TRILL Working Group                                      Donald Eastlake
INTERNET-DRAFT                                              Mingui Zhang
Intended status: Proposed Standard                                Huawei
                                                          Puneet Agarwal
                                                             Dinesh Dutt
                                                           Radia Perlman
                                                              Intel Labs
Expires: January 10, 2012                                  July 11, 2011

                    RBridges: Fine-Grained Labeling


   The IETF has standardized RBridges (Routing Bridges), devices that
   implement the TRILL (TRansparent Interconnection of Lots of Links)
   protocol, a solution for least cost transparent frame routing in
   multi-hop networks with arbitrary topologies, using link-state
   routing and encapsulation with a hop count.

   The TRILL base protocol standard supports up to 4K VLAN IDs (Virtual
   Local Area Network IDentifiers). However, there are applications that
   require more fine-grained labeling of data and end stations. This
   document specifies extensions to the TRILL protocol to accomplish

Status of This Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

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Table of Contents

      1. Introduction............................................3
      1.1 Terminology............................................3

      2. Fine-Grained Labeling...................................4
      2.1 Requirements...........................................4
      2.2 Existing TRILL VLAN Labeling...........................5
      2.3 Fine-Grained Labeling..................................6

      3. Coexistence with ST RBridges............................8

      4. Processing Finely Labeled Frames........................9
      4.1 Ingress Processing.....................................9
      4.2 Transit Processing....................................10
      4.2.1 Unicast Transit Processing..........................10
      4.2.2 Multi-Destination Transit Processing................10
      4.3 Egress Processing.....................................11
      4.4 Address Learning......................................12

      5. IS-IS Extensions.......................................13
      5.1 Announcing RBridge DT Support.........................13
      5.2 Interested Labels and Bridge Roots sub-TLV............13
      5.3 The Group Labeled MAC Address sub-TLV.................14

      6. IANA Considerations....................................16
      7. Security Considerations................................16
      7.1 Ingress Forgery and Egress Compromise.................16

      8. References.............................................17
      8.1 Normative References..................................17
      8.2 Informative References................................17

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1. Introduction

   The IETF has standardized RBridges (Routing Bridges), devices that
   implement the TRILL (TRansparent Interconnection of Lots of Links)
   protocol [RFCtrill], a solution for least cost transparent frame
   routing in multi-hop networks with arbitrary topologies, using link-
   state routing and encapsulation with a hop count.

   The TRILL base protocol standard supports up to 4,094 VLAN IDs
   (Virtual Local Area Network IDentifiers). However, there are
   applications that require more fine-grained labeling of data and end
   stations. This document specifies extensions to the TRILL protocol to
   accomplish this.

   Familiarity with [RFCtrill] and [ISIStrill] is assumed in this

1.1 Terminology

   The terminology and acronyms of [RFCtrill] are used in this document
   with the additions listed below.

      DT - Double Tagging or Double Tagged or Double Tag

      Edge RBridge - An RBridge announcing VLAN or fine-grained label
      connectivity in its LSP

      ST - Single Tagging or Single Tagged or Single Tag

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

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2. Fine-Grained Labeling

   The essence of fine-grained labeling is that (a) when TRILL Data
   frames are ingressed or created they may incorporate a label from a
   set of significantly more than 4K labels, (b) RBridge ports can be
   labeled with a set of such labels, and (c) a TRILL Data frame cannot
   be egressed through such an RBridge port unless its label matches one
   of the labels of the port.

   Section 2.1 lists fine-grained labeling requirements.  Section 2.2
   briefly outlines VLAN labeling in the TRILL base protocol standard
   [RFCtrill]. And Section 2.3 then outlines a method of fine-grained
   labeling of TRILL Data frames.

   In the remainder of this document, we commonly refer to the simple
   VLAN labeling provided by the TRILL base protocol standard as single
   tagging (ST) or coarse labeling and refer to fine-grained labeling as
   double tagging (DT).

2.1 Requirements

   There are several requirements that should be met by fine-grained
   labeling in TRILL. They are briefly described in the list below in
   approximate order by priority with the most important first.

   1. Fine-Grained

      Some networks have a large number of entities that need
      configurable isolation, whether those entities are independent
      customers, applications, or branches of a single endeavor or some
      combination of these or other entities. The VLAN tags supported by
      [RFCtrill] provides for only ( 2**12 - 2 ) valid VLAN identifiers.
      A substantially larger number is required.

