TRILL Working Group Donald Eastlake 3rd
INTERNET-DRAFT Stellar Switches
Intended status: Proposed Standard Anoop Ghanwani
Brocade
Caitlin Bestler
Quantum
Expires: January 10, 2010 July 10, 2010
RBridges: TRILL Header Options
<draft-ietf-trill-rbridge-options-01.txt>
Abstract
The TRILL base protocol specification [RFCtrill], specifies minimal
hooks for TRILL Header options. This draft specifies the format for
options and an initial set of 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 <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-
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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
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D. Eastlake, A. Ghanwani, & C. Bestler [Page 1]
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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..................................5
2.3 Options Format.........................................6
2.3.1 Summary Bits and Bit Options.........................6
2.3.2 TLV Option Format....................................7
2.3.3 Marshalling of Options...............................8
2.4 Conflict of Options....................................9
3. Specific Bit Option....................................10
3.1 ECN Bit Option........................................10
4. Specific TLV Options...................................12
4.1 Flow ID TLV Option....................................12
4.2 Additional Flags TLV Option...........................13
5. Additions to IS-IS.....................................14
5.1 Additions to Link State...............................14
5.2 Additions to Port Capabilities........................14
6. IANA Considerations....................................15
7. Security Considerations................................15
8. References.............................................16
8.1 Normative References..................................16
8.2 Informative References................................16
Change History............................................17
Version 00 to 01..........................................17
D. Eastlake, A. Ghanwani, & C. Bestler [Page 2]
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1. Introduction
The base TRILL protocol specification, which appears in [RFCtrill],
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 encoded 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 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].
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2. TRILL Header Options
The TRILL Protocol includes an option feature in the TRILL Header
(see [RFCtrill] Sections 3.5 and 3.8). 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 might affect any RBridge that receives a TRILL frame containing
such an option, 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 affects it and that it does not implement MUST discard
the frame as it is unsafe to process the frame without understanding
the critical option. Non-critical options can be safely ignored.
Any option indicating a significant change in the way later parts of
the frame are interpreted or sturctured MUST be a critical option.
Options also have a "mutability" flag which has a different meaning
for ingress-to-egress options and for hop-by-hop options.
For an ingress-to-egress option, the mutability flag indicates
whether the value associated with the option 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 normally have the keys to recompute a signature
or authentication code to take a changed value into account.
For a non-critial hop-by-hop option, the mutability flag indicates
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 never required to remove a hop-by-hop
options that it does not implement.
For critial hop-by-hop options, the mutability flag is meaningless.
If the RBridge does not implement the critial hop-by-hop option, it
MUST drop the frame. If it does implement the critial hop-by-hop
option, it will know whether or not it may/should/must remove it.
For critial hop-by-hop options, the mutability flag is set to zero 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.
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Although the hard limit on options length, their 32-bit alignment,
and the presence of critical option summary bits as described
below, are intended to assist in the efficient processing of
frames with options, 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 [RFCtrill].
All Rbridges MUST be able to detect 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 the
critical options present, they MUST discard the frame.
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 such hop-by-hop options;
o MAY change the value and/or length of a mutable ingress-to-egress
option as permitted by that option's specification and 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, 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 that they support in
their IS-IS LSP and advertise the hop-by-hop options they support in
the Hellos they send. An RBridge is not required to support any
options.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 5]
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Unless an RBridge advertises support for a critical option, it will
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 egress the frame support that
option.
"SHOULD NOT" is specified since there may be cases with multi-
destination frames where it is acceptable for those frames to be
discarded by the egress 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 four octets of the options area
consist of two summary bits and 30 option bits as described below.
The remainder of the options area, if any, consists of TLV (Type
Length Value) 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 Summary Bits and Bit Options
| 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 as
follows:
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 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
D. Eastlake, A. Ghanwani, & C. Bestler [Page 6]
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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.
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 don't 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 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 as specified an option that RBridge
implements. 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
All bit encoded options are considered mutable except the critical
hop-by-hop options. Any transit RBridge MUST transparently copy bits
16 through 31, except as permitted by an option implemented by that
RBridge, but MAY either copy or clear any of the bits from 8 through
15. 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 the 2 through 7 or 16 through 31 bits
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.
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.
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| 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 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 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 immutable
options and one for mutablable options. The IE, NC, Type, and MT
fields themselves MUST NOT be changed even for a mutable option.
