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Versions: 00 01 02 03 04 draft-ietf-trill-rbridge-options

TRILL Working Group                                  Donald Eastlake 3rd
INTERNET-DRAFT                                          Stellar Switches
Intended status: Proposed Standard                        Anoop Ghanwani
                                                                 Brocade
                                                         Caitlin Bestler
                                                              Consultant
Expires: March 27, 2009                               September 28, 2009


                     RBridges: TRILL Header Options

             <draft-eastlake-trill-rbridge-options-04.txt>


Status of This Document

   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 <rbridge@postel.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."

   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


Abstract

   The TRILL base protocol specification, draft-ietf-trill-rbridge-
   protocol-13.txt, specifies minimal hooks for options. This draft
   specifies the format for options and an initial set of options.











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Table of Contents

      Status of This Document....................................1
      Abstract...................................................1

      1. Introduction............................................3
      1.1 Conventions used in this document......................3

      2. TRILL Header Options....................................4
      2.1 RBridge Option Handling Requirements...................4
      2.2 No Surprises...........................................5
      2.3 Options Format.........................................5
      2.3.1 Bit Options and Summary Bits.........................6
      2.3.2 TLV Option Format....................................7
      2.3.3 Marshalling of Options...............................8

      3. Specific Bit Option.....................................9
      3.1 ECN Bit Option.........................................9

      4. Specific TLV Options...................................11
      4.1 Flow ID TLV Option....................................11
      4.2 Additional Flags TLV Option...........................12

      5. Additions to IS-IS.....................................13
      5.1 Additions to Link State...............................13
      5.2 Additions to Port Capabilities........................13

      6. IANA Considerations....................................14
      7. Security Considerations................................14

      8. References.............................................15
      8.1 Normative References..................................15
      8.2 Informative References................................15

      Authors' Addresses........................................16
      Copyright and IPR Provisions..............................17
















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1. Introduction

   The base TRILL protocol specification, which appears in [Protocol],
   provides an options feature and describes minimal hooks to safely
   support that feature. But it does not specify the structure of
   options nor the details of any particular options. This draft
   specifies that format and some initial options

   Section 2 below describes the general principles of operation,
   format, and ordering of TRILL Header Options. Such options are of two
   kinds: bit options, and TLV (Type, Length, Value) encoded options.

   Section 3 describes a specific bit option while Section 4 describes
   specific TLV encoded options.



1.1 Conventions used in this document

   The terminology and acronyms for [Protocol] are used herein with the
   same meaning.

   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].



























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2. TRILL Header Options

   The TRILL Protocol includes an option capability in the TRILL Header
   (see [Protocol] Section 3.5).  The 5-bit Op-Length header field gives
   the length of the options in units of 4 octets, which allows up to
   124 octets of options area. If Op-Length is zero there are no options
   present; else, the options follow immediately after the Ingress
   Rbridge Nickname field in the TRILL Header and each option is 32-bit
   aligned.

   As described below, provision is made for both hop-by-hop options,
   which could affect any RBridge which received a TRILL frame, and
   ingress-to-egress options, which would only necessarily affect the
   RBridge(s) where a TRILL frame is decapsulated. Provision is also
   made for both "critical" and "non-critical" options. An RBridge
   receiving a frame with a critical option that might affect it and
   that it does not understand MUST discard the frame as it is unsafe to
   process the frame without understanding the option.  Non-critical
   options can be safely ignored.

   Options also indicate whether the value associated with them can
   change (mutable options) or not (immutable options). For example, an
   ingress-to-egress security option could protect the value of an
   immutable ingress-to-egress option. But such a security option
   generally could not protect a mutable value as a transit RBridge
   could change that value but would not, in general, have the keys to
   recompute a signature or authentication code to take a changed value
   into account.

      Note: Most RBridges implementations are expected to be optimized
      for simple and common cases of frame forwarding and processing.
      Although the hard limit on options length, their 32-bit alignment,
      and the presence of critical option summary bits as described
      below, are intended assist in options processing, nevertheless the
      inclusion of options may cause frame processing using a "slow
      path" with inferior performance to "fast path" processing. Limited
      slow path throughput of such frames could cause them to be
      discarded.



2.1 RBridge Option Handling Requirements

   The requirements given in this section are in addition to all option
   handling requirements in [Protocol].

   All Rbridges MUST be able to detect whether there are any critical
   options present that are applicable to their processing of the frame
   as detailed below.  If they do not implement all such options
   present, they MUST discard the frame.


