TCP OPTION NUMBERS 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. Kind Length Meaning Reference ---- ------ ------------------------------- --------- 0 - End of Option List [RFC793] 1 - No-Operation [RFC793] 2 4 Maximum Segment Size [RFC793] 3 3 WSOPT - Window Scale [RFC1323] 4 2 SACK Permitted [RFC2018] 5 N SACK [RFC2018] 6 6 Echo (obsoleted by option 8) [RFC1072] 7 6 Echo Reply (obsoleted by option 8)[RFC1072] 8 10 TSOPT - Time Stamp Option [RFC1323] 9 2 Partial Order Connection Permitted[RFC1693] 10 3 Partial Order Service Profile [RFC1693] 11 CC [RFC1644] 12 CC.NEW [RFC1644] 13 CC.ECHO [RFC1644] 14 3 TCP Alternate Checksum Request [RFC1146] 15 N TCP Alternate Checksum Data [RFC1146] 16 Skeeter [Knowles] 17 Bubba [Knowles] 18 3 Trailer Checksum Option [Subbu & Monroe] 19 18 MD5 Signature Option [RFC2385] 20 SCPS Capabilities [Scott] 21 Selective Negative Acknowledgements [Scott] 22 Record Boundaries [Scott] 23 Corruption experienced [Scott] 24 SNAP [Sukonnik] 25 Unassigned (released 12/18/00) 26 TCP Compression Filter [Bellovin] TCP ALTERNATE CHECKSUM NUMBERS Number Description Reference ------- ------------------------------- ---------- 0 TCP Checksum [RFC-1146] 1 8-bit Fletchers's algorithm [RFC-1146] 2 16-bit Fletchers's algorithm [RFC-1146] 3 Redundant Checksum Avoidance [Kay] REFERENCES [KAY] Kay, J. and Pasquale, J., "Measurement, Analysis, and Improvement of UDP/IP Throughput for the DECstation 5000," Proceedings of the Winter 1993 Usenix Conference, January 1993 (available for anonymous FTP in ucsd.edu:/pub/csl/fastnet/fastnet.tar.Z). [RFC793] Postel, J., "Transmission Control Protocol - DARPA Internet Program Protocol Specification", STD 7, RFC 793, DARPA, September 1981. [RFC1323] Jacobson, V., Braden, R., and D. Borman, "TCP Extensions for High Performance", RFC 1323, LBL, ISI, Cray Research, May 1992. [RFC1072] Jacobson, V., and R. Braden, "TCP Extensions for Long-Delay Paths", RFC 1072, LBL, ISI, October 1988. [RFC1644] Braden, R. "T/TCP -- TCP Extensions for Transactions Functional Specification", RFC 1644, ISI, July 1994 [RFC1693] Connolly, T., et al, "An Extension to TCP : Partial Order Service", RFC 1693, University of Deleware, November 1994. [RFC1146] Zweig, J., and C. Partridge, "TCP Alternate Checksum Options", RFC 1146, UIUC, BBN, March 1990. [RFC2018] Mathis, M., Mahdavi, J., Floyd, S., and Romanow, A., TCP Selective Acknowledgement Options. RFC 2018, April 1996. [RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5 Signature Option", RFC 2385, Cisco Systems, August 1998. PEOPLE [Bellovin] Steve Bellovin, , March 2000. [Braden] Bob Braden, , March 1995. [Bridges] Monroe Bridges, , September 1994. [Knowles] Stev Knowles, , March 1995. [Kay] J. Kay, , Septermber 1994. [Scott] Keith Scott , February 1999. [Subbu] Subbu Subramaniam, , September 1994. [Sukonnik] Vladimir Sukonnik , February 1999. []