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.


  • 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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