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Internet Engineering Task Force (IETF)                   D. Eastlake 3rdRequest for Comments: 7179                                        HuaweiUpdates:6325                                                A. GhanwaniCategory: Standards Track                                           DellISSN: 2070-1721                                                V. Manral                                                             Ionos Corp.                                                                   Y. Li                                                                  Huawei                                                              C. Bestler                                                         Nexenta Systems                                                                May 2014Transparent Interconnection of Lots of Links (TRILL): Header ExtensionAbstract   The IETF Transparent Interconnection of Lots of Links (TRILL) base   protocol (RFC 6325) specifies minimal hooks to safely support TRILL   Header extensions.  This document specifies an initial extension   providing additional flag bits and specifies some of those bits.  It   updatesRFC 6325.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7179.Eastlake, et al.             Standards Track                    [Page 1]

RFC 7179                 TRILL: Header Extension                May 2014Copyright Notice   Copyright (c) 2014 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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.Table of Contents1. Introduction ....................................................31.1. Conventions Used in This Document ..........................32. TRILL Header Extensions .........................................32.1. RBridge Extended Flag Handling Requirements ................52.2. No Critical Surprises ......................................52.3. Extended Header Flags ......................................62.3.1. Critical Summary Bits ...............................72.4. Conflict of Extensions .....................................83. Specific Extended Header Flags ..................................93.1. RBridge Channel Alert Extended Flags .......................94. Additions to IS-IS ..............................................95. IANA Considerations ............................................106. Security Considerations ........................................107. Acknowledgements ...............................................118. References .....................................................118.1. Normative References ......................................118.2. Informative References ....................................11Eastlake, et al.             Standards Track                    [Page 2]

RFC 7179                 TRILL: Header Extension                May 20141.  Introduction   The base IETF Transparent Interconnection of Lots of Links (TRILL)   protocol [RFC6325] provides a TRILL Header extension feature and   describes minimal hooks to safely support header extensions.  (This   feature is called "options" inSection 3.8 of [RFC6325].)  But,   except for the first two bits, the TRILL base protocol document does   not specify the structure of extensions to the TRILL Header nor the   details of any particular extension.   This document is consistent with [RFC6325] and provides further   details.  It specifies an initial extension word providing additional   flag bits and specifies some of those bits.  Additional extensions,   including TLV-encoded options, may be specified in later documents,   for example, [Options] and [Options2].Section 2 below describes some general principles of TRILL Header   extensions and an initial extension.Section 3 specifies a pair of   flags in this initial extension.1.1.  Conventions Used in This Document   The terminology and acronyms defined in [RFC6325] are used herein   with the same meaning.  Devices implementing the TRILL protocol are   referred to as RBridges (Routing Bridges) or TRILL Switches.   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described in [RFC2119].2.  TRILL Header Extensions   The base TRILL protocol includes a feature for extension of the TRILL   Header (see [RFC6325], Sections3.5 and3.8).  The 5-bit Op-Length   header field gives the length of the extensions to the TRILL Header   in units of 4 octets, which allows up to 124 octets of header   extension.  If Op-Length is zero, there are no header extensions   present; else, the extension area follows immediately after the   Ingress RBridge Nickname field of the TRILL Header.  The first 32-bit   word of the optional extensions area consists of an extended flags   area and critical summary bits as specified in this document.Eastlake, et al.             Standards Track                    [Page 3]

RFC 7179                 TRILL: Header Extension                May 2014   As described below, provision is made for   o  hop-by-hop flags, which might affect any RBridge that receives a      TRILL Data frame with such a flag set,   o  ingress-to-egress flags, which would only necessarily affect the      RBridge(s) where a TRILL frame is decapsulated,   o  flags affecting an as-yet-unspecified class of RBridges, for      example, border RBridges in a TRILL campus extended to support      multi-level IS-IS (Intermediate System to Intermediate System)      [MultiLevel], and   o  both "critical" and "non-critical" flags.   Any RBridge receiving a frame with a critical hop-by-hop extension   that it does not implement MUST discard the frame because it is   unsafe to process the frame without understanding such a critical   extension.   Any egress RBridge receiving a frame with a critical ingress-to-   egress extension it does not implement MUST drop the frame if it is a   unicast frame (TRILL Header M bit = 0); if it is a multi-destination   TRILL Data frame (M=1), then it MUST NOT be egressed at that RBridge,   but the egress RBridge still forwards such a frame on the   distribution tree.   Non-critical extensions can be safely ignored.   Any extended flag indicating a significant change in the structure or   interpretation of later parts of the frame that, if the extended flag   were ignored, could cause a failure of service or violation of   security policy MUST be a critical extension.  If such an extended   flag affects any fields that transit RBridges will examine, it MUST   be a hop-by-hop critical extended flag.      Note: Most RBridge implementations are expected to be optimized      for simple and common cases of frame forwarding and processing.      Although the hard limit on the header extensions area length, the      32-bit alignment of the extension area, and the presence of      critical extension summary bits, as described below, are intended      to assist in the efficient hardware processing of frames with a      TRILL Header extensions area, nevertheless the inclusion of      extensions may cause frame processing using a "slow path" with      inferior performance to "fast path" processing.  Limited slow path      throughput of such frames could cause some of them to be      discarded.Eastlake, et al.             Standards Track                    [Page 4]

