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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                   Donald Eastlake 3rd
                                                   Motorola Laboratories
                                                             Silvano Gai
                                                           Nuova Systems
                                                          Dinesh G. Dutt
                                                                   Cisco
Expires: May 2008                                          November 2007


                 Rbridges: Base Protocol Specification

               <draft-ietf-trill-rbridge-protocol-06.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 <rbridge@postel.org>.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   http://www.ietf.org/shadow.html














R. Perlman, D. Eastlake, S. Gai, D. Dutt                        [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, Joel Halpern, Erik Nordmark,
   Sanjay Sane, and Joe Touch. We invite you to join the mailing list at
   http://www.postel.org/rbridge.























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


INTERNET-DRAFT                                          RBridge Protocol


Table of Contents

      Status of This Document....................................1
      Abstract...................................................2
      Acknowledgements...........................................2
      Table of Contents..........................................3

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

      2. RBridges................................................8
      2.1 End Station Addresses..................................9
      2.2 RBridge Architecture...................................9
      2.3 RBridges and VLANs....................................11
      2.4 Forwarding of Different Frame Types...................12
      2.4.1 Known-Unicast.......................................13
      2.4.2 Multi-destination...................................13

      3. Details of the TRILL Header............................14
      3.1 TRILL Header Format...................................14
      3.2 Version (V)...........................................14
      3.3 Reserved (R)..........................................15
      3.4 Multi-destination (M).................................15
      3.5 TRILL Header Options..................................15
      3.6 Hop Count.............................................16
      3.7 RBridge Nicknames.....................................16
      3.7.1 Egress RBridge Nickname.............................17
      3.7.2 Ingress RBridge Nickname............................17
      3.7.3 RBridge Nickname Allocation.........................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..............................24
      4.2.2 IS-IS Instances.....................................25
      4.2.3 TRILL IS-IS Information.............................25
      4.2.3.1 Core IS-IS Information............................25
      4.2.3.2 Optional Per-VLAN IS-IS Instance Information......27
      4.2.4 Designated RBridge..................................27
      4.2.5 Appointed VLAN-x Forwarder..........................28
      4.3 Distribution Trees....................................29
      4.3.1 Distribution Tree Calculation and Checks............30
      4.3.2 Pruning the Distribution Tree.......................31
      4.3.3 Forwarding Using a Distribution Tree................32
      4.4 Forwarding Behavior...................................33


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


INTERNET-DRAFT                                          RBridge Protocol


Table of Contents Continued

      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
      4.4.3 Tree Distribution Optimization......................37
      4.5 IGMP, MLD, and MRD Learning...........................37
      4.6 End Station Address Details...........................38
      4.6.1 Learning End Station Addresses......................39
      4.6.2 Forgetting End Station Addresses....................40
      4.7 Shared VLAN Learning..................................40

      5. Pseudo Code............................................41
      5.1 802MUL Destination Frames.............................41
      5.1.1 All Bridges Frames..................................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 Multicast 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..........................46
      5.2.2.2 TRILL Frame Multi-destination Forwarding..........47
      5.2.2.3 TRILL Data Frame Tree Transmission................47
      5.2.2.4 TRILL Data Frame Transmission.....................48
      5.2.3 TRILL Ethertype Frames..............................48
      5.2.3.1 TRILL IS-IS Frames................................48
      5.2.3.2 TRILL Data Frames.................................49
      5.2.4 Native Frame Receipt................................50
      5.2.4.1 Native IPv4 Multicast Frame.......................52
      5.2.4.2 Native IPv6 Multicast Frame.......................53
      5.2.5 IGMP and MLD Frames.................................54
      5.2.6 MRD Frames..........................................54
      5.3 Frames Spontaneously Sourced..........................54
      5.3.1 Bridge/Media Frames Sourced.........................54
      5.3.2 IS-IS Frames Sourced................................55
      5.3.2.1 Core IS-IS Frames.................................55
      5.3.2.2 Per-VLAN IS-IS Frames.............................56
      5.3.3 Other Frames Sourced................................57

      6. Incremental Deployment Considerations..................58
      6.1 VLAN Connectivity Changes.............................58
      6.2 Link Cost Determination...............................58
      6.3 Appointed Forwarders and Bridged LANs.................59
      6.4 Wiring Closet Topology................................60


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


INTERNET-DRAFT                                          RBridge Protocol


Table of Contents Continued

      6.4.1 The RBridge Solution................................61
      6.4.2 The Spanning Tree Solution..........................61
      6.4.3 The VLAN Solution...................................62
      6.4.4 Comparison of Solutions.............................62

      7. RBridge Addresses, Parameters, and Constants...........64

      8. Security Considerations................................65

      9. Assignment Considerations..............................66
      9.1 IANA Considerations...................................66
      9.2 IEEE 802 Assignment Considerations....................66

      10. Normative References..................................67
      11. Informative References................................68

      Appendix A: Revision History..............................69
      Changes from -03 to -04...................................69
      Changes from -04 to -05...................................70
      Changes from -05 to -06...................................71

      Disclaimer................................................72
      Additional IPR Provisions.................................72

      Authors' Addresses........................................73
      Expiration and File Name..................................73
























R. Perlman, D. Eastlake, S. Gai, D. Dutt                        [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  VLANs can partition, perhaps unexpectedly, when spanning tree
      reconfigures due to a node failure or topology change.

   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
   [RBridges]) which implement the TRILL protocol and are poetically
   summarized below.  Rbridges combine the advantages of bridges and
   routers.  While they can be applied to a variety of link protocols,
   this specification concentrates on IEEE 802.3 links [802.3].
















R. Perlman, D. Eastlake, S. Gai, D. Dutt                        [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

   "TRILL" normally 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, D. Eastlake, S. Gai, D. Dutt                        [Page 7]


INTERNET-DRAFT                                          RBridge Protocol


2. RBridges

   RBridges run a link state protocol amongst themselves. This enables
   them to have enough information to compute pair-wise optimal paths
   for unicast, and to calculate distribution trees for delivery of
   frames either to unknown MAC destinations, or to multicast/broadcast
   groups. [RBridges] [RP1999]

   To mitigate temporary loop issues, RBridges forward based on a header
   with a hop count. RBridges also specify the next hop RBridge as the
   frame destination when forwarding unicast frames across a shared-
   media link, which avoids spawning additional copies of frames during
   a temporary loop.  A Reverse Path Forwarding Check and other checks
   are performed on multi-destination frames.

   The first RBridge that a unicast 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-octet nickname for each RBridge, unique within the campus,
   which is an abbreviation for the 6-octet IS-IS system ID of the
   RBridge.  The 2-octet nicknames are used to specify the ingress and
   egress RBridges in the TRILL header.

   Multipathing of multi-destination frames through alternative
   distribution tree roots and ECMP (Equal Cost MultiPath) of unicast
   frames are enabled but not fully specified in this document.
   Multipathing may introduce frame reordering as can frame priorities
   or changes in network topology.

   RBridges run the IS-IS election protocol to elect a "Designated
   RBridge" (DRB) on each bridged LAN ("link").  As with an IS-IS
   router, the DRB gives a pseudonode name to the link, issues an LSP on
   behalf of the pseudonode, and issues CSNPs on the link.
   Additionally, the DRB specifies which VLAN will be the common VLAN to
   use for communication between RBridges on that link.  The DRB either
   encapsulates/decapsulates all data traffic to/from the link, or for
   load splitting, delegates this responsibility, for one or more VLANs,
   to other RBridges on the LAN.  There must at all times be at most one
   RBridge on the bridged LAN that encapsulates/decapsulates traffic for
   a particular VLAN. We will refer to the RBridge appointed to forward
   VLAN x traffic on behalf of the link as the "appointed VLAN-x
   forwarder".  (Section 2.3 discusses further implications of VLANs.)