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   Transit RBridges MUST transparently forward all immutable ingress-to-
   egress options in frames that they forward. Any changes made by a
   transit RBridge to a mutable ingress-to-egress option value MUST be a
   change permitted by the specification of that option.

   In addition, a transit RBridge:

   o  MAY add, if space is available, or remove, hop-by-hop options as
      specified for that option;
   o  MAY change the value and/or length of a mutable option as
      permitted by that option's specification (provided there is enough
      room if lengthening the option);
   o  MUST adjust the length of the options area, including changing Op-
      Length in the TRILL header as appropriate for any changes it has
      made in the options;
   o  MUST NOT add or remove an ingress-to-egress option.
   o  with regard to any non-critical hop-by-hop options that the
      transit RBridge does not understand, it MAY remove them if they
      are mutable but MUST transparently copy them when forwarding a
      frame if they are immutable.



2.2 No Surprises

   RBridges advertise the ingress-to-egress options that they support in
   the core TRILL IS-IS instance and advertise the hop-by-hop options
   they support in Hellos they send.  An RBridge is not required to
   support any options.

   Unless an RBridge advertises support for a critical option, it would
   not normally receive frames with that option except due to errors or
   transient conditions.

   An RBridge SHOULD NOT add a critical option to a frame unless,
   -  for a critical hop-by-hop option, it has determined that the next
      hop RBridge or RBridges to which the frame will be sent support
      that option, or
   -  for a critical ingress-to-egress option, it has determined that
      the RBridge or RBridges that will receive the frame with the
      option and egress it support that option.



2.3 Options Format

   If any options are present in a TRILL header, as indicated by a non-
   zero Op-Length field, the first four octets of the options area
   consist of two summary bits and 30 option bits as described below.
   The remainder of the options area consists of TLV (Type Length Value)


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   encoded options aligned on 32-bit boundaries. Section 2.3.2 specifies
   the format of an individual TLV option. Section 2.3.3 describes the
   marshalling of TLV options.



2.3.1 Bit Options and Summary Bits

         |   0      1    2  3  4  5  6  7| 8 - 15|16 - 23|24 - 31|
         +------+------+--+--+--+--+--+--+-------+-------+-------+
         | CHbH | CItE |                 |       |       |       |
         +------+------+--+--+--+--+--+--+-------+-------+-------+

                Figure 1: Options Area Initial Four Octets

   The top two bits of the options area, bits 0 and 1 above, are called
   summary bits and summarize the presence of critical options.  The
   following summary bit description text is copied from [Protocol] for
   convenience:

      If the CHbH (Critical Hop by Hop) bit is one, one or more critical
      hop-by-hop options are present so transit RBridges that support no
      options MUST drop the frame. If the CHbH bit is zero, the frame is
      safe, from the point of view of options processing, for a transit
      RBridge to forward, even if the forwarding RBridge doesn't
      understand any options. A transit RBridge that supports no options
      and forwards a frame MUST transparently forward the options area.

      If the CItE (Critical Ingress to Egress) bit is a one, one or more
      critical ingress-to-egress options are present. If it is zero, no
      such options are present.  If either CHbH or CItE is non-zero,
      egress RBridges that don't support any options MUST drop the
      frame.  If both CHbH and CItE are zero, the frame is safe, from
      the point of view of options, for any egress RBridge to process,
      even if it doesn't understand any options.

   The remaining 30 bits in the initial four octets of the options area
   are available for bit-encoded options. Any RBridge adding an options
   area to a TRILL Header must set these 30 bits to zero except when
   permitted to set one or more by an option that RBridge understands.
   The 30 bits are categorized as follows:

       Bits   Category
      ---------------------
       2- 7   Critical hop-by-hop
       8-15   Non-critical hop-by-hop
      16-23   Critical ingress-to-egress
      24-31   Non-critical ingress-to-egress

   Any transit RBridge must transparently copy bits 2-31 except as


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   permitted by an option implemented by that RBridge. Even if a transit
   RBridge removes all TLV options from a TRILL Header, it MUST NOT
   eliminate the options area in a forwarded frame if any of these 30
   bits is non-zero.