   2. Silicon Considerations

      Fine-grained labeling should, to the extent practical, use
      existing features, processing, and fields that are already
      supported in at least some of the many existing TRILL fast path
      silicon implementations.

   3. Base RBridge Compatibility

      To support some incremental conversion scenarios, it is desirable
      that not all RBridges in a campus using fine-grained labeling be
      required to be fine-grained label aware. That is, it is desirable
      that RBridges not implementing the fine-grained labeling feature
      and performing at least the transit forwarding function can

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      usefully process TRILL Data frames that incorporate fine-grained

   4. Alternate Priority

      It would be desirable for an ingress RBridge to be able to assign
      a different priority to a fine grain labeled TRILL Data frame for
      its ingress-to-egress propagation from the priority of the
      original native frame. The original priority should be restored on

2.2 Existing TRILL VLAN Labeling

   This section provides a brief review of existing TRILL Data frame
   coarse VLAN labeling.

   Currently TRILL Data frames have the single tagged (ST) structure
   shown below:

               | Link Header  |
               | TRILL Header |
               | Inner.MacDA  |
               | Inner.MacSA  |
               | Inner.VLAN   | <-- Coarse VLAN Label
               | Payload      |
               | Link Trailer |

   The Inner.VLAN tag is always present and is specified as a C-tag
   [802.1Q] providing ( 2**12 - 2 ) labels (the values 0 and 0xFFF are
   reserved) that is structured as follows:

                      0 1 2 3 4 5 6 7 8 9 A B C D E F
                     |       Ethertype 0x8100        |
                     | PRI |C|       VLAN ID         |

   The PRI field above is the 3-bit unsigned priority field where larger
   numbers represent higher priority except that the default zero

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   priority is above priority 1 and below priority 2 [802.1Q]. Under the
   TRILL base protocol [RFCtrill], in the Inner.VLAN the C bit is
   required to be set to zero, transparently forwarded, and ignored on
   receipt by RBridges.

   For an RBridge conformant to the TRILL base protocol, incoming frames
   are classified as to their VLAN ID and priority by the port on which
   they are received as described in Appendix D of [RFCtrill].

2.3 Fine-Grained Labeling

   In the proposed form, fine-grained labeling expands the 12-bit coarse
   VLAN label available under the TRILL base protocol standard to a
   24-bit label. In this document, fine-grained labels are sometimes
   denoted as "(X.Y)" where X is the high order 12 bits and Y is the low
   order 12 bits. The fine grained label information appears in the same
   location in a TRILL Data frame as the coarse VLAN label did, as shown
   below, although it is encoded as two consecutive VLAN tags (DT).

               | Link Header  |
               | TRILL Header |
               | Inner.MacDA  |
               | Inner.MacSA  |
               | Inner.Label  | <-- Fine-Grained Label
               | Payload      |
               | Link Trailer |

   The fine-grained label is encoded as two sequential C-tags as shown
   below. The high order 12 bits of the fine-grained label appear in the
   VLAN ID field of the first C-tag and the low order 12 bits appear in
   the VLAN ID field of the second. Because some silicon might subject
   the high order part of the fine-grained label to the same constraints
   as VLAN IDs and for other reasons such as the reporting described in
   Section 4.2.2, the values zero and 0xFFF are reserved for the high
   order part of a TRILL fine-grained label. [[[ Should 0 and 0xFFF be
   prohibited in the low order 12 bits also? ]]]

   [[[ Alternative Ethertype sequences could be specified. Perhaps the
   most obvious alternative would be for the first VLAN tag to be as S-
   tag (Ethertype 0x88A8) and the second a C-tag. However, this might

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   cause problems for some ST RBridges; if they check the Ethertype of
   the first VLAN tag, they might reject such frames. ]]]

                      0 1 2 3 4 5 6 7 8 9 A B C D E F
                     |       Ethertype 0x8100        |
                     | PRI |C| High Order Label Bits |
                     |       Ethertype 0x8100        |
                     | PRI |C| Low Order Label Bits  |

   The appropriate DT for an ingressed native frame is determined by the
   input RBridge port as specified in Section 4.1.  The priority in the
   second tag is that associated by the ingress port with the native
   frame as with ST ingress. The priority in the first tag is either a
   copy of the second tag priority or that priority mapped at ingress,
   depending on the capabilities of the ingress RBridge.  Ports of
   RBridges supporting DT also have capabilities to transmit frames
   being forwarded or egressed as untagged or C-tagged as specified in
   Section 4.3.

