path: root/doc/rfc/rfc8397.txt

Internet Engineering Task Force (IETF)                          M. Zhang
Request for Comments: 8397                               D. Eastlake 3rd
Category: Standards Track                                         Huawei
ISSN: 2070-1721                                               R. Perlman
                                                                Dell EMC
                                                                 H. Zhai
                                                                     JIT
                                                                  D. Liu
                                                  China Telecom Co., Ltd
                                                                May 2018


    Transparent Interconnection of Lots of Links (TRILL) Multilevel
                         Using Unique Nicknames

Abstract

   TRILL (Transparent Interconnection of Lots of Links) routing can be
   extended to support multiple levels by building on the multilevel
   feature of IS-IS routing.  Depending on how nicknames are managed,
   there are two primary alternatives to realize TRILL multilevel: the
   unique nickname approach and the aggregated nickname approach as
   discussed in RFC 8243.  This document specifies a unique nickname
   approach.  This approach gives unique nicknames to all TRILL switches
   across the multilevel TRILL campus.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8397.












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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1. Introduction ....................................................3
   2. Acronyms and Terminology ........................................4
   3. Data Routing ....................................................4
      3.1. Unicast Routing ............................................4
      3.2. Multi-destination Routing ..................................5
           3.2.1. Local Distribution Trees ............................6
           3.2.2. Global Distribution Trees ...........................6
   4. Protocol Basics and Extensions ..................................8
      4.1. Multilevel TRILL Basics ....................................8
      4.2. Nickname Allocation ........................................9
      4.3. Nickname Announcements .....................................9
      4.4. Capability Indication .....................................11
   5. Mix with Aggregated Nickname Areas .............................11
   6. Security Considerations ........................................12
   7. IANA Considerations ............................................13
   8. References .....................................................13
      8.1. Normative References ......................................13
      8.2. Informative References ....................................14
   Contributors ......................................................15
   Authors' Addresses ................................................15














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1.  Introduction

   The multiple-level feature of [IS-IS] can increase the scalability of
   TRILL as discussed in [RFC8243].  However, multilevel IS-IS needs
   some extensions to support the TRILL multilevel feature.  The two
   most significant extensions are how TRILL switch nicknames are
   managed and how distribution trees are handled [RFC8243].

   There are two primary alternatives to realize TRILL multilevel
   [RFC8243].  One approach, which is referred to as the "aggregated
   nickname" approach, involves assigning nicknames to the areas, and
   allowing nicknames to be reused in different areas by having the
   border TRILL switches rewrite nickname fields when entering or
   leaving an area.  For more description of the aggregated nickname
   approach, one can refer to [RFC8243] and [SingleN].  The other
   approach, which is referred to as the "unique nickname" approach, is
   specified in this document.  The unique nickname approach gives
   unique nicknames to all the TRILL switches in the multilevel campus
   by having the TRILL switches at the Level 1 / Level 2 border
   advertise into the Level 1 area those nicknames are not available for
   assignment in that area and advertising into the Level 2 area those
   nicknames that are used by the Level 1 area so that other areas
   cannot use them anymore.  The advertising of Level 1 nicknames
   informs the rest of the campus how to reach the nicknames residing in
   that area.  In this document, protocol extensions that support such
   advertisement are specified.

   Each RBridge in a unique nickname area calculates two types of trees:
   local distribution trees and global distributions trees.  For multi-
   destination traffic that is limited to an area, the packets will be
   flooded on a local distribution tree.  Otherwise, the multi-
   destination packets will be flooded along a global distribution tree.

   In the unique nickname approach, nicknames are globally valid so that
   border RBridges do not rewrite the nickname field of TRILL data
   packets that transition between Level 1 and Level 2, as border
   RBridges do in the aggregated nickname approach.  If a border RBridge
   is a transit node on a forwarding path, it does not learn MAC
   addresses of the TRILL data packets forwarded along this path.
   Testing and maintenance operations that originate in one area and
   terminate in a different area are also simplified [RFC8243].  For
   these reasons, the unique nickname approach might realize simpler
   border RBridges than the aggregated nickname approach.  However, the
   unique nickname approach is less scalable and may be less well suited
   for very large campuses.