2.3.2 TLV Option Format

   TRILL Header options, other than bit options described above, are TLV
   encoded, with some flag bits in the Type and Length octets, in the
   format show in Figure 2.

   | 0  1  2  3  4  5  6  7| 8|    9-15         |
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+---
   |IE|NC|      Type       |MT|     Length      | value...
   +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+---

                      Figure 2. Option TLV Structure

   The highest order bit of the first octet (IE) is zero for hop-by-hop
   options and one for ingress-to-egress options.  Hop-by-hop options
   are potentially applicable to every RBridge that receives the frame.
   Ingress-to-egress options are only added at the ingress RBridge and
   are potentially applicable only at egress RBridges. Ingress-to-egress
   options MAY also be examined and acted upon by transit RBridges as
   specified in the particular option.

   The next to highest order bit of the first octet (NC) is zero for
   critical options and one for non-critical options.

   The highest order bit of the second octet (MT) is zero for options
   with immutable values, that is where the value and Length will not
   change. It is one for such options that have a mutable value. The IE,
   NC, Type, and MT fields themselves are always immutable.

   The bottom six bits of the first octet give the option Type code. The
   option Type may constrain the values of the IE, NC, and MT bits. For
   example, if the Type indicates a Flow ID option, then it MUST be
   marked as a hop-by-hop, non-critical, mutable option. If the IE, NC,
   or MT bits have a value not permitted by the option Type
   specification for an option that an RBridge would otherwise act on,
   the RBridge MUST discard the frame.

   The Length field is an unsigned quantity giving the length of the
   option value in octets.  It gives the amount of option value data, if
   any, beyond the initial two Type and Length octets.  The Length field
   MUST NOT be such that the option value extends beyond the end of the
   total options area as specified by the TRILL Header Op-Length. Thus,
   the value of Length can vary from zero to 120. The meaning of


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   "Length" values of 121 through 127 is reserved and, when such values
   are noticed in a frame, the frame MUST be discarded.



2.3.3 Marshalling of Options

   In a TRILL Header with options, those options start immediately after
   the Ingress RBridge Nickname and completely fill the options area.

   TLV options start immediately after the initial four octets of option
   and summary bits and MUST appear in ascending order by the value of
   their first octet considered as an unsigned 8-bit integer.  As a
   result, all hop-by-hop options MUST be placed before all ingress-to-
   egress options and, within each of those two categories, all critical
   options MUST appear before all non-critical options. A particular
   option first octet value MUST NOT appear more than once in a TRILL
   Header.  Frames that violate this paragraph are erroneous, will
   produce unspecified results, and MAY be discarded. ("MAY" is chosen
   to minimize the format checking burden required of transit RBridges.)

   Options are 32-bit aligned.  Should an option not consist of a
   multiple of four octets, the option is padded at the end up to the
   next multiple of four octets with octets that MUST be zero.

   If any options are present, those options, both flag and TLV, MUST be
   correctly summarized into the CHbH and CItE bits at the top of the
   initial two octets of the options area.
























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3. Specific Bit Option

   The table below shows the state of TRILL Header bit option
   assignments. See Section 6 for IANA Considerations.

        Bit    Purpose         Section
      -----------------------------------
        0-1    Summary           2.3
        2-7    available for critical hop-by-hop options
        8-9    ECN               3.1
       10-15   available for non-critical hop-by-hop options
       16-23   available for critical ingress-to-egress options
       24-31   available for non-critical ingress-to-egress options

                           Table 1. Flag Options



3.1 ECN Bit Option

   RBridges may implement an ECN (Explicit Congestion Notification)
   option [RFC3168]. If implemented, it SHOULD be enabled by default but
   can be disable on a per RBridge basis by configuration.

   RBridges that do not implement this option or on which it is disabled
   simply (1) set bits 8 and 9 of the bit options area zero when they
   add an options area to a TRILL Header and (2) transparently copy
   those bits, if an options area is present, when they forward a frame
   with a TRILL Header.

   An RBridge that implements the ECN option does the following when
   that option is enabled:

   o  When ingressing an IP frame that is ECN enabled, it MUST add an
      options area to the TRILL Header and copy the two ECN bits from
      the IP header into option bits 8 and 9.
   o  When ingressing a frame for a non-IP protocol with a means of
      indicating ECN that is understood by the RBridge, it MAY add an
      options are to the TRILL Header with the ECN bits set from the
      ingressed frame.
   o  When forwarding a frame encountering congestion at an RBridge, if
      an options area is present with option bits 8 and 9 indicate ECN-
      capable transport, the RBridge MUST modify them to the congestion
      experienced value.
   o  When egressing an IP frame, if the TRILL Header has an options
      area with option bits 8 and 9 non-zero, it copies those bits into
      the ECN bits in the IP header.
   o  When egressing a non-IP protocol frame with a means of indicating
      ECN that is understood by the RBridge, it MAY transfer the ECN
      information from the ECN bits in the options area to the egressed


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      native frame.

