the "primary" and the other VLANs in the group
   are "secondaries". An example of this is where traffic from different
   communities are separated using VLAN tags, and yet some resource
   (such as an IP router or DHCP server) is to be shared by all the
   communities. A method of implementing this feature is to give a VLAN
   tag, say Z, to a link containing the shared resource, and have the
   other VLANs, say A, C, and D, be part of the group {primary=Z,
   secondaries = A, C, D}. An RBridge, aware of this grouping, attached
   to one of the secondary VLANs in the group also claims to be attached
   to the primary VLAN. So an RBridge attached to A would claim to also
   be attached to Z. An RBridge attached to the primary would claim to
   be attached to all the VLANs in the group.

   This specification does not specify how VLAN groups might be used.
   Only RBridges that participate in a VLAN group will be configured to
   know about the VLAN group. However, to detect misconfiguration, an
   RBridge configured to know about a VLAN group SHOULD report the VLAN
   group in its LSP.




















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5. Pseudo Code

   WARNING: The Psuedo Code below has NOT been update to correspond to
   changes made in other Sections of this document but rather
   corresponds to draft version -04.

   This section provides partial high level pseudo code for the
   processing of all possible types of received and generated frames. In
   case of conflict between this section and any of the earlier sections
   in this document, the pseudo code is authoritative.

   Frame destination address abbreviations used in this section are as
   follows:

      Abbreviation   Destination Address(es)
      ------------------------------------------------------------
      802MUL   Multicast address in the range 01-80-C2-00-00-00
                  to 01-80-C2-00-00-0F.
      ALLRB    The All-Rbridges multicast address, <tbd>.
      BROAD    The broadcast address: FF-FF-FF-FF-FF-FF
      IP4MUL   IPv4 based multicast addresses (the range
                  00-01-5E-00-00-00 to 00-01-5E-7F-FF-FF)
      IP6MUL   IPv6 based multicast addresses (the range
                  33-33-00-00-00-00 to 33-33-FF-FF-FF-FF)
      OTHERM   Multicast addresses other than ALLRB, IP4MUL,
                  IP6MUL, or 802MUL.
      OTHERU   Unicast addresses other than SELF.
      SELF     The unicast address of the Rbridge at which an
                  operation is occurring.

   Section 5.1 below discusses 802MUL addressed frames, most of which
   are handled by the Ethernet port and are partially or fully out of
   scope for TRILL. Section 5.2 then discusses other received frames and
   frames emitted in direct response to such other received frames.
   Section 5.3 discusses spontaneously emitted frames.



5.1 802MUL Destination Frames

   Frames addressed to an 802MUL multicast address are usually handled
   by a port under IEEE 802 protocols which are out of scope for
   RBridges proper as show in Figure 9.  Such frames, by definition, are
   not forwarded by 802.1 bridges and thus are not forwarded by
   RBridges.

   An RBridge MAY learn source MAC address from such frames as described
   in Section 5.2.2.1.




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INTERNET-DRAFT                                          RBridge Protocol


                     +------------------------------------------+
                     |   +--------+                 +---------+ |
                     |   |  Port  |                 | Rbridge | |
                     |   |        |     RBridge     | Proper  | |
                     |   |  +--+  |                 |         | |
                     |   | \|  |  |                 |         | |
       ---------------------+  |  |                 |         | |
                     |   | /|  |/ |                 |   \     | |
       802MUL Frames |   |  |  +- | - - - - - - - - - - - -   | |
       /             |   |  |  |\ |                 |   /     | |
       ---------------------+  |  |                 |         | |
       \             |   |  |  |  |                 |         | |
                     |   |  +--+  |                 |  +---+  | |
                     | \ |       \|                 | \|   |  | |
       ----------------- | -------| -------------------+   |  | |
                     | / |       /|                 | /|   |  | |
        Other Frames |   |        |   Other Frames  |  |   |  | |
       /             |   | /      | /               |  |   |  | |
       ----------------- | -------| -------------------+   |  | |
       \             |   | \      | \               |  |   |  | |
                     |   |        |                 |  +---+  | |
                     |   +--------+                 +---------+ |
                     +------------------------------------------+

                     Figure 9. 802MUL and RBridge Frames

   The following table give the sections where the various protocols
   which use 802MUL multicast addresses are discussed:

      Address              Section and Description
      ---------------------------------------------------------
      01-80-C2-00-00-00    5.1.1 All Bridges: Used for BPDUs.
      01-80-C2-00-00-01    5.1.2 [802.3] Clause 31
      01-80-C2-00-00-02    5.1.2 [802.3] Clause 43 ( Link
                            Aggregation) and Clause 57 (OAM)
      01-80-C2-00-00-03    5.1.3 [802.1X] Port Authenticator
                            Entity (PAE)
      01-80-C2-00-00-04/5  5.1.2 Reserved.
      01-80-C2-00-00-06/7  5.1.6 Reserved.
      01-80-C2-00-00-08    5.1.6 All Provider Bridges
      01-80-C2-00-00-09/C  5.1.6 Reserved.
      01-80-C2-00-00-0D    5.1.5 Provider Bridge GVRP Address
      01-80-C2-00-00-0E    5.1.4 [802.1AB] Link Layer Discovery
                            Protocol
      01-80-C2-00-00-0F    5.1.2 Reserved.







R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 42]


INTERNET-DRAFT                                          RBridge Protocol


5.1.1 Spanning Tree Protocol

   Frames sent with the All Bridges multicast address use the bridge
   spanning tree protocol NSAP 0x42 so the frame begins LL-
   LL-42-42-03-00-00 where 0xLLLL is the length and the trailing 0x0000
   indicate the frame is a BPDU (Bridge Protocol Data Unit), used to
   implement the spanning tree protocol (see also Section 5.1.5).
   RBridge ports MUST adopt one of four strategies as listed below in
   connection with these frames and SHOULD adopt strategy 2.  Note: It
   is never the case that a bridging spanning tree extends through an
   RBridge between two of its ports. Those ports always terminate the
   spanning tree.