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2.  Acronyms and Terminology

   Border RBridge: An RBridge that is located on the border between two
      or more RBridge areas.

   Data Label: VLAN or FGL [RFC7172]

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

   RBridge: A device implementing the TRILL protocol.

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

   TRILL switch: An alternative name for an RBridge.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Data Routing

             Area X                level 2             Area Y
       +-----------------+ +---------------------+ +------------+
       |                 | |                     | |            |
     S---RB27---Rx--Rz---RB2---Rb---Rc--Rd---Re--RB3---Rk--RB44---D
       |  27             | |                     | |        44  |
       |                 | |                     | |            |
       +-----------------+ +---------------------+ +------------+

            Figure 1: An Example Topology for TRILL Multilevel

   Figure 1 is adapted from the example topology of [RFC8243], where S
   is Source, and D is Destination.

   The routing processes are described in the following two subsections.

3.1.  Unicast Routing

   The plain RBridge RB27 has a different view of the topology of the
   TRILL campus than its border RBridge RB2.  For an outward path that
   reaches an RBridge not in the same area (say, RB44), RB27 calculates
   the segment of the path in Area X, the border RBridge RB2 calculates
   the segment in Level 2, while the border RBridge to the destination
   area, RBridge RB3, calculates the segment from itself to RB44.




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   Let us say that S transmits a frame to destination D and let us say
   that D's location is learned by the relevant TRILL switches already.
   These relevant switches have learned the following:

   1) RB27 has learned that D is connected to nickname 44.
   2) RB2 has learned that nickname 44 is accessible through RB3.

   The following sequence of events will occur:

   -  S transmits an Ethernet frame with source MAC = S and destination
      MAC = D.

   -  RB27 encapsulates with a TRILL header with ingress RBridge
      nickname 27, and egress RBridge nickname 44 producing a TRILL Data
      packet.

   -  RB2 has announced in the Level 1 IS-IS instance in Area X that it
      owns all nicknames of other areas, including 44.  Therefore, IS-IS
      routes the packet to RB2.

   -  The packet is forwarded through Level 2, from RB2 to RB3, which
      has advertised, in Level 2, it owns the nickname 44.

   -  RB3, when forwarding into Area Y, does not change the ingress
      nickname 27 or the egress nickname 44.

   -  RB44, when decapsulating, learns that S is attached to nickname
      27.

3.2.  Multi-destination Routing

   The scope of Multi-destination routing is defined by the tree root
   nickname.  A tree with a Level 2 tree root nickname is global, and a
   tree with a Level 1 tree root nickname is local.  See Section 4.2 for
   the Level 1 and Level 2 nickname allocation.

   Border RBridges announce the global trees to be calculated only for
   those Data Labels that span across areas.  APPsub-TLVs as specified
   in Section 3.2 of [RFC7968] will be advertised for this purpose.
   Based on the Data Label, an ingress RBridge can determine whether a
   global tree or a local tree is to be used for a TRILL multi-
   destination Data packet.

   If there are legacy TRILL switches that do not understand the APPsub-
   TLVs for tree selection, configuration MUST guarantee that Data
   Labels [RFC7172] being used globally in Level 2 are disabled on these
   legacy TRILL switches.  (Otherwise, the legacy TRILL switches might
   use local trees for multi-destination traffic with a global scope.)



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   These legacy TRILL switches may use global trees to flood multi-
   destination packets with a scope of the local area.  Those global
   trees MUST be pruned at the border TRILL switches based on Data
   Labels.

3.2.1.  Local Distribution Trees

   The root RBridge RB1 of a local distribution tree resides in the
   area.  RBridges in this area calculate this local tree based on the
   link state information of this area, using RB1's nickname as the
   root.  Protocol behaviors for local distribution trees have been
   specified in Section 4.5 of [RFC6325].  The sole difference is that
   the local distribution tree spans this area only.  A multi-
   destination packet with an egress nickname of the root RBridge of a
   local tree MUST NOT be leaked into Level 2 at the border RBridge.

3.2.2.  Global Distribution Trees

   Within Level 2, the RBridge with the highest tree root priority
   advertises the set of global trees by providing a list of Level 2
   RBridge nicknames as defined in Section 4.5 of [RFC6325].

