TRILL Working Group Donald Eastlake INTERNET-DRAFT Huawei Intended status: Proposed Standard Anoop Ghanwani Brocade Vishwas Manral IP Infusion Caitlin Bestler Quantum Expires: September 9, 2011 March 10, 2011 RBridges: TRILL Header Options Abstract The TRILL base protocol standard specifies minimal hooks to safely support TRILL Header options. This draft specifies the format for options and some initial options. Status of This Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Distribution of this document is unlimited. Comments should be sent to the TRILL working group mailing list . Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- 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 D. Eastlake, et al [Page 1] INTERNET-DRAFT TRILL Header Options Table of Contents 1. Introduction............................................3 1.1 Conventions used in this document......................3 2. TRILL Header Options....................................4 2.1 RBridge Option Handling Requirements...................5 2.2 No Critical Surprises..................................6 2.3 Options Format.........................................6 2.3.1 Extended Header Flags Area...........................7 2.3.1.1 Critical Summary Bits..............................8 2.3.1.2 MEF, More Extended Flags...........................8 2.3.1.3 Specific Initial Bit Extended Flags................9 2.3.1.4 TLV Summary Bits...................................9 2.3.1.5 Flow ID............................................9 2.3.2 TLV Option Format...................................10 2.3.3 Marshaling of Options...............................11 2.4 Conflict of Options...................................11 3. Specific Extended Header Flag..........................13 3.1 The ECN Option........................................13 4. Specific TLV Option....................................16 4.1 Test/Pad Option.......................................16 5. Additions to IS-IS.....................................17 6. IANA Considerations....................................18 7. Security Considerations................................18 8. Acknowledgements.......................................18 9. References.............................................19 9.1 Normative References..................................19 9.2 Informative References................................19 Change History............................................20 Version 00 to 02..........................................20 Version 02 to 03..........................................20 Version 03 to 04..........................................20 D. Eastlake, et al [Page 2] INTERNET-DRAFT TRILL Header Options 1. Introduction The base TRILL protocol standard [RFCtrill] provides a TRILL Header options feature and describes minimal hooks to safely support that feature. But, except for the first two bits, it does not specify the structure of the options extension to the TRILL Header nor the details of any particular options. This draft specifies that format and some initial options: a special Flow ID field, ECN (Explicit Congestion Notification) extended header flags, and a test/pad option. Section 2 below describes the general principles of operation, format, and ordering of TRILL Header Options. Other than the special Flow ID option, TRILL Header options are of two kinds: extended header flags and TLV (Type, Length, Value) encoded options. Section 3 describes a specific extended flag option while Section 4 describes a specific TLV encoded option. 1.1 Conventions used in this document The terminology and acronyms defined in [RFCtrill] are used herein with the same meaning. In this documents, "IP" refers to both IPv4 and IPv6. 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]. D. Eastlake, et al [Page 3] INTERNET-DRAFT TRILL Header Options 2. TRILL Header Options The base TRILL Protocol includes an option feature for extension of the TRILL Header (see [RFCtrill] Sections 3.5 and 3.8). The 5-bit Op-Length header field gives the length of the extension to the TRILL Header in units of 4 octets, which allows up to 124 octets of header extension. If Op-Length is zero there is no header extension present; else, this area follows immediately after the Ingress Rbridge Nickname field of the TRILL Header. The optional extensions area consists of an extended flags area possibly followed by TLV options. Each TLV option present is 32-bit aligned. There is a special Flow ID option that may also occur in the extended flags area. As described below, provision is made for both hop-by-hop options, which might affect any RBridge that receives a TRILL Data frame containing such an extension, 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. Any RBridge receiving a frame with a critical hop- by-hop option that it does not implement MUST discard the frame because it is unsafe to process the frame without understanding the critical option. Any egress RBridge receiving a frame with a critical ingress-to-egress option it does not implement MUST drop the frame if it is a known