2025-09-26 2026-04-09 Values reserved for Experimental Use are not expected to be used on the Internet but are expected to be used for experiments that are confined to closed environments. 0x0000 Reserved 0x0001-0x7F00 Specification Required 0x7F01-0x7FE0 Experimental Use 0x7FE1-0x7FFF Private Use 0x8000-0xFFFE IETF Review 0xFFFF Reserved Unassigned 0x0000 Reserved IETF 0x7F01-0x7FE0 Reserved for Experimental Use IETF 0x7FE1-0x7FFF Reserved for Private Use IETF 0xACE1 Test Setup PDU IETF 0xACE2 Test Activation PDU IETF 0xBEEF Load PDU IETF 0xDEAD Null PDU IETF 0xFEED Status Feedback PDU IETF 0xFFFF Reserved IETF 0-19 Reserved 20-40960 IETF Review 40961-53248 Specification Required 53249-65534 Experimental Use 65535 Reserved Unassigned 20 IETF 00000000-01111111 IETF Review 10000000 Reserved 0x00 No modifications 0x01 Allow Jumbo datagram sizes above sending rates of 1 Gbps 0x02 Use Traditional MTU (1500 bytes with an IP header) 0-59 IETF Review 60-63 Experimental Use 64-255 Reserved 0 Not used 1 Required authentication for the Control phase 2 Required authentication for the Control and Data phases 0-127 IETF Review 128-239 Specification Required 240-249 Experimental Use 250-254 Private Use 255 Reserved Unassigned 0 None (used by client in Request) IETF 1 Acknowledgment IETF 2 Bad protocol version IETF 3 Invalid Jumbo datagram option IETF 4 Unexpected authentication in Setup Request IETF 5 Authentication missing in Setup Request IETF 6 Invalid authentication method IETF 7 Authentication failure IETF 8 Authentication time is invalid in Setup Request IETF 9 No maximum test bit rate specified IETF 10 Server maximum bit rate exceeded IETF 11 MTU option does not match server IETF 12 Multi-connection parameters rejected by server IETF 13 Connection allocation failure on server IETF 14-239 Unassigned 240-249 Reserved for Experimental Use IETF 250-254 Reserved for Private Use IETF 255 Reserved IETF 0-127 IETF Review 128-239 Specification Required 240-249 Experimental Use 250-254 Private Use 255 Reserved Unassigned 0 No Request IETF 1 Request test in upstream direction (client to server) IETF 2 Request test in downstream direction (server to client) IETF 3-239 Unassigned 240-249 Reserved for Experimental Use IETF 250-254 Reserved for Private Use IETF 255 Reserved IETF 00000000-01111111 IETF Review 10000000 Reserved 0x00 No modifications 0x01 Set when srIndexConf is start rate for search 0x02 Set for randomized UDP payload A-Y IETF Review Z Reserved The algorithm identifier is a capitalized alphabetic UTF-8 value (A-Z), specified by the corresponding incremental numeric. A(n/a) Not used B(0) Rate algorithm Type B Y.1540Amd2 C(1) Rate algorithm Type C TR-471 0-127 IETF Review 128-239 Specification Required 240-249 Experimental Use 250-254 Private Use 255 Reserved Unassigned 0 None (used by client in Request) IETF 1 Server acknowledgment IETF 2 Server indicates an error IETF 3-239 Unassigned 240-249 Reserved for Experimental Use IETF 250-254 Reserved for Private Use IETF 255 Reserved IETF