\scalebox{0.5}{
\begin{tikzpicture}[
every node/.style={font=\bfseries},
basebox/.style={anchor=north west, minimum height=2em, draw, rectangle},
bitbox/.style={basebox, minimum width=2em},
bytebox/.style={basebox, minimum width=16em},
wordbox/.style={basebox, minimum width=32em},
qwordbox/.style={basebox, minimum width=64em},
]

\path
(-9em, 2em) node[basebox, minimum width=5em] {Offsets}
(-9em, 0em) node[basebox, minimum width=5em] {Octet}
(-4em, 2em) node[basebox, minimum width=4em] {Octet}
(-4em, 0em) node[basebox, minimum width=4em] {Bit}
;

\foreach \x in {0,...,3}
	\node[bytebox] at (\x * 16em, 2em) {\scriptsize \x};
\foreach \x in {0,...,31}
	\node[bitbox] at (\x * 2em, 0em) {\scriptsize \x};

\foreach \x in {0,32,...,160}
	\node[basebox, minimum width=4em] at (-4em, \x * -1/16*1em - 2em) {\scriptsize \x};

\foreach \x in {0,4,...,20}
	\node[basebox, minimum width=5em] at (-9em, \x * -0.5em - 2em) {\scriptsize \x};

\path
(0em, -1 * 2em) node[basebox, minimum width=8em] {Version}
(8em, -1 * 2em) node[basebox, minimum width=8em] {IHL}
(16em, -1 * 2em) node[basebox, minimum width=16em] {TOS}
(32em, -1 * 2em) node[wordbox] {Packet length}

(0em, -2 * 2em) node[wordbox] {Identification}
(32em, -2 * 2em) node[bitbox] {X}
(34em, -2 * 2em) node[bitbox] {D}
(36em, -2 * 2em) node[bitbox] {M}
(38em, -2 * 2em) node[basebox, minimum width=26em] {Fragement offset}

(0em, -3 * 2em) node[bytebox] {TTL}
(16em, -3 * 2em) node[bytebox] {Protocol}
(32em, -3 * 2em) node[wordbox] {Header checksum}

(0em, -4 * 2em) node[qwordbox] {Source ip address}
(0em, -5 * 2em) node[qwordbox] {Destination ip address}
(0em, -6 * 2em) node[qwordbox] {Options (variable length)}

%(0em, -7 * 2em) node[qwordbox, minimum height=4 em] {Payload}
;

\end{tikzpicture}
}