IS-IS 2003-05-06 2026-03-05 For IS-IS registries and value ranges maintained via the "Expert Review" registration procedure, guidance for IESG-designated experts can be found in . Expert Review Top-level TLVs for the IS-IS protocol Chris Hopps, Hannes Gredler, Les Ginsberg IETF SHALL keep JTC1/SC6 informed of TLV codepoint values allocated, and JTC1/SC6 SHALL refer allocation requests arising within JTC1 constituencies to the IANA registry process. Codepoints greater than 255 can only be used in PDUs designated to support extended TLVs. 0 Reserved 1 Area Addresses y y n n n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 2 IIS Neighbors n y n n n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 3 ES Neighbors n y n n n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 4 Part. DIS n y n n n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 5 Prefix Neighbors n y n n n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 6 IIS Neighbors y n n n n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 7 Instance Identifier y y y y y 8 Padding y n n n n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 9 LSP Entries n n y n n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 10 Authentication y y y y n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 11 ESN TLV y n y n n 12 Opt. Checksum y n y n n 13 Purge Originator Identification n n n y n 14 LSPBufferSize n y n n n ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 15 Router-Fingerprint y y n y n 16 Reverse Metric y n n n n 17 IS-IS Area Node IDs n y n n n 18 IS-IS Flooding Path n y n n n 19 IS-IS Flooding Request y n n n n 20 Area Proxy n y n n y 21 Flooding Parameters TLV y n y n y 22 Extended IS reachability n y n n y 23 IS Neighbor Attribute n y n n y 24 IS Alias ID n y n n n 25 L2 Bundle Member Attributes n y n n y 26 Unassigned 27 SRv6 Locator n y n n y 28 Zone ID (DEPRECATED - temporarily registered 2020-11-20, allowed to expire 2025-10-15) n y n n n 29-41 Unassigned 42 DECnet Phase IV y n n n n DEC (ancient) 43-65 Unassigned 66 Lucent Proprietary n y n n n 67-125 Unassigned 126 IPv4 Algorithm Prefix Reachability n y n n n RFC9502, Section 6.1 127 IPv6 Algorithm Prefix Reachability n y n n n RFC9502, Section 6.2 128 IP Int. Reach n y n n n 129 Prot. Supported y y n n n 130 IP Ext. Address n y n n n 131 IDRPI n y y n n 132 IP Intf. Address y y n n n 133 Illegal n n n n n (not used) 134 Traffic Engineering router ID n y n n n 135 Extended IP reachability n y n n y 136 Unassigned 137 Dynamic Name n y n y n 138 GMPLS-SRLG n y n n y 139 IPv6 SRLG n y n n n 140 IPv6 TE Router ID n y n n n 141 Inter-AS Reachability Information n y n n y 142 GADDR-TLV n y n n y 143 MT-Port-Cap-TLV y n n n y 144 MT-Capability TLV n y n n y 145 TRILL Neighbor TLV y n n n n 146 Unassigned 147 MAC-RI TLV n y n n y 148 BFD-Enabled TLV y n n n y 149 Segment Identifier / Label Binding n y n n y 150 Multi-Topology Segment Identifier / Label Binding n y n n y 151-160 Unassigned 161 Flood Reflection y n n n n 162-175 Unassigned 176 Nortel Proprietary n y n n n 177 Nortel Proprietary n y n n n 178-210 Unassigned 211 Restart TLV y n n n n 212-221 Unassigned 222 MT-ISN n y n n y 223 MT IS Neighbor Attribute n y n n y 224-228 Unassigned 229 M-Topologies y y n n n 230-231 Unassigned 232 IPv6 Intf. Addr. y y n n n 233 IPv6 Global Interface Address TLV y n n n n 234 Unassigned 235 MT IP. Reach n y n n y 236 IPv6 IP. Reach n y n n y 237 MT IPv6 IP. Reach n y n n y 238 Application-Specific SRLG n y n n y 239 Unassigned 240 P2P 3-Way Adj. State y n n n n 241 Unassigned 242 IS-IS Router CAPABILITY TLV n y n n y 243 Scope Flooding Support y n n n n 244-250 Unassigned 251 Generic Information n y n n y 252-65535 Unassigned Expert Review Type Codes for Authentication TLV (10) Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 1 Cleartext Password ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 2 ISO 10589 Reserved ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. 