RFC 7179                 TRILL: Header Extension                May 20142.1.  RBridge Extended Flag Handling Requirements   All RBridges MUST check whether there are any critical flags set that   are necessarily applicable to their processing of the frame.  To   assist in this task, critical summary bits are provided that cover   not only the extended flags specified herein but will cover any   further extensions that may be specified in future documents, for   example, [Options] and [Options2].  If an RBridge does not implement   all critical flags in a TRILL Data frame, it MUST treat the frame as   having an unimplemented critical extension as described inSection 2.   A transit or egress RBridge may assume that the critical summary bits   are correct.   In addition, a transit RBridge:   o  MAY set or clear hop-by-hop flags as specified for such flags;   o  MUST adjust the length of the extensions area, including changing      Op-Length in the TRILL Header, as appropriate if it adds or      removes the extended header flags word;   o  MUST, if it adds the word of extended header flags or changes any      critical flags, correctly set the critical summary bits in the      extended header flags word;   o  MUST NOT remove the extended header flags word unless it is all      zero (either on arrival or after permitted modifications); and   o  MUST NOT set or clear ingress-to-egress or reserved extended      header flags except as specifically permitted in the specification      of such flags.2.2.  No Critical Surprises   RBridges advertise the extended header flags they support in IS-IS   PDUs (Protocol Data Units) [RFC7176].  Unless an RBridge advertises   support for a critical extended header flag, it will not normally   receive frames with that flag set.  An RBridge is not required to   support any extensions.   An RBridge SHOULD NOT set a critical extended flag in a frame unless,   o  for a critical hop-by-hop extended header flag, it has determined      that the next hop RBridge or RBridges that will accept the frame      support that flag,Eastlake, et al.             Standards Track                    [Page 5]

RFC 7179                 TRILL: Header Extension                May 2014   o  for a critical ingress-to-egress extended header flag, it has      determined that the RBridge or RBridges that will egress the frame      support that flag, or   o  for a critical reserved extended header flag, it may set such a      flag only if it understands which RBridges it is applicable to and      has determined that those RBridges that will accept the frame      support that flag.   "SHOULD NOT" is specified above since there may be cases where it is   acceptable for those frames, particularly for the multi-destination   case, to be discarded or not egressed by any RBridges that do not   implement the extended flag.2.3.  Extended Header Flags   If any extensions are present in a TRILL Header, as indicated by a   non-zero Op-Length field, the first 32 bits of the extensions area   consist of extended header flags, as described below.  The remainder   of the extensions area, if any, after the initial 32 bits may be   specified in later documents, for example, [Options] and [Options2].   Any RBridge adding an extensions area to a TRILL Header must set the   first 32 bits to zero except when permitted or required to set one or   more of those bits as specified.  For TRILL Data frames with   extensions present, any transit RBridge that does not discard the   frame MUST transparently copy the extended flags word, except for   modifications permitted by an extension implemented by that RBridge.   The extended header flags word is illustrated below and the meanings   of these bits is further described in the list following the figure.    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  |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   | ... additional optional 32-bit aligned words of extension     |   |     possibly including TLV extensions ...   (The first two critical summary bits are as specified in [RFC6325].   In this document, an "S", for Summary, has been added at the end of   their acronyms.  A third critical summary bit is also specified   herein and its acronym also ends with an "S" for consistency.)Eastlake, et al.             Standards Track                    [Page 6]