   Rbridges can be managed with SNMP [RFC3410].  The Rbridge MIB will be
   specified in a separate document.  This management can be used,
   within a campus, even by an RBridge that lacks an IP or other Layer 3
   transport stack or which is zero configuration and has no Layer 3
   address, by transporting SNMP with Ethernet (see [RFC4789]).


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


INTERNET-DRAFT                                          RBridge Protocol


2.1 End Station Addresses

   An RBridge, RB1, that is the VLAN-x forwarder on any of its links
   MUST learn the location of VLAN-x endnodes, both on the links for
   which it is VLAN-x forwarder, and on other links in the campus. RB1
   learns the location and Layer 2 addresses of endnodes on links for
   which it is VLAN-x forwarder from the source address of frames, as
   bridges do (for example, see section 8.7 of [802.1Q]). RB1 learns the
   Layer 2 address of distant VLAN-x 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 it is decapsulating onto a
   link.

   Additionally, a VLAN-x instance of IS-IS MAY be used by the appointed
   VLAN-x forwarder on a link to announce some or all of the attached
   VLAN-x end nodes on that link. The intention is that such an
   announcement would be used to announce end nodes that have been
   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 (for
   example by [802.1X]), but IS-IS also supports cryptographic
   authentication of its messages.  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.

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

   (See Section 4.6 for further end station address details.)



2.2 RBridge Architecture

   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, this document specifies only an IEEE 802.3 encapsulation
   [802.3].

   Figure 1 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.


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


INTERNET-DRAFT                                          RBridge Protocol


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

                     Figure 1. Interconnected RBridges

   Figure 2 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 2. An Ethernet Encapsulated TRILL Frame

   In the case of media different from Ethernet, the outer Ethernet
   header is replaced by the header specific to that media. For example,
   Figure 3 shows a TRILL encapsulation over PPP.

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

                 Figure 3. 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 which is encapsulated with a TRILL


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


INTERNET-DRAFT                                          RBridge Protocol


   header as it travels 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; and,

   4. to provide VLAN labeling to get the frame through bridged LANs
      while preserving the original VLAN.

   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 any 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.



2.3 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.

   IEEE 802.1Q bridges have the capability of supporting multiple VLANs
   over a single link by inserting/removing a VLAN tag in the frame.
   Rbridges can be configured to provide similar VLAN support.  Some end
   nodes have the same capability.  The VLAN tag is structured according
   to IEEE 802.1Q. As shown in Figure 2, 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 an end station frame originating in a
   particular inner VLAN only to other links in the same inner VLAN;
   however, there are a few differences in the handling of VLANs between
   RBridged LANs and 802.1 bridged LANs.

   802.1 bridges will only forward a data frame over a link if that link
   is configured to be part of the VLAN to which that frame belongs. (By
   default a link belongs only to VLAN 1.) The GVRP (see [802.1Q])


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


INTERNET-DRAFT                                          RBridge Protocol


   protocol and proprietary features of some bridges (i.e., "trunk
   links") are designed to support full connectivity between all end
   stations in a particular VLAN. However, bridges can be configured so
   as to partition one or more particular VLANs into unconnected
   islands.  RBridges, on the other hand, have a campus wide view
   through the IS-IS link state database and can use arbitrary outer
   VLAN labeling for connectivity and to send data for any VLAN over any
   link.  As a result, RBridges connect all campus end stations in a
   particular VLAN (unless those end stations are cut off by bridges or
   configuration from access to any RBridge).

   It is possible that a link which is a bridged LAN might be
   partitioned with respect to some VLANs. If the bridged LAN were
   partitioned with respect to, say, VLAN x, and RBridges RB1 and RB2
   were to send IS-IS Hellos on that link tagged with VLAN x, they might
   not see each other's Hellos, and as a result, both conclude they
   should be DRB (Designated RBridge) on that link, both performing the
   encapsulation/decapsulation of data packets to/from that link, and
   thereby forming a loop. Therefore, it is important for RBridges to
   tag IS-IS Hellos with a VLAN that is not partitioned on the link. If
   the link is misconfigured, and the VLAN on which they are sending
   Hellos is partitioned, TRILL provides mechanisms whereby the
   duplicate DRBs will be detected and loops will be prevented.

   By default, RBridges tag IS-IS Hellos with VLAN 1. However, an
   RBridge MAY be configured to transmit Hellos on a set of VLANs, and
   if elected DRB, to specify to the other RBridges on the link which
   VLAN to tag Hellos with. Once the DRB, say RB1, is elected, and
   specifies the VLAN, say VLAN x, on which to send Hellos, all RBridges
   on the link, except the DRB, transmit Hellos tagged only with VLAN x,
   and all RBridge-RBridge communication (including Hellos, forwarded
   data packets, and LSPs) are tagged with VLAN x. To maximize the
   probability that even if VLAN x is partitioned, other RBridges will
   know that RB1 is the DRB, RB1 will continue to transmit Hellos on the
   set of VLANs for which it is configured to send Hellos on.  Note that
   the set of VLANs RB1 is configured to send Hellos on need not be all
   the VLANs that RB1 can send and receive on.  An RBridge that is not
   DRB MAY ignore any IS-IS messages (including Hellos) sent on any
   VLANs other than the common VLAN. The DRB, however, MUST continue to
   send and receive IS-IS Hellos on all VLANs that the DRB has been
   configured to send Hellos on.



2.4 Forwarding of Different Frame Types

   There are several types of transit frames between RBridges that are
   forwarded differently. They are here classified into two main
   categories: known-unicast and multi-destination.



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


INTERNET-DRAFT                                          RBridge Protocol


2.4.1 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.



2.4.2 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 [RFC4286]
          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 address: the Inner.MacDA is
      broadcast.

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












R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [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 gives pseudo-code.



3.1 TRILL Header Format

   The TRILL header is shown in Figure 4 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 | R |M|Op-Length| Hop Count |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Egress RBridge Nickname     |  Ingress RBridge Nickname     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                          Figure 4. TRILL Header

   The header contains the following fields which are described in the
   sections referenced.

   o  V (Version): 2-bits. See Section 3.2.

   o  R (Reserved): 2-bits. See Section 3.3.

   o  M (Multi-destination): 1-bit. See Section 3.4.

   o  Op-Length (Options Length): 5-bits. See Section 3.5.

   o  Hop Count: 6-bit unsigned integer. See Section 3.6.

   o  Egress RBridge Nickname: 16-bit address. See Section 3.7.1.

   o  Ingress RBridge Nickname: 16-bit address. See Section 3.7.2.



3.2 Version (V)

   According to IEEE's Ethertype 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. Adhering to this guideline, there is a two
   bit Version field in the TRILL header. Version zero of TRILL is
   specified in this document. An RBridge that sees a message with a
   Version value it does not understand MUST silently discard the


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


INTERNET-DRAFT                                          RBridge Protocol


   message because it may not be able to parse it.



3.3 Reserved (R)

   The two reserved bits are reserved for future use in extensions to
   the TRILL protocol. They MUST be zero on transmission and are ignored
   on receipt.



3.4 Multi-destination (M)

   The Multi-destination bit (see Section 2.4.2) indicates the frame is
   to be delivered to a class of destination end stations via a
   distribution tree. 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 by the source RBridge for a per VLAN TRILL IS-IS frame.



3.5 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 octets which allows up to 124 octets 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-octet 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 VLANs, IP multicast, and the like. 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.



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INTERNET-DRAFT                                          RBridge Protocol


   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
   option can be safely ignored.

   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 such frames to be
   lost.



3.6 Hop Count

   The Hop Count field is 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 on that path to the most distant RBridge. To
   accomplish this, RBridge RBn calculates, for each branch of the
   distribution 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 tree rooted at RBi.

