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Versions: (draft-eastlake-trill-rfc7180bis) 00 01 02 03 04 05 06 07 RFC 7780

TRILL Working Group                                      Donald Eastlake
INTERNET-DRAFT                                              Mingui Zhang
Intended status: Proposed Standard                                Huawei
Obsoletes: 7180                                            Radia Perlman
Updates: 6325, 7177, 7179                                            EMC
                                                           Ayan Banerjee
                                                                   Cisco
                                                          Anoop Ghanwani
                                                                    Dell
                                                             Sujay Gupta
                                                             IP Infusion
Expires: May 1, 2016                                    November 2, 2015


            TRILL: Clarifications, Corrections, and Updates
                  <draft-ietf-trill-rfc7180bis-07.txt>


Abstract

   Since publication of the TRILL (Transparent Interconnection of Lots
   of Links) base protocol in 2011, active development and deployment of
   TRILL has revealed errata in RFC 6325 and areas that could use
   clarifications or updates. RFCs 7177, 7357, and draft-eastlake-trill-
   rfc6439bis provide clarifications and updates with respect to
   Adjacency, the TRILL ESADI (End Station Address Distribution
   Information) protocol, and Appointed Forwarders respectively.  This
   document provides other known clarifications, corrections, and
   updates. It obsoletes RFC 7180 (the previous TRILL clarifications,
   corrections, and updates RFC), updates RFC 7177, updates RFC 7179,
   and updates RFC 6325.


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: <trill@ietf.org>.

   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-
   Drafts.

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





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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
   http://www.ietf.org/shadow.html.
















































D. Eastlake, et al                                              [Page 2]


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Table of Contents

      1. Introduction (Changed)..................................5
      1.1 Precedence (Changed)...................................5
      1.2 Changes That Are Not Backward Compatible (Unchanged)...6
      1.3 Terminology and Acronyms (Changed).....................6

      2. Overloaded and/or Unreachable RBridges (Unchanged)......8
      2.1 Reachability...........................................8
      2.2 Distribution Trees.....................................9
      2.3 Overloaded Receipt of TRILL Data Packets...............9
      2.3.1 Known Unicast Receipt...............................10
      2.3.2 Multi-Destination Receipt...........................10
      2.4 Overloaded Origination of TRILL Data Packets..........10
      2.4.1 Known Unicast Origination...........................10
      2.4.2 Multi-Destination Origination.......................11
      2.4.2.1 An Example Network................................11
      2.4.2.2 Indicating OOMF Support...........................12
      2.4.2.3 Using OOMF Service................................12

      3. Distribution Trees and RPF Check (Changed).............14
      3.1 Number of Distribution Trees (Unchanged)..............14
      3.2 Distribution Tree Update Clarification (Unchanged)....14
      3.3 Multicast Pruning Based on IP Address (Unchanged).....14
      3.4 Numbering of Distribution Trees (Unchanged)...........15
      3.5 Link Cost Directionality (Unchanged)..................15
      3.6 Alternative RPF Check (New)...........................15
      3.6.1 Example of the Potential Problem....................16
      3.6.2 Solution and Discussion.............................17

      4. Nicknames Selection (Unchanged)........................19

      5. MTU (Maximum Transmission Unit) (Unchanged)............21
      5.1 MTU-Related Errata in RFC 6325........................21
      5.1.1 MTU PDU Addressing..................................21
      5.1.2 MTU PDU Processing..................................22
      5.1.3 MTU Testing.........................................22
      5.2 Ethernet MTU Values...................................22

      6. TRILL Port Modes (Unchanged)...........................24
      7. The CFI/DEI Bit (Unchanged)............................25

      8. Other IS-IS Considerations (Changed)...................26
      8.1 E-L1FS Support (New)..................................26
      8.1.1 Backward Compatibility..............................26
      8.1.2 E-L1FS Use for Existing (sub)TLVs...................27
      8.2 Control Packet Priorities (New).......................28
      8.3 Unknown PDUs (New)....................................29
      8.4 Nickname Flags APPsub-TLV (New).......................29
      8.5 Graceful Restart (Unchanged)..........................31
      8.6 Purge Originator Identification (New).................31

D. Eastlake, et al                                              [Page 3]


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Table of Contents (continued)

      9. Updates to [RFC7177] (Adjacency) (Changed).............32

      10. TRILL Header Update (New).............................33
      10.1 Color Bit............................................34
      10.2 Flag Word Changes (update to [RFC7179])..............34
      10.2.1 Extended Hop Count.................................34
      10.2.1.1 Advertising Support..............................34
      10.2.1.2 Ingress Behavior.................................35
      10.2.1.3 Transit Behavior.................................35
      10.2.1.4 Egress Behavior..................................36
      10.2.2 Extended Color Field...............................36
      10.3 Updated Flag Word Summary............................36

      11. Appointed Forwarder Status Lost Counter (New).........38

      12. IANA Considerations (Changed).........................39
      12.1 Previously Completed IANA Actions (Unchanged)........39
      12.2 New IANA Actions (New)...............................39
      12.2.1 Reference Updated..................................39
      12.2.2 The 'E' Capability Bit.............................40
      12.2.3 NickFlags APPsub-TLV Number and Registry...........40
      12.2.4 Updated TRILL Extended Header Flags................40
      12.2.5 TRILL-VER Sub-TLV Capability Flags.................41
      12.2.6 Example Nicknames..................................41

      13. Security Considerations (Changed).....................42

      Normative References......................................43
      Informative References....................................44
      Acknowledgements..........................................46

      Appendix A: Life Cycle of a TRILL Switch Port (New).......47

      Appendix B: Example TRILL PDUs (New)......................50
      B.1 LAN Hello over Ethernet...............................50
      B.2 LSP Over PPP..........................................51
      B.3 TRILL Data Over Ethernet..............................52
      B.4 TRILL Data Over PPP...................................53

      Appendix C: Changes to Previous RFCs (New)................55
      C.1 Changes to Obsoleted [RFC7180]........................55
      C.1.1 Changes.............................................55
      C.1.2 Additions...........................................55
      C.1.3 Deletions...........................................56
      C.2 Changes to [RFC6325]..................................57
      C.3 Changes to [RFC7177]..................................57
      C.4 Changes to [RFC7179]..................................57

      Appendix Z: Change History................................58

D. Eastlake, et al                                              [Page 4]


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1. Introduction (Changed)

   Since the TRILL base protocol [RFC6325] was published in 2011, active
   development and deployment of TRILL has revealed errors in the
   specification [RFC6325] and several areas that could use
   clarifications or updates.

   [RFC7177], [RFC7357], and [rfc6439bis] provide clarifications and
   updates with respect to Adjacency, the TRILL ESADI (End Station
   Address Distribution Information) protocol, and Appointed Forwarders
   respectively.  This document provides other known clarifications,
   corrections, and updates to [RFC6325], [RFC7177], and [RFC7179]. This
   document obsoletes [RFC7180], the previous TRILL clarifications,
   corrections, and updates document, updates [RFC6325], updates
   [RFC7177] as described in Section 9, and updates [rfc7179] as
   described in Section 10.2 and 10.3. The charges to these RFCs are
   summarized in Appendix C.

   Sections of this document are annotated as to whether they are "New"
   technical material, material that has been technically "Changed", or
   material that is technically "Unchanged", by the appearance of one of
   these three words in parenthesis at the end of the section header. A
   section with only editorial changes is annotated as "(Unchanged)". If
   no such notation appears, then the first notation encountered on
   going to successively higher-level headers (those with shorter
   numbers) applies. Appendix C describes changes, summarizes material
   added, and lists material deleted.



1.1 Precedence (Changed)

   In case of conflict between this document and [RFC6325], [RFC7177],
   or [RFC7179] this document takes precedence.

   In addition, Section 1.2 (Normative Content and Precedence) of
   [RFC6325] is updated to provide a more complete precedence ordering
   of the sections of [RFC6325] as show below, where sections to the
   left take precedence over sections to their right. There are no known
   conflicts between these sections but Sections 1 and 2 are less
   detailed and do not mention every corner case while later sections of
   [RFC6325] are more detailed. This precedence is specified as a fall
   back in case some conflict is found in the future.

                         4 > 3 > 7 > 5 > 2 > 6 > 1







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1.2 Changes That Are Not Backward Compatible (Unchanged)

   The change made by Section 3.4 below, which was also present in
   [RFC7180], is not backward compatible with [RFC6325] but has
   nevertheless been adopted to reduce distribution tree changes
   resulting from topology changes.

   The several other changes herein that are fixes to errata for
   [RFC6325] -- [Err3002] [Err3003] [Err3004] [Err3052] [Err3053]
   [Err3508] -- may not be backward compatible with previous
   implementations that conformed to errors in the specification.



1.3 Terminology and Acronyms (Changed)

   This document uses the acronyms defined in [RFC6325], some of which
   are repeated below for convenience, along with some additional
   acronyms and terms as follows:

   Campus - a TRILL network consisting of TRILL switches, links, and
       possibly bridges bounded by end stations and IP routers. For
       TRILL, there is no "academic" implication in the name "campus".

   CFI  - Canonical Format Indicator [802].

   DEI  - Drop Eligibility Indicator [802.1Q-2014].

   FGL  - Fine Grained Labeling [RFC7172]

   OOMF - Overload Originated Multi-destination Frame.

   PDU  - Protocol Data Unit.

   RBridge - Routing Bridge, an alternative name for a TRILL Switch.

   RPFC - Reverse Path Forwarding Check.

   SNPA - SubNetwork Point of Attachment (for example, MAC address).

   TRILL - Transparent Interconnection of Lots of Links or Tunneled
       Routing in the Link Layer.

   TRILL Switch - A device implementing the TRILL protocol. 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
   [RFC2119].


D. Eastlake, et al                                              [Page 6]


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   In this document a "packet" usually refers to a TRILL Data packet or
   TRILL IS-IS packet received from or sent to a TRILL switch while a
   "frame" usually refers to a native frame being received from or sent
   to an end station. (The word frame also occurs in other contexts such
   as the "Frame Check Sequence" that is at the end of Ethernet
   transmissions.)














































D. Eastlake, et al                                              [Page 7]


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2. Overloaded and/or Unreachable RBridges (Unchanged)

   In this Section 2, the term "neighbor" refers only to actual RBridges
   and ignores pseudonodes.

   RBridges may be in overload as indicated by the [IS-IS] overload flag
   in their LSPs (Link State PDUs).  This means that either (1) they are
   incapable of holding the entire link-state database and thus do not
   have a view of the entire topology or (2) they have been configured
   to have the overload bit set.  Although networks should be engineered
   to avoid actual link-state overload, it might occur under various
   circumstances.  For example, if a very large campus included one or
   more low-end TRILL Switches.

   It is a common operational practice to set the overload bit in an
   [IS-IS] router (such as a TRILL Switch) when performing maintenance
   on that router that might affect its ability to correctly forward
   packets; this will usually leave the router reachable for maintenance
   traffic, but transit traffic will not be routed through it.  (Also,
   in some cases, TRILL provides for setting the overload bit in the
   pseudonode of a link to stop TRILL Data traffic on an access link
   (see Section 4.9.1 of [RFC6325]).)

   [IS-IS] and TRILL make a reasonable effort to do what they can even
   if some TRILL Switches/routers are in overload.  They can do
   reasonably well if a few scattered nodes are in overload.  However,
   actual least-cost paths are no longer assured if any TRILL Switches
   are in overload.

   For the effect of overload on the appointment of forwarders, see
   [rfc6439bis].



2.1 Reachability

   Packets are not least-cost routed through an overloaded TRILL Switch,
   although they may originate or terminate at an overloaded TRILL
   Switch.  In addition, packets will not be least-cost routed over
   links with cost 2**24 - 1 [RFC5305]; such links are reserved for
   traffic- engineered packets, the handling of which is beyond the
   scope of this document.

   As a result, a portion of the campus may be unreachable for least-
   cost routed TRILL Data because all paths to it would be through
   either a link with cost 2**24 - 1 or through an overloaded RBridge.
   For example, an RBridge (TRILL Switch) RB1 is not reachable by TRILL
   Data if all of its neighbors are connected to RB1 by links with cost
   2**24 - 1.  Such RBridges are called "data unreachable".



D. Eastlake, et al                                              [Page 8]


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   The link-state database at an RBridge, for example RB1, can also
   contain information on TRILL Switches that are unreachable by IS-IS
   link-state flooding due to link or RBridge failures.  When such
   failures partition the campus, the TRILL Switches adjacent to the
   failure and on the same side of the failure as RB1 will update their
   LSPs to show the lack of connectivity, and RB1 will receive those
   updates.  As a result, RB1 will be aware of the partition.  Nodes on
   the far side of the partition are both IS-IS unreachable and data
   unreachable from RB1.  However, LSPs held by RB1 for TRILL Switches
   on the far side of the failure will not be updated and may stay
   around until they time out, which could be tens of minutes or longer.
   (The default in [IS-IS] is twenty minutes.)



