Learning TCP options
While TCP is already an amazing protocol, it also permits various options that can be added to the TCP header to extend the functionality. The complete list, last updated in February 2021, can be found at https://www.iana.org/assignments/tcp-parameters/tcp-parameters.txt.
Keep in mind the following about TCP options:
- Not all options are used.
- Some of the options are experimental.
- Some are used for specific reasons and do not have an associated Request for Comment (RFC).
- Some have been developed and used without the proper Internet Assigned Numbers Authority (IANA) assignment.
The seven most common options are listed in the following table:
Table 10.1 – TCP options
The first three, EOL, NOP, and MSS, are from the original TCP RFC 793. The others were developed over time. Any options will follow the TCP header and are in multiples of 8 bits (or 1 byte). The entire header must be a multiple of 32 bits...
