Internet Engineering Task Force (IETF) G. Fairhurst
Request for Comments: 7280 University of Aberdeen
Updates: 4326 June 2014
Category: Standards Track
ISSN: 2070-1721
IANA Guidance for Managing
the Unidirectional Lightweight Encapsulation (ULE) Next-Header Registry
Abstract
This document updates RFC 4326 to clarify and update the allocation
rules for the Unidirectional Lightweight Encapsulation (ULE) Next-
Header registry. This registry is used by ULE and Generic Stream
Encapsulation (GSE) to record the code points of extension headers Extension Headers
and protocols supported by these encapsulation protocols.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7280.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. The ULE Next-Header Registry . . . . . . . . . . . . . . 3
2.2. Informative Example of Using a Value from the Optional
Range . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Updated IANA Guidance on Allocation in the ULE Next-Header
Registry . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. ULE Next-Header Registry . . . . . . . . . . . . . . . . 4
3.2. Expert Review Guidelines . . . . . . . . . . . . . . . . 4 5
3.3. Reservation of Next-Header Values for Private Use . . . . 5
4. Update to Registry Information . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
1. Introduction
The Unidirectional Lightweight Encapsulation (ULE) [RFC4326]
specifies an encapsulation for links that employ the MPEG-2 Transport
Stream, with support over a wide variety of physical-layer bearers
[RFC4259]. The encapsulation header includes a Type field that
identifies payload types and extension headers Extension Headers (e.g., [RFC5163]).
The ULE specification requested IANA to maintain the ULE Next-Header
registries
registry to record the allocation of the values used to derive this
Type field.
The Digital Video Broadcast (DVB) Project has published an
encapsulation for second-generation DVB physical layers. This
specifies the Generic Stream Encapsulation [GSE]. This encapsulation
shares many of the network properties of ULE and uses a common format
for the Type field [RFC5163]. The ULE Next-Header registries are registry is
therefore also applicable to this encapsulation.
This document updates the IANA rules and guidance defined in
Section 11.1 of [RFC4326] in the following way:
o The document clarifies use of the ULE Next-Header registry by GSE
as well as for by ULE.
o Section 3 specifies that new allocations in the ULE Next-Header
registry are to be assigned by IANA using the "Specification
Required" policy and provides guidance to the expert reviewer.
o Section 3.3 reserves a range of allocated values.
o Section 4 adds an explanatory note to clarify the encoding used in
the ULE Next-Header registry.
2. Terminology
This document assumes familiarity with the ULE terminology used in
[RFC4326] and [RFC5163].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2.1. The ULE Next-Header Registry
The mandatory extension headers Mandatory Extension Headers are allocated in the ULE Next-Header
registry with integer values in the decimal range 0-255. The
registered value corresponds to a 16-bit Type value (converted by
setting the most significant 8 bits of the 16-bit value to zero).
This Type value may identify a mandatory extension header Mandatory Extension Header or a
specific protocol.
The optional extension headers Optional Extension Headers are allocated in the ULE Next-Header
registry with integer values in the decimal range 256-511. The
registered value corresponds to the 16-bit Type value that would be
used for an optional extension header Optional Extension Header with a length (H-LEN) of 1.
2.2. Informative Example of Using a Value from the Optional Range
This section provides an informative example of how a registry entry
is constructed to identify an optional Optional ULE extension header. Extension Header.
Values registered by IANA in the optional Optional ULE extension header Extension Header range
correspond to a 16-bit Type value with the H-LEN field (in bits 5 to
7) set to a decimal value of 1. This registration format is used
irrespective of the H-LEN value to be used. Bits 8 to 15 of the
value in the registry are combined with the actual required H-LEN
value (bits 5 to 7) to form the 16-bit Type field.
For example, the decimal value 256 has been allocated to denote the
padding extension header. Extension Header.
o Type value 256: When a 2-byte padding extension header Extension Header is used,
the H-LEN is 1, resulting in a Type value with a decimal value of
256 (as allocated), corresponding to a hexadecimal value of 0x100.
o Type value 768: When a 6-byte padding extension header Extension Header is used,
the H-LEN is 3, resulting in a Type value with a decimal value of
768, corresponding to a hexadecimal value of 0x300.
3. Updated IANA Guidance on Allocation in the ULE Next-Header Registry
The rules for allocation were defined in Section 11 of [RFC4326].
This document updates these rules by replacing them with the rules in
this section:
Allocations in the ULE Next-Header registry are to be assigned by
IANA using the "Specification Required" policy defined in [RFC5226].
Applications must include a reference to a specification of the Next-
Header extension in a standards document. "permanent and readily available public
specification" [RFC5226]. An IETF Standards Track RFC can provide
such a reference. Other specifications are also permitted. The
Designated Expert shall advise IANA on whether a particular
specification constitutes a standards document. "permanent and readily available public
specification".