   The following table is modified from [RFC3168] and shows the meaning
   of bit values in TRILL Header option bits 8 and 9, bits 6 and 7 in
   the IPv4 TOS Byte, and bits 6 and 7 in the IPv6 Traffic Class Octet:

      Binary  Meaning
      ------  -------
        00     Not-ECT (Not ECN-Capable Transport)
        01     ECT(1) (ECN-Capable Transport(1))
        10     ECT(0) (ECN-Capable Transport(0))
        11     CE (Congestion Experienced)

                       Table 2. ECN Bit Combinations


   An RBridge detects congestion either by monitoring its own queue
   depths or from participation in a link-specific protocol. An RBridge
   implementing the ECN option MAY be configured to add congestion
   experienced marking using ECN to any frame with a TRILL Header that
   encounters congestion even if the frame was not previously marked as
   ECN-capable.






























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4. Specific TLV Options

   The table below shows the state of TRILL Header TLV option Type
   assignment. See Section 6 for IANA Considerations.

          Type        Purpose             Section
         -----------------------------------------
          0x00       reserved
          0x01-0x07  available
          0x08       Flow ID               4.1
          0x09-0x3B  available
          0x3C       Additional Flags      4.2
          0x39-0x3E  available
          0x3F       reserved

                         Table 3. TLV Option Types

   The following subsections specify particular TRILL TLV options.



4.1 Flow ID TLV Option

   In connection with multi-pathing of frames, frames that are part of
   the same order dependent flow need to follow the same path for
   correct performance.  Methods to determine flows are beyond the scope
   of the TRILL standard; however, it may be useful, once the flow of a
   frame has been determined, to preserve and transmit that information
   for use by subsequent RBridges.

   This is a non-critical option. It is considered hop-by-hop because it
   can be added by a transit RBridge and can be used by transit RBridges
   to make forwarding decisions. Because the ingress RBridge may know
   the most about a frame, it is expected that this option would most
   commonly be added at the ingress RBridge. Once in a frame, the option
   SHOULD NOT be removed or changed unless, for example, a campus is
   divided into regions such that different flow IDs would make sense in
   different regions.

   The value length of this option is fixed for efficiency. Since 2
   octets might be insufficient for some purposes, the length is set at
   six, the next size fitting evenly into the 32-bit alignment of
   options. Should there be less than 6 octets of significance to the
   flow ID, the value SHOULD be right justified by prefixing zero
   octets. If an RBridge is incapable of using all six octets for flow
   ID purposes, it SHOULD use a smaller number of lower order octets
   from the value.

   The option fields and flags are as follows:



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      o  Type is 0x08.
      o  Length is 6. The data is an unsigned integer that is the flow
         ID. If there are less than six value octets of significance,
         they SHOULD be right justified by prefixing zero octets.
      o  IE MUST be zero. This is a hop-by-hop option.
      o  NC and MT MUST be one. This is a non-critical mutable option.



4.2 Additional Flags TLV Option

   The option provides a means of adding a variety of additional flags
   to the TRILL Header beyond the bit options available in the first
   four octets of the options area.

   The value of the flags option consists of additional flags, eight per
   octet, numbered from the high-order to the low-order bit. Thus flag 1
   is the 0x80 bit of the first octet, flag 8 is the 0x01 bit of that
   octet, flag 9 is the 0x80 bit of the second octet, etc. The number of
   additional flags that can be defined is bounded only by the options
   space that can be available. All flags not present, because they
   would be in value octets beyond those specified by the option Length,
   are considered zero.

   This option can appear up to four times in a frame to provide
   independent sets of all combinations of ingress-to-egress, hop-by-
   hop, non-critical, and critical flags. To simplify canonicalization
   for security, this option MUST NOT be included if all of the flag
   bits would be zero and the value MUST NOT have any trailing zero
   octets. Thus its Length MUST be at least 1 and at least the last
   octet of the value present MUST be non-zero.

   The option fields and flags are as follows:

      o  Type is 0x3C.
      o  Length is variable with a minimum value of 1.
      o  IE and NC are variable producing, in effect, four versions of
         this option.
      o  MT MUST be zero. This is an immutable option.













