Registries included below
IESG Approval or Standards Action
The Transmission Control Protocol (TCP) has provision for optional
header fields identified by an option kind field. Options 0 and 1 are
exactly one octet which is their kind field. All other options have
their one octet kind field, followed by a one octet length field,
followed by length-2 octets of option data.
[*] It is only appropriate to use these values in explicitly-
configured experiments; they MUST NOT be shipped as defaults in
implementations. See [RFC3692] for details.
[**] These values have been deployed in the Internet without proper
IANA assignment. At some point, these numbers may be officially
allocated for some new purpose. It is therefore strongly recommended
that implementers migrate to mechanisms with IANA-assigned values to
avoid potential issues with their systems or products at a later point.
[***] This value has been deployed on the Internet in ways that are
not compatible with the documented use in this IANA allocation.
| Kind | Length | Meaning | Reference |
|---|---|---|---|
| 0 | - | End of Option List | [RFC793] |
| 1 | - | No-Operation | [RFC793] |
| 2 | 4 | Maximum Segment Size | [RFC793] |
| 3 | 3 | Window Scale | [RFC7323] |
| 4 | 2 | SACK Permitted | [RFC2018] |
| 5 | N | SACK | [RFC2018] |
| 6 | 6 | Echo (obsoleted by option 8) | [RFC1072][RFC6247] |
| 7 | 6 | Echo Reply (obsoleted by option 8) | [RFC1072][RFC6247] |
| 8 | 10 | Timestamps | [RFC7323] |
| 9 | 2 | Partial Order Connection Permitted (obsolete) | [RFC1693][RFC6247] |
| 10 | 3 | Partial Order Service Profile (obsolete) | [RFC1693][RFC6247] |
| 11 | CC (obsolete) | [RFC1644][RFC6247] | |
| 12 | CC.NEW (obsolete) | [RFC1644][RFC6247] | |
| 13 | CC.ECHO (obsolete) | [RFC1644][RFC6247] | |
| 14 | 3 | TCP Alternate Checksum Request (obsolete) | [RFC1146][RFC6247] |
| 15 | N | TCP Alternate Checksum Data (obsolete) | [RFC1146][RFC6247] |
| 16 | Skeeter | [Stev_Knowles] | |
| 17 | Bubba | [Stev_Knowles] | |
| 18 | 3 | Trailer Checksum Option | [Subbu_Subramaniam][Monroe_Bridges] |
| 19 | 18 | MD5 Signature Option (obsoleted by option 29) | [RFC2385] |
| 20 | SCPS Capabilities | [Keith_Scott] | |
| 21 | Selective Negative Acknowledgements | [Keith_Scott] | |
| 22 | Record Boundaries | [Keith_Scott] | |
| 23 | Corruption experienced | [Keith_Scott] | |
| 24 | SNAP | [Vladimir_Sukonnik] | |
| 25 | Unassigned (released 2000-12-18) | ||
| 26 | TCP Compression Filter | [Steve_Bellovin] | |
| 27 | 8 | Quick-Start Response | [RFC4782] |
| 28 | 4 | User Timeout Option (also, other known unauthorized use) [***][1] | [RFC5482] |
| 29 | TCP Authentication Option (TCP-AO) | [RFC5925] | |
| 30 | N | Multipath TCP (MPTCP) | [RFC6824] |
| 31 | Reserved (known unauthorized use without proper IANA assignment) [**] | ||
| 32 | Reserved (known unauthorized use without proper IANA assignment) [**] | ||
| 33 | Reserved (known unauthorized use without proper IANA assignment) [**] | ||
| 34 | variable | TCP Fast Open Cookie | [RFC7413] |
| 35-68 | Reserved | ||
| 69 | Reserved (known unauthorized use without proper IANA assignment) [**] | ||
| 70 | Reserved (known unauthorized use without proper IANA assignment) [**] | ||