RFC 7179                 TRILL: Header Extension                May 2014   Bits    Description   --------------------   0-2     Crit.: Critical summary bits.           0 CHbHS: Critical Hop-by-Hop extension(s) are present.           1 CItES: Critical Ingress-to-Egress extension(s) are present.           2 CRSVS: Critical Reserved extension(s) are present.   3-7     CHbH: Critical Hop-by-Hop extended flag bits.   8-13    NCHbH: Non-critical Hop-by-Hop extended flag bits.   14-16   CRSV: Critical Reserved extended flag bits.   17-20   NCRSV: Non-critical Reserved extended flag bits.   21-26   CItE: Critical Ingress-to-Egress extended flag bits.   27-31   NCItE: Non-critical Ingress-to-Egress extended flag bits.2.3.1.  Critical Summary Bits   The top three bits of the extended header flags area, bits 0, 1, and   2 above, are called the critical summary bits.  They summarize the   presence of critical extensions as follows:   CHbHS: If the CHbHS (Critical Hop-by-Hop Summary) bit is one, one or      more critical hop-by-hop extensions are present.  These might be      critical hop-by-hop extended header flags or critical hop-by-hop      extensions after the first word in the extensions area.  Transit      RBridges that do not support all of the critical hop-by-hop      extensions present, for example, an RBridge that supported no      critical hop-by-hop extensions, MUST drop the frame.  If the CHbHS      bit is zero, the frame is safe, from the point of view of      extensions processing, for a transit RBridge to forward,      regardless of what extensions that RBridge does or does not      support.   CItES: If the CItES (Critical Ingress-to-Egress Summary) bit is a      one, one or more critical ingress-to-egress extensions are      present.  These might be critical ingress-to-egress extended      header flags or critical ingress-to-egress extensions after the      first word in the extensions area.  If the CItES bit is zero, no      such extensions are present.  If either CHbHS or CItES is non-      zero, egress RBridges that do not support all critical extensions      present, for example, an RBridge that supports no critical      extensions, MUST drop the frame.  If both CHbHS and CItES are      zero, the frame is safe, from the point of view of extensions, for      an egress RBridge to process, regardless of what extensions that      RBridge does or does not support.Eastlake, et al.             Standards Track                    [Page 7]

RFC 7179                 TRILL: Header Extension                May 2014   CRSVS: If the CRSVS (Critical Reserved Summary) bit is a one, one or      more critical extensions are present that are reserved to apply to      a class of RBridges to be specified in the future, for example,      border RBridges in a TRILL campus extended to support multi-level      IS-IS.  This class will be a subset of transit RBridges.  RBridges      in this class MUST drop frames with the CRSVS bit set unless they      implement all critical hop-by-hop and all critical reserved      extensions present in the frame.   The critical summary bits enable simple and efficient processing of   TRILL Data frames by egress RBridges that support no critical   extensions, by transit RBridges that support no critical hop-by-hop   extensions, and by RBridges in the reserved class that support no   critical hop-by-hop or reserved extensions.  Such RBridges need only   check whether Op-Length is non-zero and, if it is, check the top one,   two, or three bits just after the fixed portion of the TRILL Header.   Based on those three bits, such RBridges can decide whether to   discard or forward/process the frame.2.4.  Conflict of Extensions   Defining TRILL extensions including extended header flags that   conflict with each other would be undesirable.  Should conflicting   extensions appear in the same packet, the results would be   unpredictable if different implementations processed them in   different orders.  While rules could be defined to specify how to   predictably process conflicting extensions, such rules would also   limit implementation flexibility and could impose substantial   processing burdens.   Conflicting extensions SHOULD NOT be defined, but if they are,   careful thought should be given as to whether and how to specify the   handling of conflicting extensions.Eastlake, et al.             Standards Track                    [Page 8]

RFC 7179                 TRILL: Header Extension                May 20143.  Specific Extended Header Flags   The table below shows the state of TRILL Header extended flag   assignments.  SeeSection 5 for IANA Considerations.   Bits    Purpose                                          Section   ----------------------------------------------------------------    0-2    Critical Summary Bits                              2.3.1    3-6    available critical hop-by-hop flags    7      Critical Channel Alert flag                          3.1    8      Non-critical Channel Alert flag                      3.1    9-13   available non-critical hop-by-hop flags   14-16   available critical reserved flags   17-20   available non-critical reserved flags   21-26   available critical ingress-to-egress flags   27-31   available non-critical ingress-to-egress flags             Table 1: Extended Header Flags Area3.1.  RBridge Channel Alert Extended Flags   The RBridge Channel Alert extended header flags indicate that the   frame is an RBridge Channel frame [RFC7178] that requests processing   at each hop.   If the Critical Channel Alert flag (bit 7) is a one and the RBridge   does not implement the RBridge Channel feature or the particular   RBridge Channel protocol involved [RFC7178] or the frame does not   actually appear to be an RBridge Channel message, then the frame is   discarded.  This permits implementation, for example, of a channel   message requiring strict source routing or the like, with assurance   that it will be discarded rather than deviate from the directed path.   If the frame is not discarded as described above, then the presence   of either the Critical or Non-critical Channel Alert flag alerts   transit RBridges to the presence of an RBridge Channel message   [RFC7178] that may require special handling.  The non-critical alert   flag supports, for example, an RBridge Channel protocol message   including a "record route" function where not recording transit   RBridges that do not support this function is acceptable.4.  Additions to IS-IS   RBridges use IS-IS Link State PDUs (LSPs) to inform other RBridges   which extended header flags they support.  The IS-IS PDU(s), TLV(s),   or sub-TLV(s) used to encode and advertise this information are   specified in a separate document [RFC7176].Eastlake, et al.             Standards Track                    [Page 9]