unicast frame; if it is a multi-destination TRILL Data frame with a critical ingress-to-egress option that the RBridge does not implement, then it MUST NOT be egressed at that RBridge but it is still forwarded on the distribution tree. Non-critical options can be safely ignored. Any option indicating a significant change in the structure or interpretation of later parts of the frame which, if the option were ignored, could reasonably cause a failure of service or violation of security policy MUST be a critical option. If such an extension affects any fields that transit RBridges will examine, it MUST be a hop-by-hop critical option. TLV options also have a "mutability" flag that has a different meaning for ingress-to-egress and for hop-by-hop. For an ingress-to-egress option, the mutability flag indicates whether the value associated with the option can change at a transit RBridge (mutable options) or cannot so change (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 might not have the keys to recompute a signature or authentication code to take a changed value into account. For a non-critical hop-by-hop option, the mutability flag indicates D. Eastlake, et al [Page 4] INTERNET-DRAFT TRILL Header Options whether a transit RBridge that does not implement the option is permitted (mutable) or not permitted (immutable) to remove the option. A transit RBridge is not required to remove a hop-by-hop option that it does not implement. For critical hop-by-hop options, the mutability flag is meaningless. If the RBridge does not implement the critical hop-by-hop option, it MUST drop the frame. If it does implement the critical hop-by-hop option, it will know whether or not it may/should/must remove it. For critical hop-by-hop options, the mutability flag is set to zero ("immutable") on transmission and ignored on receipt. Note: Most RBridges implementations are expected to be optimized for simple and common cases of frame forwarding and processing. Although the hard limit on the header options area length, the 32-bit alignment of TLV options, and the presence of critical option summary bits, as described below, are intended to assist in the efficient hardware based processing of frames with a TRILL header options area, nevertheless the inclusion of options, particularly TLV 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 the option handling requirements in [RFCtrill]. All RBridges MUST be able to check whether there are any critical options present that are necessarily applicable to their processing of the frame as detailed below. If they do not implement all such critical options present, they MUST discard the frame or, in some circumstances as described above for certain multi-destination frames, continue to forward the frame but MUST NOT egress the frame. Transit RBridges MUST transparently forward all immutable ingress-to- egress header 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 such options; o MAY change the value and/or length of a mutable ingress-to-egress TLV option as permitted by that option's specification and provided there is enough room if lengthening it; D. Eastlake, et al [Page 5] INTERNET-DRAFT TRILL Header Options 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; o MUST NOT add, remove, or re-order ingress-to-egress options. o with regard to any non-critical hop-by-hop options that the transit RBridge does not implement, it MAY remove them if they are mutable but MUST transparently copy them when forwarding a frame if they are immutable. 2.2 No Critical Surprises RBridges advertise the ingress-to-egress options they support in their IS-IS LSP and advertise the hop-by-hop options they support at a port on the link connected to that port. An RBridge is not required to support any options. Unless an RBridge advertises support for a critical option, it will not normally receive frames with that option. 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 that will accept the frame support that option, or - for a critical ingress-to-egress option, it has determined that the RBridge or RBridges that will egress the frame support that option. "SHOULD NOT" is specified since there may be cases where it is acceptable for those frames, particularly for the multi-destination case, to be discarded by any RBridges that do not implement the 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 32 or 64 bits of the options area consist of extended header flags and the Flow ID, as described below. The remainder of the options area, if any, after this initial 32 or 64 bits, consists of TLV (Type Length Value) options aligned on 32-bit boundaries. Section 2.3.2 specifies the format of a TLV option. Section 2.3.3 describes the marshaling of TLV options. D. Eastlake, et al [Page 6] INTERNET-DRAFT TRILL Header Options 2.3.1 Extended Header Flags Area The first 32 bits of the Options Area are organized as follows: | 0 1 2 3-4 5-7 8-10 11-12 13 14 15 | 16 - 31 | +----+----+----+----+----+----+-----+----+----+----+---------+ |CHbH|CItE|MEF |CHHF|NHHF|CIEF|NIEF |NHHT|CIET|NIET| Flow ID | +----+----+----+----+----+----+-----+----+----+----+---------+ Figure 1: Options Area Initial 32 Bits Any RBridge adding an options area to a TRILL Header must set these 32 bits to zero except when permitted or required to set one or more of them as specified. The meanings of these bits are listed in the table below and then further described. Bit(s) Description --------------------- 0 CHbH: Critical Hop-by-Hop option(s) are present. 