2.2 Distribution Trees

   An RBridge in overload cannot be trusted to correctly calculate
   distribution trees or correctly perform the RPFC (Reverse-Path
   Forwarding Check).  Therefore, it cannot be trusted to forward multi-
   destination TRILL Data packets.  It can only appear as a leaf node in
   a TRILL multi-destination distribution tree.  Furthermore, if all the
   immediate neighbors of an RBridge are overloaded, then it is omitted
   from all trees in the campus and is unreachable by multi-destination
   packets.

   When an RBridge determines what nicknames to use as the roots of the
   distribution trees it calculates, it MUST ignore all nicknames held
   by TRILL Switches that are in overload or are data unreachable.  When
   calculating RPFCs for multi-destination packets, an RBridge, such as
   RB1 MAY, to avoid calculating unnecessary RPFC state information,
   ignore any trees that cannot reach to RB1 even if other RBridges list
   those trees as trees that other TRILL Switches might use.  (But see
   Section 3.)



2.3 Overloaded Receipt of TRILL Data Packets

   The receipt of TRILL Data packets by overloaded RBridge RB2 is
   discussed in the subsections below.  In all cases, the normal Hop
   Count decrement is performed, and the TRILL Data packets are
   discarded if the result is less than one or if the egress nickname is
   illegal.








D. Eastlake, et al                                              [Page 9]


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2.3.1 Known Unicast Receipt

   RB2 will not usually receive unicast TRILL Data packets unless it is
   the egress, in which case it egresses and delivers the data normally.
   If RB2 receives a unicast TRILL Data packet for which it is not the
   egress, perhaps because a neighbor does not yet know it is in
   overload, RB2 MUST NOT discard the packet because the egress is an
   unknown nickname as it might not know about all nicknames due to its
   overloaded condition.  If any neighbor, other than the neighbor from
   which it received the packet, is not overloaded, it MUST attempt to
   forward the packet to one of those neighbors selected at random
   [RFC4086].  If there is no such neighbor, the packet is discarded.



2.3.2 Multi-Destination Receipt

   If RB2 in overload receives a multi-destination TRILL Data packet,
   RB2 MUST NOT apply an RPFC since, due to overload, it might not do so
   correctly.  RB2 egresses and delivers the frame locally where it is
   Appointed Forwarder for the frame's VLAN (or, if the packet is FGL,
   for the VLAN that FGL maps to at the port), subject to any multicast
   pruning.  But since, as stated above, RB2 can only be the leaf of a
   distribution tree, it MUST NOT forward a multi-destination TRILL Data
   packet (except as an egressed native frame where RB2 is Appointed
   Forwarder).



2.4 Overloaded Origination of TRILL Data Packets

   Overloaded origination of unicast TRILL Data packets with known
   egress and of multi-destination packets is discussed in the
   subsections below.



2.4.1 Known Unicast Origination

   When RB2, an overloaded RBridge, ingresses or creates a known
   destination unicast data packet, it delivers it locally if the
   destination is local.  Otherwise, RB2 unicasts it to any neighbor
   TRILL Switch that is not overloaded.  It MAY use what routing
   information it has to help select the neighbor.








D. Eastlake, et al                                             [Page 10]


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2.4.2 Multi-Destination Origination

   Overloaded RBridge RB2 ingressing or creating a multi-destination
   data packet is more complex than for the known unicast case as
   discussed below.



2.4.2.1 An Example Network

   For example, consider the network below in which, for simplicity, end
   stations and any bridges are not shown.  There is one distribution
   tree of which RB4 is the root, as represented by double lines.  Only
   RBridge RB2 is overloaded.

            +-----+    +-----+     +-----+     +-----+
            | RB7 +====+ RB5 +=====+ RB3 +=====+ RB1 |
            +-----+    +--+--+     +-++--+     +--+--|
                          |          ||           |
                      +---+---+      ||           |
               +------+RB2(ov)|======++           |
               |      +-------+      ||           |
               |                     ||           |
            +--+--+    +-----+   ++==++=++     +--+--+
            | RB8 +====+ RB6 +===++ RB4 ++=====+ RB9 |
            +-----+    +-----+   ++=====++     +-----+

   Since RB2 is overloaded, it does not know what the distribution tree
   or trees are for the network.  Thus, there is no way it can provide
   normal TRILL Data service for multi-destination native frames.  So
   RB2 tunnels the frame in a TRILL Data packet to a neighbor that is
   not overloaded if it has such a neighbor that has signaled that it is
   willing to offer this service.  RBridges indicate this in their
   Hellos as described below.  This service is called OOMF (Overload
   Originated Multi- destination Frame) service.

   -  The multi-destination frame MUST NOT be locally distributed in
      native form at RB2 because this would cause the frame to be
      delivered twice. Instead it is tunneling to a neighbor as provided
      in this section.  For example, if RB2 locally distributed a
      multicast native frame and then tunneled it to RB5, RB2 would get
      a copy of the frame when RB3 transmitted it as a TRILL Data packet
      on the multi-access RB2-RB3-RB4 link.  Since RB2 would, in
      general, not be able to tell that this was a frame it had tunneled
      for distribution, RB2 would decapsulate it and locally distribute
      it a second time.

   -  On the other hand, if there is no neighbor of RB2 offering RB2 the
      OOMF service, RB2 cannot tunnel the frame to a neighbor.  In this
      case, RB2 MUST locally distribute the frame where it is Appointed


D. Eastlake, et al                                             [Page 11]


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      Forwarder for the frame's VLAN and optionally subject to multicast
      pruning.



2.4.2.2 Indicating OOMF Support

   An RBridge RB3 indicates its willingness to offer the OOMF service to
   RB2 in the TRILL Neighbor TLV in RB3's TRILL Hellos by setting a bit
   associated with the SNPA (SubNetwork Point of Attachment, also known
   as MAC address) of RB2 on the link (see IANA Considerations).
   Overloaded RBridge RB2 can only distribute multi-destination TRILL
   Data packets to the campus if a neighbor of RB2 not in overload
   offers RB2 the OOMF service.  If RB2 does not have OOMF service
   available to it, RB2 can still receive multi-destination packets from
   non-overloaded neighbors and, if RB2 should originate or ingress such
   a frame, it distributes it locally in native form.



2.4.2.3 Using OOMF Service

   If RB2 sees this OOMF (Overload Originated Multi-destination Frame)
   service advertised for it by any of its neighbors on any link to
   which RB2 connects, it selects one such neighbor by a means beyond
   the scope of this document.  Assuming RB2 selects RB3 to handle
   multi-destination packets it originates, RB2 MUST advertise in its
   LSP that it might use any of the distribution trees that RB3
   advertises so that the RPFC will work in the rest of the campus.
   Thus, notwithstanding its overloaded state, RB2 MUST retain this
   information from RB3 LSPs, which it will receive as it is directly
   connected to RB3.

   RB2 then encapsulates such frames as TRILL Data packets to RB3 as
   follows: M bit = 0, Hop Count = 2, ingress nickname = a nickname held
   by RB2, and, since RB2 cannot tell what distribution tree RB3 will
   use, egress nickname = a special nickname indicating an OOMF packet
   (see IANA Considerations).  RB2 then unicasts this TRILL Data packet
   to RB3.  (Implementation of Item 4 in Section 4 below provides
   reasonable assurance that, notwithstanding its overloaded state, the
   ingress nickname used by RB2 will be unique within at least the
   portion of the campus that is IS-IS reachable from RB2.)

   On receipt of such a packet, RB3 does the following:

   -  changes the Egress Nickname field to designate a distribution tree
      that RB3 normally uses,
   -  sets the M bit to one,
   -  changes the Hop Count to the value it would normally use if it
      were the ingress, and


D. Eastlake, et al                                             [Page 12]


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   -  forwards the TRILL Data packet on that tree.

   RB3 MAY rate limit the number of packets for which it is providing
   this service by discarding some such packets from RB2.  The provision
   of even limited bandwidth for OOMFs by RB3, perhaps via the slow
   path, may be important to the bootstrapping of services at RB2 or at
   end stations connected to RB2, such as supporting DHCP and ARP/ND
   (Address Resolution Protocol / Neighbor Discovery).  (Everyone
   sometimes needs a little OOMF (pronounced "oomph") to get off the
   ground.)










































D. Eastlake, et al                                             [Page 13]


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3. Distribution Trees and RPF Check (Changed)

   Two corrections, a clarification, and two updates related to
   distribution trees appear in the subsections below along with an
   alternative, stronger RPF (Reverse Path Forwarding) Check.  See also
   Section 2.2.



3.1 Number of Distribution Trees (Unchanged)

   In [RFC6325], Section 4.5.2, page 56, Point 2, 4th paragraph, the
   parenthetical "(up to the maximum of {j,k})" is incorrect [Err3052].
   It should read "(up to k if j is zero or the minimum of (j, k) if j
   is non-zero)".



3.2 Distribution Tree Update Clarification (Unchanged)

   When a link-state database change causes a change in the distribution
   tree(s), there are several possibilities.  If a tree root remains a
   tree root but the tree changes, then local forwarding and RPFC
   entries for that tree should be updated as soon as practical.
   Similarly, if a new nickname becomes a tree root, forwarding and RPFC
   entries for the new tree should be installed as soon as practical.
   However, if a nickname ceases to be a tree root and there is
   sufficient room in local tables, the forwarding and RPFC entries for
   the former tree MAY be retained so that any multi-destination TRILL
   Data packets already in flight on that tree have a higher probability
   of being delivered.



3.3 Multicast Pruning Based on IP Address (Unchanged)

   The TRILL base protocol specification [RFC6325] provides for and
   recommends the pruning of multi-destination packet distribution trees
   based on the location of IP multicast routers and listeners; however,
   multicast listening is identified by derived MAC addresses as
   communicated in the Group MAC Address sub-TLV [RFC7176].

   TRILL Switches MAY communicate multicast listeners and prune
   distribution trees based on the actual IPv4 or IPv6 multicast
   addresses involved.  Additional Group Address sub-TLVs are provided
   in [RFC7176] to carry this information.  A TRILL Switch that is only
   capable of pruning based on derived MAC address SHOULD calculate and
   use such derived MAC addresses from the multicast listener IPv4/IPv6
   address information it receives.



D. Eastlake, et al                                             [Page 14]


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3.4 Numbering of Distribution Trees (Unchanged)

   Section 4.5.1 of [RFC6325] specifies that, when building distribution
   tree number j, node (RBridge) N that has multiple possible parents in
   the tree is attached to possible parent number j mod p.  Trees are
   numbered starting with 1, but possible parents are numbered starting
   with 0.  As a result, if there are two trees and two possible
   parents, in tree 1, parent 1 will be selected, and in tree 2, parent
   0 will be selected.

   This is changed so that the selected parent MUST be (j-1) mod p.  As
   a result, in the case above, tree 1 will select parent 0, and tree 2
   will select parent 1.  This change is not backward compatible with
   [RFC6325].  If all RBridges in a campus do not determine distribution
   trees in the same way, then for most topologies, the RPFC will drop
   many multi-destination packets before they have been properly
   delivered.



3.5 Link Cost Directionality (Unchanged)

   Distribution tree construction, like other least-cost aspects of
   TRILL, works even if link costs are asymmetric, so the cost of the
   hop from RB1 to RB2 is different from the cost of the hop from RB2 to
   RB1. However, it is essential that all RBridges calculate the same
   distribution trees, and thus, all must either use the cost away from
   the tree root or the cost towards the tree root. As corrected in
   [Err3508], the text in Section 4.5.1 of [RFC6325] is incorrect.  It
   says:

      In other words, the set of potential parents for N, for the tree
      rooted at R, consists of those that give equally minimal cost
      paths from N to R and ...

   but the text should say "from R to N":

      In other words, the set of potential parents for N, for the tree
      rooted at R, consists of those that give equally minimal cost
      paths from R to N and ...



3.6 Alternative RPF Check (New)

   [RFC6325] mandates a Reverse Path Forwarding (RPF) Check on multi-
   destination TRILL Data packets to avoid possible multiplication
   and/or looping of multi-destination traffic during TRILL campus
   topology transients. This check is logically performed at each TRILL
   switch input port and determines whether it is arriving on the


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   expected port based on where the packet started (the ingress
   nickname) and the tree on which it is being distributed. If not, the
   packet is silently discarded. This check is fine for point-to-point
   links; however, there are rare circumstances involving multi-access
   ("broadcast") links where a packet can be duplicated despite this RPF
   Check and other checks performed by TRILL.