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



3.7 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


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INTERNET-DRAFT                                          RBridge Protocol


   more compact encoding. This assignment allows specifying up to 2**16
   RBridges; however, the value 0x0000 is reserved to indicate that a
   nickname is not specified and the value 0xFFFF is reserved for future
   specification.  RBridges piggyback a nickname acquisition protocol on
   the link state protocol (see Section 3.7.3) to acquire a nickname
   unique within the campus.



3.7.1 Egress RBridge Nickname

   There are three cases for the contents of the egress RBridge nickname
   field, depending on the M-bit (see Section 3.4) 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-
      IS-IS-RBridges, 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.  This
      root MUST NOT be changed by transit RBridges.

   o  For core instance TRILL IS-IS frames M = 0, the Inner.MacDA is
      All-IS-IS-Rbridge, and the 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.



3.7.2 Ingress RBridge Nickname

   The ingress RBridge nickname contains the nickname of the ingress
   RBridge in two cases: (1) Data frames (those with Inner.MacDA other
   than All-IS=IS-Rbridges) and (2) Per VLAN TRILL IS-IS frames (those
   with Inner.MacDA equal to All-IS-IS-Rbridges and an inner VLAN tag
   present). Note: The per-VLAN-x TRILL IS-IS frame is used for the
   purpose of the ingress RBridge R1 optionally advertising attachment
   of a set of VLAN-x endnodes to R1.

   For core TRILL IS-IS frames, that is those with Inner.MacDA equal to
   All-IS-IS-Rbridges and no inner VLAN tag present, this field is not
   used.  Such frames may be sent before nicknames have been established
   and are only sent one hop.  In that case this field MUST be set to
   zero by the source RBridge and is ignored by other RBridges. Note:


R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 17]


INTERNET-DRAFT                                          RBridge Protocol


   Core IS-IS frames include Hello messages, SNPs, and LSPs.



3.7.3 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 0x0000 and 0xFFFF are reserved and may not be
      selected or configured. In some cases the value 0x0000 is used to
      indicate that the nickname is not known.

   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 in priority, the RBridge with the numerically
      higher System ID keeps the nickname, and the other RBridge MUST
      choose a new nickname.

   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.


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INTERNET-DRAFT                                          RBridge Protocol


   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.





































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INTERNET-DRAFT                                          RBridge Protocol


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 2). 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 TRILL Ethertype (see Section 9.2) is used in the
   outer header.

   Figure 6 details a data frame with an outer VLAN tag traveling on the
   Ethernet cloud of Figure 1 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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INTERNET-DRAFT                                          RBridge Protocol


   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 | R |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:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Ethertype of Original Payload |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
      |                                  Original Ethernet Payload    |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Frame CheckSum:
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  New FCS (Frame CheckSum)                     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

             Figure 6. TRILL Data Encapsulation over Ethernet



4.1.1 VLAN Tag Information

   The information in a "VLAN Tag", also known as a "C-tag" (formerly Q-
   tag), is more than just a VLAN ID. It always includes a priority
   field as shown in Figure 7. 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 |                  VLAN ID                      |
     +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

                      Figure 7. VLAN Tag Information

   As recommended in [802.1Q] Rbridges SHOULD be implemented so as to
   allow use of the full range of VLAN IDs from 0x001 through 0xFFE.
   VLAN ID zero is the null VLAN identifier and indicates that no VLAN
   is specified while VLAN ID 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. RBridges (and
   bridges), 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 C-Tag (formerly Q-Tag) Ethertype is 0x8100.



4.1.2 Outer VLAN Info

   RBridges send IS-IS Hellos on a link in order to discover RBridge
   neighbors. The default is to send IS-IS Hellos only on VLAN 1.
   However, an RBridge MAY be configured to send Hellos on a set of,
   say, k different VLAN numbers, including one preferred value.  In
   that case, the RBridge will transmit k times as many Hellos, sending
   Hellos tagged with each of the k values in turn.

   As with traditional IS-IS, one RBridge is elected DRB (Designated
   RBridge), based on configured priority (most significant field), and
   system ID. The DRB continues to send k times as many Hellos, but
   specifies in all the Hellos, the preferred VLAN ID for the link. All
   RBridges that are not DRB transmit Hellos only on the single
   preferred VLAN number specified by the DRB.

   This VLAN number is used in all RBridge-RBridge communication,
   including forwarded encapsulated data packets and IS-IS messages,
   except for the additional k-1 Hellos transmitted by the DRB on the
   VLAN numbers other than the preferred VLAN number.


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INTERNET-DRAFT                                          RBridge Protocol


   On forwarded data packets, 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 TRILL 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
      RBridge 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
      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 with it both the port VLAN ID, which defaults
      to 1, and the priority provided in the priority tag in the frame.
      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 immediately 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 in the frame, what actual
      priority will be associated with the frame by the RBridge.

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


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INTERNET-DRAFT                                          RBridge Protocol


   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 the 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.

   The VLAN ID 0xFFF is reserved and MUST NOT be used. Rbridges MUST
   discard any frame they receive with a VLAN 0xFFF tag.



4.1.4 Frame CheckSum (FCS)

   Each frame has a single Frame CheckSum (FCS) that is computed to
   cover the entire  frame for detecting errors due to communications
   failures. It is calculated before transmission and checked on
   receipt. Any frame for which the FCS fails is discarded. The FCS
   generally changes on every hop due to changes in the outer
   destination and source addresses and the decrementing of the hop
   count.

   It is desirable, when practical, for the FCS to accompany a frame
   transiting an RBridge and be dynamically updated to account for all
   changes to the frame during that transit.  This is helpful in
   detecting a class of RBridge equipment failures.



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;



4.2.1 IS-IS RBridge Identity

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




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INTERNET-DRAFT                                          RBridge Protocol


4.2.2 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 never use the Layer 3 IS-IS
   multicast addresses (AllL1ISs and AllL2ISs) as their outer MAC
   destination address.  All TRILL IS-IS frames have an Inner.MacDA of
   All-IS-IS-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 appointed VLAN-x forwarder for a link having an
   end station in a particular VLAN-x 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 actual
   encoding of this information and the IS-IS Type values for any new
   IS-IS TLV or sub-TLV data elements are specified in a separate
   document.



4.2.3.1 Core IS-IS Information

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

   1. The IS-IS IDs of neighbors (pseudonodes as well as RBridges) of


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INTERNET-DRAFT                                          RBridge Protocol


      RBridge RBn, and the cost of the link to each of those neighbors.

   2. The nickname of RBridge RBn (2 octets) and the unsigned 8-bit
      priority for RBn to have that nickname (see Section 3.7.3);

   3. The TRILL Header Versions supported by RBridge RBn (4 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).  If the list is empty or not provided, RBn can
      only select itself (if RBn's Request Tree flag is true) or the
      RBridge with the lowest System ID (if RBn's Request Tree flag is
      false).

   6. The list of VLAN IDs of VLANs directly connected to RBn for links
      on which RBn is the appointed forwarder for that VLAN.  (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 link state contains the
      following information on a per VLAN basis:

      6.1 Per VLAN Multicast Router attached flags: This is two bits of
         information 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 Per VLAN Other Multicast flag. This is a flag bit, which
         defaults to true, that indicates that the RBridge wishes to
         receive non-IP derived multicast for that VLAN.  It defaults to
         true (one). Within each VLAN, all non-IP derived multicast
         traffic MUST be sent to an RBridge in the VLAN that asserts
         this flag.

      6.3 Per VLAN mandatory announcement of the set of IDs of Root
         bridges for any of RBn's links on which RBn is forwarder for
         that VLAN. Where MSTP (Multiple Spanning Tree Protocol) is


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INTERNET-DRAFT                                          RBridge Protocol


         running on a link, the root bridge is of the CIST (Common and
         Internal Spanning Tree).  This is to 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.)

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

   7. Optionally, a 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 for
   which each RBridge is an appointed forwarder and for IP based
   multicast optimization (see Section 4.3.2).  If RBn is forwarding a
   multi-destination frame tagged with VLAN-x, RBn SHOULD NOT forward it
   onto branches of the distribution tree that have no downstream VLAN-x
   links.