1 CItE: Critical Ingress-to-Egress option(s) are present. 2 MEF: More Extended Flags, indicates that an additional 32-bit extended flags area is present as described below. 3-4 CHHF: Critcial Hob-by-Hop extended Flag bits. 5-7 NHHF: Non-critical Hop-by-Hop extended Flag bits. 8-10 CIEF: Critical Ingress-to-Egress extended Flag bits. 11-12 NIEF: Non-critical Ingress-to-Egress extended Flag bits. 13 NHHT: Non-critical Hop-by-Hop TLV option(s) are present. 14 CIET: Critical Ingress-to-Egress TLV option(s) are present. 15 NIET: Non-critical Ingress-to-Egress TLV option(s) are present. 16-31 Flow ID if non-zero. All extended flags are considered mutable except the critical hop-by- hop extended flags. For TRILL Data frames with options present, any transit RBridge MUST transparently copy bits 8 through 12, except as permitted by an option implemented by that RBridge, but MAY either copy or clear any of the bits 5 through 7. Even if a transit RBridge removes all TLV options from a TRILL Header when allowed to do so, it MUST NOT eliminate the options area in a forwarded frame if any of bits 3, 4, or 8 through 12 remain non-zero; however, if there are no TLV options and all of bits 2 through 31 are zero, then the summary bits will also be zero and the transit RBridge MAY eliminate the Options area in the frame, setting Op-Length to zero. D. Eastlake, et al [Page 7] INTERNET-DRAFT TRILL Header Options 2.3.1.1 Critical Summary Bits The top two bits of the options area, bits 0 and 1 above, are called the critical summary bits. They summarize the presence of critical options as follows: CHbH: If the CHbH (Critical Hop by Hop) bit is one, one or more critical hop-by-hop options are present in the options area. Transit RBridges that do not support all of the critical hop-by- hop options present, for example an RBridge that supported no hop- by-hop 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, regardless of what options that RBridge does or does not support. A transit RBridge that supports none of the options present MUST transparently forward the options area when it forwards a frame, except that it MAY remove mutable hop-by-hop options. CItE: If the CItE (Critical Ingress to Egress) bit is a one, one or more critical ingress-to-egress options are present in the options area. If it is zero, no such options are present. If either CHbH or CItE is non-zero, egress RBridges that do not support all critical options present, for example an RBridge that supports no 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, regardless of what options that RBridge does or does not support. The critical summary bits enable efficient processing of TRILL Data frames by RBridges that support no critical options and by transit RBridges that support no critical hop-by-hop options. Such RBridges need only check whether Op-Length is non-zero and, if it is, the top one or two bits just after the fixed portion of the TRILL Header. 2.3.1.2 MEF, More Extended Flags Bit 2, if set, indicates there are an additional 32 bits of extended flags. They are organized as shown below. The start of the TLV options, if any, is moved to after these additional bit options. | 32 - 39 | 40 - 47 | 48 - 55 | 56 - 63 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Critical HbH |NonCritical HbH| Critical ItE |NonCritical ItE| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Extended Flag Bits 32 to 63 D. Eastlake, et al [Page 8] INTERNET-DRAFT TRILL Header Options 2.3.1.3 Specific Initial Bit Extended Flags CHHB, bits 3 and 4, are Critical Hob-by-Hop Bits. NHHB, bits 5 through 7, are Non-critical Hop-by-Hop Bits. CIEB, bits 8 through 10, are Critical Ingress-to-Egress Bits. NIEB, bits 11 and 12, are Non-critical Ingress-to-Egress Bits. The bits above are available for indicating extended header flags, except for two NHHF allocated by Section 3.1 below. 