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5. Additions to IS-IS

   RBridges use IS-IS PDUs to inform other RBridges which options they
   support. The specific IS-IS TLVs or sub-TLVs used to encode this
   information are specified in a separate document.



5.1 Additions to Link State

   Rbridges indicate in their link state which ingress-to-egress TLV and
   bit options they support. In addition, if they support the ingress-
   to-egress Additional Flags TLV option, they indicate which critical
   ingress-to-egress Additional Flags TLV option flags they support, if
   any.



5.2 Additions to Port Capabilities

   Rbridges indicate in their Hellos which hop-by-hop TLV and bit
   options they support. In addition, if they support the Additional
   Flags TLV option, they indicate which critical hop-by-hop Additional
   Flags TLV option flags they support.




























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6. IANA Considerations

   IANA will create two subregistries within the TRILL registry. A
   "TRILL Header Bit Options" subregistry that is initially populated as
   specified in Table 1 in Section 3.  And a "TRILL TLV Option Types"
   subregistry that is initially populated as specified in Table 3 in
   Section 4. References in both of those tables to sections of this
   document are to be replaced in the IANA subregistries by references
   to this document as an RFC.

   New TRILL bit options and TLV option types are allocated by IETF
   Review [RFC5226].

   IANA will create a third subregistry within the TRILL registry for
   flags in the four variations of the Additional Flags TLV option (the
   four combinations of critical and non-critical, ingress-to-egress and
   hop-by-hop) which is initially empty. Such flags are allocated by RFC
   Publication if the RFC allocates no more than three bits, which may
   be a mixture of the four types, or by IETF Review for any number of
   bits [RFC5226].




7. Security Considerations

   For general TRILL protocol security considerations, see [Protocol].

   RBridges should not trust that the options that appear in a TRILL
   header reflect the intent of the previous or earlier hop RBridges,
   including the ingress RBridge, unless the option is appropriately
   secured. For example, through inclusion of a TRILL authentication
   option, which may be specified in another document.

   In order to facilitate authentication, options SHOULD be specified so
   they do not have alternative equivalent forms. Authentication of
   anything with alternative equivalent forms almost always requires
   canonicalization which an authenticating RBridge ignorant of the
   option would be unable to do.













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8. References



8.1 Normative References

   [Protocol] - Perlman, R., D. Eastlake, D. Dutt, S. Gai, and A.
      Ghanwani, "RBridges: Base Protocol Specification", draft-ietf-
      trill-rbridge-protocol-13.txt, work in progress.

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

   [RFC3168] -  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
      of Explicit Congestion Notification (ECN) to IP", RFC 3168,
      September 2001.

   [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
      IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.



8.2 Informative References

   None at this time.



























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Authors' Addresses

   Donald E. Eastlake 3rd
   Stellar Switches
   155 Beaver Street
   Milford, MA 01757

   tel: +1-508-634-2066
   email: d3e3e3@gmail.com


   Anoop Ghanwani
   Brocade Communications Systems
   1745 Technology Drive
   San Jose, CA 95110 USA

   Phone: +1-408-333-7149
   Email: anoop@brocade.com


   Caitlin Bestler
   Consultant
   555 E. El Camino Real #104
   Sunnyvale, CA 94087

   tel: +1-949-528-3085
   email: cait@asomi.com

























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Copyright and IPR Provisions

   Copyright (c) 2009 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 in effect on the date of
   publication of this document (http://trustee.ietf.org/license-info).
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.

   The definitive version of an IETF Document is that published by, or
   under the auspices of, the IETF. Versions of IETF Documents that are
   published by third parties, including those that are translated into
   other languages, should not be considered to be definitive versions
   of IETF Documents. The definitive version of these Legal Provisions
   is that published by, or under the auspices of, the IETF. Versions of
   these Legal Provisions that are published by third parties, including
   those that are translated into other languages, should not be
   considered to be definitive versions of these Legal Provisions.  For
   the avoidance of doubt, each Contributor to the IETF Standards
   Process licenses each Contribution that he or she makes as part of
   the IETF Standards Process to the IETF Trust pursuant to the
   provisions of RFC 5378. No language to the contrary, or terms,
   conditions or rights that differ from or are inconsistent with the
   rights and licenses granted under RFC 5378, shall have any effect and
   shall be null and void, whether published or posted by such
   Contributor, or included with or in such Contribution.
























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