| TCP option 4, SACK permitted |
Description:
RFC 1072, pg 6:
To minimize the impact on the TCP protocol, the selective acknowledgment extension uses the form of two new TCP options. The first is an enabling option, "SACK-permitted", that may be sent in a SYN segment to indicate that the the SACK option may be used once the connection is established. The other is the SACK option itself, which may be sent over an established connection once permission has been given by SACK-permitted.
| MAC header | IP header | TCP header | TCP option | Data |
TCP Option 4:
| 00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Kind | Length | ||||||||||||||
Kind. 8 bits. Set to 4.
Length. 8 bits. Set to 2.
Glossary:
RFCs:
[RFC 1323] TCP Extensions for High Performance.
[RFC 2018] TCP Selective Acknowledgment Options.
Obsolete RFCs:
[RFC 1072] TCP Extensions for Long-Delay Paths.