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Versions: 00 01 02 03                                                   
TRILL Working Group                                      Donald Eastlake
INTERNET-DRAFT                                              Mingui Zhang
Updates: 6325                                                     Huawei
Intended status: Proposed Standard                         Radia Perlman
                                                              Intel Labs
                                                          Vishwas Manral
                                                           Ayan Banerjee
Expires: January 15, 2013                                  July 16, 2012

                        Multiple Topology TRILL


   The IETF TRILL (TRansparent Interconnection of Lots of Links)
   protocol is a solution for least cost transparent frame routing in
   multi-hop networks with arbitrary topologies and link technologies,
   using IS-IS (Intermediate System to Intermediate System) link-state
   routing and encapsulation with a hop count.  IS-IS supports multiple
   topology routing. This document specifies a TRILL data plane encoding
   and procedures to make use of such routing.

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-

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   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html. The list of Internet-Draft
   Shadow Directories can be accessed at

D. Eastlake, et al                                              [Page 1]

INTERNET-DRAFT                                     TRILL: Multi-Topology

Table of Contents

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

      2. TRILL Multi-Topology....................................4
      2.1 Nicknames and Topology Abbreviation....................4
      2.2 Nickname Allocation....................................5
      2.3 SPF and Distribution Tree Calculation..................6
      2.3.1 Base Topology SPF....................................6
      2.3.2 Non-Zero Topology SPF................................6
      2.3.3 Distribution Tree Calculation........................6

      3. Processing Multi-Topology Frames........................8
      3.1 Ingress Processing.....................................8
      3.2 Transit Processing.....................................8
      3.3 Egress Processing......................................9
      3.4 Address Learning and Asymmetric Topologies.............9

      5. IS-IS Extensions.......................................10
      6. IANA Considerations....................................11
      7. Security Considerations................................11
      8. Acknowledgements.......................................11

      9. References.............................................12
      9.1 Normative References..................................12
      9.2 Informative References................................12

D. Eastlake, et al                                              [Page 2]

INTERNET-DRAFT                                     TRILL: Multi-Topology

1. Introduction

   The IETF has standardized RBridges (Routing Bridges), devices that
   implement the TRILL (TRansparent Interconnection of Lots of Links)
   protocol [RFC6325], a solution for least cost transparent frame
   routing in multi-hop networks with arbitrary topologies, using IS-IS
   (Intermediate System to Intermediate System) link-state routing [IS-
   IS] [RFC1195] [RFC6326bis] and encapsulation with a hop count.

   TRILL supports VLANs (Virtual Local Area Networks) but the
   segregation provided by VLANs in TRILL is logical, not physical.
   While maintaining logical separation, the base TRILL standard shares
   inter-RBridge links across all VLANs and by default interconnects all
   end stations that are in the same VLAN and have connectivity to any
   RBridge in the campus.

   IS-IS multi-topology [RFC5120] can provide physical separation of
   sub-sets of TRILL Data frames, assuming that the RBridges in a campus
   can be trusted. This can be used for a variety of purposes including
   such things as confining a sub-set traffic to an island within an
   RBridge campus, quality of service traffic engineering, excluding
   some frames from links that are particularly exposed to interception,
   and providing significant protection against some covert channels

   Familiarity with the TRILL base protocol standard [RFC6325], TRILL
   use of IS-IS [RFC6326bis], and IS-IS multi-topology [RFC5120] is
   assumed in this document.

1.1 Terminology

   The terminology and acronyms of [RFC6325] are used in this document
   with the additions listed below.

      Highest Priority RBridge - The RBridge in the campus that is the
         highest priority to be a base topology tree root.

      MT - Multi-Topology

      TAS - Topology Abbreviation Size

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

D. Eastlake, et al                                              [Page 3]

INTERNET-DRAFT                                     TRILL: Multi-Topology

2. TRILL Multi-Topology

   The essence of TRILL multi-topology (MT) is that (a) when TRILL Data
   frames are ingressed or created they are assigned to a topology, (b)
   links can be labeled with one or more topologies and different cost,
   etc., for different topologies, and (c) a TRILL Data frame is only
   allowed on a link labeled with the frame's topology.  In addition,
   there is a base topology: all links are considered to be in the base
   topology, and, by default, TRILL Data frames are considered to be
   base topology frames.

   With minor exceptions, it is important that all transit RBridges
   believe a TRILL Data frame is in the same topology to avoid
   persistent routing loops. This document specifies how to encode this
   information into the egress nickname in a TRILL Data frame. (Note: It
   is believed that this technique is supportable by most if not all
   TRILL fast path silicon implementations.)