   Use of S-tags or tags stacked beyond that indicated are beyond the
   scope of this document but are an obvious extension.

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3. Coexistence with ST RBridges

   ST (single tag) RBridges will operate properly as transit RBridges.
   Transit RBridges look at the Inner.VLAN ID only for the filtering of
   multi-destination frames.  If an RBridge does not perform filtering,
   or filters on only some of the fields in the packet, the only
   consequence is that multi-destination frames will use more bandwidth
   than necessary. Because ST RBridges could only look at the initial
   VLAN tag in the fine-grained label of a DT (double tag) multi-
   destination frame, they will not be able to prune as effectively as
   transit DT RBridges could.

   It would be more serious if an ST edge RBridge, RB1, unaware of the
   double tag, forwarded a DT frame with DT label (X.Y) onto a link
   configured as ST VLAN-X, with RB1 stripping the "X" and forwarding
   the packet. This violates the separation of VLANs, and might cause
   other problems on a link in which the VLAN tag should have been
   stripped. It would also be problematic if a malicious end station
   could forge an apparent DT label (X.Y) frame by including extra tags
   in native frames ingressed by an ST edge RBridge. Therefore, it is
   highly desirable for all the edge RBridges to be DT RBridges.

   DT RBridges will report the DT capability in LSPs, so DT RBridges
   (and any management system with access to the link state database)
   will be able to detect the existence of ST edge RBridges.

   It might be useful, in a particular campus with mixed DT and ST
   RBridges, to have some end station VLANs accessible via ST edge
   RBridges.  This is supported by reserving some number of VLANs (say
   the first k), to be ST-addressable.  These VLANs will be specified
   with a single Inner.VLAN tag, whether or not the edge RBridges
   attached to these VLANs are DT-capable.  When ST-specifiable VLANs
   are used in a DT campus, and where there are ST edge RBridges
   advertising connectivity to those VLANs, the first VLAN tag in a
   double tag MUST NOT be equal to the value of any ST-specifiable VLAN.

   If this rule is violated, the network misconfiguration is detected by
   the DT RBridges that will then refuse in ingress to or egress from
   label (X.Y) while VLAN X connectivity is being advertised by an ST
   edge RBridge.

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4. Processing Finely Labeled Frames

   This section specifies ingress, transit, and egress processing of
   TRILL Data frames with regard to fine-grained labels, also known as
   double tagging (DT). A transit or egress DT RBridge detects DT TRILL
   Data frames by noticing that the Ethertype immediately after the
   first Inner.Label VLAN tag is the C-tag Ethertype.

4.1 Ingress Processing

   There is no change in Appointed Forwarder logic [RFCaf] for the ports
   of a DT RBridge.

   A DT RBridge may be configured, on one or more ports, to double tag
   ingressed native frames. There is no change in ST ingress processing,
   which is the default unless a port has been configured for DT.

   DT RBridges MUST remove any extra C-tags from incoming native frames
   being ingressed, regardless of whether the ingress port is configured
   as ST or DT (see Section 7.1).

   DT RBridges MUST support configurable per port mapping from the C-
   VLAN ID associated with a native frame to a 24-bit fine-grained
   label. DT RBridges MAY support other methods to determine the DT ID
   of an incoming native frame. If the resulting label (X.Y) is such
   that VLAN X connectivity is being advertised by an ST edge RBridge in
   the campus, the ingressed frame MUST be dropped.

   The DT ingress process MUST place the priority associated with an
   ingressed native frame in the second Inner.Label C-tag. It SHOULD
   also associate a possibly different mapped priority with an ingressed
   frame. The mapped priority is placed in the initial Inner.Label C-
   tag. If such mapping is not supported then the original priority is
   also placed in the initial inner C-tag.