4.2.3.2 Optional Per-VLAN IS-IS Instance Information

   The information in the link state 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 octet
   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 to be the Designated RBridge
   (DRB), i.e. to have special duties. The Designated RBridge:

   o  chooses, for the link, the common VLAN tag to be used for all
      inter-Bridge communication (forwarded data packets, IS-IS
      messages), and announces it in its Hello.



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   o  decides whether the link should be represented in the IS-IS
      topology as a pseudonode, and if so, chooses a pseudonode ID and
      announces that in the Hello.  Although it is not necessary to
      standardize the algorithm that the DRB uses to determine whether
      the link should be represented by a pseudonode or not, the
      following algorithm is recommended.  If the link contains only one
      or two RBridges (the DRB plus potentially one other), then the DRB
      does not use a pseudonode for the link. If the link contains five
      or more RBridges (the DRB has at least 4 RBridge neighbors), then
      the DRB creates a pseudonode for the link. If the DRB has 2 or 3
      neighbors, then the DRB does not change the state of the link; in
      other words, if there was a pseudonode because at some point in
      the past there were 5 RBridges on the link, then the link remains
      represented as a pseudonode until the population of RBridges on
      the link drops to 2 or fewer.  Likewise, if there is no pseudonode
      for the link, the DRB will not create one until there are at least
      5 RBridges on the link.

   o  issues an LSP on behalf of the pseudonode (if the link is to be
      represented by a pseudonode).

   o  issues CSNPs.

   o  for each VLAN x appearing on the link, chooses an RBridge on the
      link to be the appointed VLAN-x forwarder (the DRB MAY choose to
      be the appointed VLAN-x forwarder for all or some of the VLANs).

   o  before forwarding traffic off the link, or appointing a VLAN-x
      forwarder, wait at least 5 Hello intervals (to ensure you are
      DRB).

   o  continues sending IS-IS Hellos on all the VLANs that the DRB has
      been configured to send Hellos on (whereas non-DRBs send Hellos
      only on the common VLAN as specified by the DRB).



4.2.5 Appointed VLAN-x Forwarder

   The appointed VLAN-x forwarder is responsible for

   o  forwarding VLAN x data traffic to-from the link.

   o  learning the location of local VLAN-x endnodes based on looking at
      the source address of native VLAN-x packets on the link.

   o  optionally learning the location of local VLAN-x endnodes based on
      any sort of layer 2 enrollment protocols.

   o  keeping track of (RBridge, MAC address) of distant VLAN endnodes,


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      learned by looking at the fields (ingress RBridge, source address
      in inner Ethernet header) from packets being decapsulated onto the
      link.

   o  optionally listening to the messages in the VLAN-x instance of IS-
      IS to learn (RBridge, MAC address) pairs of explicitly advertised
      endnodes.

   o  optionally advertising VLAN x endnodes, on links for which you are
      appointed VLAN-x forwarder, in a VLAN-x instance of IS-IS.

   o  listening to BPDUs on the common spanning tree to learn the root
      bridge.

   o  reporting in its LSP, the complete set of root bridges on any link
      for which this RBridge is appointed forwarder for any VLAN.

   o  loop avoidance: not decapsulating a packet from ingress RBridge
      RB3 unless it has RB3's LSP, and the root bridge on the link it is
      about to forward onto is not listed in RB3's list of root bridges
      for the same VLAN.

   o  duplicate avoidance: not forwarding packets off a link until
      waiting several Hello intervals on each of its links, and, for
      each link, receiving all the LSPs listed in the first CSNP (if
      any) it has received from the neighbor on that link.

   o  including a "port number" in its Hellos, and if it sees its own
      Hello on port p, where the port number in the received Hello is
      "q", then if q>p, forwarding traffic to/from port p.



4.3 Distribution Trees

   RBridges use distribution trees to forward multi-destination frames
   (see Section 2.4.2). 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
      known by the RBridges, the path to the destination is the same as


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      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 multi-destination 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 core 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 System 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 for
   the pseudonode.



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
   information.


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   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 is called 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 several cases: (1) IGMP [RFC3376],
   MLD [RFC2710], and MRD [RFC4286] messages, where these are to be
   delivered only to ports with IP Multicast routers; (2) other
   multicast frames derived from an IP multicast which should be
   delivered only to links that have registered listeners, plus links
   which have IP Multicast routers; and (3) other multicast traffic not
   derived from an IP address which is only delivered to links for which
   the appointed forwarder has the Other Multicast requested flag set.
   All of these cases are scoped per VLAN.

   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


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   each tree, RBn marks:

   o  the set of VLANs reachable downstream,

   o  for each one of those VLANs, flags indicating whether there are
      IPv4 or IPv6 multicast routers downstream and whether there are
      one or more RBridge downstream with the Other Multicast flag set,
      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 a TRILL header indicating that 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 an
      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 of the corresponding type (IPv4 or
      IPv6), as well as adjacencies that indicate there are downstream
      VLAN A receivers for that group address (see Section 4.4);

   o  else, if the frame is for a Layer 2 multicast address not derived
      from an IP multicast group, then the frame is forwarded onto
      adjacencies in the RBi-tree that indicate there are downstream
      RBridges in VLAN A with the Other Multicast flag set;

   o  else (the inner frame is for an unknown destination 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 appointed forwarder, RBn additionally
   checks to see if it should decapsulate the frame and send it to the


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   link, or process the frame.

   The per-VLAN instance TRILL IS-IS frames will be delivered only to
   RBridges which are appointed forwarders 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 other non-IP-derived multicast data
   packets, on the distribution tree chose by the RBridge which created
   the per-VLAN IS-IS message, and pruned according to the inner VLAN
   tag. Thus they are received by all the RBridges who are appointed
   forwarders for a link in that VLAN unless the RBridge has cleared its
   Other Multicast bit for that VLAN and has no appointed forwarders
   downstream in the tree with the Other Multicast bit set.



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 the 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
   determined, if RB1 is not the appointed forwarder for that VLAN for
   the link from which the frame was received, the frame is discarded.
   If it is appointed forwarder for that VLAN, 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 Rbridge 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 M = 0,


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   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 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
   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 or All-IS-IS-Rbridge,
   the frame is processed as described below. A native (non-TRILL) frame
   sent to the All-Rbridges or All-IS-IS-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
   (see Section 4.3.2).  In the encapsulation, M = 1 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


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   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 never blocked because of that RBridge's
   appointed forwarder or Designated RBridge 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
   this check, further processing of TRILL frames is independent of the
   Outer.MacDA.

   If the Version field in the TRILL Header is greater than 0, the frame
   is discarded. The Inner.MacDA is then tested. If it is the All-IS-IS-
   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, the frame 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, the frame is a per VLAN instance TRILL
   IS-IS frame. If M == 0, the frame is discarded.  The egress nickname
   designates the 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 an appointed forwarder for a link in the
   specified VLAN and implements a per VLAN IS-IS instance for that
   VLAN, the inner frame is decapsulated and provided to that local per
   VLAN IS-IS instance.



4.4.2.2 TRILL Data Frames

   The port on which the frame was received is first checked and the
   frame discarded if there is no 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.




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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 zero, in which case
   the frame is discarded.

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

   A known unicast TRILL data frame can arrive at the egress Rbridge
   only to find that the MAC destination address is not actually known
   by that RBridge. One way this can happen is that the destination MAC
   address may have timed out in the egress RBridge cache. In this case,
   the egress RBridge decapsulates the frame to native form and sends it
   out on all links that are in the frame's VLAN for which the RBridge
   is appointed forwarder except that it is MAY refrain from sending the
   frame on links where it knows there can not be an end station with
   the destination MAC address, for example the link is known to be a
   point-to-point link to another RBridge.

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 described in Section 4.3.2.