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 (see Section 4.1),
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 must act on (any
critial ingress-to-egress option at an egress RBridge and any critial
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-critial 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 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
"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.
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TLV options start immediately after the initial four octets of option
and summary bits and MUST appear in ascending order by the value of
the two high order bits of the Type octet considered as an unsigned
2-bit integer. That is, they MUST be ordered as follows: (1)
critical hop-by-hop options, (2) non-critial hop-by-hop options, (3)
critical ingress-to-egress options, and (4) non-critial 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.
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. These padding octets may be any value
and MAY be changed by transit RBridges.
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 four octets of the options area.
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 procesing the frame to do
conflict 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
changes in way later parts of the frame are interpreted or
structured MUST be discarded.
2. Critical options always override non-critical options.
2. Withing the two categories of critical and non-critical options,
the option appearing first in lexical order in the frame always
overrides an optiona appearing later in the frame. Thus a conflict
between a bit option and a TLV option is always resolved in favor
of the bit option. Bit options with lower bit numbers are
considered to have occured before bit options with higher bit
numbers.
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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 area 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 10]
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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 or did not have an options area.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 11]
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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 Flow ID 4.1
0x02-0x2F available
0x30 Additional Flags 4.2
0x31-0x3E 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 operation. Methods to determine flows are beyond the scope
of the this document; 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 transit RBridges may wish to
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 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 at 2 for efficiency. In a
TRILL data frame with only this option, the size of the option plus
the size of the initial 4 summary and flag option octets is such as
to maintain 64-bit alignment of the encpasulated frame.
The option fields and flags are as follows:
o Type is 0x01.
o Length is 2. The data is an unsigned integer that is the flow
ID.
o IE MUST be zero. This is a hop-by-hop option.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 12]
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o NC and MT MUST be one. This is a non-critical mutable option.
4.2 Additional Flags TLV Option
This 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 a 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 once in a frame for each possible combination
of ingress-to-egress, hop-by-hop, non-critical, critical, mutable and
immutable flags (all combinations except for mutable critical hop-by-
hop flags which is a meaningless). 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 0x30.
o Length is variable with a minimum value of 1.
o IE, NC, MT can be any valid combination producing several
variations of this 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 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 and the specification of a
particular non-critial option may impose an implementation
requirement higher than "MAY" for the advertising of that option by
RBridges that implement it.
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 any ingress-to-egress Additional Flags
TLV options, they MUST indicate which critical ingress-to-egress
Additional Flags TLV option flags they support and MAY indicate which
non-critial Additional Flags they support.
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 hop-by-hop Additional Flags TLV options,
they MUST indicate which critical hop-by-hop Additional Flags TLV
option flags they support and MAY indicate which non-critial hop-by-
hop Additional Flags TLV options they support.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 14]
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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 variations of the Additional Flags TLV option that is
initially empty. Such flags are allocated by TRILL Expert Review
[RFC5226].
7. Security Considerations
For general TRILL protocol security considerations, see [RFCtrill].
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, or authentication
information internal to the option itself.
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.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 15]
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8. References
Normative and informative references for this document are given
below.
8.1 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.
[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.
8.2 Informative References
None.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 16]
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Change History
The sections below summarize changes between successive versions of
this draft. RFC Editor: Please delete this section before
publication.
Version 00 to 01
Liberalize requirement for TLV options to be strictly ordered by the
value of their first octet to (1) require ordering by the top two
bits of the first octet and (2) require that transit RBridges not re-
order ingress-to-egress options. Liberalize requirements on contents
TLV option padding octets that assure 32-bit alignment.
Specify meaning of mutability bit for hop-by-hop options.
Fix length of Flow ID Value at 2.
D. Eastlake, A. Ghanwani, & C. Bestler [Page 17]
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Authors' Addresses
Donald E. Eastlake 3rd
Stellar Switches
155 Beaver Street
Milford, MA 01757
Phone: +1-508-333-2270
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
Quantum
1650 Technology Drive , Suite 700
San Jose, CA 95110
Phone: +1-408-944-4000
email: cait@asomi.com
D. Eastlake, A. Ghanwani, & C. Bestler [Page 18]
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Copyright and IPR Provisions
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D. Eastlake, A. Ghanwani, & C. Bestler [Page 19]