   A DT ingress RBridge MAY serially unicast a multi-destination DT
   frame to the relevant egress RBridge or RBridges after encapsulating
   it as a TRILL known unicast data frame. The relevant egress RBridges
   are determined by starting with those announcing connectivity to the
   frame's (X.Y) label. That set SHOULD be further filtered based on
   multicast listener and router connectivity if the native frame was a
   multicast frame.

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4.2 Transit Processing

   TRILL Data frame transit processing is fairly straightforward as
   described in Section 4.2.1 for known unicast TRILL Data frames and in
   Section 4.2.2 for multi-destination TRILL Data frames.

4.2.1 Unicast Transit Processing

   There is almost no change in TRILL unicast transit processing. A
   transit RBridge forwards any TRILL unicast data frame to the next hop
   towards the egress RBridge as specified in the TRILL Header. Just as
   RBridges conformant to the TRILL base protocol standard [RFCtrill] do
   not examine the Inner.VLAN ID of ST transit known unicast TRILL Data
   frames, DT RBridges do not examine either the high or low order part
   of the 24-bit ID in the Inner.Label for transit DT known unicast
   TRILL Data frames.

   However, as provided in the TRILL base protocol standard [RFCtrill],
   all transit RBridges, whether ST or DT, MUST take the priority used
   for a forwarded frame from the Inner.VLAN tag, which will be the
   first of the two DT VLAN tags for a DT TRILL Data frame.

4.2.2 Multi-Destination Transit Processing

   All multi-destination TRILL Data frames are forwarded on a
   distribution tree selected by the ingress RBridge. The distribution
   trees for DT multi-destination frames are the same trees as for ST
   multi-destination frames, calculated as provided for in the TRILL
   base protocol standard [RFCtrill]. There is no change in the Reverse
   Path Forwarding Check.

   A DT RBridge, say RB1, having a DT multi-destination frame for label
   (X.Y) to forward, SHOULD prune as in the base specification, based on
   whether there are any edge RBridges on the tree branch that are
   connected to label (X.Y). In addition, RB1 SHOULD prune multicast
   frames based on reported multicast listener and multicast router
   attachment in (X.Y). Finally, a transit DT RBridge MAY drop any
   multi-destination frame for label (X.Y) if some DT RBridge is
   advertising connectivity to VLAN X. "MAY" is chosen in this case to
   minimize the mandatory burden on transit RBridges.

   To ensure that a transit ST RBridge does not falsely filter traffic
   for DT label (X.Y), a DT edge RBridge attached to DT label (X.Y) MUST
   report connection to VLAN X, as if X were a ST VLAN, in addition to
   reporting connectivity to label (X.Y).  Because of this, DT transit
   RBridges can safely apply pruning to all TRILL Data frames, both ST

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   and DT, based on the first Inner.VLAN ID and the reported VLAN-X
   connectivity of all downstream RBridges.

   To ensure that a transit ST RBridge does not falsely prune traffic
   for DT label (X.Y) base on multicast filtering, a DT edge RBridge
   attached to label (X.Y) MUST report for VLAN X either (1) that it is
   attached to both IPv4 and IPv6 multicast routers or (2) its actual DT
   label (X.Y) multicast listener and router connectivity situation.

4.3 Egress Processing

   Egress processing is generally the reverse of ingress progressing
   described in Section 4.1.

   If any ST RBridge in the campus is announcing connectivity to VLAN-X,
   a DT RBridge MUST NOT egress a frame with DT label (X.Y) but must
   drop such a frame.

   A DT RBridge MUST be able to configurably convert the 24-bit fine
   grained label in a DT TRILL Data frame it is egressing to a 12-bit C-
   VLAN ID for the resulting native frame on a per port basis. A port
   MAY be configured to strip such tagging. It is the responsibility of
   the network manager to properly configure the DT RBridges and ports
   in the campus to obtain the desired mappings.

   A DT RBridge egresses DT frames with the above tag conversion
   similarly to the egressing of ST frames, as follows:

   1. A known unicast DT frame is egressed to the DT port matching its
      fine-grained label and Inner.MacDA. Or, if there is no such port,
      it is flooded out all DT ports with its fine-grained label unless
      the RBridge has knowledge that the frames Inner.MacDA cannot be
      out that port.

   2. A multi-destination DT frame is decapsulated and flooded out all
      ports with its fine-grained label subject to multicast pruning.