3 Cryptographic Authentication (CRYPTO_AUTH) 4-53 Unassigned 54 HMAC-MD5 Authentication 55-254 Unassigned 255 Routing Domain private authentication method ISO 10589, "Intermediate System to Intermediate System Intra- Domain Routeing Exchange Protocol for use in Conjunction with the Protocol for Providing the Connectionless-mode Network Service (ISO 8473)", International Standard 10589: 2002, Second Edition, 2002. Expert Review Sub-TLVs for Reverse Metric TLV (16) Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1-17 Unassigned 18 Traffic Engineering Metric n RFC8500, Section 2 19-255 Unassigned Expert Review This registry defines sub-TLVs for TLVs advertising neighbor information. The list of TLVs includes: Extended IS reachability (22) IS Neighbor Attribute (23) L2 Bundle Member Attributes (25) inter-AS reachability information (141) MT-ISN (222) MT IS Neighbor Attribute (223) Chris Hopps, Hannes Gredler, Les Ginsberg Allocations within this registry require documentation of the use of the allocated value and approval by the Designated Expert assigned by the IESG. The column for TLV 25 may be marked as follows: y - sub-TLV may appear in TLV 25 but MUST NOT be shared by multiple L2 Bundle Members y(s) - sub-TLV may appear in TLV 25 and MAY be shared by multiple L2 Bundle Members n - sub-TLV MUST NOT appear in TLV 25 0-2 Unassigned 3 Administrative group (color) y y y(s) y y y n 4 Link Local/Remote Identifiers y y y(s) y y y n 5 Unassigned 6 IPv4 interface address y y y(s) y y y n 7 Unassigned 8 IPv4 neighbor address y y y(s) y y y n 9 Maximum link bandwidth y y y(s) y y y n 10 Maximum reservable link bandwidth y y y(s) y y y n 11 Unreserved bandwidth y y y(s) y y y n 12 IPv6 Interface Address y y y(s) y y y n 13 IPv6 Neighbor Address y y y(s) y y y n 14 Extended Administrative Group y y y(s) y y y n 15 Link MSD y y y y y y y 16 Application-Specific Link Attributes y y y(s) y y y y 17 Generic Metric y y y y y y n RFC9843, Section 2.1 18 TE Default metric y y y(s) y y y n 19 Link-attributes y y y(s) y y y n 20 Link Protection Type y y y(s) y y y n 21 Interface Switching Capability Descriptor y y y(s) y y y y 22 Bandwidth Constraints y y y(s) y y y n 23 Unconstrained TE LSP Count (sub-)TLV y y y(s) y y y n 24 Remote AS Number n n n y n n n 25 IPv4 Remote ASBR Identifier n n n y n n n 26 IPv6 Remote ASBR Identifier n n n y n n n 27 Interface Adjustment Capability Descriptor (IACD) y y y(s) y y y y 28 MTU y y n n y y n 29 SPB-Metric y y y(s) n y y n 30 SPB-A-OALG y y y(s) n y y y 31 Adjacency Segment Identifier y y n y y y n 32 LAN Adjacency Segment Identifier y y n y y y n 33 Unidirectional Link Delay y y y y y y n 34 Min/Max Unidirectional Link Delay y y y y y y n 35 Unidirectional Delay Variation y y y y y y n 36 Unidirectional Link Loss y y y y y y n 37 Unidirectional Residual Bandwidth y y y y y y n 38 Unidirectional Available Bandwidth y y y y y y n 39 Unidirectional Utilized Bandwidth y y y y y y n 40 RTM Capability y y n n y y n 41 L2 Bundle Member Adj-SID n n y n n n y 42 L2 Bundle Member LAN Adj-SID n n y n n n y 43 SRv6 End.X SID y y y y y y y RFC9352, Section 8.1 44 SRv6 LAN End.X SID y y y y y y y RFC9352, Section 8.2 45 IPv6 Local ASBR Identifier n n n y n n n 46-160 Unassigned 161 Flood Reflector Adjacency y y n y y y n 162-249 Unassigned 250-254 