   Section 3.6.1 gives an example of the potential problem and Section
   3.6.2 specifies a solution. This solution is an alternative, stronger
   RPF Check that TRILL Switches can be implemented in place of the RFF
   Check in [RFC6325].



3.6.1 Example of the Potential Problem

   Consider this network:

         F--A--B--C--o--D
                     |
                     E

   All the links except the link between C, D, and E are point-to-point
   links.  C, D, and E are connected over a broadcast link represented
   by the pseudonode "o". For example, they could be connected by a
   bridged LAN.  (Bridged LANs are transparent to TRILL.)

   Although the choice of root is unimportant here, assume that D or F
   is chosen as the root of a distribution tree so it is obvious the
   tree looks just like the diagram above.

   Now assume a link comes up from A to the same bridged LAN. The
   network then looks like this:

            +--------+
            |        |
         F--A--B--C--o--D
                     |
                     E

   Let's say the resulting tree in steady state includes all links
   except the B-C link. After the network has converged, a packet that
   starts from F will go F->A. Then A will send one copy on the A-B link
   and another copy into the bridge LAN from which it will be received
   by C and D.

   Now consider a transition stage where A and D have acted on the new
   LSPs and programmed their forwarding plane, while B and C have not
   yet done so.  This means that B and C both consider the link between
   them to still be part of the tree. In this case, a packet that starts


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   out from F and reaches A will be copied by A into the A-B link and to
   the bridge LAN. D's RPF check says to accept packets on this tree
   coming from F over its port on the bridged LAN, so it gets accepted.
   D is also adjacent to A on the tree, so the tree adjacency check, a
   separate check mandated by [RFC6325] also passes.

   However, the packet that gets to B gets sent out by B to C. C's RPF
   check still has the old state, and it thinks the packet is OK. C
   sends the packet along the old tree, which is into the bridge LAN. D
   receives one more packet, but the tree adjacency check passes at D
   because C is adjacent to D in the new tree as well. The RPF Check
   also passes at D because D's port on the bridged LAN is OK for
   receiving packets from F.

   So, during this transient state, D gets duplicates of every multi-
   destination packet ingressed at F (unless the packet gets pruned)
   until B and C act on the new LSPs and program their forwarding
   tables.



3.6.2 Solution and Discussion

   The problem stems from the RPF Check in [RFC6325] depending only on
   the port at which a TRILL Data packet is received, the ingress
   nickname, and the tree being used, that is, a check if {ingress
   nickname, tree, input port} is a valid combination according to the
   receiving TRILL switch's view of the campus topology. A multi-access
   link actually has multiple adjacencies overlaid on one physical link
   and to avoid the problem shown in Section 3.6.1, a stronger check is
   needed that includes the Layer 2 source address of the TRILL Data
   packet being received. (TRILL is a Layer 3 protocol and TRILL
   switches are true routers that logically strip the Layer 2 header
   from any arriving TRILL Data packets and add the appropriate new
   Layer 2 header to any outgoing TRILL Data packet to get it to the
   next TRILL switch, so the Layer 2 source address in a TRILL Data
   packet identifies the immediately previous TRILL Switch that
   forwarded the packet.)

   What is needed, instead of checking the validity of the triplet
   {ingress nickname, tree, input port} is to check that the quadruplet
   {ingress nickname, source SNPA, tree, input port} is valid (where
   "source SNPA" (Sub-Network Point of Access) is the Outer.MacSA for an
   Ethernet link). Although it is true that [RFC6325] also requires a
   check that a multi-destination TRILL Data packet is from a TRILL
   switch that is adjacent in the distribution tree being used, this is
   a separate check from the RPF Check and these two independent checks
   are not as powerful as the single unified check for a valid
   quadruplet.



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               _______
              /       \
            RB1 ------ o ----- RB2
              \_______/

   However, this stronger RPF Check is not without cost. In the simple
   case of a multi-access link where each TRILL switch has only one port
   on the link, it merely increases the size of validity entries by
   adding the source SNPA (Outer.MacSA). However, assume some TRILL
   Switch RB1 has multiple ports attached to a multi-access link. In the
   figure above, RB1 is show with three ports on the multi-access link.
   RB1 is permitted to load split multi-destination traffic it is
   sending into the multi-access link across those ports (Section 4.4.4
   [RFC6325]).  Assume RB2 is another TRILL Switch on the link and RB2
   is distribution tree adjacent to RB1. The number of validity
   quadruplets at RB2 for ingress nicknames whose multi-destination
   traffic would arrive through RB1 is multiplied by the number of ports
   RB1 has on the access-link because RB2 has to accept such traffic
   from any of such ports.  Although such instances seem to be very rare
   in practice, the number of ports an RBridge has on a link could in
   principle be tens or even a hundred or more ports, vastly increasing
   the RPF check state at RB2 when this stronger RPF check is used.

   Another potential cost of the stronger RPF Check is increased
   transient loss of multi-destination TRILL Data packets during a
   topology change.  For TRILL switch D, the new stronger RPF Check is
   (tree->A, Outer.MacSA=A, ingress=A, arrival port=if1) while the old
   one was ( tree->A, Outer.MacSA=C, ingress=A, arrival port=if1).
   Suppose both A and B have switched to the new tree for multicast
   forwarding while D has not updated its RPF Check yet, then the
   multicast packet will be dropped at D's input port since D still
   expects packet from "Outer.MacSA=C". But we do not have this packet
   loss issue if the weaker triplet check (tree->A, ingress=A, arrival
   port=if1) is used.  Thus, the stronger check can increase the RPF
   Check discard of multi-destination packets during topology
   transients.

   Because of these potential costs, implementation of this stronger RPF
   Check is optional. The TRILL base protocol is updated to provide that
   TRILL Switches MUST, for multi-destination packets, either implement
   the RPF and other checks in [RFC6325] or implement this stronger RPF
   Check as a substitute for the [RFC6325] RPF and tree adjacency
   checks. There is no problem with a campus having a mixture of TRILL
   switches some of which implement one of these RPF checks and some of
   which implement the other.







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4. Nicknames Selection (Unchanged)

   Nickname selection is covered by Section 3.7.3 of [RFC6325].
   However, the following should be noted:

   1. The second sentence in the second bullet item in Section 3.7.3 of
      [RFC6325] on page 25 is erroneous [Err3002] and is corrected as
      follows:

      o  The occurrence of "IS-IS ID (LAN ID)" is replaced with
         "priority".

      o  The occurrence of "IS-IS System ID" is replaced with "seven-
         byte IS-IS ID (LAN ID)".

      The resulting corrected sentence in [RFC6325] reads as follows:

         "If RB1 chooses nickname x, and RB1 discovers, through receipt
         of an LSP for RB2 at any later time, that RB2 has also chosen
         x, then the RBridge or pseudonode with the numerically higher
         priority keeps the nickname, or if there is a tie in priority,
         the RBridge with the numerically higher seven-byte IS-IS ID
         (LAN ID) keeps the nickname, and the other RBridge MUST select
         a new nickname."

   2. In examining the link-state database for nickname conflicts,
      nicknames held by IS-IS unreachable TRILL Switches MUST be
      ignored, but nicknames held by IS-IS reachable TRILL Switches MUST
      NOT be ignored even if they are data unreachable.

   3.  An RBridge may need to select a new nickname, either initially
      because it has none or because of a conflict.  When doing so, the
      RBridge MUST consider as available all nicknames that do not
      appear in its link-state database or that appear to be held by IS-
      IS unreachable TRILL Switches; however, it SHOULD give preference
      to selecting new nicknames that do not appear to be held by any
      TRILL Switch in the campus, reachable or unreachable, so as to
      minimize conflicts if IS-IS unreachable TRILL Switches later
      become reachable.

   4. An RBridge, even after it has acquired a nickname for which there
      appears to be no conflicting claimant, MUST continue to monitor
      for conflicts with the nickname or nicknames it holds.  It does so
      by checking in LSP PDUs it receives that should update its link-
      state database for the following: any occurrence of any of its
      nicknames held with higher priority by some other TRILL Switch
      that is IS-IS reachable from it.  If it finds such a conflict, it
      MUST select a new nickname, even when in overloaded state.  (It is
      possible to receive an LSP that should update the link-state
      database but does not do so due to overload.)


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   5. In the very unlikely case that an RBridge is unable to obtain a
      nickname because all valid RBridge nicknames (0x0001 through
      0xFFBF inclusive) are in use with higher priority by IS-IS
      reachable TRILL Switches, it will be unable to act as an ingress,
      egress, or tree root but will still be able to function as a
      transit TRILL Switch.  Although it cannot be a tree root, such an
      RBridge is included in distribution trees computed for the campus
      unless all its neighbors are overloaded.  It would not be possible
      to send a unicast RBridge Channel message specifically to such a
      TRILL Switch [RFC7178]; however, it will receive unicast RBridge
      Channel messages sent by a neighbor to the Any-RBridge egress
      nickname and will receive appropriate multi-destination RBridge
      Channel messages.







































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5. MTU (Maximum Transmission Unit) (Unchanged)

   MTU values in TRILL key off the originatingL1LSPBufferSize value
   communicated in the IS-IS originatingLSPBufferSize TLV [IS-IS].  The
   campus-wide value Sz, as described in Section 4.3.1 of [RFC6325], is
   the minimum value of originatingL1LSPBufferSize for the RBridges in a
   campus, but not less than 1470.  The MTU testing mechanism and
   limiting LSPs to Sz assures that the LSPs can be flooded by IS-IS and
   thus that IS-IS can operate properly.

   If an RBridge knows nothing about the MTU of the links or the
   originatingL1LSPBufferSize of other RBridges in a campus, the
   originatingL1LSPBufferSize for that RBridge should default to the
   minimum of the LSP size that its TRILL IS-IS software can handle and
   the minimum MTU of the ports that it might use to receive or transmit
   LSPs.  If an RBridge does have knowledge of link MTUs or other
   RBridge originatingL1LSPBufferSize, then, to avoid the necessity to
   regenerate the local LSPs using a different maximum size, the
   RBridge's originatingL1LSPBufferSize SHOULD be configured to the
   minimum of (1) the smallest value that other RBridges are or will be
   announcing as their originatingL1LSPBufferSize and (2) a value small
   enough that the campus will not partition due to a significant number
   of links with limited MTU.  However, as provided in [RFC6325], in no
   case can originatingL1LSPBufferSize be less than 1470.  In a well-
   configured campus, to minimize any LSP regeneration due to re-sizing,
   all RBridges will be configured with the same
   originatingL1LSPBufferSize.

   Section 5.1 below corrects errata in [RFC6325], and Section 5.2
   clarifies the meaning of various MTU limits for TRILL Ethernet links.



5.1 MTU-Related Errata in RFC 6325

   Three MTU-related errata in [RFC6325] are corrected in the
   subsections below.



5.1.1 MTU PDU Addressing

   Section 4.3.2 of [RFC6325] incorrectly states that multi-destination
   MTU-probe and MTU-ack TRILL IS-IS PDUs are sent on Ethernet links
   with the All-RBridges multicast address as the Outer.MacDA [Err3004].
   As TRILL IS-IS PDUs, when multicast on an Ethernet link, these multi-
   destination MTU-probe and MTU-ack PDUs MUST be sent to the All-IS-IS-
   RBridges multicast address.




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5.1.2 MTU PDU Processing

   As discussed in [RFC6325] and, in more detail, in [RFC7177], MTU-
   probe and MTU-ack PDUs MAY be unicast; however, Section 4.6 of
   [RFC6325] erroneously does not allow for this possibility [Err3003].
   It is corrected by replacing Item numbered "1" in Section 4.6.2 of
   [RFC6325] with the following quoted text to which TRILL Switches MUST
   conform:

   "1. If the Ethertype is L2-IS-IS and the Outer.MacDA is either All-
       IS-IS-RBridges or the unicast MAC address of the receiving
       RBridge port, the frame is handled as described in Section
       4.6.2.1"

   The reference to "Section 4.6.2.1" in the above quoted text is to
   that section in [RFC6325].



5.1.3 MTU Testing

   The last two sentences of Section 4.3.2 of [RFC6325] have errors
   [Err3053].  They currently read:

      "If X is not greater than Sz, then RB1 sets the "failed minimum
      MTU test" flag for RB2 in RB1's Hello.  If size X succeeds, and X
      > Sz, then RB1 advertises the largest tested X for each adjacency
      in the TRILL Hellos RB1 sends on that link, and RB1 MAY advertise
      X as an attribute of the link to RB2 in RB1's LSP."

   They should read:

      "If X is not greater than or equal to Sz, then RB1 sets the
      "failed minimum MTU test" flag for RB2 in RB1's Hello.  If size X
      succeeds, and X >= Sz, then RB1 advertises the largest tested X
      for each adjacency in the TRILL Hellos RB1 sends on that link, and
      RB1 MAY advertise X as an attribute of the link to RB2 in RB1's
      LSP."