   According to [RFC6325], the RBridge with the highest root priority
   advertises the tree roots for a Level 1 area.  There has to be a
   border RBridge with the highest root tree priority in each area so
   that it can advertise the global tree root nicknames into the area.
   Also, this border RBridge MUST advertise the set of local
   distribution trees by providing another set of nicknames.  Since
   nicknames of global tree roots and local tree roots indicate
   different flooding scopes, these two sets MUST NOT overlap.  If a
   border RBridge has been assigned both as a global tree root and a
   local tree root, it MUST acquire both global tree root nickname(s)
   and local tree root nickname(s).  However, non-border RBridges in an
   area do not differentiate between a global tree root nickname and a
   local tree root nickname.

   Suppose RB3 is the RBridge with the highest tree root priority within
   Level 2, and RB2 is the highest tree root priority in Area X.  RB2
   advertises in Area X that nickname RB3 is the root of a distribution
   tree.  Figures 2 through 5 illustrate how different RBridges view the
   global distribution tree.










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                                RB2,RB3,Rb,Rc,Rd,Re,Rk,RB44
                                 o
                                /
                            Rz o
                              /
                          Rx o
                            /
                      RB27 o

           Figure 2: RB27's View of the Global Distribution Tree

                                RB3,Rk,RB44
                                 o
                                /
                            Re o
                              /
                          Rd o
                            /
                        Rc o
                          /
                      Rb o
                        /
                   RB2 o
                      /
                  Rz o
                    /
                Rx o
                  /
            RB27 o

           Figure 3: RB2's View of the Global Distribution Tree

                                RB3
                                 o
                                / \
                            Re o   o Rk
                              /     \
                          Rd o       o RB44
                            /
                        Rc o
                          /
                      Rb o
                        /
         R27,Rx,Rz,RB2 o

           Figure 4: RB3's View of the Global Distribution Tree





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                                RB3,RB27,RBx,RBz,RB2,Rb,Rc,Rd,Re
                                 o
                                  \
                                   o Rk
                                    \
                                     o RB44

           Figure 5: RB44's View of the Global Distribution Tree

   The following sequence of events will occur when a multi-destination
   TRILL Data packet is forwarded using the global distribution tree:

   -  RB27 produces a multi-destination (M bit is one) TRILL Data packet
      with ingress RBridge nickname 27 and egress RBridge nickname 3.
      RB27 floods this packet using the segment of the global
      distribution tree that resides in Area X.

   -  RB2, when flooding the packet in Level 2, uses the segment of the
      global distribution tree that resides in Level 2.

   -  RB3, when flooding the packet into Area Y, uses the segment of the
      global distribution tree that resides in Area Y.

   -  The multicast listener RB44, when decapsulating the received
      packet, learns that S is attached to nickname 27.

4.  Protocol Basics and Extensions

4.1.  Multilevel TRILL Basics

   Multilevel TRILL builds on the multilevel feature of [IS-IS].  Border
   RBridges are in both a Level 1 area and in Level 2.  They establish
   adjacency with Level 1 RBridges as specified in [RFC7177] and
   [RFC6325].  They establish adjacency with Level 2 RBridges in exactly
   the same way except that (1) for a LAN link, the IS-IS Hellos used
   are Level 2 Hello PDUs [IS-IS] and (2) for a point-to-point link, the
   Level is configured and indicated in flags in the point-to-point
   Hello.  The state machines for Level 1 and Level 2 adjacency are
   independent, and two RBridges on the same LAN link can have any
   adjacency state for Level 1 and, separately, any adjacency state for
   Level 2.  Level 1 and Level 2 link state flooding are independent
   using Level 1 and Level 2 versions of the relevant IS-IS PDUs (LSP,
   CSNP, PSNP, FS-LSP, FS-CSNP, and FS-PSNP [RFC7356] [RFC7780]).  Thus,
   Level 1 link state information stays within a Level 1 area and Level
   2 link state information stays in Level 2 unless there are specific
   provisions for leaking (copying) information between levels.  This is
   why multilevel can address the TRILL scalability issues as specified
   in Section 2 of [RFC8243].