Reserved for Cisco-specific extensions 255 Reserved for future expansion Expert Review Chris Hopps, Hannes Gredler, Les Ginsberg This registry defines bit values for the Link-attributes sub-TLV (19) advertised in TLVs advertising neighbor information. These TLVs are listed in the description of the “IS-IS Sub-TLVs for TLVs Advertising Neighbor Information” registry. The "L2BM" column indicates applicability to the L2 Bundle Member Attributes TLV. The options for the "L2BM" column are: Y - This bit MAY appear in the L2 Bundle Member Attributes TLV. N - This bit MUST NOT appear in the L2 Bundle Member Attributes TLV. 0x1 Local Protection Available N 0x2 Link Excluded from Local Protection N 0x4 Local Edge Enabled for Flooding (LEEF) N Expert Review This registry defines sub-TLVs for TLVs advertising prefix reachability. The list of TLVs includes: SRv6 Locator (27) IPv4 Algorithm Prefix Reachability (126) IPv6 Algorithm Prefix Reachability (127) Extended IP reachability (135) MT IP Reach (235) IPv6 IP Reach (236) MT IPv6 IP Reach (237) Chris Hopps, Hannes Gredler, Les Ginsberg Allocations within this registry require documentation of the use of the allocated value and approval by the Designated Expert assigned by the IESG. 0 Unassigned 1 32-bit Administrative Tag Sub-TLV y y y y y y y y 2 64-bit Administrative Tag Sub-TLV y y y y y y y y 3 Prefix Segment Identifier n n n y y y y n 4 Prefix Attribute Flags y y y y y y y n 5 SRv6 End SID y n n n n n n y RFC9352, Section 7.2 6 Flexible Algorithm Prefix Metric (FAPM) n n n y y y y n RFC9350, Section 8 7-10 Unassigned 11 IPv4 Source Router ID y y y y y y y n 12 IPv6 Source Router ID y y y y y y y n 13-31 Unassigned 32 BIER Info n n n y y y y y 33-255 Unassigned Expert Review This registry defines bit values for the Prefix Attribute Flags (4) sub-TLV advertised in Prefix Reachability TLVs. These TLVs are listed in the description of the "IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability” registry. Chris Hopps, Hannes Gredler, Les Ginsberg 0 External Prefix Flag (X-flag) 1 Re-advertisement Flag (R-flag) 2 Node Flag (N-flag) 3 ELC Flag (E-flag) 4 Anycast Flag (A-flag) RFC9352, Section 6 5 U-Flag RFC9929, Section 3.2 6 UP-Flag RFC9929, Section 3.2 Expert Review This registry defines Group Address Type Codes for the GADDR-TLV (142). Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1 GMAC-ADDR 2 GIP-ADDR 3 GIPV6-ADDR 4 GLMAC-ADDR 5 GLIP-ADDR 6 GLIPV6-ADDR 7-254 Unassigned 255 Reserved Expert Review This registry defines sub-TLVs for the MT-Port-Cap-TLV (143). Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1 VLAN-FLAGs 2 Enabled-VLANs 3 AppointedFwrdrs 4 SPB-MCID 5 SPB-Digest 6 SPB-B-VID 7 PORT-TRILL-VER 8 VLANs-Appointed 9-254 Unassigned 255 Reserved Expert Review This registry defines sub-TLVs for the MT-Capability TLV (144). Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1 SPB-Inst n 2 SPB-I-OALG y 3 SPBM-SI y 4 SPBV-ADDR y 5 Unassigned 6 NICKNAME y 7 TREES n 8 TREE-RT-IDs y 9 TREE-USE-IDs y 10 INT-VLAN y 11-12 Unassigned 13 TRILL-VER n 14 VLAN-GROUP y 15 INT-LABEL y 16 RBCHANNELS y 17 AFFINITY y 18 LABEL-GROUP y 19-20 Unassigned 21 Topology sub-TLV y 22 Hop sub-TLV n 23 Bandwidth Constraint sub-TLV n 24 Bandwidth Assignment sub-TLV n 25 Timestamp sub-TLV n 26-254 Unassigned 255 Reserved Expert Review This registry defines sub-TLVs for the IS-IS Router CAPABILITY TLV (242). Chris Hopps, Hannes Gredler, Les Ginsberg Allocations within this registry require documentation of the use of the allocated value and approval by the Designated Expert assigned by the IESG. 0 Reserved 1 TE Node Capability Descriptor n 2 Segment Routing