5.2 Ethernet MTU Values

   originatingL1LSPBufferSize is the maximum permitted size of LSPs
   starting with and including the 0x83 Intradomain Routeing Protocol
   Discriminator byte.  In Layer 3 IS-IS, originatingL1LSPBufferSize
   defaults to 1492 bytes.  (This is because, in its previous life as
   DECnet Phase V, IS-IS was encoded using the SNAP SAP (Sub-Network
   Access Protocol Service Access Point) [RFC7042] format, which takes 8
   bytes of overhead and 1492 + 8 = 1500, the classic Ethernet maximum.


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   When standardized by ISO/IEC [IS-IS] to use Logical Link Control
   (LLC) encoding, this default could have been increased by a few bytes
   but was not.)

   In TRILL, originatingL1LSPBufferSize defaults to 1470 bytes.  This
   allows 27 bytes of headroom or safety margin to accommodate legacy
   devices with the classic Ethernet maximum MTU despite headers such as
   an Outer.VLAN.

   Assuming the campus-wide minimum link MTU is Sz, RBridges on Ethernet
   links MUST limit most TRILL IS-IS PDUs so that PDUz (the length of
   the PDU starting just after the L2-IS-IS Ethertype and ending just
   before the Ethernet Frame Check Sequence (FCS)) does not to exceed
   Sz.  The PDU exceptions are TRILL Hello PDUs, which MUST NOT exceed
   1470 bytes, and MTU-probe and MTU-ack PDUs that are padded by an
   amount that depends on the size being tested (which may exceed Sz).

   Sz does not limit TRILL Data packets.  They are only limited by the
   MTU of the devices and links that they actually pass through;
   however, links that can accommodate IS-IS PDUs up to Sz would
   accommodate, with a generous safety margin, TRILL Data packet
   payloads of (Sz - 24) bytes, starting after the Inner.VLAN and ending
   just before the FCS.

   Most modern Ethernet equipment has ample headroom for frames with
   extensive headers and is sometimes engineered to accommodate 9K byte
   jumbo frames.

























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6. TRILL Port Modes (Unchanged)

   Section 4.9.1 of [RFC6325] specifies four mode bits for RBridge ports
   but may not be completely clear on the effects of all combinations of
   bits in terms of allowed frame types.

   The table below explicitly indicates the effect of all possible
   combinations of the TRILL port mode bits.  "*" in one of the first
   four columns indicates that the bit can be either zero or one.  The
   following columns indicate allowed frame types.  The Disable bit
   normally disables all frames, but, as an implementation choice, some
   or all low-level Layer 2 control message can still be sent or
   received. Examples of Layer 2 control messages are those control
   frames for Ethernet identified in Section 1.4 of [RFC6325] or PPP
   link negotiation messages [RFC6361].

            +-+-+-+-+--------+-------+-------+-------+-------+
            |D| | | |        |       |       |       |       |
            |i| |A| |        |       | TRILL |       |       |
            |s| |c|T|        |native | Data  |       |       |
            |a| |c|r|        |ingress|       |       |       |
            |b|P|e|u|        |       |  LSP  |       |       |
            |l|2|s|n|Layer 2 |native |  SNP  | TRILL |  P2P  |
            |e|P|s|k|Control |egress |  MTU  | Hello | Hello |
            +-+-+-+-+--------+-------+-------+-------+-------+
            |0|0|0|0|  Yes   |  Yes  |  Yes  |  Yes  |  No   |
            +-+-+-+-+--------+-------+-------+-------+-------+
            |0|0|0|1|  Yes   |  No   |  Yes  |  Yes  |  No   |
            +-+-+-+-+--------+-------+-------+-------+-------+
            |0|0|1|0|  Yes   |  Yes  |  No   |  Yes  |  No   |
            +-+-+-+-+--------+-------+-------+-------+-------+
            |0|0|1|1|  Yes   |  No   |  No   |  Yes  |  No   |
            +-+-+-+-+--------+-------+-------+-------+-------+
            |0|1|0|*|  Yes   |  No   |  Yes  |  No   |  Yes  |
            +-+-+-+-+--------+-------+-------+-------+-------+
            |0|1|1|*|  Yes   |  No   |  No   |  No   |  Yes  |
            +-+-+-+-+--------+-------+-------+-------+-------+
            |1|*|*|*|Optional|  No   |  No   |  No   |  No   |
            +-+-+-+-+--------+-------+-------+-------+-------+

   The formal name of the "access bit" above is the "TRILL traffic
   disable bit". The formal name of the "trunk bit" is the "end-station
   service disable bit" [RFC6325].









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7. The CFI/DEI Bit (Unchanged)

   In May 2011, the IEEE promulgated IEEE Std 802.1Q-2011, which changed
   the meaning of the bit between the priority and VLAN ID bits in the
   payload of C-VLAN tags.  Previously, this bit was called the CFI
   (Canonical Format Indicator) bit [802] and had a special meaning in
   connection with IEEE 802.5 (Token Ring) frames.  Now, after
   802.1Q-2011 and in subsequent versions the current of which is
   [802.1Q-2014], it is a DEI (Drop Eligibility Indicator) bit, similar
   to that bit in S-VLAN/B-VLAN tags where this bit has always been a
   DEI bit.

   The TRILL base protocol specification [RFC6325] assumed, in effect,
   that the link by which end stations are connected to TRILL Switches
   and the restricted virtual link provided by the TRILL Data packet are
   IEEE 802.3 Ethernet links on which the CFI bit is always zero.
   Should an end station be attached by some other type of link, such as
   a Token Ring link, [RFC6325] implicitly assumed that such frames
   would be canonicalized to 802.3 frames before being ingressed, and
   similarly, on egress, such frames would be converted from 802.3 to
   the appropriate frame type for the link.  Thus, [RFC6325] required
   that the CFI bit in the Inner.VLAN, which is shown as the "C" bit in
   Section 4.1.1 of [RFC6325], always be zero.

   However, for TRILL Switches with ports conforming to the change
   incorporated in the IEEE 802.1Q-2011 standard, the bit in the
   Inner.VLAN, now a DEI bit, MUST be set to the DEI value provided by
   the port interface on ingressing a native frame.  Similarly, this bit
   MUST be provided to the port when transiting or egressing a TRILL
   Data packet.  As with the 3-bit Priority field, the DEI bit to use in
   forwarding a transit packet MUST be taken from the Inner.VLAN.  The
   exact effect on the Outer.VLAN DEI and priority bits and whether or
   not an Outer.VLAN appears at all on the wire for output frames may
   depend on output port configuration.

   TRILL campuses with a mixture of ports, some compliant with versions
   of 802.1Q from IEEE Std 802.1Q-2011 onward and some compliant with
   pre-802.1Q-2011 standards, especially if they have actual Token Ring
   links, may operate incorrectly and may corrupt data, just as a
   bridged LAN with such mixed ports and links would.












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8. Other IS-IS Considerations (Changed)

   This section covers E-L1FS Support, Control Packet Priorities,
   Unknown PDUs, the Nickname Flags APPsub-TLV, Graceful Restart, and
   Purge Originator Identification.



8.1 E-L1FS Support (New)

   TRILL switches MUST support Extended Level 1 Flooding Scope PDUs (E-
   L1FS) [RFC7356] and MUST include a Scoped Flooding Support TLV
   [RFC7356] in all TRILL Hellos they send indicating support for this
   scope and any other FS-LSP scopes that they support. This support
   increases the number of fragments available for link state
   information by over two orders of magnitude. (See Section 9 for
   further information on support of the Scoped Flooding Support TLV.)

   In addition, TRILL switches MUST advertise their support of E-L1FS
   flooding in a TRILL Version sub-TLV capability bit (see [RFC7176] and
   Section 12.2).  This bit is used by a TRILL switch, say RB1, to
   determine support for E-L1FS by some remote RBx. The alternative of
   simply looking for an E-L1FS FS-LSP originated by RBx fails because
   (1) RBx might support E-L1FS flooding but not be originating any E-
   L1FS FS-LSPs and (2) even if RBx is originating E-L1FS FS-LSPs there
   might, due to legacy TRILL switches in the campus, be no path between
   RBx and RB1 through TRILL switches supporting E-L1FS flooding. If
   that were the case, no E-L1FS FS-LSP originated by RBx could get to
   RB1.

   E-L1FS will commonly be used to flood TRILL GENINFO TLVs and enclosed
   TRILL APPsub-TLVs [RFC7357]. For robustness, E-L1FS fragment zero
   MUST NOT exceed 1470 bytes in length; however, if such a fragment is
   received that is larger, it is processed normally. It is anticipated
   that in the future, some particularly important TRILL APPsub-TLVs
   will be specified as being flooded in E-L1FS fragment zero. TRILL
   GENINFO TLVs MUST NOT be sent in LSPs; however, if one is received in
   an LSP, it is processed normally.



8.1.1 Backward Compatibility

   A TRILL campus might contain TRILL switches supporting E-L1FS
   flooding and legacy TRILL switches that do not support E-L1FS or
   perhaps do not support any [RFC7356] scopes.

   A TRILL switch conformant to this document can always tell which
   adjacent TRILL switches support E-L1FS flooding from the adjacency
   table entries on its ports (see Section 9). In addition, such a TRILL


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   switch can tell which remote TRILL switches in a campus support E-
   L1FS by the presence of a TRILL Version sub-TLV in that TRILL
   switch's LSP with the E-L1FS support bit set in the Capabilities
   field; this capability bit is ignored for adjacent TRILL switches for
   which only the adjacency table entry is consulted to determine E-L1FS
   support.

   TRILL specifications making use of E-L1FS MUST specify how situations
   involving mixed TRILL campus of TRILL switches will be handled.



8.1.2 E-L1FS Use for Existing (sub)TLVs

   In a campus where all TRILL switches support E-L1FS, all TRILL sub-
   TLVs listed in Section 2.3 of [RFC7176], except the TRILL Version
   sub-TLV, MAY be advertised by inclusion in Router Capability or MT-
   Capability TLVs in E-L1FS FS-LSPs [RFC7356]. (The TRILL Version sub-
   TLV still MUST appear in an LSP fragment zero.)

   In a mixed campus where some TRILL switches support E-L1FS and some
   do not, then only the following four sub-TLVs of those listed in
   Section 2.3 of [RFC7176] can appear in E-L1FS and then only under the
   conditions discussed below. In the following list, each sub-TLV is
   preceded by an abbreviated acronym used only in this Section 8.1.2:

      IV:  Interested VLANs and Spanning Tree Roots sub-TLV
      VG:  VLAN Groups sub-TLV
      IL:  Interested Labels and Spanning Tree Roots sub-TLV
      LG:  Label Groups sub-TLV

   An IV or VG sub-TLV MUST NOT be advertised by TRILL switch RB1 in an
   E-L1FS FS-LSP (instead being advertised in an LSP) unless the
   following conditions are met:
   -  E-L1FS is supported by all of the TRILL switches that are data
      reachable from RB1 and are interested in the VLANs mentioned in
      the IV or VG sub-TLV, and
   -  there is E-L1FS connectivity between all such TRILL switches in
      the campus interested in the VLANs mentioned in the IV or VG sub-
      TLV (connectivity involving only intermediate TRILL switches that
      also support E-L1FS).

   Any IV and VG sub-TLVs MAY still be advertised via core TRILL IS-IS
   LSP by any TRILL switch that has enough room in its LSPs.

   The conditions for using E-L1FS for the IL and LG sub-TLVs are the
   same as for IV and VG but with Fine Grained Labels [RFC7172]
   substituted for VLANs.

      Note, for example, that the above would permit a contiguous subset


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      of the campus that supported Fine Grained Labels and E-L1FS to use
      E-L1FS to advertise IL and LG sub-TLVs even if the remainder of
      the campus did not support Fine Grained Labels or E-L1FS.



8.2 Control Packet Priorities (New)

   When deciding what packet to send out a port, control packets used to
   establish and maintain adjacency between TRILL switches SHOULD be
   treated as being in the highest priority category. This includes
   TRILL IS-IS Hello and MTU PDUs and possibly other adjacency [RFC7177]
   or link technology specific packets. Other control and data packets
   SHOULD be given lower priority so that a flood of such other packets
   cannot lead to loss of or inability to establish adjacency. Loss of
   adjacency causes a topology transient that can result in reduced
   throughput, re-ordering, increased probability of loss of data, and,
   in the worst case, if the adjacency is a cut point, network
   partition.

   Other important control packets should be given second highest
   priority. Lower priorities should be given to data or less important
   control packets.