3.1. ULE Next-Header Registry
The ULE Next-Header registry allocates 0-511 decimal (0x0000-0x01FF
hexadecimal). IANA must not allocate values greater than 511
(decimal). For each allocated value, it also specifies the set of
allowed H-LEN values (see [RFC4326], Section 5). The combination of
the IANA-registered value and the H-LEN are used by ULE and GSE to
derive a set of allowed 16-bit integer values in the range 0-1535
(decimal). This forms the first part of the ULE Type space (see
[RFC4326], Section 4.4.1).
The registry is divided into two ranges:
1. 0-255 (decimal) IANA-assigned values, indicating Mandatory
Extension Headers (or link-dependent Type fields). [RFC4326]
made initial assignments to this range of values in the registry,
updated by later requests.
2. 256-511 (decimal) IANA-assigned values, indicating Optional
Extension Headers. The entry MUST define the need for the
Optional Extension and the intended use. [RFC4326] made initial
assignments to this range of values in the registry, updated by
later requests.
3.2. Expert Review Guidelines
The Specification Required policy also implies use of a Designated
Expert [RFC5226]. The Designated Expert shall review a proposed
registration for the following REQUIRED information:
For requests in the range 0-255 (decimal) - Mandatory Extension
Headers:
o The value and the name associated with the Extension Header;
o The procedure for processing the Extension Header;
o A definition of the Extension Header and the intended use; and
o The size of the Extension Header (by default, the entire remaining
payload).
For requests in the range 256-511 (decimal) - Optional Extension
Headers:
o The value and the name associated with the Optional Extension
Header;
o The procedure for processing the Extension Header;
o A definition of the Extension Header and the intended use
(including any extension ordering requirements); and
o The range of allowable H-LEN values that are permitted (in the
range 1-5).
If the registration information does not have any of the above
required information, the Designated Expert shall not approve the
registration to IANA.
3.3. Reservation of Next-Header Values for Private Use
This document reserves the range 144-159 decimal (0x80-0x8F
hexadecimal) for Private Use [RFC5226].
These values are not available for allocation by IANA. Appropriate
use includes development of experimental options for which either no
general-purpose solution was planned, insufficient operational
experience was available to understand if a general solution is
needed, or a more general solution is not yet mature. This use is
not coordinated between users of these values, so the uniqueness of a
particular value can not be guaranteed.
Authors of specifications MUST contact IANA to request a new value to
be allocated in the ULE Next-Header registry. An IANA-allocated
value uniquely identifies the method. Such an allocation is REQUIRED
for any method that is to be standardised.
4. Update to Registry Information
IANA has recorded an additional explanatory note in the ULE Next-
Header registry:
The Mandatory Extension Header range in the ULE Next-Header
registry is used to allocate integer values in the range 0-255
(decimal). These values are used to identify mandatory extension
headers. Mandatory Extension
Headers. The registered value corresponds to the 16-bit Type
value for the mandatory extension header Mandatory Extension Header or the specified
protocol.
The Optional Extension Header range in the ULE Next-Header
registry is used to allocate integer values in the range 256-511
(decimal). These values are used to identify optional extension
headers. Optional Extension
Headers. The registered value corresponds to the 16-bit Type
value that would be used for an optional extension header Optional Extension Header with a
header length (H-LEN) of 1.
This additional note has been placed before the existing note.
5. Security Considerations
This document does not present new security considerations.
6. IANA Considerations
Section 3 specifies updated IANA allocation rules.
Per Section 3.3, IANA has reserved the range 144-159 decimal
(0x80-0x8F hexadecimal) marked it as Reserved for Private Use.
Per Section 4, IANA has updated the ULE Next-Header registry
information.
7. Acknowledgments
The author acknowledges feedback from IANA, Thomas Narten, Margaret
Wasserman, Wes Eddy, and the IETF Gen-ART team. Helpful reviews and
comments on usage of this registry were also received from Alexander
Adolf and Hans-Peter Lexow.
8. References
8.1. Normative References
[GSE] European Telecommunication Standards Institute (ETSI),
"Digital Video Broadcasting (DVB); Generic Stream
Encapsulation (GSE) Protocol", 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4326] Fairhurst, G. and B. Collini-Nocker, "Unidirectional
Lightweight Encapsulation (ULE) for Transmission of IP
Datagrams over an MPEG-2 Transport Stream (TS)", RFC 4326,
December 2005.
[RFC5163] Fairhurst, G. and B. Collini-Nocker, "Extension Formats
for Unidirectional Lightweight Encapsulation (ULE) and the
Generic Stream Encapsulation (GSE)", RFC 5163, April 2008.
[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
[RFC4259] Montpetit, M., Fairhurst, G., Clausen, H., Collini-Nocker,
B., and H. Linder, "A Framework for Transmission of IP
Datagrams over MPEG-2 Networks", RFC 4259, November 2005.
Author's Address
Godred Fairhurst
University of Aberdeen
School of Engineering
Fraser Noble Building
Aberdeen, Scotland AB24 3UE
UK
EMail: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk