IANA Guidance for Managing the Unidirectional Lightweight Encapsulation (ULE) Next-Header Registry

The policy was changed from RFC 4326's original allocation rules to 'Specification Required' (rather than a more permissive policy) to ensure each registry entry is backed by a permanent and readily available public specification, providing long-term stability and implementer guidance.

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The Private Use range (144-159) was reserved to support experimental Extension Headers where no general-purpose solution was planned, operational experience was insufficient, or a more general solution was not yet mature — deliberately avoiding premature standardization of experimental features.

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The DVB Generic Stream Encapsulation (GSE) for second-generation DVB physical layers shares the same Type field format as ULE and therefore also uses the ULE Next-Header registry. RFC 7280 explicitly clarifies that the registry applies to both ULE and GSE.

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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, and such an allocation is REQUIRED for any method that is to be standardised.

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IANA must not allocate values greater than 511 decimal in the ULE Next-Header registry. The combination of each IANA-registered value and the H-LEN field derives a set of allowed 16-bit integer values in the range 0-1535 decimal, forming the first part of the ULE Type space.

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New allocations in the ULE Next-Header registry are to be assigned by IANA using the 'Specification Required' policy as defined in RFC 5226. Applications must include a reference to a permanent and readily available public specification; an IETF Standards Track RFC satisfies this requirement, but other specifications are also permitted.

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The range 144-159 decimal (0x80-0x8F hexadecimal) is reserved for Private Use and is not available for IANA allocation. These values may be used for experimental or proprietary purposes without coordination, so uniqueness cannot be guaranteed.

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The Designated Expert must verify four required items for Optional Extension Header registrations (256-511): the value and name, the processing procedure, a definition with intended use and ordering requirements, and the range of allowable H-LEN values (1-5). Missing information must block approval.

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Values 0-255 decimal in the ULE Next-Header registry identify Mandatory Extension Headers (or link-dependent Type fields). The registered integer value corresponds to a 16-bit Type value with the most significant 8 bits set to zero.

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Values 256-511 decimal in the ULE Next-Header registry identify Optional Extension Headers. Each entry MUST define the need for the Optional Extension and the intended use. The registered value corresponds to the 16-bit Type value for an Optional Extension Header with H-LEN equal to 1.

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The ULE Next-Header registry allocates decimal values 0-511 (0x0000-0x01FF hexadecimal) for use by both ULE and GSE encapsulations to identify Extension Headers and payload protocols. IANA must not allocate values greater than 511 decimal. This document updates the allocation rules from RFC 4326 Section 11.1.

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RFC 7280 does not present new security considerations. The document is an administrative update to IANA allocation rules and does not change the security properties of the ULE or GSE encapsulations.

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For Mandatory Extension Headers, the 16-bit Type field is formed by setting the most significant 8 bits to zero and the lower 8 bits to the registry value (0-255). For Optional Extension Headers, the 16-bit Type field combines bits 8-15 from the registry value with the actual H-LEN (bits 5-7), yielding 16-bit values in the range 0-1535 decimal.

Optional Extension Header Type values registered at decimal 256 with H-LEN=1 yield Type 256 (0x0100); the same extension with H-LEN=3 yields Type 768 (0x0300). Bits 8-15 come from the registry entry; bits 5-7 carry the actual H-LEN value used.