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
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provisions of BCP 78 and BCP 79.
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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.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 1]
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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)
D. Eastlake, A. Ghanwani, & C. Bestler [Page 5]
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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
D. Eastlake, A. Ghanwani, & C. Bestler [Page 9]
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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.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 15]
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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
D. Eastlake, A. Ghanwani, & C. Bestler [Page 16]
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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
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Please review these documents carefully, as they describe your rights
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the avoidance of doubt, each Contributor to the IETF Standards
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provisions of RFC 5378. No language to the contrary, or terms,
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Contributor, or included with or in such Contribution.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 17]