Transmission Control Protocol (TCP) Parameters (original) (raw)

Last Updated

2025-03-26

Available Formats

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Registries Included Below

TCP Option Kind Numbers

Registration Procedure(s)

Standards Action or IESG Approval

Reference

[RFC2780]

Note

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. 

Note

Values 16-18 were assigned before October 1994 (see [RFC1700]), and values 20-26 were assigned between Feb 9, 1999 and May 10, 2000. No further documentation is available.

Available Formats

CSV

Kind Length Meaning Reference
0 - End of Option List [RFC9293]
1 - No-Operation [RFC9293]
2 4 Maximum Segment Size [RFC9293]
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) [RFC8684]
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 N Encryption Negotiation (TCP-ENO) [RFC8547]
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) [**]
79-171 Reserved
172 N Accurate ECN Order 0 (AccECN0) [RFC-ietf-tcpm-accurate-ecn-34]
173 Reserved
174 N Accurate ECN Order 1 (AccECN1) [RFC-ietf-tcpm-accurate-ecn-34]
175-252 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]

TCP Alternate Checksum Numbers

Registration Procedure(s)

Not defined

Reference

[RFC1146]

Available Formats

CSV

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]

Cryptographic Algorithms for TCP-AO Registration

Registration Procedure(s)

RFC Publication After Expert Review

Reference

[RFC5926]

Available Formats

CSV

Algorithm Reference
SHA1 [RFC5926]
AES128 [RFC5926]

MPTCP Option Subtypes

Registration Procedure(s)

Standards Action

Reference

[RFC8684]

Note

This registry specifies the MPTCP Option Subtypes for MPTCP v1, which obsoletes the Experimental MPTCP v0. For the MPTCP v0 subtypes, please refer to [RFC6824].

Available Formats

CSV

Value Symbol Name Reference
0x0 MP_CAPABLE Multipath Capable [RFC8684, Section 3.1]
0x1 MP_JOIN Join Connection [RFC8684, Section 3.2]
0x2 DSS Data Sequence Signal (Data ACK and Data Sequence Mapping) [RFC8684, Section 3.3]
0x3 ADD_ADDR Add Address [RFC8684, Section 3.4.1]
0x4 REMOVE_ADDR Remove Address [RFC8684, Section 3.4.2]
0x5 MP_PRIO Change Subflow Priority [RFC8684, Section 3.3.8]
0x6 MP_FAIL Fallback [RFC8684, Section 3.7]
0x7 MP_FASTCLOSE Fast Close [RFC8684, Section 3.5]
0x8 MP_TCPRST Subflow Reset [RFC8684, Section 3.6]
0x9-0xe Unassigned
0xf Reserved for Private Use [RFC8684]

MPTCP Handshake Algorithms

Registration Procedure(s)

Standards Action

Reference

[RFC8684]

Note

This registry specifies the MPTCP Handshake Algorithms for MPTCP v1, which obsoletes the Experimental MPTCP v0. For the MPTCP v0 subtypes, please refer to [RFC6824].

Available Formats

CSV

Flag Bit Meaning Reference
A Checksum required [RFC8684, Section 3.1]
B Extensibility [RFC8684, Section 3.1]
C Do not attempt to establish new subflows to the source address. [RFC8684, Section 3.1]
D-G Unassigned
H HMAC-SHA256 [RFC8684, Section 3.2]

TCP/UDP Experimental Option Experiment Identifiers (TCP/UDP ExIDs)

Registration Procedure(s)

First Come First Served

Reference

[RFC6994][RFC-ietf-tsvwg-udp-options-45]

Note

16-bit ExIDs can be used with either TCP or UDP; 32-bit ExIDs can be used with TCP or their first 16 bits can be used with UDP. Use with each transport (TCP, UDP) is indicated in the protocol column, as defined in the corresponding reference.

Note

IANA will record known duplicate uses.

Available Formats

CSV

Value Protocol Description Reference
0x00AC TCP TCP ACK Rate Request [draft-gomez-tcpm-ack-rate-request-02]
0x0348 TCP HOST_ID [RFC7974]
0x0A0D TCP Autonomous System Compensation [draft-donnerhacke-linktax-02]
0x0CA0 TCP TCP Capability Option [draft-boucadair-tcpm-capability-option-00]
0x0ED0 TCP Extended Data Offset [draft-ietf-tcpm-tcp-edo-00]
0x454E TCP TCP-ENO [2] [RFC8547]
0x5323 TCP Service Number [draft-touch-tcpm-sno-00]
0x75ECFFEE TCP Timestamp Interval [draft-trammell-tcpm-timestamp-interval-00]
0xACC0 TCP AccECN Experimental Option - Order 0 (current and new implementations SHOULD use option kind 172) [RFC-ietf-tcpm-accurate-ecn-34]
0xACC1 TCP AccECN Experimental Option - Order 1 (current and new implementations SHOULD use option kind 174) [RFC-ietf-tcpm-accurate-ecn-34]
0xACCE TCP AccECN Experimental Option (current and new implementations SHOULD use option kinds 172 or 174) [RFC-ietf-tcpm-accurate-ecn-34]
0xE2D4C3D9 TCP Shared Memory Communications over RMDA protocol [RFC7609]
0xF989 TCP Fast Open (current and new implementations SHOULD use option 34) [RFC7413]
0xF990 TCP Low Latency [draft-wang-tcpm-low-latency-opt-00]

TCP Encryption Protocol Identifiers

Registration Procedure(s)

IETF Review or Expert Review with RFC Required

Expert(s)

Unassigned

Reference

[RFC8547]

Available Formats

CSV

Value Meaning Reference
0x20 Experimental Use [RFC8547]
0x21 TCPCRYPT_ECDHE_P256 [RFC8548]
0x22 TCPCRYPT_ECDHE_P521 [RFC8548]
0x23 TCPCRYPT_ECDHE_Curve25519 [RFC8548]
0x24 TCPCRYPT_ECDHE_Curve448 [RFC8548]
0x25-0x6f Unassigned
0x70-0x7f Reserved for extended values [RFC8547]

tcpcrypt AEAD Algorithms

Registration Procedure(s)

IETF Review or Expert Review with RFC Required

Expert(s)

Unassigned

Reference

[RFC8548]

Available Formats

CSV

Value AEAD Algorithm Reference
0x0000 Reserved
0x0001 AEAD_AES_128_GCM [RFC8548]
0x0002 AEAD_AES_256_GCM [RFC8548]
0x0003-0x000f Unassigned
0x0010 AEAD_CHACHA20_POLY1305 [RFC8548]
0x0011-0xffff Unassigned

MPTCP MP_TCPRST Reason Codes

Registration Procedure(s)

Specification Required

Expert(s)

Unassigned

Reference

[RFC8684]

Available Formats

CSV

Code Meaning Reference
0x00 Unspecified error [RFC8684, Section 3.6]
0x01 MPTCP-specific error [RFC8684, Section 3.6]
0x02 Lack of resources [RFC8684, Section 3.6]
0x03 Administratively prohibited [RFC8684, Section 3.6]
0x04 Too much outstanding data [RFC8684, Section 3.6]
0x05 Unacceptable performance [RFC8684, Section 3.6]
0x06 Middlebox interference [RFC8684, Section 3.6]
0x07-0xff Unassigned

TCP Header Flags

Registration Procedure(s)

Standards Action

Reference

[RFC9293]

Available Formats

CSV

Contact Information

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

Footnotes