   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 distribution 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
   VLAN pruned earlier in the tree distribution. 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, and 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 mixture 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 distribution. They silently discard such frames.

   An RBridge that does not examine IGMP [RFC3376], MLD [RFC2710], and
   MRD [RFC4286] frames that it ingresses MUST advertise that it has
   IPv4 and IPv6 IP multicast routers attached for all the VLANs for
   which it is an appointed forwarder.  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 appointed
   forwarder where the VLAN of the traffic matches the VLAN for which it
   is appointed forwarder 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.)

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



4.5 IGMP, MLD, and MRD Learning

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

   An IGMP or MLD membership report received in native form from a link


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   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 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 End Station Address Details

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

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

   o  decide for an incoming native unicast frame from a link, where the
      RBridge is the appointed forwarder, 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 also appointed forwarder so it can be
         directly forwarded in native form or

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






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4.6.1 Learning End Station Addresses

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

   1. For links where it is the appointed VLAN-x forwarded and for VLAN
      x frames, 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 octet 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
      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 confidence than that in the database
      entry.



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4.6.2 Forgetting End Station Addresses

   While RBridges need to learn end station addresses as described
   above, it is equally important that they be able to forget such
   information. Otherwise, frames for end stations that have moved to a
   different part of the campus could be indefinitely black holed by
   RBridges with stale information as to the link to which the end
   station is attached.

   The RBridge time out for locally learned end station address
   information from the last time a native frame was received or
   decapsulated with the information conforms to the recommendations of
   [802.1Q]. It is configurable per RBridge with a default value of 300
   seconds.

   The situation is different for end station address information
   acquired via a per VLAN IS-IS instance. It is up to the originating
   RBridge to decide when to remove such information from the link state
   (or up to IS-IS timeouts if the originating RBridge becomes
   inaccessible).



4.7 Shared VLAN Learning

   Although outside the scope of this specification, there are some
   Layer 2 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.







R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 40]


INTERNET-DRAFT                                          RBridge Protocol


5. Pseudo Code

   This section provides partial high level pseudo code for the RBridge
   processing of all possible types of received and generated IEEE 802.3
   frames. In case of conflict between this section and any of the other
   sections in this document, the pseudo code is authoritative; however,
   certain optional processing is shown in the pseudo code with such
   optionality being indicated. Of course, any other arrangement of
   processing is fine as long as the results are the same as the pseudo
   code in this section.

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

      Abbreviation   Destination Address(es)
      ------------------------------------------------------------
      ****     Any address.
      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>.
      ALLRBI   The All-IS-IS-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 port at which
                  an operation is occurring.

   Section 5.1 below discusses 802MUL addressed frames, most of which
   are handled by the 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 sometimes handled
   by a port under IEEE 802 protocols which are out of scope for
   RBridges proper as show in Figure 8.  Such frames, by definition, are
   never forwarded by 802.1 customer bridges and are not forwarded by
   RBridges.

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


R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 41]


INTERNET-DRAFT                                          RBridge Protocol


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

                     Figure 8. 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.
      01-80-C2-00-00-01    5.1.2 [802.3] Clause 31 (PAUSE, etc)
      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, D. Eastlake, S. Gai, D. Dutt                       [Page 42]


INTERNET-DRAFT                                          RBridge Protocol


5.1.1 All Bridges Frames

   Frames sent with the All Bridges multicast address
   (01-80-C2-00-00-00) use the bridge protocol NSAP 0x42 so the frame
   begins LL-LL-42-42-03-PP-PP where 0xLLLL is the length and the
   trailing 0xPPPP indicates the particular All Bridges protocol.

   If 0xPPPP is 0x0000 the frame is a BPDU (Bridge Protocol Data Unit),
   used to implement the spanning tree protocol  and further discussed
   below.  If 0xPPPP is 0x0001 the frame is a GARP (General Attribute
   Registration Protocol) PDU discussed in Section 5.1.5 below.

   An RBridge port MUST 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,
   the control octet is 0x03, 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.) When MSTP (Multiple Spanning Tree Protocol) is running on
   a link, this is the CIST (Common and Internal Spanning Tree) root.

   Note: RBridges do not implement spanning tree or the spanning tree
   state machine. Frames are not blocked from admission to an RBridge
   except as provided in this TRILL protocol specification.  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. See also section 5.3.1.



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
   MAY be used to increase the confidence in end station MAC addresses
   reported via the optional per VLAN IS-IS instance (see Section
   4.6.1).  These frames are also identified by Ethertype 0x888E.



R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 43]


INTERNET-DRAFT                                          RBridge Protocol


   An amendment to 802.1X [802.1af] is under development such that
   802.1X authentication would produce keying material usable in
   [802.1AE] 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] 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 but see
   Section 5.3.1.



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 and 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.  RBridges do not implement any of these applications.
   They treat such frames as any other non-IP-derived 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 Layer 2 multicast addresses. However,
   RBridges provide for optional automatic IP based multicast
   optimization instead.

   The GVRP application of GARP uses multicast address
   01-80-C2-00-00-21.  It provides for the registration of VLANs and is
   not supported by RBridges.








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


INTERNET-DRAFT                                          RBridge Protocol


5.1.6 Other Bridge Multicast Frames

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



5.2 Processing a Frame Received by an RBridge

   The RBridge performing the processing is RBn.

   /* Ethertype abbreviations used are as follows:
      ------------------------------------------------------
      ****            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.
   */

   if ( port administratively disabled )
      {
      exit; /* discard frame */
      }

   /* Set per frame global data */

   Frame-VLAN = Determine Frame VLAN per Section 4.1.3;
   Frame-priority = Determine Frame Priority per Section 4.1.3;
   Frame-protocol = Extract Frame Ethertype / NSAP;

   AF = Appointed Forwarder status of RBn for Frame-VLAN for
           receiving port;

   The Frame-protocol, Outer.MacDA, and AF 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.

   The "AF" column is "Y" if the RBridge must be the appointed forwarder
   on that port for Frame-VLAN, "N" if it must not be the appointed
   forwarder, and "*" if it does not matter.









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


INTERNET-DRAFT                                          RBridge Protocol


           Sequential Table: Search from top for first match
      Ethertype  Dest.   AF    Section/Description
      ------------------------------------------------------------
      TRILL      SELF    *     5.2.3 TRILL encapsulated frame.
      TRILL      OTHERU  *     TRILL encapsulated frame addressed
                                 to another Rbridge; discard.
      TRILL      ALLRB   *     5.2.3 TRILL encapsulated frame.
      TRILL      BROAD   *     Erroneous frame but MAY be treated
                                 as if Destination was ALLRB.
      ****       ALLRB   *     Erroneous frame; discard.
      ****       ALLRBI  *     Erroneous frame; discard.
      ****       802MUL  *     5.1 Should not get here.
      IP**       ****    Y     5.2.1 Process IP frame.
      ****       IPMUL   *     Erroneous frame; discard.
      ****       ****    Y     5.2.4 Process native frame.
      ****       ****    N     Discard native 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**   ****    5.2.4 Other



5.2.2 Common Subroutines

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



5.2.2.1 Learn Source MAC Address

   If this pseudo code subroutine 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.



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


INTERNET-DRAFT                                          RBridge Protocol


   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 Frame Multi-destination Forwarding

   Forward a TRILL Frame over a distribution tree with VLAN pruning.