   DT RBridges MUST accept multi-destination encapsulated frames that
   are sent to them as TRILL unicast frames (TRILL Header M bit = 0).
   They locally egress such frames, if appropriate, and MUST NOT forward
   them (other than egressing them as native frames on their local

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4.4 Address Learning

   A DT RBridge learns addresses on DT ports based on the fine-grained
   label rather than VLAN ID. Addresses learned from ingressed native
   frames are logically represented by { MAC address, fine-grained
   label, port, confidence, timer } while remote addresses learned from
   egressing DT frames are logically represented by { MAC address, fine
   grained label, remote RBridge nickname, confidence, timer }.

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5. IS-IS Extensions

   [[[ Most of the following may be moved to an ISIS draft. ]]]

5.1 Announcing RBridge DT Support

   An RBridge announces that it is DT in its LSP by ... TBD.

5.2 Interested Labels and Bridge Roots sub-TLV

   A DT RBridge announces its DT connectivity and related information in
   the "Interested Labels and Bridge Spanning Tree Roots sub-TLV" (INT-
   LABEL) which is a variation of the "Interested VLANs and Spanning
   Tree Roots sub-TLV" (INT-VLAN) structured as below. All fields not
   defined here are as specified in [ISIStrill].

   |Type= INT-LABEL|                  (1 byte)
   |   Length      |                  (1 byte)
   |   Interested Labels                                 |  (7 bytes)
   |   Appointed Forwarder Status Lost Counter           |  (4 bytes)
   |         Root Bridges                                |  (6*n bytes)

   o  Type: Router Capability sub-TLV Type, set to TBD (INT-LABEL).

   o  Length: 13 + 6*n where n is the number of root bridge IDs.

   o  Interested Labels: The Interested Labels field is seven bytes long
      and formatted as shown below.

        0  1  2  3  4  5  6  7
      |M4|M6| R| R| R| R| R| R|
      |                  Label.start - 24 bits                    |
      |                  Label.end - 24 bits                      |

      -  M4, M6: These bits indicate, respectively, that there is an

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         IPv4 or IPv6 multicast router on a link for which the
         originating IS is appointed forwarder for every label in the
         indicated range.

      -  R: These reserved bits MUST be sent as zero and are ignored on

      - Label.start and Label.end: This fine-grained label ID range is
         inclusive.  A range of one label ID is indicated by setting
         them both to that label ID value.

5.3 The Group Labeled MAC Address sub-TLV

   The existing GMAC-ADDR sub-TLV of the Group Address (GADDR) TLV is
   specified in [ISIStrill]. It provides for only a 12-bit VLAN-ID. The
   Group Labeled MAC Address sub-TLV, below, extends this to a 24-bit

   |Type=GLMAC-ADDR|                  (1 byte)
   |   Length      |                  (1 byte)
   |  RESV |     Topology-ID       |  (2 bytes)
   |          24-Bit Label                         |(3 bytes)
   |Num Group Recs |                  (1 byte)
   |                   GROUP RECORDS (1)                           |
   |                   .................                           |
   |                   GROUP RECORDS (N)                           |

   where each group record is of the form:

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   | Num of Sources|                  (1 byte)
   |                   Group Address         (6 bytes)             |
   |                   Source 1 Address      (6 bytes)             |
   |                   Source 2 Address      (6 bytes)             |
   |                    .....                                      |
   |                   Source M Address      (6 bytes)             |

   o  Type: GADDR sub-TLV Type, set to TBD (GLMAC-ADDR).

   o  Length: Variable, minimum 6.

   o  RESV: Reserved. 4-bit field that MUST be sent as zero and ignored
      on receipt.

   o  Topology-ID: This field is not currently used in TRILL, where it
      is sent as zero and ignored on receipt, but is included for use by
      other technologies.

   o  Label: This carries the 24-bit fine-grained label identifier for
      all subsequent MAC addresses in this sub-TLV, or the value zero if
      no label is specified.

   o  Number of Group Records: A 1-byte integer that is the number of
      group records in this sub-TLV.

   o  Group Record: Each group record carries the number of sources.  It
      then has a 48-bit multicast address followed by 48-bit source MAC
      addresses.  If the sources do not fit in a single sub-TLV, the
      same group address may be repeated with different source addresses
      in another sub-TLV of another instance of the Group Address TLV.