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   The former "campus wide" minimum acceptable link size Sz is
   calculated as before: by Level 1 RBridges (including border RBridges)
   using the originatingLSPBufferSize advertised in the Level 1 LSP so
   it is area local in multilevel TRILL.  A minimum acceptable link size
   in Level 2, called Sz2, is calculated by the RBridges participating
   in Level 2 in the same way as Sz is calculated but using the
   originatingLSPBufferSize distributed in Level 2 LSPs.

4.2.  Nickname Allocation

   Level 2 RBridges contend for nicknames in the range from 0xF000
   through 0xFFBF the same way as specified in [RFC6325]: using Level 2
   LSPs.  The highest-priority border router for a Level 1 area should
   contend with others in Level 2 for blocks of nicknames for the range
   from 0x0001 to 0xEFFF.  Blocks of 64 aligned on boundaries of
   multiples of 64 are RECOMMENDED in this document.

   The nickname contention in Level 2 will determine which blocks of
   nicknames are available for an area and which blocks of nicknames are
   used elsewhere.  The NickBlockFlags APPsub-TLV as specified in
   Section 4.3 will be used by the border RBridge(s) to announce the
   nickname availability.

4.3.  Nickname Announcements

   Border RBridges need to exchange nickname information between Level 1
   and Level 2; otherwise, forwarding paths inward or outward will not
   be calculated.  For this purpose, border RBridges need to fabricate
   nickname announcements.  Sub-TLVs used for such announcements are
   specified as follows.

   Besides its own nickname(s), a border RBridge MUST announce, in its
   area, the ownership of all external nicknames that are reachable from
   this border RBridge.  These external nicknames include nicknames used
   in other unique nickname areas and nicknames in Level 2.  Non-border
   RBridge nicknames within aggregated nickname areas are excluded.
   Also, a border RBridge MUST announce, in Level 2, the ownership of
   all nicknames within its area.  From listening to these Level 2
   announcements, border RBridges can figure out the nicknames used by
   other areas.

   RBridges in the TRILL base protocol use the Nickname Sub-TLV as
   specified in Section 2.3.2 of [RFC7176] to announce the ownership of
   nicknames.  However, it becomes uneconomic to use this Sub-TLV to
   announce a mass of internal/external nicknames.  To address this
   issue, border RBridges SHOULD make use of the NickBlockFlags





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   APPsub-TLV to advertise into the Level 1 area the inclusive range of
   nicknames that are or are not available for self allocation by the
   Level 1 RBridges in that area.  Its structure is as follows:

               0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |     Type = 24                                 |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |     Length                                    |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |OK|                RESV                        |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |     Nickname Block 1                          |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |  ...
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |     Nickname Block K                          |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

      o  Type: 24 (TRILL NickBlockFlags)

      o  Length: 2 + 4*K, where K is the number of nickname blocks.

      o  OK:

         - When this bit is set to 1, the blocks of nicknames in this
           APPsub-TLV are associated to the border RBridge's attached
           Level 1 area.  The APPsub-TLV will be advertised in both
           Level 1 and Level 2.  For nicknames that fall in the ranges
           of the nickname blocks, RBridges of Level 2 always route to
           the originating border RBridge, just as if this border
           RBridge owns these nicknames.

         - When this bit is set to 0, it indicates that the nicknames
           covered by the nickname blocks are being used in Level 2 or
           other areas so that they are not available for use in the
           border RBridge's attached Level 1 area.  The APPsub-TLV will
           be advertised into Level 1 only.  For nicknames that fall in
           the ranges of the nickname blocks, RBridges of the area
           always route to the originating border RBridge, just as if
           this border RBridge owns these nicknames.  For nicknames in
           these ranges, other RBridges will deem that they are owned by
           the originating border RBridge.  The paths to nicknames that
           fall in these ranges will be calculated to reach the
           originating border RBridge.  TRILL Data packets with egress
           nicknames that are neither in these ranges nor announced by
           any RBridge in the area MUST be discarded.




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      o  RESV: reserved for future flag allocation.  MUST be sent as
         zero and ignored on receipt.

      o  Nickname Block: a starting and ending nickname as follows:

             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |     starting nickname                         |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
             |     ending nickname                           |
             +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

   Nickname Sub-TLV as specified in Section 2.3.2 of [RFC7176] is still
   allowed to be used, given the above NickBlockFlags APPsub-TLV is
   being used.