RFC 7179                 TRILL: Header Extension                May 20145.  IANA Considerations   IANA has created a "TRILL Extended Header Flags" subregistry within   the TRILL Parameters registry.  The "TRILL Extended Header Flags"   subregistry is initially populated as specified in Table 1 inSection3.  References in that table to sections of this document have been   replaced in the IANA subregistry by references to this document as an   RFC.   New TRILL extended header flags are allocated by IETF Review   [RFC5226].   To indicate support of extended header flags, IANA has assigned the   following bits in the TRILL-VER and PORT-TRILL-VER Sub-TLV Capability   Flag registries created by [RFC7176]:   o  Bits 3-13 of the PORT-TRILL-VER Sub-TLV Capability Flags have been      assigned to indicate support of TRILL hop-by-hop extended header      flags 3-13.   o  Bits 14-31 of the TRILL-VER Sub-TLV Capability Flags have been      assigned to indicate support of TRILL extended header flags 14-31.6.  Security Considerations   For general TRILL protocol security considerations, see [RFC6325].   For security considerations related to extended header flags, see the   document where the flag is specified.   It is important that the critical summary bits in the extended header   flags word be set properly.  If set when critical extensions of the   appropriate category are not present, frames may be unnecessarily   discarded.  If not set when critical extensions are present, frames   may be mishandled or corrupted, and intended security policies may be   violated.   The RBridge Channel Alert extended header flags have the following   security considerations.  Implementations should keep in mind that   they might be erroneously set in a frame.  If either RBridge Channel   Alert flag is found set in a frame that is not an RBridge Channel   message [RFC7178], the flag MAY be cleared and should have no effect   except, possibly, delaying processing of the frame.  If either   RBridge Channel Alert flag is erroneously omitted from a frame,   desired per-hop processing for the frame may not occur.Eastlake, et al.             Standards Track                   [Page 10]

RFC 7179                 TRILL: Header Extension                May 20147.  Acknowledgements   The following, listed in alphabetic order, are thanked for their   valuable contributions:  Ben Campbell, Adrian Farrel, Barry Leiba,   and Thomas Narten.8.  References8.1.  Normative References   [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate                 Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC5226]     Narten, T. and H. Alvestrand, "Guidelines for Writing                 an IANA Considerations Section in RFCs",BCP 26,RFC5226, May 2008.   [RFC6325]     Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and                 A. Ghanwani, "Routing Bridges (RBridges): Base Protocol                 Specification",RFC 6325, July 2011.   [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.   [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 2014.8.2.  Informative References   [MultiLevel]  Perlman, R., Eastlake 3rd, D., Ghanwani, A., and H.                 Zhai, "Flexible Multilevel TRILL (Transparent                 Interconnection of Lots of Links)", Work in Progress,                 January 2014.   [Options]     Eastlake 3rd, D., Ghanwani, A., Manral, V., and C.                 Bestler, "RBridges: Further TRILL Header Extensions",                 Work in Progress, June 2012.   [Options2]    Eastlake 3rd, D., "RBridges: More Proposed TRILL Header                 Options", Work in Progress, October 2011.Eastlake, et al.             Standards Track                   [Page 11]

RFC 7179                 TRILL: Header Extension                May 2014Authors' Addresses   Donald Eastlake 3rd   Huawei R&D USA   155 Beaver Street   Milford, MA 01757   USA   Phone: +1-508-333-2270   EMail: d3e3e3@gmail.com   Anoop Ghanwani   Dell   5450 Great America Parkway   Santa Clara, CA  95054   USA   EMail: anoop@alumni.duke.edu   Vishwas Manral   Ionos Corp.   4100 Moorpark Ave.   San Jose, CA  95117   USA   EMail: vishwas@ionosnetworks.com   Yizhou Li   Huawei Technologies   101 Software Avenue,   Nanjing 210012   China   Phone: +86-25-56622310   EMail: liyizhou@huawei.com   Caitlin Bestler   Nexenta Systems   455 El Camino Real   Santa Clara, CA 95050   USA   EMail: caitlin.bestler@nexenta.comEastlake, et al.             Standards Track                   [Page 12]