rfc9885v2.txt		rfc9885.txt
	skipping to change at line 114 ¶		skipping to change at line 114 ¶
	defining new attributes, further adding to the scaling pressures.		defining new attributes, further adding to the scaling pressures.
	The original TLV definition limits each TLV to a maximum of 255		The original TLV definition limits each TLV to a maximum of 255
	octets of payload, which is becoming increasingly problematic.		octets of payload, which is becoming increasingly problematic.
	Some TLV definitions have addressed this by explicitly stating that a		Some TLV definitions have addressed this by explicitly stating that a
	TLV may appear multiple times inside of a Link State PDU (LSP).		TLV may appear multiple times inside of a Link State PDU (LSP).
	However, this has not been done for many currently defined TLVs,		However, this has not been done for many currently defined TLVs,
	leaving the situation somewhat ambiguous.		leaving the situation somewhat ambiguous.
	For example, [RFC5305] defines the Extended IS reachability TLV (22)		For example, [RFC5305] defines the Extended IS reachability TLV (22)
	and [RFC5120] defines the MT Intermediate Systems TLV (222). These		and [RFC5120] defines the MT-ISN TLV (222). These documents do not
	documents do not specify sending multiple TLVs for the same object		specify sending multiple TLVs for the same object and no other
	and no other mechanism for expanding the information carrying		mechanism for expanding the information carrying capacity of the TLV
	capacity of the TLV has been specified.		has been specified.
	The intent of this document is to clarify and codify the situation by		The intent of this document is to clarify and codify the situation by
	explicitly making multiple occurrences of a TLV the standard		explicitly making multiple occurrences of a TLV the standard
	mechanism for scaling TLV contents. Any future document that		mechanism for scaling TLV contents. Any future document that
	proposes a different mechanism for scaling TLV contents for a given		proposes a different mechanism for scaling TLV contents for a given
	codepoint must explain why multiple occurrences of a TLV is not		codepoint must explain why multiple occurrences of a TLV is not
	appropriate.		appropriate.
	This document does not alter the encoding of any TLV where multiple		This document does not alter the encoding of any TLV where multiple
	occurrences of a TLV are already defined. Some examples of this are:		occurrences of a TLV are already defined. Some examples of this are:
	skipping to change at line 139 ¶		skipping to change at line 139 ¶
	* Router CAPABILITY TLV (Type 242) [RFC7981]		* Router CAPABILITY TLV (Type 242) [RFC7981]
	* Application-Specific SRLG (Type 238) [RFC9479]		* Application-Specific SRLG (Type 238) [RFC9479]
	* Instance Identifier (Type 7) [RFC8202]		* Instance Identifier (Type 7) [RFC8202]
	* Application-Specific Link Attributes (sub-TLV Type 16) [RFC9479]		* Application-Specific Link Attributes (sub-TLV Type 16) [RFC9479]
	[RFC7356] has defined a 16-bit Length field for TLVs in flooding		[RFC7356] has defined a 16-bit Length field for TLVs in flooding
	scoped Protocol Data Units (PDUs), in which case the problem		scoped Protocol Data Units (PDUs), in which case the problem
	addressed by this document would not exist. However, introduction of		addressed by this document would likely not be encountered. However,
	these new PDU types is not backwards compatible. Therefore, there is		introduction of these new PDU types is not backwards compatible.
	a need to address how to expand the information advertised in		Therefore, there is a need to address how to expand the information
	existing PDUs that use 8-bit length TLVs.		advertised in existing PDUs that use TLVs with 8-bit Length fields.
	The mechanism described in this document has not been documented for		The mechanism described in this document has not been documented for
	all TLVs previously. This document provides the necessary protocol		all TLVs previously. This document provides the necessary protocol
	definition and discusses potential interoperability issues and		definition and discusses potential interoperability issues and
	deployment challenges.		deployment challenges.
	This document specifies a means for extending TLVs where no extension		This document specifies a means for extending TLVs where no extension
	mechanism has been previously explicitly specified, and defines this		mechanism has been previously explicitly specified, and defines this
	mechanism as the default extension mechanism for future TLVs. The		mechanism as the default extension mechanism for future TLVs. The
	mechanism described in this document is applicable to top level TLVs		mechanism described in this document is applicable to top level TLVs
	skipping to change at line 379 ¶		skipping to change at line 379 ¶
	Type: 30 (1 octet)		Type: 30 (1 octet)
	Length: 0 (1 octet)		Length: 0 (1 octet)
	Routers that support MP-TLV for codepoints for which existing		Routers that support MP-TLV for codepoints for which existing
	specifications do not explicitly define such support, but for which		specifications do not explicitly define such support, but for which
	MP-TLV is applicable, SHOULD include this sub-TLV in a Router		MP-TLV is applicable, SHOULD include this sub-TLV in a Router
	CAPABILITY TLV.		CAPABILITY TLV.