   Based on the above, control packets can be ordered into priority
   categories as shown below based on the relative criticality of these
   types of messages, where the most critical relate to the core routing
   between TRILL switches and the less critical are closer to
   "application" information.  (There may be additional control packets,
   not specifically listed in any category below, that SHOULD be handled
   as being in the most nearly analogous category.)  Although few
   implementations will actually treat these four categories with
   different priority, an implementation MAY choose to prioritize more
   critical messages over less critical.  However, an implementation
   SHOULD NOT send control packets in a lower priority category with a
   priority above those in a higher priority category as, under
   sufficiently congested conditions, this could block control packets
   in a higher priority category, resulting in network disruption.

      Priority
      Category   Description
      --------  --------------

      4.        Hello, MTU-probe, MTU-ack, and other packets critical to
                establishing and maintaining adjacency. (Normally sent
                with highest priority 7.)

      3.        LSPs, CSNP/PSNPs, and other important control packets,

      2.        Circuit scoped FS-LSP, FS-CSNP, and FS-PSNPs.


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      1.        Non-circuit scoped FS-LSP, FS-CSNP, and FS-PSNPs.



8.3 Unknown PDUs (New)

   TRILL switches MUST silently discard [IS-IS] PDUs they receive with
   PDU numbers they do not understand, just as they ignore TLVs and sub-
   TLVs they receive that have unknown Types and sub-Types; however,
   they SHOULD maintain a counter of how many such PDUs have been
   received, on a per PDU number basis. (This is not burdensome as the
   PDU number is only a 5-bit field.)

      Note: The set of valid [IS-IS] PDUs was stable for so long that
         some IS-IS implementations may treat PDUs with unknown PDU
         numbers as a serious error and, for example, an indication that
         other valid PDUs from the sender are not to be trusted or that
         they should drop adjacency to the sender if it was adjacent.
         However, the MTU-probe and MTU-ack PDUs were added by [RFC7176]
         and now [RFC7356] has added three more new PDUs.  While the
         authors of this document are not aware of any Internet drafts
         calling for further PDUs, the eventual addition of further new
         PDUs should not be surprising.



8.4 Nickname Flags APPsub-TLV (New)

   An optional Nickname Flags APPsub-TLV within the TRILL GENINFO TLV
   [RFC7357] is specified below.

                           1 1 1 1 1 1
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Type = NickFlags (#tbd2)      |   (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Length = 4*K                  |   (2 bytes)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   NICKFLAG RECORD 1               (4 bytes)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   NICKFLAG RECORD K               (4 bytes)                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Where each NICKFLAG RECORD has the following format:






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        0  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      |   Nickname                                    |
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
      |IN|      RESV                                  |
      +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

      o  Type: NickFlags TRILL APPsub-TLV, set to tbd2 (NICKFLAGS)

      o  Length: 4 times the number of NICKFLAG RECORDS present.

      o  Nickname: A 16-bit TRILL nickname held by the advertising TRILL
         switch ([RFC6325] and Section 4).

      o  IN: Ingress. If this flag is one, it indicates the advertising
         TRILL switch may use the nickname in the NICKFLAG RECORD as the
         ingress nickname of TRILL Headers it creates. If the flag is
         zero, that nickname will not be used for that purpose.

      o  RESV: Reserved for additional flags to be specified in the
         future.  MUST be sent as zero and ignored on receipt.

   The entire NickFlags APPsub-TLV is ignored if the Length is not a
   multiple of 4.  A NICKFLAG RECORD is ignored if the nickname it lists
   is not a nickname owned by the TRILL switch advertising the enclosing
   NickFlags APPsub-TLV.

   If a TRILL switch intends to use a nickname in the ingress nickname
   field of TRILL Headers it constructs, it can advertise this through
   E-L1FS FS-LSPs (see Section 8.1) using a NickFlags APPsub-TLV entry
   with the IN flag set. If it owns only one nickname, there is no
   reason to do this because, if a TRILL switch advertises no NickFlags
   APPsub-TLVs with the IN flag set for nicknames it owns, it is assumed
   that the TRILL switch might use any or all nicknames it owns as the
   ingress nickname in TRILL Headers it constructs. If a TRILL switch
   advertises any NickFlags APPsub-TLV entries with the IN flag set,
   then it MUST NOT use any other nickname(s) it owns as the ingress
   nickname in TRILL Headers it constructs.

   Every reasonable effort should be made to be sure that Nickname sub-
   TLVs [RFC7176] and NickFlags APPsub-TLVs remain in sync. If all TRILL
   switches in a campus support E-L1FS, so that Nickname sub-TLVs can be
   advertised in E-L1FS FS-LSPs, then the Nickname sub-TLV and any
   NickFlags APPsub-TLVs for any particular nickname SHOULD be
   advertised in the same fragment. If they are not in the same fragment
   then, to the extent practical, all fragments involving those sub-TLVs
   for the same nickname should be propagated as an atomic action. If a
   TRILL switch sees multiple NickFlags APPsub-TLV entries for the same
   nickname, it assumes that nickname might be used as the ingress in a
   TRILL Header if any of the NickFlags APPsub-TLV entries have the IN


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   bit set.

   It is possible that a NickFlags APPsub-TLV would not be propagated
   throughout the TRILL campus due to legacy TRILL switches not
   supporting E-L1FS. In that case, Nickname sub-TLVs MUST be advertised
   in LSPs and TRILL switches not receiving NickFlags APPsub-TLVs having
   entries with the IN flag set will simply assume that the source TRILL
   switch might use any of its nicknames as ingress in constructing
   TRILL Headers. Thus the use of this optional APPsub-TLV is backwards
   compatible with legacy lack of E-L1FS support.

   (Additional flags are assigned from those labeled RESV above and
   specified in [irb] and [centralized-replication], works in progress.)



8.5 Graceful Restart (Unchanged)

   TRILL Switches SHOULD support the features specified in [RFC5306],
   which describes a mechanism for a restarting IS-IS router to signal
   to its neighbors that it is restarting, allowing them to reestablish
   their adjacencies without cycling through the down state, while still
   correctly initiating link-state database synchronization. If this
   feature is not supported, it may increase the number of topology
   transients cause by a TRILL switch rebooting due to errors or
   maintenance.



8.6 Purge Originator Identification (New)

   To ease debugging of any purge related problems, TRILL switches
   SHOULD include the Purge Originator Identification TLV [RFC6232] in
   all purge PDUs in TRILL IS-IS including Flooding Scoped purges
   [RFC7356] and in ESADI [RFC7357].

















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9. Updates to [RFC7177] (Adjacency) (Changed)

   To support the E-L1FS flooding scope [RFC7356] mandated by Section
   8.1 and backwards compatibility with legacy RBridges not supporting
   E-L1FS flooding, the following changes are made to [RFC7177]:

   1. The list in the second paragraph of [RFC7177] Section 3.1 has the
      following item added:

      -  The Scoped Flooding Support TLV.

   In addition, the sentence immediately after that list is modified to
      read as follows:

      Of course, the priority, Desired Designated VLAN, Scoped Flooding
      Support TLV, and possibly the inclusion or value of the PORT-
      TRILL-VER sub-TLV, and/or BFD-Enabled TLV could change on
      occasion, but then the new value(s) must similarly be used in all
      TRILL Hellos on the LAN port, regardless of VLAN.

   2. An additional bullet item is added to the end of Section 3.2 of
      [RFC7177] as follows:

      o  The value from the Scoped Flooding Support TLV or a null string
         if none was included.

   3. Near the bottom of Section 3.3 of [RFC7177] a bullet item as
      follows is added:

      o  The variable length value part of the Scoped Flooding Support
         TLV in the Hello or a null string if that TLV does not occur in
         the Hello.

   4. At the beginning of Section 4 of [RFC7177], a bullet item is added
      to the list as follows:

      o  The variable length value part of the Scoped Flooding Support
         TLV used in TRILL Hellos sent on the port.

   5. Add a line to Table 4: TRILL Hello Contents in Section 9.1 of
      [RFC7177] as follows:

         LAN  P2P  Number  Content Item
         ---  ---  ------  -----------------------------

          M    M     1      Scoped Flooding Support TLV






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10. TRILL Header Update (New)

   The TRILL header has been updated from its original specification in
   [RFC6325] by [RFC7455] and [RFC7179] and is further updated by this
   document.  The TRILL header is now as shown in the figure below which
   is followed by references for all of the fields. Those fields for
   which the reference is only to [RFC6325] are unchanged from that RFC.

                                   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                   | V |A|C|M| RESV  |F| Hop Count |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Egress Nickname             |   Ingress Nickname            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   :   Optional Flag Word                                          :
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   In calculating a TRILL Data packet hash as part of equal-cost multi-
   path selection, a TRILL switch MUST ignore the value of the "A" and
   "C" bits.

   In [RFC6325] and [RFC7179] there is an "Ex-Length" or TRILL Header
   Extensions Length field which is hereby changed to consist of the
   RESV and F fields above.

   o  V (Version): 2-bit unsigned integer. See Section 3.2 of [RFC6325].

   o  A (Alert): 1 bit. See [RFC7455].

   o  C (Color): 1 bit. See Section 10.1.

   o  M (Multi-destination): 1 bit. See Section 3.4 of [RFC6325].

   o  RESV: 4 bits. These bits are reserved and MUST be sent as zero.
      Due to the previous use of these bits specified in [RFC6325], most
      TRILL fast path hardware implementations trap and do not forward
      TRILL Data packets with these bits non-zero. A TRILL switch
      receiving a TRILL Data packet with any of these bits non-zero MUST
      discard the packet unless the non-zero bit or bits have some
      future use specified that the TRILL switch understands.

   o  F: 1 bit. If this field is non-zero, then the optional Flag Word
      described in Section 10.2 is present. If it is zero, the Flag Word
      is not present.

   o  Hop Count: 6 bits. See Section 3.6 of [RFC6325] and Section 10.2.1
      below.

   o  Egress Nickname. See Section 3.7.1 of [RFC6325].

   o  Ingress Nickname. See Section 3.7.2 of [RFC6325].


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   o  Optional Flag Word: See [RFC7179] and Section 10.2.



10.1 Color Bit

   The Color bit provides an optional way ingress TRILL switches MAY
   mark TRILL Data packets for implementation specific purposes.
   Transit TRILL switches MUST NOT change this bit. Transit and egress
   TRILL switches MAY use the Color bit for implementation dependent
   traffic labeling or statistical or other traffic study or analysis.



10.2 Flag Word Changes (update to [RFC7179])

   When the F bit in the TRILL Header is non-zero, the first 32 bits
   after the Ingress nickname field provides additional flags. These
   bits are as specified in [RFC7179] except as changed by the
   subsections below that provide extended Hop Count and extended Color
   fields. See Section 10.3 for a diagram and summary of these fields.



10.2.1 Extended Hop Count

   The TRILL base protocol [RFC6325] specifies the Hop Count field in
   the header, to avoid packets persisting in the network due to looping
   or the like. However, the Hop Count field size (6 bits) limits the
   maximum hops a TRILL Data packet can traverse to 64. Optionally,
   TRILL switches can use a field composed of bits 14 through 16 in the
   Flag Word, as specified below, to extend this field to 9 bits. This
   increases the maximum Hop Count to 512. Except in rare circumstances,
   reliable use of Hop Counts in excess of 64 requires support of this
   optional capability at all TRILL switches along the path of a TRILL
   Data packet.



10.2.1.1 Advertising Support

   In case of a TRILL campus such that the unicast calculated path, plus
   a reasonable allowance for alternate pathing, or the distribution
   tree calculated path, traverse more than 64 hops, it may be that not
   all the TRILL switches support the extended Hop Count mechanism. As
   such it is required that TRILL switches advertise their support by
   setting bit 14 in the TRILL Version Sub-TLV Capabilities and Header
   Flags Supported field [RFC7176]; bits 15 and 16 of that field are now
   specified as Unassigned (see Section 12.2.5).



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10.2.1.2 Ingress Behavior

   If an ingress TRILL switch determines it should set the hop count for
   a TRILL Data packet to 63 or less, then behavior is as specified in
   the TRILL base protocol [RFC6325]. If the optional TRILL Header Flag
   Word is present, bits 14, 15, and 16 and the Critical Reserved bit of
   the Critical Summary Bits are zero.

   If the hop count for a TRILL Data packet should be set to some value
   greater than 63 but less than 512 and all TRILL switches that the
   packet is reasonably likely to encounter support extended Hop Count,
   then the resulting TRILL Header has the Flag Word extension present,
   the high order three bits of the desired hop count are stored in the
   extended Hop Count field in the Flag Word, the five low order bits
   are stored in the Hop Count field in the first word of the TRILL
   Header, and bit two (the Critical Reserved bit of the Critical
   Summary Bits) in the Flag Word is set to one.