   There might be multiple border RBridges connected to the same area.
   Each border RBridge may advertise a subset of the entire
   internal/external nickname space in order to realize load balance.
   However, optimization of such load balance is an implementation issue
   and is outside the scope of this document.

   As specified in Section 4.2.6 of [RFC6325], multiple border RBridges
   may claim the same nicknames outwardly and/or inwardly.  Other
   RBridges add those nicknames as if they are attached to all of those
   border RBridges.

4.4.  Capability Indication

   All border RBridges MUST understand the NickBlockFlags APPsub-TLV.
   Non-border RBridges in an area should understand the NickBlockFlags
   APPsub-TLV.  If an RBridge within an area understands the
   NickBlockFlags APPsub-TLV, it MUST indicate this capability by
   announcing it in its TRILL-VER Sub-TLV.  (See Section 7.)

   If there are RBridges that do not understand the NickBlockFlags
   APPsub-TLV, border RBridges of the area MUST also use the traditional
   Nickname Sub-TLV [RFC7176] to announce into the area those nicknames
   covered by the nickname blocks of the NickBlockFlags APPsub-TLV whose
   OK is 0.  The available range of nicknames for this area should be
   configured on these traditional RBridges.

5.  Mix with Aggregated Nickname Areas

   The design of TRILL multilevel allows a mixture of unique nickname
   areas and aggregated nickname areas (see Section 1.2 of [RFC8243]).
   Usage of nickname space MUST be planned so that nicknames used in any
   one unique nickname area and Level 2 are never used in any other
   areas, including unique nickname areas as well as aggregated nickname



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   areas.  In other words, nickname reusage is merely allowed among
   aggregated nickname areas.

   Border RBridges of an aggregated area MUST announce nicknames heard
   from Level 2 into their area like just like a unique nickname border
   RBridge.  However, these RBridges do not announce nicknames of their
   area into Level 2.

   Each border RBridge of the aggregated areas will appear on the global
   tree, as specified in Section 4.1, as a single node.  The global
   trees for unique nickname areas span unique nickname areas and Level
   2 but never reach the inside of aggregated areas.

6.  Security Considerations

   Since TRILL multilevel uses the existing IS-IS multilevel facilities
   [IS-IS], flooding of control traffic for link-state information is
   automatically confined to a Level 1 area or to Level 2 (except for
   limited types of information that can be specifically flagged for
   wider flooding).  This addresses the TRILL scalability issues as
   specified in Section 2 of [RFC8243], and also, except for the wider
   flooding case, this confines the scope of the effects of malicious
   events that could be communicated through the link state.  However,
   due to the fact that unique nickname areas share a common nickname
   space, border RBridges still have to leak nickname information
   between levels.  Such leaking means that nickname-related events in
   one area can affect other areas.

   For this purpose, border RBridges need to fabricate the nickname
   announcements as specified in Section 4.3.  Malicious devices may
   also fake the NickBlockFlags APPsub-TLV to announce a range of
   nicknames.  By doing this, the attacker can attract TRILL data
   packets that were originally sent to a bunch of other RBridges.  For
   this reason, RBridges SHOULD be configured to use the IS-IS
   Authentication TLV (10) in the IS-IS PDUs, particularly those
   containing the NickBlockFlags APPsub-TLV, so that IS-IS security
   [RFC5310] can be used to authenticate those PDUs and discard them if
   they are forged.

   If border RBridges do not prune multi-destination distribution tree
   traffic in Data Labels that are configured to be area local, then
   traffic that should have been contained within an area might be
   wrongly delivered to end stations in that Data Label in other areas.
   That is, the Data Label would no longer be area local.  This would
   generally violate security constraints that require traffic to be
   delivered only to end stations in that Data Label in a single area.

   For general TRILL Security Considerations, see [RFC6325].



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7.  IANA Considerations

   IANA has registered a new flag bit under the "TRILL-VER Sub-TLV
   Capability Flags" registry.

         Bit    Description             Reference
         ---    -----------             ---------
          5     Able to handle the      RFC 8397
                NickBlockFlags
                APPsub-TLV

   IANA has assigned a new type for the NickBlockFlags APPsub-TLV from
   the range available below 256 and add the following entry to the
   "TRILL APPsub-TLV Types under IS-IS TLV 251 Application Identifier 1"
   registry as follows:

         Type    Name            Reference
         ----    ------          ---------
          24     NickBlockFlags  RFC 8397

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6325]  Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
              Ghanwani, "Routing Bridges (RBridges): Base Protocol
              Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,
              <https://www.rfc-editor.org/info/rfc6325>.