	Scope of the associated Router CAPABILITY TLV is per level (S-bit		Scope of the associated Router CAPABILITY TLV is per level (S-bit
	clear).		clear) [RFC7981].
	This advertisement is for informational purposes only. IS-IS		This advertisement is for informational purposes only. IS-IS
	protocol implementations MUST NOT alter what is sent or how what is		protocol implementations MUST NOT alter what is sent or how what is
	received is processed based on these advertisements.		received is processed based on these advertisements.
	The sub-TLV intentionally does not provide a syntax to specify MP-TLV		The sub-TLV intentionally does not provide a syntax to specify MP-TLV
	support on a per-codepoint basis. It is presumed that if such		support on a per-codepoint basis. It is presumed that if such
	support is provided that it applies to all relevant codepoints. It		support is provided that it applies to all relevant codepoints. It
	is understood that in reality, a given implementation might limit MP-		is understood that in reality, a given implementation might limit MP-
	TLV support to particular codepoints based on the needs of the		TLV support to particular codepoints based on the needs of the
	skipping to change at line 475 ¶		skipping to change at line 475 ¶
	existing TLV, as long as there is space in the TLV, information		existing TLV, as long as there is space in the TLV, information
	SHOULD NOT be split into multiple TLVs. If there is no space in the		SHOULD NOT be split into multiple TLVs. If there is no space in the
	current LSP to fit the now larger TLV, the TLV SHOULD be moved to a		current LSP to fit the now larger TLV, the TLV SHOULD be moved to a
	new LSP.		new LSP.
	9. IANA Considerations		9. IANA Considerations
	9.1. MP-TLV Support Sub-TLV		9.1. MP-TLV Support Sub-TLV
	IANA has registered the following code point from the "IS-IS Sub-TLVs		IANA has registered the following code point from the "IS-IS Sub-TLVs
	for IS-IS Router CAPABILITY TLV" registry:		for IS-IS Router CAPABILITY TLV" registry (see
			<https://www.iana.org/assignments/isis-tlv-codepoints>):
	Type: 30		Type: 30
	Description: MP-TLV Support for TLVs with Implicit Support		Description: MP-TLV Support for TLVs with Implicit Support
	MP-TLV Applicability: N		MP-TLV Applicability: N
	Reference: Section 7 of RFC 9885		Reference: Section 7 of RFC 9885
	9.2. Extension to IS-IS Top-Level TLV Registries		9.2. Extension to IS-IS Top-Level TLV Registries
	IANA has extended a number of registries under the "IS-IS TLV		IANA has extended a number of registries under the "IS-IS TLV
	Codepoints" registry group (<https://www.iana.org/assignments/isis-		Codepoints" registry group (<https://www.iana.org/assignments/isis-
	skipping to change at line 500 ¶		skipping to change at line 501 ¶
	The following subsections provide the initial contents of the new		The following subsections provide the initial contents of the new
	column for a number of existing registries. The initial values for		column for a number of existing registries. The initial values for
	MP-TLV applicability defined in the following subsections are based		MP-TLV applicability defined in the following subsections are based
	on the rule that MP-TLV is applicable to any codepoint that supports		on the rule that MP-TLV is applicable to any codepoint that supports
	sub-TLVs, without regard to whether the sub-TLVs that are currently		sub-TLVs, without regard to whether the sub-TLVs that are currently
	defined are sufficient to require MP-TLVs to be sent.		defined are sufficient to require MP-TLVs to be sent.
	9.2.1. MP-TLV for IS-IS Top-Level TLV Codepoints		9.2.1. MP-TLV for IS-IS Top-Level TLV Codepoints
			IANA has added the MP column to the "IS-IS Top-Level TLV Codepoints"
			registry (<https://www.iana.org/assignments/isis-tlv-codepoints>) and
			populated it as shown in Table 1.
	+===========+====================================+====+		+===========+====================================+====+
	| Value | Name | MP |		| Value | Name | MP |
	+===========+====================================+====+		+===========+====================================+====+
	| 0 | Reserved | |		| 0 | Reserved | |
	+-----------+------------------------------------+----+		+-----------+------------------------------------+----+
	| 1 | Area Addresses | N |		| 1 | Area Addresses | N |
	+-----------+------------------------------------+----+		+-----------+------------------------------------+----+
	| 2 | IIS Neighbors | N |		| 2 | IIS Neighbors | N |
	+-----------+------------------------------------+----+		+-----------+------------------------------------+----+
	| 3 | ES Neighbors | N |		| 3 | ES Neighbors | N |
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