   {{ This code needs to be extended to perform similar pruning for
   multicast frames being forwarded to that done by Section 5.2.4 on
   received multicast native frames.}}

   if ( (Trill.HopCount = 0 ) or
        (RPF check fails on Outer.MacSA (Section 4.3.1) )
      {
      Exit; /* do not forward the frame */
      }
   else
      {
      For ( all ports from RBn on the tree rooted at the
            Trill.EgressNickname except that on which the
            frame was received )
         {
         if ( no downstream RBridges for Inner.VLAN )
            {
            Continue to next "for" value;
            }
         Execute 5.2.2.3;
         }
      }



5.2.2.3 TRILL Data Frame Tree Transmission

   Trill.HopCount -= 1 /* at least, see Section 3.4 */
   Outer.MacDA = ALLRB (or optionally, if there is
      only one destination, its unicast address).;
   Execute 5.2.2.4








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


INTERNET-DRAFT                                          RBridge Protocol


5.2.2.4 TRILL Data Frame Transmission

   Outer.MacSA = MAC address of the port on which the
      frame is being sent;
   Outer.VLAN = DRB specified RBridge traffic VLAN for
      the port on which the frame is being sent;
   Outer.priority = Inner.priority;
   Include or omit Outer C-tag / priority tag as per
      802.1Q customer bridge port transmission rules;
   Transmit frame out port;



5.2.3 TRILL Ethertype Frames

   if (Version > 0)
      {
      Discard the frame, unknown format.
      }
   elseif (Inner.MacDA == ALLRBI)  /* IS-IS */
      {
      Execute Section 5.2.3.1.
      }
   else  /* Inner.MacDA != ALLRBI, Data */
      {
      Execute Section 5.2.3.2.
      }



5.2.3.1 TRILL IS-IS Frames

   /* get here for TRILL Ethertype frames where Outer.MacDA is
      either ALLRB or SELF and the Inner.MacDA is
      All-IS-IS-Rbridges. TRILL Ethertype frames with other
      Outer.MacDA values are discarded by the dispatch table */

   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.
     }


R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 48]


INTERNET-DRAFT                                          RBridge Protocol


   else /* inner VLAN tag is present */
     {
     If RBn has end stations on links for which it is the
     appointed forwarder for the indicated VLAN, give the
     IS-IS message to the per VLAN IS-IS instance if
     implemented.

     Execute 5.2.2.2;  /* forward VLAN pruned */
     }



5.2.3.2 TRILL Data Frames

   /* get here for TRILL Ethertype frames where Outer.MacDA is
      either ALLRB or SELF and the Inner.MacDA is not
      All-IS-IS-Rbridges. TRILL Ethertype frames with other
      Outer.MacDA values are discarded by the dispatch table */

   if (Trill.M == 1)
     {                /* a multi-destination frame */
     If (Outer.MacSA !=
             a tree adjacency for tree indicated) )
       {
       Discard the frame.
       }
     else
       {
       If RBn is an appointed forwarder for the indicated VLAN,
       decapsulate the data frame and forward it onto appropriate
       links in the VLAN.

       Execute Section 5.2.2.2.
       }
     }
   else /* Trill.M == 0 */
      {
      if (Trill.EgressNickname == RBn)
         {
         If (Inner.MacDA is a group address)
           {
           Discard the frame.
           }
         Convert to native format and forward the extracted
         frame onto the link containing the destination or,
         if you don't know the destination, onto all local
         links in the Inner.VLAN for which you are an
         appointed forwarder.

         Locally process the frame if the Inner.MacDA == RBn.


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


INTERNET-DRAFT                                          RBridge Protocol


         }
      else
         { /* The frame needs to be forwarded to another RBridge */
         if (Trill.HopCount = 0)
            {
            Discard the frame.
            }
         else
            {
            if (Trill.EgressNickname unknown)
               {
               Discard the frame.
               }
            Outer.MacDA = LookUpNextHop(Trill.EgressNickname);
            Outer.MacSA = MAC address of the port on which the
               frame is being sent;
            Outer.VLAN = DRB specified RBridge traffic VLAN for
               the port on which the frame is being sent;
            Outer.priority = Inner.priority;
            Include or omit Outer C-tag / priority tag as per
               802.1Q customer bridge port transmission rules;
            Transmit frame out port;
            }
      }



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 appointed forwarder (see Section 4.2.4).

   Execute Section 5.2.2.1.
   if (Outer.MacDA == SELF)
      {
      Process locally;
      /* A native frame for the RBridge received from a local
         link, for example a management protocol frame from a
         directly connected management station. */
      }
   elseif (Outer.MacDA is a known unicast address)
      {
      if (Outer.MacDA is on the directly connected link on
            which the frame was received)
         {
         Exit; /* Destination has already seen it */
         }
      elseif (Outer.MacDA in Frame-VLAN is on another
                directly connect link)


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


INTERNET-DRAFT                                          RBridge Protocol


         {
         Include or omit Outer C-tag / priority tag as per
            802.1Q customer bridge port transmission rules;
         Forward the native frame out the port for the link.
         }
      else
         {
         /* Assume that the egress RBridge is RBm */
         Inner.VLAN = Frame-VLAN;
         Inner.priority = Frame-priority;
         Trill.V = 0;
         Trill.R = 0;
         Trill.M = FALSE; /* this is not multi-destination */
         Trill.HopCount = determined value (see Section 3.4);
         Trill.EgressNickname = RBm;
         Trill.IngressNickname = RBn;
         Outer.MacDA = LookUpNextHop(Trill.EgressNickname);
         Outer.Ethertype = TRILL;
         Execute Section 5.2.2.4;
         }
   else
      { /* unknown unicast or general multicast or broadcast */
      Forward in native form to other links where RBn is the
        appointed forwarder for Frame-VLAN;
      Inner.VLAN = Frame-VLAN;
      Inner.priority = Frame-priority;
      Trill.V = 0;
      Trill.R = 0;
      Trill.M = TRUE; /* this is a multi-destination frame */
      Trill.EgressNickname = RBi /* Distribution Tree, See below */
      Trill.IngressNickname = RBn;
      Outer.Ethertype = TRILL;
      For ( all ports from RBn on the tree rooted at the
            Trill.EgressNickname )
         {
         if ( no downstream RBridges for Frame-VLAN for this port )
            {
            Continue to next "for" value;
            }
         if ( ( Inner.MacDA <= 00-01-5E-7F-FF-FF ) and
              ( Inner.MacDA >= 00-01-5E-00-00-00 ) )
            {
            returnValue = Execute 5.2.4.1;
            }
         elseif ( ( Inner.MacDA <= 33-33-FF-FF-FF-FF ) and
                  ( Inner.MacDA >= 33-33-00-00-00-00 ) )
            {
            returnValue = Execute 5.2.4.2;
            }
         elseif ( ( Inner.MacDA == FF-FF-FF-FF-FF-FF ) or


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


INTERNET-DRAFT                                          RBridge Protocol


                  ( Inner.MacDA == ALLRBI ) )
            {
            returnValue = True;
            }
         elseif ( no downstream RBridges with Other Multicast
                    bit set for Frame-VLAN )
            {
            returnValue = False;
            }
         else
            {
            returnValue = True;
            }
         if ( returnValue )
            {
            Trill.HopCount = determined value (see Section 3.4);
            Execute 5.2.2.3;
            }
         } /* end For */
      }

   In the last case above, the egress nickname indicates the chosen
   distribution tree RBi. The default is for RBn to put its own address
   there. However, if RBn is configured to decline to be a tree root,
   then RBn 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.