   For known unicast traffic (TRILL Header M bit zero), an ingress TRILL
   switch discards the frame if it determines that the least cost path
   to the egress is (1) more than 64 hops and not all TRILL switches on
   that path support the extended Hop Count feature or (2) more than 512
   hops.

   For multi-destination traffic, when a TRILL switch determines that
   one or more tree paths from the ingress are more than 64 hops and not
   all TRILL switches in the campus support the extended Hop Count
   feature, the encapsulation uses a total Hop Count of 63 to obtain at
   least partial distribution of the traffic.



10.2.1.3 Transit Behavior

   A transit TRILL switch supporting extended Hop Count behaves like a
   base protocol [RFC6325] TRILL switch in decrementing the hop count
   except that it considers the hop count to be a 9 bit field where the
   extended Hop Count field constitutes the high order three bits.

   To be more precise: a TRILL switch supporting extended Hop Count
   takes the first of the following actions that is applicable:

   1. If both the Hop Count and extended Hop Count fields are zero, the
      packet is discarded.

   2. If the Hop Count is non-zero, it is decremented. As long as the
      extended Hop Count is non-zero, no special action is taken. If the
      result of this decrement is zero, the packet is processed
      normally.



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   3. If the Hop Count is zero, it is set to the maximum value of 63 and
      the extended Hop Count is decremented. If this results in the
      extended Hop Count being zero, the Critical Reserved bit in the
      Critical Summary bits is set to zero.



10.2.1.4 Egress Behavior

   No special behavior is required when egressing a TRILL Data packet
   that uses the extended Hop Count. The Flag Word, if present, is
   removed along with the rest of the TRILL Header during decapsulation.



10.2.2 Extended Color Field

   Flag Word bits 27 and 28 are specified to be a two-bit Extended Color
   field (see Section 10.3). These bits are in the non-critical ingress-
   to-egress region of the Flag Word.

   The Extended Color field provides an optional way by which ingress
   TRILL switches MAY mark TRILL Data packets for implementation
   specific purposes. Transit TRILL switches MUST NOT change these bits.
   Transit and egress TRILL switches MAY use the Extended Color bits for
   implementation dependent traffic labeling or statistical or other
   traffic study or analysis.

   As provided in Section 2.3.1 of [RFC7176], support for these bits is
   indicated by the same bits (27 and 28) in the Capabilities and Header
   Flags Supported field of the TRILL Version Sub-TLV. If these bits are
   zero in those capabilites, Extended Color is not supported. A TRILL
   switch that does not support Extended Color will ignore the
   corresponding bits in any TRILL Header Flag Word it receives as part
   of a TRILL Data Packet and will set those bits to zero in any TRILL
   Header Flag word it creates. A TRILL switch that sets or senses the
   Extended Color field on transmitting or receiving TRILL Data packets
   MUST set the corresponding 2-bit field in the TRILL Version Sub-TLV
   non-zero. Any difference in meaning of the three possible non-zero
   values of this 2-bit capability field (0b01, 0b10 or 0b11) is
   implementation dependent.



10.3 Updated Flag Word Summary

   With the changes above, the 32-bit Flag Word extension to the TRILL
   Header [RFC7179], appearing as the "TRILL Extended Header Flags"
   registry on the TRILL Parameters IANA web page, is now as follows:



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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Crit.|  CHbH   |   NCHbH   |CRSV | NCRSV |   CItE    |  NCItE  |
   |.....|.........|...........|.....|.......|...........|.........|
   |C|C|C|       |C|N|         | Ext |       |           |Ext|     |
   |R|R|R|       |R|C|         | Hop |       |           |Clr|     |
   |H|I|R|       |C|C|         | Cnt |       |           |   |     |
   |b|t|s|       |A|A|         |     |       |           |   |     |
   |H|E|v|       |F|F|         |     |       |           |   |     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Bit 0 to 2 are the Critical Summary bits as specified in [RFC7179]
   consisting of the Critical Hop-by-Hop, Critical Ingres-to-Egress, and
   Critical Reserved bits, respectively. The next two fields are
   specific Critical and Non-Critical Hop-by-Hop bits, CHbH and NCHbH,
   respectively, containing the Critical and Non-Critical Channel Alert
   flags as specified in [RFC7179]. The next field is the Critical
   Reserved bits (CRSV) that are specified herein to be the Extended Hop
   Count. Then the Non-Critical Reserved Bits (NCRSV) and the Critical
   Ingress-to-Egress bits (CITE) as specified in [RFC7179]. Finally,
   there is the Non-Critical Ingress-to-Egress field including bits 27
   and 28 that are specified herein as the Extended Color field.





























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11. Appointed Forwarder Status Lost Counter (New)

   Strict conformance to the provisions of Section 4.8.3 of [RFC6325] on
   the value of the Appointed Forwarder Status Lost Counter can result
   in splitting of Interested VLANs and Spanning Tree Roots sub-TLVs
   [RFC7176] (or the corresponding Interested Labels sub-TLVs where a
   VLAN is mapped to an FGL) due to differences in this counter value
   for adjacent VLAN IDs (or 24-bit FGLs). This counter is a mechanism
   to optimize data plane learning by trimming the expiration timer for
   learned addresses on a per VLAN/FGL basis under some circumstances.

   The requirement to increment this counter by one whenever a TRILL
   switch loses appointed forwarder status on a port is hereby changed
   from the mandatory provisions of [RFC6325] to the enumerated
   provisions below.  To the extent that this might cause the Appointed
   Forwarder Status Lost Counter to be increased when [RFC6325]
   indicates it should not, this will cause data plane address learning
   timeouts at remote TRILL switches to be reduced.  To the extent that
   this might cause the Appointed Forwarder Status Lost Counter to
   remain unchanged when [RFC6325] indicate it should be increased, this
   will defeat a reduction in such timeouts that would otherwise occur.

   (1) If any of the following apply, either data plane address learning
       is not in use or Appointed Forwarder status is irrelevant. In
       these cases the Appointed Forwarder Status Lost Counter MAY be
       left zero or set to any convenient value such as the value of the
       Appointed Forwarder Status Lost Counter for an adjacent VLAN ID
       or FGL.

       (1a) The TRILL switch port has been configured with the "disable
       end station traffic" bit on (also known as the trunk bit).

       (1b) The TRILL switch port has been configured in IS-IS as an IS-
       IS point-to-point link.

       (1C) If the TRILL switch is relying on ESADI [RFC7357] or
       Directory Assist [RFC7379] and not using data plane learning.

   (2) In cases other than those numerated in point 1 above, the
       Appointed Forwarder Status Lost Counter SHOULD be incremented as
       described in [RFC6325]. Such incrementing has the advantage of
       optimizing data plane learning. Alternatively, the value of the
       Appointed Forwarder Status Lost Counters can deviate from that
       value, for example to make it match the value for an adjacent
       VLAN ID (or FGL), so as to permit greater aggregation of
       Interested VLANs and Spanning Tree Roots sub-TLVs.






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12. IANA Considerations (Changed)

   This section gives IANA actions previously completed and new IANA
   actions.



12.1 Previously Completed IANA Actions (Unchanged)

   The following IANA actions were completed as part of [RFC7180] and
   are included here for completeness, since this document obsoletes
   [RFC7180].

   1. The nickname 0xFFC1, which was reserved by [RFC6325], is allocated
      for use in the TRILL Header Egress Nickname field to indicate an
      OOMF (Overload Originated Multi-destination Frame).

   2. Bit 1 from the seven previously reserved (RESV) bits in the per-
      neighbor "Neighbor RECORD" in the TRILL Neighbor TLV [RFC7176] is
      allocated to indicate that the RBridge sending the TRILL Hello
      volunteers to provide the OOMF forwarding service described in
      Section 2.4.2 to such frames originated by the TRILL Switch whose
      SNPA (MAC address) appears in that Neighbor RECORD.  The
      description of this bit is "Offering OOMF service".

   3. Bit 0 is allocated from the Capability bits in the PORT-TRILL-VER
      sub-TLV [RFC7176] to indicate support of the VLANs Appointed sub-
      TLV [RFC7176] and the VLAN inhibition setting mechanisms specified
      in [rfc6439bis].  The description of this bit is "Hello reduction
      support".



12.2 New IANA Actions (New)

   The following are new IANA actions for this document:



12.2.1 Reference Updated

   All references to [RFC7180] in the TRILL Parameters Registry are
   replaced with references to this document except that the Reference
   for bit 0 in the PORT-TRILL-VER Sub-TLV Capability Flags is changed
   to [rfc6439bis].







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12.2.2 The 'E' Capability Bit

   There is an existing TRILL Version sub-TLV, sub-TLV #13 under both
   TLV #242 and TLV #144 [RFC7176]. This TRILL Version sub-TLV contains
   a capability bits field for which assignments are documented in the
   "TRILL-VER Sub-TLV Capability Flags" registry on the TRILL Parameters
   IANA web page.  IANA has allocated tbd1 from the previous reserved
   bits in this TRILL-VER Sub-TLV Capability Flags registry to indicate
   support of the E-L1FS flooding scope as specified in Section 8.1.
   This capability bit is referred to as the "E" bit. The following is
   the addition to the TRILL-VER Sub-TLV Capability Flags registry:

        Bit     Description             References
        ----   ---------------------   ---------------
        tbd1   E-L1FS FS-LSP support   [this document][RFC7356]



12.2.3 NickFlags APPsub-TLV Number and Registry

   IANA has assigned tbd2 APPsub-TLV number under the TRILL GENINFO TLV
   from the range less than 255.

        Type      Name           References
        ----    ---------       -----------
        tbd2    NICKFLAGS       [this document]

   In addition, IANA has created a registry on the TRILL Parameters web
   page for NickFlags bit assignments as follows:

        Name: NickFlags Bits
        Registration Procedure: IETF Review
        Reference: [this document]

         Bit   Mnemonic  Description      Reference
        -----  --------  -----------      ---------
         0       IN      Used as ingress  [this document]
        1-15      -      Unassigned       [this document]



12.2.4 Updated TRILL Extended Header Flags

   Update the "TRILL Extended Header Flags" registry as follows:








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     Bits     Purpose                                     References
     -----   ------------------------------------------  ------------

     14-16   Extended Hop Count                          [this document]

     27-28   Extended Color                              [this document]

     29-31   Available non-critical ingress-to-egress flags
                                               [RFC7179] [this document]



12.2.5 TRILL-VER Sub-TLV Capability Flags

   Update the "TRILL-VER Sub-TLV Capability Flags" registry as follows:

      Bit    Description                   Reference
     -----  --------------------------    ----------------

        14  Extended Hop Count support     [this document]

     15-16  Unassigned                     [this document]

     27-28  Extended Color support         [this document]

     29-31  Extended header flag support   [RFC7179] [this document]



12.2.6 Example Nicknames

   IANA has assigned a block of four nicknames for use as examples in
   documentation such as in Appendix B below. The TRILL Nicknames
   registry has been updated by changing the previous "0xFFC2-0xFFFE
   Unassigned" line to the following:

         Name        Description                        Reference
     -------------  --------------                     -----------
     0xFFC2-0xFFD7  Unassigned
     0xFFD8-0xFFDF  For use in documentation examples  [this document]
     0xFFE0-0xFFFE  Unassigned











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13. Security Considerations (Changed)

   See [RFC6325] for general TRILL security considerations.

   This memo improves the documentation of the TRILL protocol, corrects
   five errata in [RFC6325], updates [RFC6325], [RFC7177], and [RFC7179]
   and obsoletes [RFC7180]. It does not change the security
   considerations of those RFCs except as follows:

   E-L1FS FS-LSPs can be authenticated with IS-IS security [RFC5310],
      that is, through the inclusion of an IS-IS Authentication TLV in
      E-L1FS PDUs.

   As discussed in Section 3.6, when using an allowed weaker RPF check
      under very rare topolgoies and transient conditions, multi-
      destination TRILL Data packets can be duplicated, which could have
      secuirty consequences for some protocols.



































D. Eastlake, et al                                             [Page 42]


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Normative References

   [802.1Q-2014] - IEEE, "IEEE Standard for Local and metropolitan area
         networks -- Media Access Control (MAC) Bridges and Virtual
         Bridged Local Area Networks", IEEE Std 802.1Q-2014, 19 December
         2014.

   [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)", Second Edition, November 2002.

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

   [RFC5305] - Li, T. and H. Smit, "IS-IS Extensions for Traffic
         Engineering", RFC 5305, October 2008.

   [RFC5306] - Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS",
         RFC 5306, October 2008.

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

   [RFC6232] - Wei, F., Qin, Y., Li, Z., Li, T., and J. Dong, "Purge
         Originator Identification TLV for IS-IS", RFC 6232, May 2011,
         <http://www.rfc-editor.org/info/rfc6232>.