   1. An RBridge port MAY silently discard all received BPDUs and not
      issue an BPDUs.

   2. An RBridge port SHOULD examine received BPDUs to determine the
      current root bridge and advertise what it sees as the current root
      bridge on that port via the core IS-IS instance (see Section
      4.2.3). It would be sufficient for the RBridge to test that the
      DSAP/SSAP are 0x4242 and the first four octets of the BPDU payload
      are zero.  If so, the spanning tree root bridge identifier is the
      eight octets from the sixth octet through the 13th octet. (The
      fifth octet is an octet of flags that need not be examined by the
      RBridge.)  The last six of these eight octets are the part of the
      root identifier reported in the LSP.(Octets six and seven include
      a priority.)

   3. An RBridge port MAY participate in spanning tree in such a way as
      to become spanning tree root if it should be the Designated
      RBridge. See Section 4.2.4.

   4. As an alternative to item 3, an RBridge port may optionally
      participate in spanning tree in such a way as to force an attached
      bridged LAN to partition as discussed in Section 6.2,



5.1.2 Media Multicast Frames

   These frames are for media specific port features or are reserved for
   the future standardization of such features. Such features are
   outside of the scope of TRILL which is generally media independent.



5.1.3 802.1X Frames

   This port protocol provides for the authentication of end stations as
   specified in [802.1X]. That an end station has been so authenticated


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INTERNET-DRAFT                                          RBridge Protocol


   MAY be used to increase the confidence in end station MAC addresses
   reported via the optional per VLAN IS-IS instance (see Section 4.6).

   An amendment to 802.1X [802.1af] is under development such that
   802.1X authentication would produce keying material usable in
   [802.1AE] tags which can in turn be used to authenticate and encrypt
   frames between ports.



5.1.4 802.1AB Frames

   Frames with this multicast address are used in the Station and Media
   Access Control Connectivity Discovery standard 802.1AB [802.1AB]
   which specifies the Local Link Discovery Protocol (LLDP). These
   frames are also identified by the Ethertype 0x88CC.

   This protocol is generally outside of the scope of TRILL. However, if
   LLDP frames containing the System Capabilities 802.1AB TLV are issued
   by an RBridge port, it is RECOMMENDED that the "bridge" bit be
   asserted in the "system capabilities" subfield and if that port is
   participating in spanning tree (see Section 5.1.1), then it is
   RECOMMENDED that the "bridge" bit be asserted in the "enabled
   capabilities" subfield.



5.1.5 GARP, GMRP, and GVRP

   IEEE [802.1D] bridging defines a Generic Attribute Registration
   Protocol, GARP, on which a GARP Multicast Registration Protocol,
   GMRP, and a GARP VLAN Registration Protocol, GVRP, are based. GARP
   uses the bridge spanning tree protocol NSAP 0x42 so the frame begins
   LL-LL-42-42-03-00-01 where 0xLLLL is the length and the trailing
   0x0001 indicate the frame is a GARP PDU (see also Section 5.1.1).

   The multicast addresses in the range 01-80-C2-00-00-20 to
   01-80-C2-00-00-2F have been reserved for GARP applications.  [802.1D]
   requires that bridges transparently propagate frames to any multicast
   address in this range if they do not implement the corresponding GARP
   application. Since RBridges do not implement any of these
   applications, they treat such frames as any other layer 2 multicast.

   The GMRP application of GARP uses multicast address
   01-80-C2-00-00-20.  It would provide a basis for the optimization of
   the distribution of frames with all layer 2 multicast addresses.
   However, RBridges provide for IP based multicast optimization
   instead.

   The GVRP application of GARP uses multicast address


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 44]


INTERNET-DRAFT                                          RBridge Protocol


   01-80-C2-00-00-21.  It provides for the registration of VLANs and is
   not supported by RBridges.



5.1.6 Other Bridge Frames

   These frames relate to other bridge features outside of the scope of
   TRILL or are reserved for future standardization.



5.2 Processing a Frame Received by an RBridge

   "Ethertype" abbreviations used in this section are as follows:

      Ethernet Protocol Type Abbreviations
      ------------------------------------------------------------
      ****    Any Ethertype.
      IP**    IPv4 or IPv6 message Ethertype.
      IPv4    0x0800, IP version 4 message Ethertype.
      IPv6    0x86DD, IP version 6 message Ethertype.
      ISIS    0xFE,   IS-IS Message NSAP value.
      TRILL   <TBD>,  TRILL frame Ethertype.

   When an Rbridge RB1 receives a frame, it determines the VLAN ID and
   priority for that frame as described in Section 4.1.3.  The VLAN ID
   and priority are then available as meta data accompanying the frame.

   The destination address of the received frame, its payload protocol
   type, and the Designated RBridge status of the receiving RBridge RBn
   for the link and VLAN in question are then used to sequentially
   search the table below from the top.  As soon as a match is found,
   the processing indicated (either discard the frame or process as give
   in the reference) is performed.  Of course, any other arrangement of
   processing incoming frames is fine as long as the results are the
   same as the pseudo-code in this section.

   The initial sequential match and dispatch table is as shown below.
   The "DRB" column is "Y" if the RBridge must be the Designated Rbridge
   to match, "N" if it must not be the Designated Rbridge, and "*" if it
   does not matter.










R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 45]


INTERNET-DRAFT                                          RBridge Protocol


      Dest.   DRB   Ethertype   Section/Description
      ------------------------------------------------------------
      SELF    *     TRILL      5.2.3 TRILL encapsulated frame.
      SELF    N     ****       Discard.
      SELF    *     ****       5.2.4 Local destination frame.
      OTHERU  *     TRILL      TRILL encapsulated frame addressed to
                                 another Rbridge; discard.
      OTHERU  N     ****       Discard.
      OTHERU  Y     IP**       5.2.1 unicast IP frame.
      OTHERU  Y     ****       5.2.4 Other unicast frame.
      ALLRB   *     TRILL      5.2.3 TRILL encapsulated frame.
      ALLRB   *     ****       Erroneous frame; discard.
      802MUL  *     ****       5.1 Should not get here.
      IPMUL   N     IP**       Discard.
      IPMUL   Y     IP**       5.2.1 multicast IP frame.
      IPMUL   *     ****       Erroneous frame; discard.
      OTHERM  N     ****       Discard.
      OTHERM  Y     ****       5.2.4 non-IP based multicast frame.
      BROAD   *     TRILL      Erroneous frame but MAY be treated as if
                                 Destination was ALLRB (see above).
      BROAD   N     ****       Discard.
      BROAD   Y     IP**       5.2.1 Broadcast IP frame.
      BROAD   Y     ****       5.2.4 Other broadcast frame.