5.2.4.1 Native IPv4 Multicast Frame

   if ( Frame-protocol != IPv4 )
      {
      return ( False );  /* inconsistent frame */
      }
   elseif ( frame is an IGMP announcement )
      {
      if ( there are downstream IPv4 multicast routers )
         {
         return ( True );
         }
      else
         {
         return ( False );
         }
      }
   elseif ( IPv4 Destination multicast address is in the range
              which must be broadcast )
      {


R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 52]


INTERNET-DRAFT                                          RBridge Protocol


      return ( True );
      }
   elseif ( there is a downstream listener or IPv4
            multicast router for Inner.MacDA )
      {
      return ( True );
      }
   else
      {
      return ( False );
      }



5.2.4.2 Native IPv6 Multicast Frame

   if ( Frame-protocol != IPv6)
      {
      return ( False );  /* inconsistent frame */
      }
   elseif ( frame is an NLD announcement )
      {
      if ( there are downstream IPv6 multicast routers )
         {
         return ( True );
         }
      else
         {
         return ( False );
         }
      }
   elseif ( IPv6 Destination multicast address is in the range
              which must be broadcast )
      {
      return ( True );
      }
   elseif ( there is a downstream listener or IPv6
            multicast router for Inner.MacDA )
      {
      return ( True );
      }
   else
      {
      return ( False );
      }







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


INTERNET-DRAFT                                          RBridge Protocol


5.2.5 IGMP and MLD Frames

   An IGMP (IPv4 [RFC3376]) or MLD (IPv6 [RFC2710]) announcement
   received from a link by the appointed forwarder for Frame-VLAN
   teaches RBn a group membership on that link. RBn adds receiver for
   that Layer 2 group address for Frame-VLAN in its core link state
   instance.

   Then execute Section 5.2.4.



5.2.6 MRD Frames

   An MRD [RFC4286] reply or IGMP [RFC3376] query or MLD [RFC2710] query
   received from a link by the appointed forwarder for Frame-VLAN
   teaches RBn that there is an IP multicast router on that link. RBn
   adds that information, for IPv4 or IPv6 as appropriate, into its core
   IS-IS link state information for Frame-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 Bridge/Media Frames Sourced

   RBridges are not required to originate any of the frames discussed in
   Section 5.1 (although it may be necessary for an 802.3 port to
   implement PAUSE to operate correctly in the presence of allowed clock
   skew).

   An RBridge port may optionally emit BPDUs as described in Section
   6.2.2. However, RBridges do not implement spanning tree or the
   spanning tree state machine.  It is never the case that a bridging
   spanning tree extends through an RBridge between its ports. Those
   ports always terminate the spanning tree.

   If an Rbridge port implements [802.1X], this MAY be used in
   determining the confidence level of learned addresses (see Section
   5.1.3).

   If an RBridge port sources [802.1AB] frames, also known as Local Link
   Discovery frames, containing the System Capabilities 802.1AB TLV, it


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


INTERNET-DRAFT                                          RBridge Protocol


   is RECOMMENDED that the "bridge" bit be asserted in the "system
   capabilities" subfield and if that port is participating in spanning
   tree, then it is RECOMMENDED that the "bridge" bit be asserted in the
   "enabled capabilities" subfield.

   Other bridge/media frames may also be sourced by an RBridge port and
   are generally out of scope for this document.



5.3.2 IS-IS Frames Sourced

   An RBridge R1 MUST spontaneously emit core instance TRILL IS-IS
   frames as described in 5.3.2.1. In addition, if it is appointed
   forwarder for a link that has end stations in a particular VLAN, it
   MAY run an IS-IS instance for that VLAN and emit TRILL per-VLAN 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.



5.3.2.1 Core IS-IS Frames

   For core IS-IS frames, a TRILL header is added and no VLAN tag is
   included in the inner frame. The 802.3 LLC NSAP format MUST be used,
   that is LL-LL-FE-FE-03 where 0xLLLL is the length, 0x03 is the CTL
   octet, and 0xFE is the NSAP for IS-IS.  (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.)

   The frame it is formed as follows:

      Outer.MacDA = ALLRB;
      Outer.MacSA = RBn; // MAC address of transmission port
      Outer.Ethertype = TRILL.
      Trill.V = 1;
      Trill.R = 0;
      Trill.M = 1;
      Trill.HopCount = 1;
      Trill.IngressNickname = 0;
      Trill.EgressNickname = 0;
      Inner.MacDA = ALLRBI;
      Inner.MacSA = RBn;
      Inner.FrameLength = IS-IS frame length;
      Inner.DSAP = 0xFE;
      Inner.SSAP = 0xFE;
      Inner.CTL = 3;


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


INTERNET-DRAFT                                          RBridge Protocol


      followed by the rest of the IS-IS Frame.

   The frame is then sent out all ports of the RBridge if it is a Hello.
   If it is a non-Hello, it is sent out all ports on which there is an
   IS-IS adjacency.  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 VLAN ID = ID 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.

   The Inner.MacDA is always All-IS-IS-Rbridges for all TRILL IS-IS
   frames. Furthermore, core instance TRILL IS-IS Hellos MUST always be
   send out all enabled ports to the All-Rbridges multicast address.
   However, non-Hello core TRILL IS-IS messages for which there is only
   one destination MAY be send to a unicast Outer.MacDA as follows:

      Outer.MacDA = DestinationRBridge;
      Outer.MacSA = RB1;  // MAC address of transmission port
      Outer.Ethertype = TRILL.
      Trill.V = 1;
      Trill.R = 0;
      Trill.M = 0;
      Trill.HopCount = 1;
      Trill.IngressNickname = 0;
      Trill.EgressNickname = 0;
      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
   multicast core TRILL IS-IS frame above.



5.3.2.2 Per-VLAN IS-IS Frames

   For per VLAN TRILL IS-IS frames, a 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 5.3.2.1.



R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 56]


INTERNET-DRAFT                                          RBridge Protocol


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

      Outer.MacDA = All-RBridges;
      Outer.MacSA = RB1;
      Outer.Ethertype = TRILL.
      Trill.V = 0;
      Trill.R = 0;
      Trill.M = 1;
      Trill.HopCount = count to reach farthest node in the
                       distribution tree;
      Trill.IngressNickname = RB1 nickname;
      Trill.EgressNickname = SelectedDistributionTree;
      Inner.MacDA = All-IS-IS-RBridges;
      Inner.MacSA = RB1;
      Ethertype = VLAN Tag;
      Inner VLAN Tag priority = 7;
      Inner.VLAN = 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.  The presence or
   absence of downstream RBridges with the Other Multicast (OM) flag on
   for that VLAN is ignored and the frame is distributed to all RBridges
   that indicate they are connected to that VLAN.  Other than this
   special handling of downstream Other Multicast flags, per VLAN
   instance TRILL IS-IS frames are distributed like any other non-IP-
   derived Layer 2 multicast.



5.3.3 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 appointed
   forwarder and on which there were no know directly connected
   stations, as described in Section 5.2.4.











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


INTERNET-DRAFT                                          RBridge Protocol


6. Incremental Deployment Considerations

   Because RBridges are generally 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 bridged LANs, appear to
   RBridges to be multi-access links.  If the bridges that were replaced
   by RBridges were un-managed, zero configuration bridges, then the
   RBridge replacements will not require configuration.

   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.



6.1 VLAN Connectivity Changes

   Even with partial RBridge deployment, RBridges will provide
   connectivity between all links in a particular VLAN that are
   connected to any one RBridge, assuming TRILL connectivity between the
   RBridges themselves. This is true even where the bridged LAN into
   which the RBridges are being introduced was myopically configured so
   as to partition one or more particular VLANs into unconnected
   islands.



6.2 Link Cost Determination

   With an RBridged campus having no bridges on the links between
   RBridges, the RBridges can accurately determine the number of
   physical hops involved in a path and the line speed of each hop
   assuming this is reported by their port logic. With intervening
   bridges, this is no longer possible. For example, as shown in Figure
   9, the two bridges B1 and B2 can completely hide a slow link so that
   both Rbridges RB1 and RB2 incorrectly believe the link is faster.

   +-----+        +----+        +----+        +-----+
   |     |  Fast  |    |  Slow  |    |  Fast  |     |
   | RB1 +--------+ B1 +--------+ B2 +--------+ RB2 |
   |     |  Link  |    |  Link  |    |  Link  |     |
   +-----+        +----+        +----+        +-----+

                   Figure 9, Link Cost of a Bridged Link

   Even in the case of a single intervening bridge, two RBridges may
   know they are connected but each see the link as a different speed


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


INTERNET-DRAFT                                          RBridge Protocol


   from how it is seen by the other.