   [RFC7172]  Eastlake 3rd, D., Zhang, M., Agarwal, P., Perlman, R., and
              D. Dutt, "Transparent Interconnection of Lots of Links
              (TRILL): Fine-Grained Labeling", RFC 7172,
              DOI 10.17487/RFC7172, May 2014,
              <https://www.rfc-editor.org/info/rfc7172>.

   [RFC7176]  Eastlake 3rd, D., Senevirathne, T., Ghanwani, A., Dutt,
              D., and A. Banerjee, "Transparent Interconnection of Lots
              of Links (TRILL) Use of IS-IS", RFC 7176,
              DOI 10.17487/RFC7176, May 2014,
              <https://www.rfc-editor.org/info/rfc7176>.






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   [RFC7177]  Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H., and
              V. Manral, "Transparent Interconnection of Lots of Links
              (TRILL): Adjacency", RFC 7177, DOI 10.17487/RFC7177, May
              2014, <https://www.rfc-editor.org/info/rfc7177>.

   [RFC7968]  Li, Y., Eastlake 3rd, D., Hao, W., Chen, H., and S.
              Chatterjee, "Transparent Interconnection of Lots of Links
              (TRILL): Using Data Labels for Tree Selection for Multi-
              Destination Data", RFC 7968, DOI 10.17487/RFC7968, August
              2016, <https://www.rfc-editor.org/info/rfc7968>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [IS-IS]    International Organization for Standardization,
              "Information technology -- Telecommunications and
              information exchange between systems -- Intermediate
              System to Intermediate System intra-domain routeing
              information exchange protocol for use in conjunction with
              the protocol for providing the connectionless-mode network
              service (ISO 8473)", ISO/IEC 10589:2002, Second Edition,
              November 2002.

8.2.  Informative References

   [SingleN]  Zhang, M., Eastlake, D., et al, "Transparent
              Interconnection of Lots of Links (TRILL) Single Area
              Border RBridge Nickname for Multilevel", draft-ietf-trill-
              multilevel-single-nickname-05, Work in Progress, January
              2018.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310, February
              2009, <https://www.rfc-editor.org/info/rfc5310>.

   [RFC7356]  Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
              Scope Link State PDUs (LSPs)", RFC 7356,
              DOI 10.17487/RFC7356, September 2014,
              <https://www.rfc-editor.org/info/rfc7356>.

   [RFC7780]  Eastlake 3rd, D., Zhang, M., Perlman, R., Banerjee, A.,
              Ghanwani, A., and S. Gupta, "Transparent Interconnection
              of Lots of Links (TRILL): Clarifications, Corrections, and
              Updates", RFC 7780, DOI 10.17487/RFC7780, February 2016,
              <https://www.rfc-editor.org/info/rfc7780>.




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   [RFC8243]  Perlman, R., Eastlake 3rd, D., Zhang, M., Ghanwani, A.,
              and H. Zhai, "Alternatives for Multilevel Transparent
              Interconnection of Lots of Links (TRILL)", RFC 8243,
              DOI 10.17487/RFC8243, September 2017,
              <https://www.rfc-editor.org/info/rfc8243>.

Contributors

   Margaret Cullen
   Painless Security
   14 Summer St. Suite 202
   Malden, MA  02148
   United States of America

   Email: margaret@painless-security.com

Authors' Addresses

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

   Phone: +86-13810702575
   Email: zhangmingui@huawei.com


   Donald Eastlake 3rd
   Huawei Technologies
   155 Beaver Street
   Milford, MA  01757
   United States of America

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


   Radia Perlman
   Dell EMC
   176 South Street
   Hopkinton, MA  01748
   United States of America

   Email: radia@alum.mit.edu






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

   Email: honjun.zhai@tom.com


   Dongxin Liu
   China Telecom Co., Ltd
   109 West Zhongshan Ave, Tianhe District
   Guangzhou  510630
   China

   Email: liudx@gsta.com



































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