   Implementation of MT has a significant impact on shortest path and
   distribution tree computation. In general, it multiplies the level of
   effort by the number of different topologies in which the average
   RBridge participates. Using the technique in this document, it also
   reduces the number of of available nicknames, generally dividing it
   by the number of topologies rounded up to the next power of two. For
   these reasons, the number of overlapping topologies in use should be

2.1 Nicknames and Topology Abbreviation

   The TRILL base protocol standard [RFC6325] specifies 16-bit nicknames
   as abbreviations for 7-bytes IS-IS IDs. In MT TRILL the nickname is
   subdivided into two fields. The least significant TAS (Topology
   Abbreviation Size) number of bits indicate the topology constraint of
   the nickname while the most significant ( 16 - TAS ) bits continue to
   act as an abbreviation for an RBridge System ID.

   The TAS value for an MT RBridge campus is dictated by the highest
   priority RBridge. To prevent transient disruption, other RBridges
   that might become the highest priority RBridge SHOULD be configured
   with the same TAS value. The value of TAS can vary from zero to
   seven. Zero indicates that only the base topology can be used.

   In IS-IS, topologies have a 12-bit ID which we refer to as an
   absolute topology number. Topology zero is the base topology. All
   links are considered to be part of the base topology. Absolute
   topology numbers are mapped into abbreviations by a table dictated by
   the highest priority RBridge. To prevent transient disruption, other
   RBridges that might become the highest priority RBridge should be

D. Eastlake, et al                                              [Page 4]

INTERNET-DRAFT                                     TRILL: Multi-Topology

   configured with the same TAS topology abbreviation table. In the
   opening remarks to this Section 2, "topology" should be read as
   referring to topology abbreviation.

   Multiple absoolute topology numbers MAY be mapped into the same
   abbreviation. This may or may not result in the merger of the mapped
   absolute topologies depending on whether their use is disjoint or
   overlapping. Absolute topology zero and topology abbreviation zero
   always refers to the base topology.

   For example, assume that absolute topologies Tp1 and Tp2 exist and
   are both mapped into the same specific abbreviation. If all RBridges
   in the campus reachable by links labeled Tp1 or Tp2 are connected
   through such links, then, since MT TRILL forwarding is based on the
   topology abbreviation, Tp1 and Tp2 are necessarily merged to the
   extent both topologies are in use. On the other hand, such RBridges
   could be divided into disjoint islands with no connection between the
   islands via links allowing Tp1 or Tp2. In that case, depending on how
   frames are topologically classified, each such island could
   independently be exclusively Tp1, exclusively Tp2, merged Tp1 and
   Tp2, or unused.

2.2 Nickname Allocation

   RBridges indicate in their LSP whether they support MT by the
   presence of the MT TLV [RFC5120]. If all RBridges in a campus support
   MT, then RBridges can be configured for and contend for nicknames as
   provided in [RFC6325], but only for nicknames that have TAS number of
   low order zero bits. If there are any RBridges in the campus that do
   not support MT, then MT RBridges must hold all nicknames from ( k *
   2**TAS ) through ( (k+1) * 2**TAS - 1 ) in order to, in effect, hold
   nickname ( k * 2**TAS ).

   RBridges not supporting MT are unaware of the subdivision of the
   TRILL nickname into subfields. Thus, they may hold artbirary 16-bit
   allowed quanities as nicknames. MT aware RBridges know that the
   bottom TAS bits of any nicknames held by such MT unaware RBridges are
   not topologically significant.

   The nickname allocation described above and in [RFC6325] runs based
   on the nickname priority values appearing in Router Capabilities TLVs
   (TLV #242), which is what MT unaware RBridges will use. The Nicknames
   sub-TLV is allowed in the MT Router Capabilities TLV (TLV #144) for
   the sole purpose of permitting nicknames to have different priorities
   to be root in different topologies; in particular, the Nicknames sub-
   TLV field giving the priority to hold that nickname is ignore for
   Nicknames sub-TLVs in the MT Router Capabilities TLV.

D. Eastlake, et al                                              [Page 5]

INTERNET-DRAFT                                     TRILL: Multi-Topology

2.3 SPF and Distribution Tree Calculation

   This section discusses MT SPF and distribution tree calculation.

2.3.1 Base Topology SPF

   Since MT TRILL cannot impose any changes on MT unaware RBridges,
   those RBridges will perform their SPF and distribution tree
   calculations as specified in [RFC6325]. For compatibility, MT aware
   RBridge MUST perform their base topology SPF and distribution tree
   calculations in the same way. In particular, the base topology
   consists of those links listed in Extended IS Reachability TLVs (TLV
   #22). For backward compatibility, MT aware RBridges use only links
   listed in TLV #22 for the base topology, which SHOULD be all links,
   even if there exist MT-ISN TLVs (TLV #222) listing topology zero or
   if one or more non-zero absolute topologies are being mapped into the
   base topology abbreviation zero.

