\documentclass{article}
\usepackage[pdftex,active,tightpage]{preview}
\setlength\PreviewBorder{2mm}
 
\usepackage{tikz}
\usetikzlibrary{shapes.multipart, calc, decorations.pathreplacing} 

\begin{document}
\begin{preview}
\begin{tikzpicture}[array/.style={rectangle split,rectangle split horizontal, rectangle split parts=#1,draw, anchor=center, rectangle split part fill={blue!20, green!20, blue!20!green!90}}]
\node[array=3] (a) {
\nodepart{one}IP-Header
\nodepart{two}UDP-Header
\nodepart{three}UDP-Daten
};

\draw [decoration={brace,raise=2pt},decorate] (a.north west) --  node[above=3pt]{IP-Datagramm}(a.north east);
\draw [decoration={brace,mirror,raise=2pt},decorate] ($(a.two) + (-0.13,-0.14)$) --  node[below=3pt]{UDP-Datagramm}(a.south east);
\end{tikzpicture}
\end{preview}
\end{document}