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

   [RFC6361] - Carlson, J. and D. Eastlake 3rd, "PPP Transparent
         Interconnection of Lots of Links (TRILL) Protocol Control
         Protocol", RFC 6361, August 2011.

   [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, May 2014.

   [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, May 2014.

   [RFC7177] - Eastlake 3rd, D., Perlman, R., Ghanwani, A., Yang, H.,
         and V. Manral, "Transparent Interconnection of Lots of Links
         (TRILL): Adjacency", RFC 7177, May 2014.



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   [RFC7179] - Eastlake 3rd, D., Ghanwani, A., Manral, V., Li, Y., and
         C. Bestler, "Transparent Interconnection of Lots of Links
         (TRILL): Header Extension", RFC 7179, May 2014,
         <http://www.rfc-editor.org/info/rfc7179>.

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

   [RFC7455] - Senevirathne, T., Finn, N., Salam, S., Kumar, D.,
         Eastlake 3rd, D., Aldrin, S., and Y. Li, "Transparent
         Interconnection of Lots of Links (TRILL): Fault Management",
         RFC 7455, March 2015, <http://www.rfc-editor.org/info/rfc7455>.



Informative References

   [802] - IEEE 802, "IEEE Standard for Local and metropolitan area
         networks: Overview and Architecture", IEEE Std 802.1-2014, 12
         June 2014.

   [centralized-replication] - Weiguo Hao, et al., "Centralized
         Replication for BUM traffic in active-active edge connection",
         draft-ietf-trill-centralized-replication, Work in Progress.

   [irb] - Weiguo Hao, et al., "TRILL Distributed Layer 3 Gateway",
         draft-ietf-trill-irb, Work in Progress.

   [Err3002] - RFC Errata, Errata ID 3002, RFC 6325, <http://www.rfc-
         editor.org>.

   [Err3003] - RFC Errata, Errata ID 3003, RFC 6325, <http://www.rfc-
         editor.org>.

   [Err3004] - RFC Errata, Errata ID 3004, RFC 6325, <http://www.rfc-
         editor.org>.

   [Err3052] - RFC Errata, Errata ID 3052, RFC 6325, <http://www.rfc-
         editor.org>.

   [Err3053] - RFC Errata, Errata ID 3053, RFC 6325, <http://www.rfc-
         editor.org>.

   [Err3508] - RFC Errata, Errata ID 3508, RFC 6325, <http://rfc-
         editor.org>.

   [RFC826] - Plummer, D., "Ethernet Address Resolution Protocol: Or
         Converting Network Protocol Addresses to 48.bit Ethernet
         Address for Transmission on Ethernet Hardware", STD 37, RFC


D. Eastlake, et al                                             [Page 44]


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         826, November 1982, <http://www.rfc-editor.org/info/rfc826>.

   [RFC792] - Postel, J., "Internet Control Message Protocol", STD 5,
         RFC 792, September 1981, <http://www.rfc-
         editor.org/info/rfc792>.

   [RFC4086] - Eastlake 3rd, D., Schiller, J., and S. Crocker,
         "Randomness Requirements for Security", BCP 106, RFC 4086, June
         2005, <http://www.rfc-editor.org/info/rfc4086>.

   [RFC6327] - Eastlake 3rd, D., Perlman, R., Ghanwani, A., Dutt, D.,
         and V. Manral, "Routing Bridges (RBridges): Adjacency", RFC
         6327, July 2011, <http://www.rfc-editor.org/info/rfc6327>.

   [RFC6439] - Perlman, R., Eastlake, D., Li, Y., Banerjee, A., and F.
         Hu, "Routing Bridges (RBridges): Appointed Forwarders", RFC
         6439, November 2011, <http://www.rfc-editor.org/info/rfc6439>.

   [RFC7042] - Eastlake 3rd, D. and J. Abley, "IANA Considerations and
         IETF Protocol and Documentation Usage for IEEE 802 Parameters",
         BCP 141, RFC 7042, October 2013.

   [RFC7175] - Manral, V., Eastlake 3rd, D., Ward, D., and A. Banerjee,
         "Transparent Interconnection of Lots of Links (TRILL):
         Bidirectional Forwarding Detection (BFD) Support", RFC 7175,
         May 2014.

   [RFC7178] - Eastlake 3rd, D., Manral, V., Li, Y., Aldrin, S., and D.
         Ward, "Transparent Interconnection of Lots of Links (TRILL):
         RBridge Channel Support", RFC 7178, May 2014.

   [RFC7180] - Eastlake 3rd, D., Zhang, M., Ghanwani, A., Manral, V.,
         and A. Banerjee, "Transparent Interconnection of Lots of Links
         (TRILL): Clarifications, Corrections, and Updates", RFC 7180,
         May 2014.

   [RFC7357] - Zhai, H., Hu, F., Perlman, R., Eastlake 3rd, D., and O.
         Stokes, "Transparent Interconnection of Lots of Links (TRILL):
         End Station Address Distribution Information (ESADI) Protocol",
         RFC 7357, September 2014, <http://www.rfc-
         editor.org/info/rfc7357>.

   [RFC7379] - Li, Y., Hao, W., Perlman, R., Hudson, J., and H. Zhai,
         "Problem Statement and Goals for Active-Active Connection at
         the Transparent Interconnection of Lots of Links (TRILL) Edge",
         RFC 7379, October 2014, <http://www.rfc-
         editor.org/info/rfc7379>.

   [rfc6439bis] - Eastlake, D., et al., "TRILL: Appointed Forwarders",
         draft-eastlake-trill-rfc6439bis, work in progress.


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Acknowledgements

   The contributions of the following individuals to this document are
   gratefully acknowledged:

      Santosh Rajagopalan, Gayle Noble

   The contributions of the following, listed in alphabetic order, to
   the preceding version of this document, [RFC7180], are gratefully
   acknowledged:

      Somnath Chatterjee, Weiguo Hao, Rakesh Kumar, Yizhou Li, Radia
      Perlman, Mike Shand, Meral Shirazipour, and Varun Shah.

   The document was prepared in raw nroff. All macros used were defined
   within the source file.




































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Appendix A: Life Cycle of a TRILL Switch Port (New)

   The contents of this informational Appendix originated in
   http://www.ietf.org/mail-archive/web/trill/current/msg06355.html

   Question: Suppose we are developing a TRILL implementation to run on
      different machines. Then what happens first? Is LSP flooding or
      ESADI started first? -> Link state database creation -> Designated
      RBridge election (How to set priority? any fixed process that
      depends on user settings?  ) -> etc. ?

   Answer:

      The first thing that happens on a port/link is any link set-up
      that is needed. For example, on a PPP link [RFC6361], you need to
      negotiate that you will be using TRILL. However, if you have
      Ethernet links [RFC6325], which are probably the most common type,
      there isn't any link set-up needed.

      As soon as the port is set-up, it can ingress or egress native
      frames if end-station service is being offered on that port.
      Offering end-station service is the default; however, if the port
      trunk bit (end-station service disable) is set or the port is
      configured as an IS-IS point-to-point link port, then end-station
      service is not offered so native frames received are ignored and
      native frames are not egressed.

      Then TRILL IS-IS Hellos get sent out the port to be exchanged with
      any other TRILL switches on the link [RFC7177].  Optionally, you
      might also exchange MTU-probe/ack PDUs [RFC7177], BFD PDUs
      [RFC7175], or other link test packets. But all these other things
      are optional. Only Hellos are required.

      TRILL doesn't send any TRILL Data or TRILL IS-IS packets out the
      port to the link except Hellos until the link gets to the Two Way
      or Report state [RFC7177].

      If a link is configured as a point-to-point link, there is no
      Designated RBridge (DRB) election. By default, an Ethernet link is
      considered a LAN link and the DRB election occurs when the link is
      in any state other than Down.  You don't have to configure
      priorities for each TRILL switch (RBridge) to be Designated
      RBridge (DRB). Things will work fine with all the RBridges on a
      link using default priority.  But if the network manager wants to
      control this, there should be a way for them to configure the
      priority to be DRB of the TRILL switch ports on the link.

      (To avoid complexity, this appendix generally describes things for
      a link that only has two TRILL switches on it. But TRILL works
      fine as currently specified on a broadcast link with multiple


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      TRILL switches on it, actually multiple TRILL switch ports, since
      a TRILL switch can have multiple ports connected to the same link.
      The most likely way to get such a multi-access link with current
      technology and the existing TRILL standards is to have more than 2
      TRILL switch Ethernet ports connected to a bridged LAN. Since the
      TRILL protocol operates above all bridging, to the first
      approximation the bridge LAN looks like a transparent broadcast
      link to TRILL.)

      When a link gets to the 2-Way or Report state, then LSP, CSNP, and
      PSNP PDUs start to flow on the link (as well as FS-LSPs, FS-CSNPs,
      and FS-PSNPs for E-L1FS (see Section 8.1)).

      When a link gets to the Report state, then there is adjacency. The
      existence of that adjacency is flooded (reported) to the campus in
      LSPs. TRILL Data packets can then start to flow on the link as
      TRILL switches recalculate the least cost paths and distribution
      trees to take the new adjacency into account. Until it gets to the
      Report state, there is no adjacency and no TRILL Data packets can
      flow over that link (with the minor corner case exception that an
      RBridge Channel message can, for its first hop only, be sent on a
      port where there is no adjacency (Section 2.4 of [RFC7178]).
      (Although this paragraph seems to be talking about link state, it
      is actually port state. It is possible for different TRILL switch
      ports on the same link to temporarily be in different states. The
      adjacency state machinery runs independently on each port.)

      ESADI [RFC7357] is built on top of the regular TRILL Data routing.
      Since ESADI PDUs look, to transit TRILL switches, like regular
      TRILL Data packets, no ESADI PDUs can flow until adjacencies are
      established and TRILL Data is flowing. Of course, ESADI is
      optional and is not used unless configured...

   Question: Does it require TRILL Full headers at the time TRILL-LSPs
      start being broadcast on a link? Because at that time it's not
      defined Egress and Ingress nicknames.

   Answer:

      TRILL Headers are only for TRILL Data packets. TRILL IS-IS
      packets, such as TRILL-LSPs, are sent in a different way that does
      not use a TRILL Header and does not depend on nicknames.

      Probably, in most implementations, a TRILL switch will start up
      using the same nickname it had when it shut down or last got
      disconnected from a campus. If you want, you can implement TRILL
      to come up initially not reporting any nickname (by not including
      an Nickname sub-TLV in its LSPs) until you get the link state
      database or most of the link state database, and then choose a
      nickname no other TRILL switch in the campus is using. Of course,


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      if a TRILL switch does not have a nickname, then it cannot ingress
      data, cannot egress known unicast data, and cannot be a tree root.

      TRILL IS-IS PDUs such as LSPs, and the link state database, all
      work based on the 7-byte IS-IS System-ID (sometimes called the LAN
      ID [IS-IS]). System-IDs always have to be unique across the campus
      so there is no problem determining topology regardless of nickname
      state. The Nickname system is built on top of that.












































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Appendix B: Example TRILL PDUs (New)

   This appendix gives example TRILL IS-IS PDUs. The primary purpose of
   these examples is to clarify bit ordering issues.



B.1 LAN Hello over Ethernet

   A TRILL Hello sent from a TRILL switch (RBridge) with 7-byte System
   ID 0x30033003300300 holding nickname 0xFFDE over Ethernet from a port
   with MAC address 0x00005E0053DE on VLAN 1 at priority 7. There is one
   neighbor that is DRB. The neighbor's port MAC is 0x00005E0053E3 and
   the neighbor's System ID is 0x44444444444400.