2.3.1.4 TLV Summary Bits It is anticipated that in most cases the interpretation of TLV encoded options in TRILL data frames will be handled by slow path software. To minimize unnecessary resort to the slow path, the TLV summary bits, plus a special check for critical hop-by-hop TLV options, enable an RBridge to quickly determine if any TLV encoded options of the category or categories it implements are present. Bits 13-15, the NHHT, CIET, and NIET bits, indicate the presence later in the TRILL Header of TLV encoded Non-critical Hop-by-Hop, Critical Ingress-to-Egress, and Non-critical Ingress-to-Egress TLV options respectively. There is no Critical Hop-by-Hop TLV flag bit because the presence of one or more such TLV options can be determined by examining Op-Length and, if Op-Length and the MEF bit indicate that there are TLV options beyond the extended flags area, examining the top two bits of the first options area byte after the extended flags area. The ordering restrictions on TLV options require that, if any Critical Hop-by-Hop TLV options are present, the appear first in the TLV options area. Thus it is adequate to check only if the first TLV option present is a Critical Hop-by-Hop option, which can be determined from the top two bits of its first byte. 2.3.1.5 Flow ID In connection with the multi-pathing of frames, frames that are part of the same order-dependent flow need to follow the same path. Methods to determine flows are beyond the scope of the this document; however, it may be useful, once the flow of a unicast frame has been determined, to preserve and transmit that information for use by subsequent RBridges. D. Eastlake, et al [Page 9] INTERNET-DRAFT TRILL Header Options The Flow ID option is a specially encoded non-critical hop-by-hop option that appears in bits 16 through 31 of the initial bit encoded options area. Its presence is indicated by a non-zero value in that field. It is considered hop-by-hop because it can be added or changed by a transit RBridge and transit RBridges can use it 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 set non-zero in a frame, the option SHOULD NOT be removed, set to zero, or changed unless, for example, a campus is divided into regions such that different Flow IDs would make sense in different regions. 2.3.2 TLV Option Format TRILL Header options, other than the extended header flags and Flow ID described above, are TLV encoded, with some flag bits in the Type and Length octets, in the format show in Figure 3. | 0 1 2 3 4 5 6 7 8 9|10| 11-15 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--- |IE|NC| Type |MT| Length | value... +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--- Figure 3. 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 inserted at the ingress RBridge and are applicable at egress RBridges. Ingress-to-egress options MAY also be examined and acted upon by transit RBridges as specified in the particular option. The second highest order bit of the first octet (NC) is zero for critical options and one for non-critical options. Bit 10 in the second octet (MT) is zero for immutable options and one for mutable options. The IE, NC, Type, and MT fields themselves MUST NOT be changed even for a mutable option. The eight-bit Type code extends from bit 2 through bit 9. The option Type may constrain the values of the IE, NC, and MT bits. For example, a certain Type might require that the option 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 must act on (any critical ingress-to-egress D. Eastlake, et al [Page 10] INTERNET-DRAFT TRILL Header Options option at an egress RBridge and any critical hop-by-hop option), the RBridge MUST discard the frame. If these bits have a value not permitted by for the Type for an option that an RBridge may ignore (any ingress-to-egress option at a transit RBridge and any non- critical option), the RBridge MAY discard the frame. "MAY" is chosen in this case to minimize the checking burden. The Length field is an unsigned quantity giving the length of the option value in units of four octets. It gives the size of the option including 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 31 is reserved and, when such a value is noticed in a frame, the frame MUST be discarded. 2.3.3 Marshaling of Options In a TRILL Header with options, those options start immediately after the Ingress RBridge Nickname and fill the options area. TLV options are 32-bit aligned. TLV options start immediately after the initial four or eight octets of extended flags area and MUST appear in ascending order by the value of the eleven high order bits (bits 0 through 10) of the Type and Length octets considered as an unsigned integer in network byte order. There MUST NOT be more than one option in a frame with any particular value of this eleven high order bits. Thus the TLV options MUST be ordered as follows: (1) critical hop-by-hop options, (2) non- critical hop-by-hop options, (3) critical ingress-to-egress options, and (4) non-critical ingress-to-egress options. Frames that violate this paragraph are erroneous, will produce unspecified results, and MAY be discarded. "MAY" is chosen to minimize the format-checking burden on transit RBridges. If any options are present, those options, both flag and TLV, MUST be correctly summarized into the CHbH, CItE, and TLV summary bits. 2.4 Conflict of Options It is possible for options to conflict. Two or more options can be present in a frame that direct an RBridge processing the frame to do conflicting things or to change its interpretation of later parts of the frame in conflicting ways. Such conflicts are resolved by applying the following rules in the order given: 1. Any frame containing options that require mutually incompatible D. Eastlake, et al [Page 11] INTERNET-DRAFT TRILL Header Options changes in way later parts of the frame, after the options area, are interpreted or structured MUST be discarded. (Such options will be critical options, normally hop-by-hop critical options.) 