Capability n 3 TE-MESH-GROUP TLV (IPv4) y 4 TE-MESH-GROUP TLV (IPv6) y 5 PCED sub-TLV n 6 NICKNAME y 7 TREES n 8 TREE-RT-IDs y 9 TREE-USE-IDs y 10 INT-VLAN y 11 IPv4 TE Router ID n 12 IPv6 TE Router ID n 13 TRILL-VER n 14 VLAN-GROUP y 15 INT-LABEL y 16 RBCHANNELS y 17 AFFINITY y 18 LABEL-GROUP y 19 Segment Routing Algorithm n 20 S-BFD Discriminators n 21 Node-Admin-Tag n 22 Segment Routing Local Block (SRLB) n 23 Node MSD y 24 Segment Routing Mapping Server Preference (SRMS Preference) n 25 SRv6 Capabilities n RFC9352, Section 2 26 Flexible Algorithm Definition (FAD) n RFC9350, Section 5.1 27 IS-IS Area Leader n 28 IS-IS Dynamic Flooding n 29 IP Algorithm n RFC9502, Section 5.1 30 MP-TLV Support for TLVs with Implicit Support n RFC9885, Section 7.2 31-160 Unassigned 161 Flood Reflection Discovery y 162-255 Unassigned Expert Review This registry defines sub-sub-TLVs for the SRv6 Capabilities sub-TLV (25) advertised in the IS-IS Router CAPABILITY TLV (242). Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1-255 Unassigned Expert Review This registry defines bit values advertised in the Flags field of the SRv6 Capabilities sub-TLV (25). This sub-TLV is advertised in the IS-IS Router CAPABILITY TLV (242). Chris Hopps, Hannes Gredler, Les Ginsberg 0 Unassigned 1 O-flag RFC9352, Section 2 2-15 Unassigned Expert Review This registry defines Application Identifiers for the Generic Information TLV (251). Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1 TRILL n 2-65535 Unassigned Expert Review This registry defines sub-sub-TLV codes which may be advertised in the BIER Info sub-TLV, which is advertised in Prefix Reachability TLVs. These TLVs are listed in the description of the "IS-IS Sub-TLVs for TLVs Advertising Prefix Reachability” registry. Chris Hopps, Hannes Gredler, Les Ginsberg 0 Unassigned 1 BIER MPLS Encapsulation n 2 BIER PHP Request n 3-255 Unassigned Expert Review This registry defines sub-TLVs for Segment Identifier/Label Binding TLVs. The list of TLVs includes: Segment Identifier/Label Binding (149) Multi-Topology Segment Identifier/Label Binding (150) Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1 SID/Label n 2 Unassigned 3 Prefix Segment Identifier n 4-255 Unassigned Expert Review This registry defines sub-sub-TLV codepoints for the Application-Specific Link Attributes sub-TLV, which is advertised in TLVs advertising neighbor information. These TLVs are listed in the description of the “IS-IS Sub-TLVs for TLVs Advertising Neighbor Information” registry. Chris Hopps, Hannes Gredler, Les Ginsberg For future codepoints, in cases where the document that defines the encoding is different from the document that assigns the codepoint, the encoding reference MUST be to the document that defines the encoding. If a link attribute can be advertised both as a sub-TLV of TLVs advertising neighbor information and as a sub-sub-TLV of the Application-Specific Link Attributes sub-TLV defined in , then the same numerical code should be assigned to the link attribute whenever possible. 0-2 Unassigned 3 Administrative group (color) n 4-8 Unassigned 9 Maximum link bandwidth n 10 Maximum reservable link bandwidth n 11 Unreserved bandwidth n 12-13 Unassigned 14 Extended Administrative Group n 15-16 Unassigned 17 Generic Metric y RFC9843, Section 2.1 18 TE Default metric n 19-32 Unassigned 33 Unidirectional Link Delay n 34 Min/Max Unidirectional Link Delay n 35 Unidirectional Delay Variation n 36 Unidirectional Link Loss n 37 Unidirectional Residual Bandwidth n 38 Unidirectional Available Bandwidth n 39 Unidirectional Utilized Bandwidth n 40-255 Unassigned Expert Review This registry defines sub-TLVs for the Application-Specific SRLG TLV (TLV 238). Chris Hopps, Hannes Gredler, Les Ginsberg For future codepoints, in cases where the document that defines the encoding is different from the document that assigns the codepoint, the encoding reference MUST be to the document that defines the encoding. 