5.2.1 Further Dispatch for IP Frames

   Frames containing IP (Internet Protocol) payload, both IPv4 and IPv6,
   are treated in different ways depending on the particular protocol
   within IP which they are carrying. The following table is searched
   sequentially from the top and the first match used.  The "Ver."
   column is the version of IP used in the frame and "Proto" is the
   Payload IP protocol for the frame.

      Ver.   Proto     Section/Description
      ------------------------------------------------------------
      IPv4   IGMP    5.2.5 Internet Group Membership Protocol
      IPv6   MLD     5.2.5 Multicast Listener Discovery
      IP**   MRD     5.2.6 Multicast Router Discovery
      IP**   PIM     5.2.6 Protocol Independent Multicast
      IP**   ****    5.2.4 Other



5.2.2 Common Subroutines

   The following subroutines are called from several places in Section
   5.



R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 46]


INTERNET-DRAFT                                          RBridge Protocol


5.2.2.1 Learn Source MAC Address

   This is a pseudo-code subroutine called several places above. Note
   that if this is called more than once for the same frame, all calls
   after the first have no effect and do not actually have to be
   performed.

   if (Outer.MacSA has the "group" bit off)
      {
      Learn Outer.MacSA for the port on which the frame was
      received for the determined VLAN unless configured
      not to do such learning.
      }



5.2.2.2 TRILL Data Frame Multi-destination Forwarding

   if (RFP check fails on Outer.MacSA (Section 4.3.1))
      {
      Exit; /* do not forward the frame */
      }
   else
      {
      Execute Section 5.2.2.3;
      }
   Outer.MacSA = RBn;
   Forward along tree indicated by Trill.EgressNickname,
     pruned as specified in Section 4.3.2.



5.2.2.3 TRILL Data Frame Outer VLAN Tag

   if ( (Inner VLAN priority != 0 ) or
         (Inner VID != 1 ) or
         (configured to always use Outer VLAN Tag) )
       {
       Create Outer VLAN Tag if none present.
       Outer VLAN Tag priority = Inner VLAN Tag priority;
       Outer VLAN Tag VID = Inner VLAN Tag VID;
       }
   else
       {
       Remove Outer VLAN Tag if present;
       }






R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 47]


INTERNET-DRAFT                                          RBridge Protocol


5.2.3 TRILL Ethertype Frames

   /* Dispatch on the TRILL message variation */
   /* The RBridge performing the processing is RBn */

   if (Variation > 1)
      {
      Discard the frame, unknown format.
      }
   elseif (Variation == 1)  /* IS-IS */
      {
      Execute Section 5.2.3.1.
      }
   else  /* Variation == 0, Data */
      {
      Execute Section 5.2.3.2.
      }



5.2.3.1 TRILL IS-IS Frames

   if (Outer.MacDA == All-RBridges) /* Note: if Outer.MacDA is
         OTHERM, discarded by dispatch table above */
      {
      if ( (Multi-Destination == 0) or
           (Inner.Protocol Type != ISIS ) or
           (Outer.MacSA !=
             a tree adjacency for tree indicated) )
         {
         Discard the frame.
         }
      elseif (inner VLAN tag not present)
         {
         Process payload as a core TRILL IS-IS message
           for RBn.
         Note: nicknames may be invalid, ignore them.
         }
      else /* inner VLAN tag present */
         {
         If RBn has end stations on links for which it is
         the DRB on the indicated VLAN, give the IS-IS
         message to the per VLAN IS-IS instance if
         implemented.

         Trill.HopCount -= 1 /* at least, see Section 3.4*/
         if (Trill.HopCount <= 0)
            {
            Discard the frame.
            }


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INTERNET-DRAFT                                          RBridge Protocol


         else
            {
            if (RFP check fails on Outer.MacSA (Section 4.3.1))
               {
               Exit; /* do not forward frame */
               }
            else
               {
               Outer.MacSA = RBn;
               Create Outer VLAN Tag if none present (could
                 have been stripped by a bridge).
               Outer VLAN Tag priority = 7;
               Outer VLAN Tag VID = Inner VLAN Tag VID;
               Forwards along tree indicated by
                 Trill.EgressNickname, VLAN pruned as
                 specified in section 4.3.2.
               }
            }
         }
      }

   else /* Outer.MacDA == SELF. Note: if Outer.MacDA is OTHERU,
           discarded by dispatch table above */
      {
      if ( (Multi-Destination == 1) or
           (Inner.Protocol Type != ISIS ) )
         {
         Discard the frame.
         }
      elseif (inner VLAN tag not present)
         {
         if (Inner.MacDA != SELF)
            {
            Discard the frame.
            }

         Process the core instance unicast IS-IS message on
           RBn.
         Note: nicknames may be invalid, ignore them.
         }
      else /* inner VLAN tag present */
         {
         if (Inner.MacDA == SELF)
            {
            Process the per VLAN instance IS-IS message on
            RBn for the indicated VLAN.
            }
         else
            {
            Trill.HopCount -= 1;


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 49]


INTERNET-DRAFT                                          RBridge Protocol


            if (Trill.HopCount == 0)
               {
               Discard the frame.
               }
            else
               {
               Outer.MacDA = lookup (Trill.EgressNickname);
               Outer.MacSA = RBn;
               Create Outer VLAN Tag if none present (could have
                 been stripped by a bridge).
               Outer VLAN Tag priority = 7;
               Outer VLAN Tag VID = Inner VLAN Tag VID;
               and forward the frame to the next hop RBridge
               }
            }
         }
      }



5.2.3.2 TRILL Data Frames

   if (Outer.MacDA == All-RBridges)
      {
      if ( (Multi-Destination == 0) of
           (Outer.MacSA !=
             a tree adjacency for tree indicated) )
         {
         Discard the frame.
         }
      else
         {
         If RBn is a DRB for the indicated VLAN, decapsulate
         the data frame and forward in onto appropriate
         links in the VLAN.

