\begin{figure}
\begin{tabular}{c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c c }
\texttt{\tiny{0}} &\texttt{\tiny{1}} & \texttt{\tiny{2}} & \texttt{\tiny{3}} & \texttt{\tiny{4}} &
\texttt{\tiny{5}} & \texttt{\tiny{6}} & \texttt{\tiny{7}} & \texttt{\tiny{8}} & \texttt{\tiny{9}} &
\texttt{\tiny{0}} & \texttt{\tiny{1}} & \texttt{\tiny{2}} & \texttt{\tiny{3}} & \texttt{\tiny{4}} &
\texttt{\tiny{5}} & \texttt{\tiny{6}} & \texttt{\tiny{7}} & \texttt{\tiny{8}} & \texttt{\tiny{9}} &
\texttt{\tiny{0}} & \texttt{\tiny{1}} & \texttt{\tiny{2}} & \texttt{\tiny{3}} & \texttt{\tiny{4}} &
\texttt{\tiny{5}} & \texttt{\tiny{6}} & \texttt{\tiny{7}} &
\texttt{\tiny{8}} & \texttt{\tiny{9}} & 
\texttt{\tiny{0}} & \texttt{\tiny{1}}  \\ \hline 
\multicolumn{number of bits here}{|c|}{content of the field here}
& \multicolumn{number of bits here}{|c|}{content of the field here}
& \multicolumn{number of bits here}{|c|}{content of the field here}
& \multicolumn{number of bits here}{|c|}{content of the field here} \\ \hline
\multicolumn{32}{|c|}{this field is one row} \\ \hline
\multicolumn{32}{|c|}{this field continues to the next row} \\ \cline{9-32}
\multicolumn{8}{|c|}{rest of the field started above}
& \multicolumn{7}{|c}{}
& \multicolumn{1}{c|}{1}
& \multicolumn{8}{|c|}{length: 1}
& \multicolumn{8}{|c|}{next: 17} \\ \hline
\end{tabular}
\caption{A message}
\label{fig:ipv4}
\end{figure}