Transmission Control Protocol (TCP) Parameters

Last Updated

• 2026-04-24

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TCP Option Kind Numbers

Registration Procedure(s)

• Standards Action or IESG Approval

Reference

• RFC 2780: IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers

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 RFC 3692 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 RFC 1700), and values 20-26 were assigned between Feb 9, 1999 and May 10, 2000. No further documentation is available.

Available Formats

• CSV

TCP Alternate Checksum Numbers

Registration Procedure(s)

• Not defined

Reference

• RFC 1146: TCP alternate checksum options

Available Formats

• CSV

Cryptographic Algorithms for TCP-AO Registration

Registration Procedure(s)

• RFC Publication After Expert Review

Reference

• RFC 5926: Cryptographic Algorithms for the TCP Authentication Option (TCP-AO)

Available Formats

• CSV

MPTCP Option Subtypes

Registration Procedure(s)

• Standards Action

Reference

• RFC 8684: TCP Extensions for Multipath Operation with Multiple Addresses

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 RFC 6824.

Available Formats

• CSV

MPTCP Handshake Algorithms

Registration Procedure(s)

• Standards Action

Reference

• RFC 8684: TCP Extensions for Multipath Operation with Multiple Addresses

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 RFC 6824.

Available Formats

• CSV

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

Registration Procedure(s)

• First Come First Served

Reference

• RFC 6994: Shared Use of Experimental TCP Options
• RFC 9868: Transport Options for UDP

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 RFC 9868.

Note

IANA will record known duplicate uses.

Available Formats

• CSV

TCP Encryption Protocol Identifiers

Registration Procedure(s)

• IETF Review or Expert Review with RFC Required

Expert(s)

• Unassigned

Reference

• RFC 8547: TCP-ENO: Encryption Negotiation Option

Available Formats

• CSV

tcpcrypt AEAD Algorithms

Registration Procedure(s)

• IETF Review or Expert Review with RFC Required

Expert(s)

• Unassigned

Reference

• RFC 8548: Cryptographic Protection of TCP Streams (tcpcrypt)

Available Formats

• CSV

MPTCP MP_TCPRST Reason Codes

Registration Procedure(s)

• Specification Required

Expert(s)

• Unassigned

Reference

• RFC 8684: TCP Extensions for Multipath Operation with Multiple Addresses

Available Formats

• CSV

TCP Header Flags

Registration Procedure(s)

• Standards Action

Reference

• RFC 9293: Transmission Control Protocol (TCP)

Available Formats

• CSV