         Trill.HopCount -= 1 /* at least, see Section 3.4 */
         if (Trill.HopCount == 0)
            {
            Discard the frame.
            }
         else
            {
            Execute Section 5.2.2.2.
            }
         }






R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 50]


INTERNET-DRAFT                                          RBridge Protocol


   else /* Outer.MacDA == SELF */
      {
      if (Trill.EgressNickname == RBn)
         {
         Convert to native format and forward the extracted
         frame onto the link containing the destination or
         locally process the frame if the Inner.MacDA == RBn.
         }
      else
         { /* The frame needs to be forwarded to another RBridge */
         Trill.HopCount -= 1;
         if (Trill.HopCount == 0)
            {
            Discard the frame.
            }
         else
            {
            Execute Section 5.2.2.3;
            if (Trill.EgressNickname unknown)
               {
               Discard the frame.
               }
            Outer.MacDA = lookup (Trill.EgressNickname);
            Outer.MacSA = RBn;
            and forward the frame
            }
      }



5.2.4 Native Frame Receipt

   The following pseudo code is executed for frames that are not of the
   TRILL Ethertype and are received on a port and VLAN for which the
   RBridge is the Designated RBridge (see Section 4.2.4).

   Learn source MAC address as specified in 5.2.2.1.

   if (Outer.MacDA == SELF)
      {
      A native frame for the RBridge received from a local
      link, for example a management protocol frame from a
      directly connected management station.
      Process locally.
      }







R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 51]


INTERNET-DRAFT                                          RBridge Protocol


   elseif (Outer.MacDA == a known unicast address)
      {
      if (Outer.MacDA is on the directly connected link on
            which the frame was received)
         {
         Discard the frame. Destination has already seen it.
         }
      elseif (Outer.MacDA for the determined VLAN is on
              another directly connect link)
         {
         Forward the native frame out the port for that link.
         }
      else
         {
         Assume that the egress RBridge is RBm.
         Outer.MacDA = next hop RBridge (in the path to RBm);
         Outer.MacSA = RB1;
         Outer.Ethertype = TRILL;
         Trill.V = 0;
         Trill.Reserved = 0;
         Trill.M = FALSE; /* this is not multi-destination */
         Trill.HopCount = determined value (see Section 3.4);
         Trill.EgressNickname = RBm;
         Trill.IngressNickname = RBn;
         Followed by the received frame;
         Create/update Inner VLAN Tag with VID and priority
           determined as specified in Section 4.1.2.
         Execute Section 5.2.2.3;
         Forward on the port for the Outer.MacDA.
         }
   else
      {  // unknown unicast or general multicast or broadcast
      Forward to other links where RBn is the DRB for the indicated
        VLAN.

      Outer.MacDA = All-Rbridges;
      Outer.MacSA = RB1;
      Outer.Ethertype = TRILL;
      Trill.V = 0;
      Trill.Reserved = 0;
      Trill.M = TRUE; /* this is a multi-destination frame */
      Trill.HopCount = determined value (see Section 3.4);
      Trill.EgressNickname = RBi /* Distribution Tree, See below */
      Trill.IngressNickname = RB1;
      Followed by the received frame with the appropriate
      Create/update Inner VLAN Tag with VID and priority
        determined as specified in Section 4.1.2.
      Execute Section at 5.2.2.3;
      }



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INTERNET-DRAFT                                          RBridge Protocol


   In the last case above, the egress nickname indicates the chosen
   distribution tree RBi. The default is for RB1 to put its own address
   there. However, if RB1 is configured to decline to be a tree root,
   then RB1 MUST select some other RBridge RBi which has elected to be a
   tree root or the RBridge with the lowest ID if none have elected to
   be a tree root.



5.2.5 IGMP and MLD Frames

   An IGMP (IPv4 [RFC3376]) or MLD (IPv6 [RFC2710]) announcement
   received from a link by the designated RBridge, teaches RBn a group
   membership on that link. The RBridge adds receiver for that layer 2
   group address in the appropriate VLAN in its core link state
   instance.  Then execute Section 5.2.4.



5.2.6 PIM and MRD Frames

   A PIM or MRD [RFC4286] message received from a link by the designated
   RBridge teaches RBn that there is an IP multicast router (for the
   determined VLAN) on its link, and adds that information into its core
   IS-IS link state information for that VLAN. Then execute Section
   5.2.4.



5.3 Frames Spontaneously Sourced

   The sections below discuss all frames that might be spontaneous
   sourced by an RBridge.



5.3.1 IS-IS Frames Sourced

   An RBridge R1 MUST spontaneously emit core instance TRILL IS-IS
   frames as described in 5.3.1.1. In addition, if it is DRB for a link
   that has end stations in a particular VLAN, it MAY run an IS-IS
   instance for that VLAN and emit TRILL IS-IS frames as described in
   5.3.1.2.

   Do not confuse the per VLAN DRB determination, which is done by the
   core IS-IS instance, with the optional per VLAN IS-IS instances used
   to distribute end station addresses.





R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 53]


INTERNET-DRAFT                                          RBridge Protocol


5.3.1.1 Core IS-IS Frames

   For core IS-IS frames, a V=1 TRILL header is added and no VLAN tag is
   included in the inner frame. Note that, in a strict sense, IS-IS has
   no Ethertype but the 802.3 LLC NSAP format MUST be used, that is LL-
   LL-FE-FE-03 where 0xLLLL is the length and 0x03 is the CTL byte. (The
   IS-IS standard also permits the less efficient SNAP SAP format LL-LL-
   AA-AA-03-00-00-00-80-FE which is not used in TRILL.)

   If the frame is multicast, it is formed as follows:

      Outer.MacDA = All-RBridges;
      Outer.MacSA = RB1;
      Outer.Ethertype = TRILL.
      Trill.V = 1;
      Trill.M = 1;
      Trill.HopCount = 1;
      Trill.IngressNickname = 0;
      Trill.EgressNickname = 0;
      Inner.MacDA = All-RBridges;
      Inner.MacSA = RB1;
      Inner.FrameLength = IS-IS frame length
      Inner.DSAP = 0xFE;
      Inner.SSAP = 0xFE.
      Inner.CTL = 3;
      followed by the rest of the IS-IS Frame.

