Introduction

Type Length Value (TLV) makes ISIS to be flexible and adopt new features, such as IP routing from original CLNS protocol. Other TLVs are used for MPLS TE using ISIS.

ISIS TLV

• Type is 1 byte, Length is 1 byte and Value is L bytes (as defined by length field).
• TLV provides a flexible way to add new header information without modifying the standard fixed format.
• TLV are inserted in the original header PDU.
• Sub-TLV are also used, but they are inserted within another TLV. Unknown sub-TLV can be ignored and skipped.
• Detailed list of TLV see additional resources section.

Additional Resources

Intermediate System-to-Intermediate System (IS-IS) TLVs - Cisco Support.

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