2. Critical options override non-critical options. 2. Within each of the two categories of critical and non-critical options, the option appearing first in lexical order in the frame always overrides an option appearing later in the frame. Thus a conflict between an extended flag and a TLV option is always resolved in favor of the extended flag. Extended flags with lower bit numbers are considered to have occurred before extended flags with higher bit numbers. D. Eastlake, et al [Page 12] INTERNET-DRAFT TRILL Header Options 3. Specific Extended Header Flag The table below shows the state of TRILL Header extended flag assignments and the location of the special Flow ID field. See Section 6 for IANA Considerations. Bits Purpose Section --------------------------------------- 0-1 Critical Summary Bits 2.3 2 More extended flags 2. 3-4 available for critical hop-by-hop flags 5 available for non-critical hop-by-hop flag 6-7 ECN 3.1 8-10 available for critical ingress-to-egress flags 11-12 available for non-critical ingress-to-egress flags 13-15 TLV Summary Bits 2.3.1.4 16-31 Flow ID 32-39 available for critical hop-by-hop flags 40-47 available for non-critical hop-by-hop flags 48-55 available for critical ingress-to-egress flags 56-63 available for non-critical ingress-to-egress flags Table 1. Extended Flag Options 3.1 The ECN 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 6 and 7 of the extended flags area to 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, which correspond to the recommended provisions of [RFC6040], when that option is enabled: o When ingressing an IP frame that is ECN enabled (non-zero ECN field), it MUST add an options area to the TRILL Header and copy the two ECN bits from the IP header into extended header flags 6 and 7. o When ingressing a frame for a non-IP protocol, where that protocol has a means of indicating ECN that is understood by the RBridge, it MAY add an options area to the TRILL Header with the ECN bits set from the ingressed frame. D. Eastlake, et al [Page 13] INTERNET-DRAFT TRILL Header Options o When forwarding a frame encountering congestion at an RBridge, if an options area is present with extended flags 6 and 7 indicating ECN-capable transport, the RBridge MUST modify them to the congestion experienced value. o When egressing an IP frame, the RBridge MUST set the outgoing native IP frame ECN field to the codepoint at the intersection of the values for that field in the encapsulated IP frame (row) and the TRILL extended Header ECN field (column) in Table 3 below or drop the frame in the case where the TRILL header indicates congestion experienced but the encapsulated native IP frame indicates a not ECN-capable transport. (Such frame dropping is necessary because IP transport that is not ECN-capable requires dropped frames to sense congestion.) o When egressing a non-IP protocol frame with a means of indicating ECN that is understood by the RBridge, it MAY set the ECN information in the egressed native frame by combining that information in the TRILL extended header and the encapsulated non- IP native frame as specified in Table 3. The following table is modified from [RFC3168] and shows the meaning of bit values in TRILL Header extended flags 6 and 7, 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 Field Bit Combinations Table 3 below (adapted from [RFC6040]) shows how, at egress, to combine the ECN information in the extended TRILL Header ECN field with the ECN information in an encapsulated frame to produce the ECN information to be carried in the resulting native frame. +---------+-----------------------------------------------+ | Inner | Arriving TRILL Header ECN Field | | Native +---------+------------+------------+-----------+ | Header | Not-ECT | ECT(0) | ECT(1) | CE | +---------+---------+------------+------------+-----------+ | Not-ECT | Not-ECT | Not-ECT(*) | Not-ECT(*) | (*) | | ECT(0) | ECT(0) | ECT(0) | ECT(1) | CE | | ECT(1) | ECT(1) | ECT(1)(*) | ECT(1) | CE | | CE | CE | CE | CE(*) | CE | +---------+---------+------------+------------+-----------+ Table 3: Egress ECN Behavior D. Eastlake, et al [Page 14] INTERNET-DRAFT TRILL Header Options 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 or did not have an options area. D. Eastlake, et al [Page 15] INTERNET-DRAFT TRILL Header Options 4. Specific TLV Option The table below shows the state of TRILL Header TLV option Type assignment. See Section 6 for IANA Considerations. Type Purpose Section --------------------------------------- 0x00 reserved 0x00-0x7F available 0x80 Test/Pad 4.1 0x81-0xFE available 0xFF reserved Table 4. TLV Option Types The following subsection specifies a particular TRILL TLV option. 