   The frame is then sent out ports of the RBridge so as to get to every
   adjacent RBridge. For each port not either known to be a point-to-
   point connection to an Rbridge or configured not to use Outer VLAN
   Tags, an Outer VLAN Tag is added as follows:

      Outer VLAN Tag priority = 7;
      Outer VLAN VID = VID associated with the logical port on which the
        frame is being sent or zero if none.

   Note that this Outer VLAN Tag may be different on different ports.

   Currently all IS-IS messages are multi-cast. However, if it were
   necessary to send a unicast core instance TRILL IS-IS message, it
   would be formatted as follows:

      Outer.MacDA = DestinationRBridge;
      Outer.MacSA = RB1;
      Outer.Ethertype = TRILL.
      Trill.V = 1;
      Trill.M = 0;
      Trill.HopCount = 1;
      Trill.IngressNickname = 0;
      Trill.EgressNickname = 0;


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 54]


INTERNET-DRAFT                                          RBridge Protocol


      Inner.MacDA = DestinationRBridge;
      Inner.MacSA = RB1;
      Inner.FrameLength = IS-IS frame length
      Inner.DSAP = 0xFE;
      Inner.SSAP = 0xFE.
      Inner.CTL = 3;
      followed by the rest of the IS-IS Frame.

   The frame is then transmitted on the port for DestinationRBridge with
   an Outer VLAN Tag possibly added using the same logic as for a multi-
   cast TRILL IS-IS frame.



5.3.1.2 Per-VLAN IS-IS Frames

   For per VLAN TRILL IS-IS frames, a V=1 TRILL header is added and a
   VLAN tag is always included in the inner frame. Note that, in a
   strict sense, IS-IS has no Ethertype but the 802.3 NSAP format must
   be used as discusses at the start of section 5.3.1.1.

   If the frame is per VLAN multicast, it is formed as follows:

      Outer.MacDA = All-RBridges;
      Outer.MacSA = RB1;
      Outer.Ethertype = TRILL.
      Trill.V = 1;
      Trill.M = 1;
      Trill.HopCount = count to reach farthest node in the
                       distribution tree;
      Trill.IngressNickname = 0;
      Trill.EgressNickname = SelectedDistributionTree;
      Inner.MacDA = All-RBridges;
      Inner.MacSA = RB1;
      Ethertype = VLAN Tag;
      Inner VLAN Tag priority = 7;
      Inner VLAN Tag VID = Relevant VLAN;
      Inner.FrameLength = IS-IS frame length
      Inner.DSAP = 0xFE;
      Inner.SSAP = 0xFE.
      Inner.CTL = 3;
      followed by the rest of the IS-IS Frame.

   The frame is then sent out the ports appropriate for the selected
   distribution tree pruned to the selected VLAN.  For each port not
   either known to be a point-to-point connection to an RBridge or
   configured not to use Outer VLAN Tags, an Outer VLAN Tag is added as
   follows:

      Outer VLAN Tag priority = 7;


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 55]


INTERNET-DRAFT                                          RBridge Protocol


      Outer VLAN VID = VID associated with the logical port on which the
        frame is being sent or zero if none.

   Note that this Outer VLAN Tag may be different on different ports.

   Currently all IS-IS messages are multicast. However, if it were
   necessary to send a unicast per VLAN instance TRILL IS-IS message, it
   would be formatted as follows:

      Outer.MacDA = NextHopRBridge;
      Outer.MacSA = RB1;
      Outer.Ethertype = TRILL.
      Trill.V = 1;
      Trill.M = 0;
      Trill.HopCount = determined value (see Section 3.4);
      Trill.IngressNickname = 0;
      Trill.EgressNickname = DestinationNickname;
      Ethertype = VLAN Tag;
      Inner VLAN Tag priority = 7;
      Inner VLAN Tag VID = Relevant VLAN;
      Inner.MacDA = DestinationRBridge;
      Inner.MacSA = RB1;
      Inner.FrameLength = IS-IS frame length
      Inner.DSAP = 0xFE;
      Inner.SSAP = 0xFE.
      Inner.CTL = 3;
      followed by the rest of the IS-IS Frame.

   The frame is then transmitted on the port for NextHopRBridge with an
   Outer VLAN Tag possibly added using the same logic as for a multi-
   cast TRILL IS-IS frame.



5.3.2 Other Frames Sourced

   Other frames may be sourced due to management protocols or general
   applications running on an RBridge. These can be handled as if they
   were received by the RBridge on a port for which it was the
   Designated RBridge and on which there were no know directly connected
   stations as described in Section 5.2.4.

   WARNING: The Psuedo Code above has NOT been update to correspond to
   changes made in other Sections of this document but rather
   corresponds to draft version -04.







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INTERNET-DRAFT                                          RBridge Protocol


6. Incremental Deployment Considerations

   Because RBridges are compatible with current IEEE 802.1 bridges, a
   LAN can be upgraded by incrementally replacing bridges with RBridges.
   Any remaining bridges are invisible to RBridges and the physical
   links directly interconnected by such bridges, which together with
   the bridges constitute a bridged LAN, appear to RBridges to be a
   single multi-access link.  If the bridges that were replaced by
   RBridges were un-managed, zero configuration bridges, then the
   RBridge replacements will not require configuration.

   Section 6.1 further explores general incremental deployment
   considerations while Section 6.2 shows a particular example.



6.1 Incremental Deployment

   The campus will work best if all IEEE 802.1 bridges are replaced with
   RBridges, assuming the RBridges have the same basic speed and
   capacity as the bridges. However, there may be intermediate states,
   where only some bridges have been replaced by RBridges.