| 71-75 | Reserved | ||
| 76 | Reserved (known unauthorized use without proper IANA assignment) [**] | ||
| 77 | Reserved (known unauthorized use without proper IANA assignment) [**] | ||
| 78 | Reserved (known unauthorized use without proper IANA assignment) [**] | ||
| 79-252 | Reserved | ||
| 253 | N | RFC3692-style Experiment 1 (also improperly used for shipping products) [*] | [RFC4727] |
| 254 | N | RFC3692-style Experiment 2 (also improperly used for shipping products) [*] | [RFC4727] |
Not defined
| Number | Description | Reference |
|---|---|---|
| 0 | TCP Checksum | [RFC1146] |
| 1 | 8-bit Fletchers's algorithm | [RFC1146] |
| 2 | 16-bit Fletchers's algorithm | [RFC1146] |
| 3 | Redundant Checksum Avoidance | [J_Kay] |
RFC Publication After Expert Review
| Algorithm | Reference |
|---|---|
| SHA1 | [RFC5926] |
| AES128 | [RFC5926] |
Standards Action
| Value | Symbol | Name | Reference |
|---|---|---|---|
| 0x0 | MP_CAPABLE | Multipath Capable | [RFC6824], Section 3.1 |
| 0x1 | MP_JOIN | Join Connection | [RFC6824], Section 3.2 |
| 0x2 | DSS | Data Sequence Signal (Data ACK and Data Sequence Mapping) | [RFC6824], Section 3.3 |
| 0x3 | ADD_ADDR | Add Address | [RFC6824], Section 3.4.1 |
| 0x4 | REMOVE_ADDR | Remove Address | [RFC6824], Section 3.4.2 |
| 0x5 | MP_PRIO | Change Subflow Priority | [RFC6824], Section 3.3.8 |
| 0x6 | MP_FAIL | Fallback | [RFC6824], Section 3.6 |
| 0x7 | MP_FASTCLOSE | Fast Close | [RFC6824], Section 3.5 |
| 0x8-0xe | Unassigned | ||
| 0xf | Reserved for Private Use | [RFC6824] |
Standards Action
| Flag Bit | Meaning | Reference |
|---|---|---|
| A | Checksum required | [RFC6824], Section 3.1 |
| B | Extensibility | [RFC6824], Section 3.2 |
| C-G | Unassigned | |
| H | HMAC-SHA1 | [RFC6824], Section 3.2 |
First Come First Served
IANA will record known duplicate uses.
| Value | Description | Reference |
|---|---|---|
| 0x0348 | HOST_ID | [RFC7974] |
| 0x0CA0 | TCP Capability Option | [draft-boucadair-tcpm-capability-option] |
| 0x0ED0 | Extended Data Offset | [draft-ietf-tcpm-tcp-edo] |
| 0x454E | TCP-ENO | [draft-ietf-tcpinc-tcpeno] |
| 0x5323 | Service Number | [draft-touch-tcpm-sno] |
| 0x75ECFFEE | Timestamp Interval | [draft-trammell-tcpm-timestamp-interval] |
| 0xACCE | AccECN Experimental Option | [draft-kuehlewind-tcpm-accurate-ecn] |
| 0xE2D4C3D9 | Shared Memory communications over RMDA protocol | [RFC7609] |
| 0xF989 | Fast Open | [RFC7413] |
| 0xF990 | Low Latency | [draft-wang-tcpm-low-latency-opt] |
| ID | Name | Contact URI | Last Updated |
|---|---|---|---|
| [J_Kay] | J. Kay | mailto:jkay&ucsd.edu | 1994-09 |
| [Keith_Scott] | Keith Scott | mailto:kscott&mitre.org | 1999-02 |
| [Monroe_Bridges] | Monroe Bridges | mailto:monroe&cup.hp.com | 1994-09 |
| [Stev_Knowles] | Stev Knowles | mailto:stev&ftp.com | 1995-03 |
| [Steve_Bellovin] | Steve Bellovin | mailto:smb&research.att.com | 2000-03 |
| [Subbu_Subramaniam] | Subbu Subramaniam | mailto:subbu&cup.hp.com | 1994-09 |
| [Vladimir_Sukonnik] | Vladimir Sukonnik | mailto:vladimir&sitaranetworks.com | 1999-02 |
| [1] |
[https://devcentral.f5.com/tech-tips/articles/accessing-tcp-options-from-irules] |