2.3.2 Non-Zero Topology SPF

   For MT aware RBridges, least cost (SPF) paths are also calculated per
   topology abbreviation for the non-zero abbreviations labeling any
   link connected to that RBridge. When paths are being calculated for a
   topology abbreviation, only links labeled with absolute topologies
   that map to that abbreviation are considered.

   For topologies other than the base toplogy, link costs from the MT-
   ISN TLV (TLV #222 [RFC5120]) are used; however, such costs are
   reported per absolute topology, not per topology abbreviation.  This
   is resolved for non-zero abbreviations by using, in SPF calculations,
   the lowest cost reported for the link for any absolute topology
   corresponding the topology abbreviation for which the calculation is
   being performed. Non-base topologies do not necessarily span the
   campus and there may be RBridges that are unreachable in such
   topologies. Frames destined for unreachable RBridges are discarded.

2.3.3 Distribution Tree Calculation

   Distribution trees are also calculated per topology abbreviation by
   MT aware RBridges. At least one distribution tree is always built as
   described in [RFC6325] for the base topology using the tree root
   nickname priorities advertised in the Router Capabilities TLV. That
   tree will span the campus. Care should be taken that the highest
   priority RBridge is configured to not request too many distribution

D. Eastlake, et al                                              [Page 6]

INTERNET-DRAFT                                     TRILL: Multi-Topology

   trees be calculated in the base topology. There may be silicon limits
   to how many distribution trees can be efficienlty handled and too
   many base topology trees could starve other topologies that should
   have a distributon tree.

   For non-zero topology abbreviations, a distribution tree will be
   composed only of links that are in at least one of the absolute
   topologies that map to that abbreviation and the tree may not span
   the campus. Such distribution trees might not span the campus and
   there might be multiple disjoint distribution trees for a particular
   topology abbreviation.

   The calculation of additional distribution trees for non-zero
   topology abbreviations is accomplished using the same method of
   building from root as described in [RFC6325] but using link costs as
   described in the preceding section on TRILL non-zero topology SPF
   calculations. The number of such trees may be constrained by the
   capabilities of RBridges in the campus as advertised in the Trees
   sub-TLV in the Router Capabilities TLV. However, that limit is of the
   number of trees actually including that RBridge and would not
   include, for example, a distribution tree for some topology present
   only in a remote island of RBridges.

   After the base topology trees are calculated, trees for non-zero
   topologies are calculated, one per topology abbreviation, starting
   with the highest topology abbreviation in use and working down to the
   lowest non-zero topology. If additional tree are available and
   requested, they are distrubted to the topology abbreviations. For the
   details see Appendix ... [[Since it is important that all RBridges
   agree on the calculation of distribution trees, I think this is going
   to need some psudo code in an appendix.]]

D. Eastlake, et al                                              [Page 7]

INTERNET-DRAFT                                     TRILL: Multi-Topology

3. Processing Multi-Topology Frames

   This section specifies ingress, transit, and egress processing of MT
   TRILL Data frames, how asymetric topologies can occur, and address

3.1 Ingress Processing

   On ingressing or creating a frame, an RBridge assigns it to an
   absolute topology ID. The method by which this 12-bit topology ID is
   assigned is beyond the scope of this document; however, different
   frames with the same source MAC address, VLAN, and egress RBridge
   SHOULD be assigned to the same topology. In TRILL, topology does not
   provide another level of VLAN but identifies a subset of traffic.

   The resulting absolute ID is mapped to a topology abbreviation. That
   abbreviation is used as the bottom TAS bits in the ingress nickname
   field of the resulting TRILL Data frame.

   For a unicast native frame the VLAN and the destination MAC address
   are used to look up the egress nickname field.

   If the destination is unknown, or the native frame is multicast or
   broadcast, the ingress RBridge selects a distribution tree for that
   topology abbreviation that includes the ingress RBridge. If more than
   one tree is available, the method of choice is beyond the scope of
   this document, but by default, it should pick the tree whose root is
   least cost from the ingress RBridge.

3.2 Transit Processing

   No change is required in transit frame processing assuming that SPF
   and distribution tree calculations have been performed as specified
   in Section 2.3.

   The next hop RBridge for TRILL unicast frames will automatically be
   restricted to the appropriate topology.  The same applies to the zero
   or more next hops for the tree that a TRILL multi-destination frame
   is being distributed on. There is no change in the Reverse Path
   Forwarding Check.

D. Eastlake, et al                                              [Page 8]

INTERNET-DRAFT                                     TRILL: Multi-Topology

3.3 Egress Processing

   There is no change in egress processing.

3.4 Address Learning and Asymmetric Topologies

   There is no change in address learning.  This can result in
   asymmetric topology use.