   [[[ Most of the above may be moved to an ISIS draft. ]]]

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6. IANA Considerations


7. Security Considerations

   See [RFCtrill] for general RBridge Security Considerations.

   As with any communications system, end-to-end encryption and
   authentication should be considered for particularly sensitive data.

   More TBD??

7.1 Ingress Forgery and Egress Compromise

   Confusion between a frame with VLAN-X coarse labeling and DT label
   (X.Y) is a potential problem.

   An end station might try to cause a forged DT TRILL Data frame by
   sending a double C-tagged frame to a port configured for ST ingress.

   The requirement in Section 4.1 that all extra C-tags be removed from
   native frames on input solves this for DT RBridges. After such
   removal, the DT RBridge will properly add ST or DT to the
   encapsulated frame. Thus there is no ingress forgery problem for DT
   RBridges. However, this does not help for ST RBridges.

   ST RBridges need only conform to the [RFCtrill] standard and are not
   subject to the requirement herein to remove extra C-tags. Thus they
   might ingress in VLAN-X a native frame double tagged by the end
   station as (X.Y), removing only the first tag, and then re-insert a
   VLAN-X tag in the encapsulated frame. The result would be an
   encapsulated frame that looks like a frame with DT label (X.Y). DT
   RBridges will think this is a DT frame in (X.Y) and might egress it
   because they could not distinguish it from a coarsely labeled VLAN-X

   Additionally, a TRILL Data frame with DT label (X.Y) could be
   egressed to VLAN-X by an ST RBridge that is Appointed Forwarder for
   VLAN-X on one of its ports. Such a frame should not arrive at such an
   ST RBridge as egress unless the frame is multi-destination.

   The above problems are both solved by the prohibition against DT
   RBridges ingressing to or egressing from DT labeling (X.Y) if the
   RBridge campus is misconfigured so that an ST edge RBridge is
   reporting connectivity to VLAN-X while label (X.Y) is in use.

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8. References

   The following sections list normative and informative references for
   this document.

8.1 Normative References

   [802.1Q] - IEEE 802.1, "IEEE Standard for Local and metropolitan area
         networks - Virtual Bridged Local Area Networks", IEEE Std
         802.1Q-2011, May 2011.

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

   [RFCtrill] - R. Perlman, D. Eastlake, D. Dutt, S. Gai, and A.
         Ghanwani, "RBridges: Base Protocol Specification", draft-ietf-
         trill-rbridge-protocol-16.txt, in RFC Editor's queue.

   [ISIStrill] - Eastlake, D., A. Banerjee, D. Dutt, R. Perlman, A.
         Ghanwani, "TRILL Use of IS-IS", draft-ietf-isis-trill-05.txt,
         in RFC Editor's queue.

8.2 Informative References

   [RFCaf] - Perlman, R., D. Eastlake, A. Banerjee, H. Fangwei,
         "RBridges: Appointed Forwarders", draft-ietf-trill-rbridge-
         af-03.txt, work in progress.

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   The comments and contributions of the following are gratefully

      Anoop Ghanwani, Sujay Gupta, Jon Hudson, Vishwas Manral, and Erik

Authors' Addresses

   Donald Eastlake 3rd
   Huawei Technologies
   155 Beaver Street
   Milford, MA 01757 USA

   Phone: +1-508-333-2270

   Mingui Zhang
   Huawei Technologies Co., Ltd
   HuaWei Building, No.3 Xinxi Rd., Shang-Di
   Information Industry Base, Hai-Dian District,
   Beijing, 100085 P.R. China


   Puneet Agarwal
   Broadcom Corporation
   3151 Zanker Road
   San Jose, CA 95134 USA

   Phone: +1-949-926-5000

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

   Phone: +1-408-527-0955

   Radia Perlman
   Intel Labs

D. Eastlake, et al                                             [Page 18]

INTERNET-DRAFT                           RBridges: Fine-Grained Labeling

   2200 Mission College Blvd.
   Santa Clara, CA 95054 USA

   Phone: +1-408-765-8080

D. Eastlake, et al                                             [Page 19]

INTERNET-DRAFT                           RBridges: Fine-Grained Labeling

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D. Eastlake, et al                                             [Page 20]