   In particular, assume the RBridges partition a bridged LAN into a
   relatively small number of relatively large remnant bridged LANs.
   Then two potential problems may occur as follows:

   1. The requirement that end station frames enter and leave a link via
      the Designated RBridge for the link can cause congestion or
      suboptimal routing.  The extent to which such a problem will occur
      is highly dependent on the network topology. For example, if a
      bridged LAN had a star-like structure with core bridges that
      connected only to other bridges and peripheral bridges that
      connected to end stations and singly connected to a core bridge,
      the replacement of all of the core bridges by RBridges without
      replacing the peripheral bridges would generally improve
      performance without inducing any Designated RBridge congestion.

   2. TRILL traffic sent to the All-Rbridge multicast address will
      typically be flooded throughout a bridged LAN link which may
      create a greater burden than necessary. In cases where there is
      actually only one intended RBridge next hop recipient, this
      problem can be eliminated by using the option of sending the TRILL
      traffic that woukd otherwise be multicast as a unicast frame to
      that recipient.

   Inserting RBridges so that all the bridged portions of the LAN stay
   connected to each other is generally the least efficient arrangement.

   There are four techniques which may help if problem 1 above occurs


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 57]


INTERNET-DRAFT                                          RBridge Protocol


   and which can, to some extent, be used in combination:

   1. Replace more IEEE 802.1 bridges with RBridges so as to minimize
      the size of the remnant bridged LANs between RBridges. This
      requires no configuration of the RBridges unless the bridges they
      replace required configuration.

   2. Re-arrange network topology to minimize the problem.  If the
      bridges and RBridges involved are configured, this may require
      changes in their configuration.

   3. Configure the RBridges and bridges so that end stations on a
      remnant bridged LAN are separated into different VLANs that have
      different Designated RBridges. If the end stations were already
      assigned to different VLANs, this is straightforward (see Section
      4.2.4). If the end stations were on the same VLAN and have to be
      split into different VLANs, this technique may lead to
      connectivity problems between end stations but it may be possible
      to overcome these problems using shared VLANs (see Section 4.7).

   4. Configure the RBridges such that their ports which are connected
      to the bridged LAN participate in the bridged LAN's spanning tree
      in such a way as to force the partition of the bridged LAN. (Note:
      a spanning tree is never formed through an RBridge but always
      terminates at RBridge ports.)  To use this technique, the RBridges
      must support this optional feature, which is discussed further in
      Section 6.2, and would need to be configured to make use of it but
      the bridges involved would rarely have to be configured.  Warning:
      This technique makes the bridged LAN unavailable for RBridge
      through traffic because the bridged LAN partitions.

   Conversely to item 3 above, there may be bridged LANs which use
   VLANs, or use more VLANs than would otherwise be necessary, to evade
   the congestion that can be caused by the spanning tree algorithm.
   Replacing the IEEE 802.1 bridges in such LANs with RBridges may
   enable a reduction in or elimination of VLANs and configuration.



6.2 Wiring Closet Topology

   If 802.1 bridges are present and RBridges are not configured, the
   bridge spanning tree or the Designate RBridge election may make
   inappropriate decisions.  Below is a detailed example of the more
   general problem that can occur when a bridge LAN is connected to
   multiple RBridges (see Section 6.1).

   For example, in cases where there are two (or more) groups of end
   nodes, each attached to a bridge (say B1 and B2 respectively), and
   each bridge is attached to an RBridge (say RB1 and RB2 respectively),


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 58]


INTERNET-DRAFT                                          RBridge Protocol


   with a additional link connecting B1 and B2 (see Figure 10), it may
   be desirable to have the B1-B2 link only as a backup in case one of
   RB1 and RB2, or one of the links B1-RB1 or B2-RB2 fail.

                    +-------------------------------+
                    |             |          |      |
                    |  Data    +-----+    +-----+   |
                    | Center  -| RB1 |----| RB2 |-  |
                    |          +-----+    +-----+   |
                    |             |          |      |
                    +-------------------------------+
                                  |          |
                                  |          |
                    +-------------------------------+
                    |             |          |      |
                    |          +----+     +----+    |
                    | Wiring   | B1 |-----| B2 |    |
                    | Closet   +----+     +----+    |
                    |                               |
                    +-------------------------------+

                     Figure 10. Wiring Closet Topology

   For example, B1 and B2 may be in a wiring closet and it may be easy
   to provide a very short high bandwidth low cost link between them
   while RB1 and RB2 are at a distant data center such that the RB1-B1
   and RB2-B2 links are slower and more expensive.

   Default behavior would be that one of RB1 or RB2 (say RB1) would
   become Designated RBridge, and forward traffic to/from the link, so
   end nodes attached to B2 would be connected to the campus via the
   path B2-B1-RB1, rather than the desired B2-RB2. This wastes the
   bandwidth of the B2-RB2 path and cuts available bandwidth between the
   end stations and the data center in half. The desired behavior would
   probably be to make maximum use of both the RB1-B1 and RB2-B2 links.



6.2.1 The RBridge Solution

   Of course, if B1 and B2 are replaced with RBridges, the right thing
   will normally happen with zero configuration, but this may not be
   immediately practical if bridges are being incrementally replaced by
   RBridges.








R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 59]


INTERNET-DRAFT                                          RBridge Protocol


6.2.2 The Spanning Tree Solution

   Another solution is to configure RB1 and RB2 to be part of a "wiring
   closet group", with a configured System ID RBx (which may be RB1 or
   RB2's System ID). Both RB1 and RB2 participate in the bridge spanning
   tree on the configured ports as root RBx, which causes the spanning
   tree to partition the bridged LAN and break the B1-B2 link as
   desired, and both RB1 and RB2 act as Designated RBridge on each of
   their respective partitions. Of course, with the partition, no
   RBridge through traffic can flow over the RB1-B1-B2-RB2 path.

   In the BPDU, the Root is "RBx", cost to Root is 0, Designated Bridge
   ID is "RB1" when R1 transmits and "RB2" when R2 transmits, and port
   ID is a value chosen independently by each of RB1 and RB2 to
   distinguish each of its own ports. If RB1 and RB2 were actually on
   the same shared medium with no bridges between them, the result is
   that the one with the larger ID sees "better" BPDUs (because of the
   tie-breaker on the third field; the ID of the transmitting RBridge),
   and turns off the port.

