TCP header

The following fields are defined for the TCP header, as described in [RFC793]:

$$\begin{tabular}{l\vert cccccccccccccccccccccccccccccccc\vert... ...e{2-33} \multicolumn{33}{l}{{\tt tcp\_data}} \\ \end{tabular}$$

TCP flags:

$$\begin{tabular}{\vert c\vert c\vert c\vert c\vert c\vert c\v... ...ST} & {\tt tcp\_SYN} & {\tt tcp\_FIN} \\ \hline \end{tabular}$$

All fields listed above are based on tcp_hdr, which in turn is defined as follows:

field tcp_hdr = ip_nexthdr if ip_proto == IPPROTO_TCP;

Therefore, accessing any TCP header field automatically adds the precondition (see section 2.6.2) ip_proto == IPPROTO_TCP.

fields.tc defines a few additional fields for TCP options. Because tcng has currently no mechanism for iterating over a list of options, these fields are of no practical use and are therefore not documented.