4.1 Test/Pad Option This option is intended for testing and padding. A specific meaning for this option with the critical flag set will not be defined so, in that form, it MUST always be treated as an unknown critical option. If the critical flag is not set, the option does nothing. In either case, it may be any length that will fit. Thus, for example, in the non-critical form, it can be used to cause the encapsulated frame staring right after the options area to be 64-bit aligned or for testing purposes. o Type is 0x80. o Length is variable. The value is ignored. o IE may be zero or one. This option has both hop-by-hop and ingress-to-egress versions. o NC is zero for the pad option and one for the test option. + The non-critical version of this option does nothing. + The critical version of this option MUST always be treated as an unknown critical option. o MT may be zero or one except that it must be zero if the other flags indicate the options is a critical hop-by-hop option. This option may be flagged as mutable or immutable. D. Eastlake, et al [Page 16] INTERNET-DRAFT TRILL Header Options 5. Additions to IS-IS RBridges use IS-IS PDUs to inform other RBridges which options they support. The specific IS-IS PDUs, TLVs, or sub-TLVs used to encode and advertise this information are specified in a separate document. Support for critical options MUST be advertised. Support for non- critical options MAY be advertised unless the specification of a particular non-critical option imposes a requirement higher than "MAY" for the advertising of that option by RBridges that implement it. D. Eastlake, et al [Page 17] INTERNET-DRAFT TRILL Header Options 6. IANA Considerations IANA will create two subregistries within the TRILL registry. A "TRILL Extended Header Flags" 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 4 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]. 7. Security Considerations For general TRILL protocol security considerations, see [RFCtrill]. 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 that an authenticating RBridge ignorant of the option would be unable to do and that may be complex and error prone even for an RBridge knowledgeable of the option. It is best for any option to have a unique encoding. 8. Acknowledgements The following are thanked for their contributions: Bob Briscoe. D. Eastlake, et al [Page 18] INTERNET-DRAFT TRILL Header Options 9. References Normative and informative references for this document are given below. 9.1 Normative References [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. [RFC6040] - Briscoe, B., "Tunneling of Explicit Congestion Notification", RFC 6040, November 2010 [RFCtrill] - Perlman, R., D. Eastlake, D. Dutt, S. Gai, and A. Ghanwani, "RBridges: Base Protocol Specification", draft-ietf- trill-rbridge-protocol-16.txt, in RFC Editor's queue. 9.2 Informative References None. D. Eastlake, et al [Page 19] INTERNET-DRAFT TRILL Header Options Change History The sections below summarize changes between successive versions of this draft. RFC Editor: Please delete this section before publication. Version 00 to 02 Change the requirement for TLV option ordering to be strictly ordered by the value of the top nine bits of their first two bytes so that the MT bit is included. Specify meaning of mutability bit for hop-by-hop options. Fix length of Flow ID Value at 2. Require that options that may significantly affect the interpretation or format of subsequent parts of the frame be critical options. Version 02 to 03 Move Test/Pad option into this document from the More Options draft and move the More Flags option from this document into the More Options draft. Prohibit multiple occurrences of a TLV option in a frame. Version 03 to 04 Restructure the bit encoded options area so that the initial 32 bits include a 16 bit Flow ID, various TLV-option-present bits, and a more extended flags bit that means another 32 bits of extended flags are present. Change the Length of TLV encoded options so that it is in units of 4 bytes, not 1, resulting in a bigger Type field. Update Explicit Congestion Notification to follow RFC 6040. Rename "bit encoded options" to be "extended header flags" or "extended flags". D. Eastlake, et al [Page 20] INTERNET-DRAFT TRILL Header Options Authors' Addresses Donald Eastlake Huawei Technologies 155 Beaver Street Milford, MA 01757 Phone: +1-508-333-2270 email: d3e3e3@gmail.com Anoop Ghanwani Brocade Communications Systems 130 Holger Way San Jose, CA 95134 USA Phone: +1-408-333-7149 Email: anoop@brocade.com Vishwas Manral IP Infusion Inc. 1188 E. Arques Ave. Sunnyvale, CA 94089 USA Tel: +1-408-400-1900 email: vishwas@ipinfusion.com Caitlin Bestler Quantum 1650 Technology Drive , Suite 700 San Jose, CA 95110 Phone: +1-408-944-4000 email: cait@asomi.com D. Eastlake, et al [Page 21] INTERNET-DRAFT TRILL Header Options Copyright and IPR Provisions Copyright (c) 2011 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 BSD License. The definitive version of an IETF Document is that published by, or under the auspices of, the IETF. 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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. D. Eastlake, et al [Page 22]