   Should either the RB1 or the RB1-B1 link or RB2 or the RB2-B2 link
   fail, the spanning tree algorithm will stop seeing one of the RBx
   roots and will re-enable the B1-B2 link maintaining connectivity of
   all the end stations with the data center.

   If the link RB1-B1-B2-RB2 is on the cut set of the campus and RB2
   and/or RB1 have been configured to believe they are part of a wiring
   closet group the campus becomes partitioned as the link partitions.



6.2.3 The VLAN Solution

   If the end stations attached to B1 and B2 are already divided among a
   number of VLANs, RB1 could be configured to have higher priority to
   become DRB on some of these VLANs and RB2 configured to have higher
   priority on the others. Should either of the RBs fail or become
   disconnected, the other will become DRB for all the VLANs.

   If the end stations are all on a single VLAN, perhaps the default
   VLAN 1, then it would be necessary to arbitrarily assign them between
   at least two VLANs to use this solution. This may lead to
   connectivity problems which might require further measures, outside
   the scope of this specification, to rectify.








R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 60]


INTERNET-DRAFT                                          RBridge Protocol


6.2.4 Comparison of Solutions

   Replacing all 802.1 bridges with RBridges is usually the best
   solution with the least amount of configuration required, possibly
   none.

   The spanning tree solution does quite well in this particular case.
   But it depends on both RB1 and RB2 having implemented the optional
   feature of being able to configure a port to participate in spanning
   tree as described in Section 6.2.2 above. It also makes the bridged
   LAN whose partition is being forced unavailable for through traffic
   Finally, while in this specific example it neatly breaks the link
   between the two bridges B1 and B2, if there were a more complex
   bridged LAN, instead of exactly two bridges, there is no guarantee
   that it would partition into roughly equal pieces. In such a case,
   you might end up with a highly unbalanced load on the RB1 link and
   the RB2 link.

   The VLAN solution works well with a relatively small amount of
   configuration if the end stations are already divided among a number
   of VLANs. If they are not, it becomes more complex and problematic.































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INTERNET-DRAFT                                          RBridge Protocol


7. RBridge Addresses, Parameters, and Constants

   IS-IS requires each RBridge to have a unique 6-byte System ID. This
   is easily obtainable, e.g., as any one of the 6-byte MAC addresses
   owned by that RBridge.

   A new Ethertype must be assigned to indicate a TRILL encapsulated
   frame.

   A layer 2 multicast address for All-RBridges must be assigned for use
   as the destination address in multi-destination frames.

   To support VLANs, RBridges (like bridges today), must be configured
   appropriately. This includes per VLAN priority for becoming DRB and
   cases where DRB status for a VLAN is determined without a DRB
   election on that VLAN but rather by copying its DRB status for a
   different VLAN on which an election was done.

   RBridges may be configured with a nickname and nickname selection
   priority.

   RBridges may be configured to have per VLAN IS-IS instances and to
   send and/or learn end station address information via such instances.
   Static end address information and priority of such end station
   information statically configured and learned in various ways can
   also be configured.

   The per RBridge parameter RequestTree that indicates whether an
   RBridge wants to be the root of a distribution tree.

   Configuration for wiring closet topology (see Section 6.2) consists
   of System ID of the RBridge with lowest System ID. If RB1 and RB2 are
   part of a wiring closet topology, only RB2 needs to be configured to
   know about this, and that RB1 is the ID it should use in the spanning
   tree protocol on the specified port.

















R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 62]


INTERNET-DRAFT                                          RBridge Protocol


8. Security Considerations

   Layer 2 bridging in not inherently secure.  It is, for example,
   subject to forgery of source addresses and bridging control messages.
   A goal for TRILL is that RBridges do not add new issues beyond those
   existing in current bridging technology.

   Countermeasures are available such as to configure the RBridge IS-IS
   instances to use IS-IS security and ignore unauthenticated control
   messages received on a port. Since such authentication requires
   configuration, RBridges where it is used are no longer zero
   configuration.

   IEEE 802.1 port admission and link security mechanisms, such as
   [802.1X] and [802.1AE], can also be used. These are best thought of
   as being implemented within a port and are outside the scope of TRILL
   proper (just as they are generally out of scope for bridging
   standards 802.1D and 802.1Q) although TRILL can make use of secure
   registration through the confidence level communicated in the
   optional per VLAN IS-IS instance (see Section 4.6).

   RBridges do not prevent nodes from impersonating other nodes, for
   instance, by issuing bogus ARP/ND replies.  However, RBridges do not
   interfere with any schemes that would secure neighbor discovery.




























R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 63]


INTERNET-DRAFT                                          RBridge Protocol


9. Assignment Considerations

   This section discuses IANA and IEEE 802 assignment considerations.



9.1 IANA Considerations

   A new IANA registry is created for TRILL.

   New TRILL Header Variation numbers are assigned by an IETF Standards
   Action [RFC2434] as modified by [RFC4020].



9.2 IEEE 802 Assignment Considerations

   The Ethertype <tbd> is assigned by IEEE 802 to indicate a TRILL
   encapsulated frame.

   The layer 2 multicast address <tbd> is assigned by IEEE 802 for "All-
   Rbridges".






























R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 64]


INTERNET-DRAFT                                          RBridge Protocol


10. Normative References

   [802.1D] "IEEE Standard for Local and metropolitan area networks /
   Media Access Control (MAC) Bridges", 802.1D-2004, 9 June 2004.

   [802.1Q] "IEEE Standard for Local and metropolitan area networks /
   Virtual Bridged Local Area Networks", 802.1Q-2005, 19 May 2006.

   [802.3]

   [ISO10589] ISO/IEC 10589:2002, "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.

   [RFC1112]  Deering, S., "Host Extensions for IP Multicasting", STD 5,
   RFC 1112, Stanford University, August 1989.

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

   [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
   IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

   [RFC2464] - Crawford, M., "Transmission of IPv6 Packets over Ethernet
   Networks", RFC 2464, December 1998.

   [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
   Listener Discovery (MLD) for IPv6", RFC 2710, October 1999.

   [RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
   Thyagarajan, "Internet Group Management Protocol, Version 3", RFC
   3376, October 2002.