   For example assume end stations ESa and ESb in the same VLAN-x
   attached to RB1 and RB2 respectively want to communicate. Generally,
   the initial frame from RB1 will be classified in topology
   abbreviation T1 and sent on a T1 distribution tree which should be
   pruned for VLAN-x. If that tree includes RB2, the frame will be
   delivered to RB2 that will egress it to ESb or, if it has not yet
   learned which of its links ESb is attached to, RB2 will egress the
   frame to all of its links in VLAN-x for which it is appointed
   forwarder [RFC6439]. In addition, RB2 will learn that ESa in VLAN-x
   is attached to RB1 but the nickname it learns from RB1 will have T1
   encoded in it so that RB1 also learns, that ESa is in T1. When ESb
   send a return frame to ESa, RB2 will classify that frame as in
   topology abbreviation T2, encode that in the ingress nickname of the
   TRILL header, and send the frame to RB1 in T1 because the egress
   nickname RB2 will use was that learned from the receipt of the above
   frame from RB1 in T1. At this point, ESa and ESb can continue
   communicating using TRILL unicast frames in each direction with
   frames from ESa to ESb in T1 while those from ESb to ESa will be in

   If it is desired that T1 equal T2, then RB1 and RB2 must be
   configured to classify the incoming native frames as in the same
   topology. Note that, if many topologies are in use but there are
   fewer distribution trees, the initial ESa frame in the example above
   might have been distributed in a T3 distribution tree. This will not
   affect RB2 learning which will learn from the T1 topology encoded
   into the ingress nickname in the encapsulated frame's TRILL Header.

D. Eastlake, et al                                              [Page 9]

INTERNET-DRAFT                                     TRILL: Multi-Topology

5. IS-IS Extensions

   For the extensions to the TRILL use of IS-IS to make use multi-
   topology, see [trill-mt].

   These include the addition of a topology mapping sub-TLV. This sub-
   TLV is across all topologies and occurs in the Router Capabilities
   TLV. It specifies the TAS for the campus and provides a mapping from
   absolute topology IDs to topology abbreviations. Absolute topology
   zero is always mapped to topology abbreviation zero. No entry is
   needed for this base topology mapping and any other mapping for
   topology zero is ignored. Multiple absolute topologies may be mapped
   to the same abbreviation. If there are mappings of the same absolute
   topology to multiple abbreviations, the largest abbreviation,
   considered as an unsigned integer dominates, and mappings of that
   absolute topology to smaller abbreviations are ignored.

D. Eastlake, et al                                             [Page 10]

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6. IANA Considerations

   IANA coniderations for this draft are in [trill-mt].

7. Security Considerations

   See [RFC6325] 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

8. Acknowledgements

   The comments and contributions of the following are gratefully

      Meenakshi Kaushik and Dinesh Dutt.

D. Eastlake, et al                                             [Page 11]

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9. References

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

9.1 Normative References

   [IS-IS] - International Organization for Standardization,
         "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, Nov

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

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

   [RFC5120] - Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
         Topology (MT) Routing in Intermediate System to Intermediate
         Systems (IS-ISs)", RFC 5120, February 2008.

   [RFC6325] - Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
         Ghanwani, "Routing Bridges (RBridges): Base Protocol
         Specification", RFC 6325, July 2011.

   [RFC6439] - Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F.
         Hu, "Routing Bridges (RBridges): Appointed Forwarders", RFC
         6439, November 2011.

   [RFC6326bis] - Eastlake, D., A. Banerjee, D. Dutt, R. Perlman, A.
         Ghanwani, "TRILL Use of IS-IS", draft-eastlake-isis-rfc6326bis,
         work in progress.

   [trill-mt] - Manral, V., D. Eastlake, M. Zhang, A. Banerjee, "Multi
         Topology Routing Extensions for Transparent Interconnection of
         Lots of Links (TRILL)", draft-manral-isis-trill-multi-topo,
         work in progress.

9.2 Informative References

   [RFC4949] - Shirey, R., "Internet Security Glossary, Version 2", FYI
         36, RFC 4949, August 2007.

D. Eastlake, et al                                             [Page 12]

INTERNET-DRAFT                                     TRILL: Multi-Topology

Authors' Addresses

   Donald Eastlake 3rd
   Huawei R&D USA
   155 Beaver Street
   Milford, MA 01757 USA

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

   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

   Email: zhangmingui@huawei.com

   Radia Perlman
   Intel Labs
   2200 Mission College Blvd.
   Santa Clara, CA 95054 USA

   Phone: +1-408-765-8080
   Email: radia@alum.mit.edu

   Vishwas Manral
   Hewlett-Packard Co.
   19111 Pruneridge Ave.
   Cupertino, CA 95014 USA

   Phone: 1-408-447-0000
   Email: vishwas.manral@hp.com

   Ayan Banerjee
   Cumulus Networks
   1089 West Evelyn Avenue
   Sunnyvale, CA 94086 USA

   Email: ayabaner@gmail.com

D. Eastlake, et al                                             [Page 13]

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D. Eastlake, et al                                             [Page 14]