      Ethernet Header
        Outer.MacDA, Outer.MacSA
          0x0180C2000041  All-IS-IS-RBridges Dest. MAC Addr.
          0x00005E0053DE  Source MAC Address
        Outer VLAN Tag (optional)
          0x8100          C-VLAN Ethertype [802.1Q]
          0xE001          Priority 7, Outer.VLAN
        IS-IS
          0x22F4          L2-IS-IS Ethertype
      IS-IS Payload
        Common Header
          0x83            Interdomain Routeing Discriminator
          0x08            Header Length
          0x01            IS-IS Version Number
          0x06            ID Length of 6 Octets
          0x0F            PDU Type (Level 1 LAN Hello)
          0x01            Version
          0x00            Reserved
          0x01            Maximum Area Addresses
        Hello PDU Specific Fields
          0x01            Circuit Type (Level 1)
          0x30033003300300 Source System ID
          0x0009          Holding Time
          0xXXXX          PDU Length
          0x40            Priority to be DRB
          0x44444444444400 LAN ID
        TLVs (the below order of TLVs or of sub-TLVs in a TLV
          is not significant.
        Area Addresses TLV
          0x01            Area Addresses Type
          0x02            Length of Value
          0x01            Length of Address
          0x00            The fixed TRILL Area Address




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        MT Port Capabilities TLV
          0x8F            MT Port Capabilities Type
          0x0011          Length of Value
          0x0000          Topology
            Special VLANs and Flags Sub-TLV
              0x01            Sub-TLV Type
              0x08            Length
              0x0123          Port ID
              0xFFDE          Sender Nickname
              0x0001          Outer.VLAN
              0x0001          Designated VLAN
            Enabled VLANs sub-TLV (optional)
              0x02            Sub-TLV Type
              0x03            Length
              0x0001          Start VLAN 1
              0x80            VLAN 1
        TRILL Neighbor TLV
          0x91            Neighbor Type
          0x0A            Length of Value
          0xC0            S & L Flags = 1, SIZE field 0
            NEIGHBOR RECORD
              0x00            Flags
              0x2328          MTU = 9K bytes
              0x00005E0053E3  Neighbor MAC Address
        Scoped Flooding Support TLV
        0xF3              Scoped Flooding Support Type
        0x01              Length of Value
        0x40              E-L1FS Flooding Scope
        More TLVs (optional)
          ...
      Ethernet Trailer
        0xXXXXXXXX      Ethernet Frame Check Sequence



B.2 LSP Over PPP

   Here is an example of a TRILL LSP PDU sent over a PPP link by the
   same source TRILL switch as the example in B.1.

      PPP Header
        0x405D          PPP TRILL Link State Protocol










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      IS-IS Payload
        Common Header
          0x83            Interdomain Routeing Discriminator
          0x08            Header Length
          0x01            IS-IS Version Number
          0x06            ID Length of 6 Octets
          0x12            PDU Type (Level 1 LSP)
          0x01            Version
          0x00            Reserved
          0x01            Maximum Area Addresses
        LSP Specific Fields
          0xXXXX          PDU Length
          0x0123          Remaining Lifetime
          0x3003300330030009 LSP ID (fragment 9)
          0x00001234      Sequence Number
          0xXXXX          Checksum
          0x01            Flags = Level 1
        TLVs (the below order of TLVs or of sub-TLVs in a TLV
          is not significant.
        Router Capability TLV
          0xF2            Router Capability Type
          0x0F            Length of Value
          0x00            Flags
            Nickname Sub-TLV
              0x06            Sub-TLV Type
              0x05            Length of Value
              NICKNAME RECORD
                0x33          Nickname Priority
                0x1234        Tree Root Priority
                0xFFDE        Nickname
            TRILL Version Sub-TLV
              0x0D            Sub-TLV Type
              0x05
              0x00            Max Version
              0x40000000      Flags = FGL Support
        More TLVs (optional
          ...
      PPP Trailer
        0xXXXXXX        PPP Frame Check Sequence



B.3 TRILL Data Over Ethernet

   Below is an IPv4 ICMP Echo [RFC792] sent in a TRILL Data packet from
   the TRILL switch that sent the Hello in B.1 to the neighbor TRILL
   switch on the link used in B.1.





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      Ethernet Header
        Outer.MacDA, Outer.MacSA
          0x00005E0053E3  Destination MAC Address
          0x00005E0053DE  Source MAC Address
        Outer VLAN Tag (optional)
          0x8100          C-VLAN Ethertype [802.1Q]
          0x0001          Priority 0, Outer.VLAN 1
        TRILL
          0x22F3          TRILL Ethertype
      TRILL Header
          0X000E          Flags, Hop Count 14
          0xFFDF          Egress Nickname
          0xFFDC          Ingress Nickname
      Inner Ethernet Header
        Inner.MacDA, Inner.MacSA
          0x00005E005322  Destination Mac Address
          0x00005E005344  Source Mac Address
        Inner VLAN Tag
          0x8100          C-VLAN Ethertype
          0x0022          Priority 0, Inner.VLAN 34
        Ethertype
          0x0800          IPv4 Ethertype
      IP Header
          0x4500          Version 4, Header Length 5, ToS 0
          0xXXXX          Total Length
          0x3579          Identification
          0x0000          Flags, Fragment Offset
          0x1101          TTL 17, ICMP = Protocol 1
          0xXXXX          Header Checksum
          0xC0000207      Source IP 192.0.2.7
          0xC000020D      Destination IP 192.0.2.13
          0x00000000      Options, Padding
      ICMP
          0x0800          ICMP Echo
          0xXXXX          Checksum
          0x87654321      Identifier, Sequence Number
          ...             Echo Data
      Ethernet Trailer
        0xXXXXXXXX      Ethernet Frame Check Sequence




B.4 TRILL Data Over PPP

   Below is an ARP [RFC826] sent in a TRILL Data packet from the TRILL
   switch that sent the Hello in B.1 over a PPP link.

      PPP Header
        0x005D          PPP TRILL Network Protocol


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      TRILL Header
          0X080D          Flags (M=1), Hop Count 13
          0xFFDD          Distribution Tree Root Nickname
          0xFFDC          Ingress Nickname
      Inner Ethernet Header
        Inner.MacDA, Inner.MacSA
          0xFFFFFFFFFFFF  Destination Mac Address
          0x00005E005344  Source Mac Address
        Inner VLAN Tag
          0x8100          C-VLAN Ethertype
          0x0022          Priority 0, Inner.VLAN 34
        Ethertype
          0x0806          ARP Ethertype
      ARP
          0x0001          Hardware Address Space = Ethernet
          0x0001          Protocol Address Space = IPv4
          0x06            Size of Hardware Address
          0x04            Size of Protocol Address
          0x0001          OpCode = Request
          0x00005E005344  Sender Hardware Address
          0xC0000207      Sender Protocol Address 192.0.2.7
          0x000000000000  Target Hardware Address
          0xC000020D      Target Protocol Address 192.0.2.13
      PPP Trailer
        0xXXXXXX        PPP Frame Check Sequence



























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Appendix C: Changes to Previous RFCs (New)



C.1 Changes to Obsoleted [RFC7180]

   This section summarizes the changes, augmentations, and excisions
   this document makes to [RFC7180] which it obsoletes and replaces.



C.1.1 Changes

   For each heading in this document ending with "(Changed)", this
   section summarizes how it was changed:

   Section 1, Introduction: numerous changes to reflect the overall
      changes in contents.

   Section 1.1, Precedence: changed to add mention of [RFC7179].

   Section 1.3, Terminology and Acronyms: numerous terms added.

   Section 3, Distribution Trees and RPF Check: changed by the addition
      of the new material in Section 3.6. See C.1.2 item 1.

   Section 8, Other IS-IS Considerations: Changed by the addition of
      Sections 8.1, 8.2, 8.3, and 8.4. See Appendix C.1.2 items 2, 3, 4,
      and 5 respectively.

   Section 9, Updates to [RFC7177] (Adjacency): Changes and additions to
      [RFC7177] to support E-L1FS. See Appendix C.1.2, item 2.

   Section 12, IANA Considerations: changed by the addition of material
      in Section 12.2. See Appendix C.1.2, item 7.

   Section 13, Security Considerations: minor changes in the RFCs
      listed.



C.1.2 Additions

   The following material was added to [RFC7180] in producing this
   document:







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    1. Addition of support for an alternative Reverse Path Forwarding
       Check (RPFC) along with considerations for deciding between the
       original [RFC6325] RPFC and this alternative RPFC. This
       alternative RPFC was originally discussed on the TRILL WG mailing
       list in http://www.ietf.org/mail-
       archive/web/trill/current/msg01852.html and subsequent messages.
       (Section 3.6)

    2. Addition of mandatory E-L1FS [RFC7356] support (Section 8.1,
       Section 9).

    3. Recommendations concerning control packet priorities. (Section
       8.2)

    4. Implementation requirements concerning unknown IS-IS PDU types
       (Section 8.3).

    5. Specification of an optional Nickname Flags APPsub-TLV and an
       ingress flag within that APPsub-TLV. (Section 8.4)

    6. Update TRILL Header to allocate a Color bit (Section 10.1) and
       update the optional TRILL Header Extension Flag Word to allocate
       a two-bit Extended Color field (Section 10.2).

    7. Some new IANA Considerations in Section 12.2 including
       reservation of nicknames for use as examples in documentation.

    8. Section 11 on the Appointed Forwarder Status Lost Counter,
       loosening mandatory update requirements in [rfc6325].

    9. Informative Appendix A on the Lifecycle of a TRILL Port.

   10. Add Appendix B with example TRILL PDUs.

   11. Add recommendation to use Purge Originator Identification TLV.
       (Section 8.6)



C.1.3 Deletions

   The following material was deleted from [RFC7180] in producing this
   document:

   1. Removal of all updates to [RFC6327] that occurred in [RFC7180].
      These have been rolled into [RFC7177] that obsoletes [RFC6327].
      However, new updates to [RFC7177] are included (see Item 1 in
      Section A.1).

   2. Removal of all updates to [RFC6439]. These have been rolled into


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      [rfc6439bis] that obsoletes [RFC6439].



C.2 Changes to [RFC6325]

   This document contains many normative changes to [RFC6325], some of
   which were in [RFC7180] that it replaces, including the following:

   1. Change nickname allocation to ignore conflicts with data-
      unreachable RBridges.

   2. Fix errors: [Err3002] [Err3003] [Err3004] [Err3052] [Err3053]
      [Err3508].

   3. Change for the requirement to use the RPF check in [RFC6325] for
      multi-destination TRILL Data packets by providing an alternative
      stronger RPF check.

   4. Adoption of the change of the CFI bit, which was required to be
      zero in the inner frame, to the DEI bit which is obtained from
      inner frame ingress or creation.

   5. Require all RBridge to support E-L1FS FS-LSPs flooding.

   6. The variable length TRILL Header extensions area is reduced to one
      optional flags word and the extensions length field reduced to one
      bit indicated that the flag word is present with the rest of the
      length field now reserved.

   7. Change the mandatory Appointed Forwarder Status Lost Counter
      increment provisions as specified in Section 11.



C.3 Changes to [RFC7177]

   All of the updates to [RFC7177] herein are in Section 9. Basically,
   this document requires a Scoped Flooding Support TLV [RFC7356] to
   appear in all Hellos and that TRILL switches retain in their
   adjacency state the information received in that TLV.



C.4 Changes to [RFC7179]

   The updates to [RFC7179] herein are in Sections 10.2 and 10.3.





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Appendix Z: Change History

   This appendix lists version changes in this document.

   RFC Ediotr: Please delete this Appendix before publicaton.

From -00 to -01:

   1. Expand Appendix C to cover changes to RFC 6325, RFC 7177, and RFC
      7179 as well as 7180 and add material to the Introduction on
      changes or previous RFCs.

   2. Add a paragraph just before the Section 8.1.1 header about the
      uses of E-L1FS FS-LSPs, the size limit on E-L1FS fragment zero,
      and handling of TRILL GENINFO TLVs.

   3. At the end of Section 9, add item 5 updating Table 4 in [RFC7177].

   4. In Section 12.2.3, add a Registry for NickFlags bits.

   5. Add Section 12.2.6 assigning nicknames for use as examples in
      documentation.

   6. Small improvements to the Security Considerations section.

   7. Augment and update references.

   8. Add a bit to Appendix A and add a lot to Appendix B.

   9. Minor editorial changes.

From -01 to -02

   1. Add Section 8.6 on Purge Originator Identification TLV.

   2. Update reference to IEEE Std 802.

   3. Move Acknowledgements after References as this is now the RFC
      Editor preference.

   4. Numerous editorial fixes.

From -02 to -03

   Updated for Shepherd comments. No technical change.

From -03 to -04

   Update reference to draft-ietf-trill-oam-fm to be to [RFC7455].



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From -04 to -05

   Fix typo at the beginning of Section 10 based on RTG Directorate
   review.

From -05 to -06

   Changes based on AD Review:

   1. Move former Appendix C to be the new Section 11, renumbering
      following sections and making corresponding updates.

   2. Several editorial improvements.

From -06 to -07

   Changes based on IESG review (which included GENART and SECDIR
   reviews).


































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Authors' Addresses

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

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


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

   EMail: zhangmingui@huawei.com


   Radia Perlman
   EMC
   2010 256th Avenue NE, #200
   Bellevue, WA 98007 USA

   EMail: radia@alum.mit.edu


   Ayan Banerjee
   Cisco

   EMail: ayabaner@cisco.com


   Anoop Ghanwani
   Dell
   5450 Great America Parkway
   Santa Clara, CA  95054 USA

   EMail: anoop@alumni.duke.edu


   Sujay Gupta
   IP Infusion,
   RMZ Centennial
   Mahadevapura Post
   Bangalore - 560048 India

   EMail: sujay.gupta@ipinfusion.com



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Copyright and IPR Provisions

   Copyright (c) 2015 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
   (http://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.






































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