| Type, Length, Value (TLV) is in the IS-IS and ES-IS PDUs that contain variable-length fields, depending on the function of the PDU. Each field contains a type code and length, followed by the appropriate values. These fields are identified by one octet of type (T), one octet of length (L) and "L" octets of value (V). The Type field indicates the type of items in the Value field. The Length field indicates the length of the Value field. The Value field is the data portion of the packet. Not all router implementations support all TLVs, but they are required to ignore and retransmit the ignored types. |