0-3 Unassigned 4 Link Local/Remote Identifiers n 5 Unassigned 6 IPv4 interface address n 7 Unassigned 8 IPv4 neighbor address n 9-11 Unassigned 12 IPv6 Interface Address n 13 IPv6 Neighbor Address n 14-255 Unassigned Expert Review This registry defines sub-sub-TLVs for SRv6 SID sub-TLVs. This includes the following sub-TLVs: SRv6 End SID (5) (Advertised in SRv6 Locator TLV (27)) SRv6 End.X SID (43) (Advertised in TLVs advertising neighbor information) SRv6 LAN End.X SID (44) (Advertised in TLVs advertising neighbor information) Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1 SRv6 SID Structure y y y n 2-255 Unassigned Expert Review This registry defines bit values advertised in the Flags field of the SRv6 Locator TLV (27). Chris Hopps, Hannes Gredler, Les Ginsberg 0 D-flag RFC9352, Section 7.1 1-7 Unassigned Expert Review This registry defines bit values advertised in the Flags field of the SRv6 End SID sub-TLV (5), which is advertised in the SRv6 Locator TLV (27). Chris Hopps, Hannes Gredler, Les Ginsberg 0-7 Unassigned Expert Review This registry defines bit values advertised in the Flags field of SRv6 SID sub-TLVs associated with adjacencies. These sub-TLVs are advertised in TLVs advertising neighbor information. The list of sub-TLVs includes: SRv6 End.X SID (43) SRv6 LAN End.X SID (44) Chris Hopps, Hannes Gredler, Les Ginsberg 0 B-flag RFC9352, Section 8.1 1 S-flag RFC9352, Section 8.1 2 P-flag RFC9352, Section 8.1 3-7 Unassigned Expert Review Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1 Flexible Algorithm Exclude Admin Group n RFC9350, Section 6.1 2 Flexible Algorithm Include-Any Admin Group n RFC9350, Section 6.2 3 Flexible Algorithm Include-All Admin Group n RFC9350, Section 6.3 4 Flexible Algorithm Definition Flags n RFC9350, Section 6.4 5 Flexible Algorithm Exclude SRLG n RFC9350, Section 6.5 6 IS-IS Exclude Minimum Bandwidth n RFC9843, Section 3.1.1 7 IS-IS Exclude Maximum Delay n RFC9843, Section 3.1.2 8 IS-IS Reference Bandwidth n RFC9843, Section 4.1.3.1 9 IS-IS Bandwidth Threshold n RFC9843, Section 4.1.3.2 10 Flexible Algorithm Exclude Reverse Admin Group n RFC9917, Section 5 11 Flexible Algorithm Include-Any Reverse Admin Group n RFC9917, Section 6 12 Flexible Algorithm Include-All Reverse Admin Group n RFC9917, Section 7 13-255 Unassigned Expert Review This registry contains assigned sub-sub-TLV identifiers for Flood Reflection Discovery purposes. Chris Hopps, Hannes Gredler, Les Ginsberg 0-160 Unassigned 161 Flood Reflection Discovery Tunnel Encapsulation Attribute n 162-255 Unassigned Expert Review with RFC Required This registry defines sub-TLVs for the Area Proxy TLV (TLV 20). Chris Hopps, Hannes Gredler, Les Ginsberg 0 Unassigned 1 Area Proxy System Identifier 2 Area SID 3-255 Unassigned Expert Review This registry defines sub-TLVs for the Flooding Parameters TLV(21). Chris Hopps, Hannes Gredler, Les Ginsberg 0 Reserved 1 LSP Burst Size 2 LSP Transmission Interval 3 LSPs per PSNP 4 Flags 5 PSNP Interval 6 Receive Window 7-255 Unassigned Expert Review This registry defines bit values for the Flags sub-TLV(4) advertised in the Flooding Parameters TLV(21). Chris Hopps, Hannes Gredler, Les Ginsberg In order to minimize encoding space, a new allocation should pick the smallest available value. 0 Ordered acknowledgment (O-flag) 1-63 Unassigned