6.3 Appointed Forwarders and Bridged LANs

   With partial RBridge deployment, the RBridges may partition a bridged
   LAN into a relatively small number of relatively large remnant
   bridged LANs. Then two potential problems can occur as follows:

   1. The requirement that end station frames enter and leave a link via
      the appointed forwarder for the link and VLAN of the frame can
      cause congestion or suboptimal routing. (Similar problems can
      occur within a bridged LAN due to the spanning tree algorithm.)
      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 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 appointed
      forwarder congestion.  Solutions to this problem are discussed
      below in this section and a particular example explored in Section
      6.4.

   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 as a unicast frame to that recipient rather than
      multicasting it. (Since one purpose of IS-IS Hello frames is to
      find previously unknown Rbridges, they must always be multicast.)

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

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



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


INTERNET-DRAFT                                          RBridge Protocol


   3. Configure the RBridges and bridges so that end stations on a
      remnant bridged LAN are separated into different VLANs that have
      different appointed forwarders. 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 emit BPDUs (see Section 5.1.1) 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, 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
      TRILL 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 protocol.
   Replacing the IEEE 802.1 bridges in such LANs with RBridges may
   enable a reduction in or elimination of VLANs and configuration
   complexity.



6.4 Wiring Closet Topology

   If 802.1 bridges are present and RBridges are not configured, the
   bridge spanning tree or the appointed forwarder designation 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.

   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), with an
   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.










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


INTERNET-DRAFT                                          RBridge Protocol


                    +-------------------------------+
                    |             |          |      |
                    |  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 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 DRB for the bridged LAN including B1 and B2 and appoint itself
   forwarded for the VLANs on that bridged LAN. As a result, RB1 would
   forward all 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 use of both
   the RB1-B1 and RB2-B2 links.

   Three solutions to this problem are described below.



6.4.1 The RBridge Solution

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



6.4.2 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


R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 61]


INTERNET-DRAFT                                          RBridge Protocol


   RB2's System ID). Both RB1 and RB2 emit BPDUs 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 and appointed forwarder on each of their
   respective partitions. Of course, with the partition, no TRILL
   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.



6.4.3 The VLAN Solution

   If the end stations attached to B1 and B2 are already divided among a
   number of VLANs, RB1 and RB2 could be configured so that which ever
   becomes DRB for this link will appoint itself for some of these VLANs
   and the other RBridge for the remaining VLANs. Should either of the
   RBs fail or become disconnected, the other will have only itself to
   appoint for all the VLANs.

   If the end stations are all on a single VLAN, 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.



6.4.4 Comparison of Solutions

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



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INTERNET-DRAFT                                          RBridge Protocol


   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 emit BPDUs as described
   in Section 6.4.2 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.






































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


INTERNET-DRAFT                                          RBridge Protocol


7. RBridge Addresses, Parameters, and Constants

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

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

   Two Layer 2 multicast addresses must be assigned. All-RBridges for
   use as the destination address in multi-destination frames.  And All-
   IS-IS-RBridges as the inner destination MAC address for TRILL IS-IS
   frames.

   To support VLANs, RBridges (like bridges today), must be configured
   appropriately. RBridge ports may also be configured to map frame
   priorities (see Section 4.1.3).

   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 which defaults to
   true.

   The per RBridge per VLAN Other Multicast bit, which defaults to true,
   to request the receipt of non-IP derived multicast traffic.

   Configuration for the spanning tree solution to the wiring closet
   topology problem (see Section 6.4.2) 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, D. Eastlake, S. Gai, D. Dutt                       [Page 64]


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.

   TRILL encapsulates native frames inside the TRILL Ethertype while
   they are in transit between that frame's ingress and egress RBridge.
   Thus, TRILL ignorant devices, such as bridges with firewall features,
   will not generally be able to examine the interior of such frames for
   security checking purposes and may be less effective.  (Since routers
   appear to RBridges to be end stations, such frames will be
   decapsulated before being sent to a router.) Such "firewall bridges"
   should be modified to understand TRILL encapsulation.

   Countermeasures are available such as to configure the RBridge IS-IS
   instances to use IS-IS security [RFC3567] and ignore unauthenticated
   control messages received on a port. Since such authentication
   requires configuration, RBridges using it 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, D. Eastlake, S. Gai, D. Dutt                       [Page 65]


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 Version numbers  and uses of TRILL Header Reserved
   bits 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 addresses <tbd1> and <tbd2> are assigned by
   IEEE 802 for "All-Rbridges" and "All-IS-IS-Rbridges".





























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


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] "IEEE Standard for Information technology /
      Telecommunications and information exchange between systems /
      Local and metropolitan area networks / Specific requirements Part
      3: Carrier sense multiple access with collision detection
      (CSMA/CD) access method and physical layer specifications",
      802.3-2005, 9 December 2005

   [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.

   [RFC3410] Case, J., Mundy, R., Partain, D., and B.  Stewart,
      "Introduction and Applicability Statements for Internet-Standard
      Management Framework", RFC 3410, December 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.



R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 67]


INTERNET-DRAFT                                          RBridge Protocol


   [RFC4789] Schoenwaelder, J. and T. Jeffree, "Simple Network
      Management Protocol (SNMP) over IEEE 802 Networks", RFC 4789,
      November 2006.



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

   [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-03.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.

   [RFC3567] Li, T. and R. Atkinson, "Intermediate System to
      Intermediate System (IS-IS) Cryptographic Authentication", RFC
      3567, July 2003.

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


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. Add end station address learning section.  Specify end station
       address learning from decapsulated native frames.


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   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.

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

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

   18. 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 transmission 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
   of the draft was so updated.




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


INTERNET-DRAFT                                          RBridge Protocol


Changes from -05 to -06

    1. Revise Section 2 discussion of DRB determination in the presence
       of VLANs and move it to Section 2.2. Adjust VLAN handling
       description.

    2. Change "V" field to be a 2-bit version fields followed by 2
       reserved bits. Make corresponding changes to eliminate the
       inclusion in the header of frame analysis indicating type of
       multi-destination pruning which is proper for frame.  Thus all
       non-ingress RBridges that wish to perform such pruning are forced
       to do full frame analysis. Make further corresponding changes in
       IANA Considerations.

    3. The Inner.MacDA for TRILL IS-IS frames is changed to a second
       multicast address: All-IS-IS-RBridges. IEEE Allocation
       Considerations, etc., are correspondingly changed.

    4. Note in Section 6 that bridges can hide slow links and generally
       make it harder from RBridges to determine the cost of an RBridge
       to RBridge hop that is a bridged LAN.

    5. Add material noting that replacement of bridges by RBridges can
       cause connectivity between previously isolated islands of the
       same VLAN.

    6. Expand Security Considerations by mentioning RFC 3567 and
       indicating that TRILL enveloping may reduce the effectively of
       TRILL-ignorant firewall functionality.

    7. Extensive updates to psuedo code.

    8. Change to one DRB per physical link which dictates the inter-
       RBridge VLAN for the link, appoints forwarders per VLAN, can be
       configured to send Hellos on multiple VLANs, etc.

    9. Add a minimal management by SNMP statement to Section 2.

   10. Delete requirement to process TRILL frames arriving on a port
       even if the port implements spanning tree and is in spanning tree
       blocked state.

   11. Drop recommendation to set "bridge" flags in some 802.1AB frame
       fields.

   12. Miscellaneous minor editing and terminology updates.






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


INTERNET-DRAFT                                          RBridge Protocol


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R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 72]


INTERNET-DRAFT                                          RBridge Protocol


Authors' Addresses

   Radia Perlman
   Sun Microsystems

   Email: Radia.Perlman@sun.com


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

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



Expiration and File Name

   This draft expires in May 2008.

   Its file name is draft-ietf-trill-rbridge-06.txt.














R. Perlman, D. Eastlake, S. Gai, D. Dutt                       [Page 73]


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