   [RFC4020] Kompella, K. and A. Zinin, "Early IANA Allocation of
   Standards Track Code Points", BCP 100, RFC 4020, February 2005.

   [RFC4286] Haberman, B., Martin, J., "Multicast Router Discovery", RFC
   4286, December 2005.



11. Informative References

   [802.1AB] "IEEE Standard for Local and metropolitan area networks /
   Station and Media Access Control Connectivity Discovery",
   802.1AB-2005, 6 May 2005.

   [802.1AE] "IEEE Standard for Local and metropolitan area networks /
   Media Access Control (MAC) Security", 802.1AE-2006, 18 August 2006


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 65]


INTERNET-DRAFT                                          RBridge Protocol


   [802.1X] "IEEE Standard for Local and metropolitan area networks /
   Port Based Network Access Control", 802.1X-2004, 13 December 2004.

   [Arch] Gray, E., "The Architecture of an RBridge Solution to TRILL",
   draft-ietf-trill-rbridge-arch-02.txt, October 2006, work in progress.

   [PAS] Touch, J., & R. Perlman, "Transparent Interconnection of Lots
   of Links (TRILL) / Problem and Applicability Statement", draft-ietf-
   trill-prob-01.txt, October 2006, work in progress.

   [RBridges] Perlman, R., "RBridges: Transparent Routing", Proc.
   Infocom 2005, March 2004.

   [RFC4541] Christensen, M., Kimball, K., and F. Solensky,
   "Considerations for Internet Group Management Protocol (IGMP) and
   Multicast Listener Discovery (MLD) Snooping Switches", RFC 4541, May
   2006.

   [RP1999] Perlman, R., "Interconnection: Bridges, Routers, Switches,
   and Internetworking Protocols", Addison Wesley Chapter 3, 1999.
































R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 66]


INTERNET-DRAFT                                          RBridge Protocol


Appendix A: Revision History

   RFC Editor: Please delete this appendix before publication.



Changes from -03 to -04

    1. Divide IANA Considerations section into IANA and IEEE parts. Add
       IANA considerations for TRILL Header variations and reserved bit
       and normative references to RFCs 2434 and 4020.

    2. Add note on the terms Rbridge and TRILL to section 1.2.

    3. Remove IS-IS marketing text.

    4. Split Section 3 into Sections 3 and 4.  Add a new top level
       section "5. Pseudo Code", renumbering following sections. Move
       pseudo code that was in old Section 3 into Section 4 and make
       section 3 more textural.  This idea is that Section 3 and 4 have
       more readable text descriptions with some corner cases left out
       for simplicity while section 5 has more structured and complete
       coverage.

    5. Revised and extended Security Considerations section.

    6. Move multicast router attachment bit and IGMP membership report
       information from the per VLAN IS-IS instance to the core IS-IS
       instance so the information can be used by core RBridges to prune
       distribution trees.

    7. Remove ARP/ND optimization.

    8. Change TRILL Header to add option feature. Add option section.

    9. Change TRILL Header to expand Version field to the Variation
       field. Add TRILL message variations (8 bits) supported to the per
       RBridge link state information.

   10. Distinguish TRILL data and IS-IS messages by using Variation = 0
       and 1.

   11. Consistently state that VLAN pruning and IP derived multicast
       pruning of distribution trees are SHOULD.

   12. Add text and pseudo code to discard TRILL Ethertype data frames
       received on a port that does not have an IS-IS adjacency on it.

   13. Specify end station address learning from decapsulated native
       frames.


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INTERNET-DRAFT                                          RBridge Protocol


   14. Add nickname allocation priority and optional nickname
       configuration. Reserve nickname values zero and 0xFFFF.

   15. Explain about multiple Designated RBridges because of multiple
       VLANS.

   14. Add Incremental Deployment Considerations Section incorporating
       expanded Wiring Closet Topology Section.

   15. Add end station address learning section.

   16. Add more detail on VLAN tag information and material on frame
       priority.

   17. Miscellaneous minor editing and terminology updates.




Changes from -04 to -05

   NOTE: Section 5 was NOT updated as indicated below but the remainder
   of the draft was so updated.

    1. Mention optional VLAN and multicast optimization in Abstract.

    2. Change to distinguish TRILL IS-IS from TRILL data frames based on
       the Inner.MacDA instead of a TRILL Header bit.

    3. Split IP multicast router attached bit in two so you can
       separately indicate attachment of IPv4 and IPv6 routers.  Provide
       that these bits must be set if an RBridge does not actually do
       multicast control snooping on ingressed traffic.

    4. Add the term "port VLAN ID" (PVID).

    5. Drop references to PIM. Improve discussions of IGMP, MLD, and MRD
       messages.

    6. Move M bit over one and create two bit pruning field at the
       bottom of the "V" combined field.

    7. Add pruning control values of V and discussion of same.

    8. Permit optional unicast tranmission of multi-destination frames
       when there is only one received out a port.

    9. Miscellaneous minor editing and terminology updates.

   NOTE: Section 5 was NOT updated as indicated above but the remainder


R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 68]


INTERNET-DRAFT                                          RBridge Protocol


   of the draft was so updated.



















































R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 69]


INTERNET-DRAFT                                          RBridge Protocol


Disclaimer

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.



Additional IPR Provisions

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
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   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
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   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
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   retain all their rights.




Authors' Addresses

   Radia Perlman
   Sun Microsystems



R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 70]


INTERNET-DRAFT                                          RBridge Protocol


   Email: Radia.Perlman@sun.com


   Silvano Gai
   Nuova Systems

   Email: sgai@nuovasystems.com


   Dinesh G. Dutt
   Cisco Systems, Inc.
   170 Tasman Drive
   San Jose, CA 95134-1706

   Phone: +1-408-527-0955
   EMail: ddutt@cisco.com


   Donald E. Eastlake, 3rd
   Motorola Laboratories
   111 Locke Drive
   Marlborough, MA 01752 USA

   Phone: +1-508-786-7554
   Email: Donald.Eastlake@motorola.com



Expiration and File Name

   This draft expires in January 2008.

   Its file name is draft-ietf-trill-rbridge-05.txt.



















R. Perlman, S. Gai, D. Dutt, D. Eastlake                       [Page 71]


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