\begin{table}[htb]
\centering
\footnotesize
+ \begin{usepicture}
\begin{tabular} {c@{\hspace{1mm}\vrule}
p{3mm}@{\vrule}p{3mm}@{\vrule}p{3mm}@{\vrule}p{3mm}@{\vrule}
p{3mm}@{\vrule}p{3mm}@{\vrule}p{3mm}@{\vrule}p{3mm}@{\vrule}
\omit\hfill\vrule &&&&&&&& &&&&&&&& &&&&&&&& &&&&&&&& \\
\cline{2-33}
-\end{tabular}
+ \end{tabular}
+ \end{usepicture}
\caption{Le classi di indirizzi secondo IPv4.}
\label{tab:IP_ipv4class}
\end{table}
\begin{table}[htb]
\centering
\footnotesize
+ \begin{usepicture}
\begin{tabular} {c@{\hspace{1mm}\vrule}
p{3mm}@{\vrule}p{3mm}@{\vrule}p{3mm}@{\vrule}p{3mm}@{\vrule}
p{3mm}@{\vrule}p{3mm}@{\vrule}p{3mm}@{\vrule}p{3mm}@{\vrule}
\multicolumn{20}{@{}c@{\vrule}}{\parbox[c]{60mm}{\centering host Id}} \\
\omit\hfill\vrule &&&&&&&& &&&&&&&& &&&&&&&& &&&&&&&& \\
\cline{2-33}
-\end{tabular}
+ \end{tabular}
+ \end{usepicture}
\caption{Uno esempio di indirizzamento CIDR.}
\label{tab:IP_ipv4cidr}
\end{table}