I want the navigation-line to show Subsection1.1, Subsection1.2 , Subsection 2.1 and Subsection2.2 instead of just Section1 and Section2. How do I do that? \insertsubsectionnavigationsymbol does not work for me.

Here is a MWE:

\documentclass{beamer}
\usetheme{Frankfurt}

\begin{document}
\section{Section1}
\subsection{Subsection1.1}
\subsection{Subsection1.2}
\section{Section2}
\subsection{2.1}
\begin{frame}
bla2.1
\end{frame}
\subsection{2.2}
\begin{frame}
bla2.2
\end{frame}

\end{document}


Navigation bars are a tricky thing to play with. But beamer has some build-in abilities which might be close enough to what you would like to accomplish.

Option 1:

You can change the headline to display all subsections of the current section instead of the sections:

\documentclass{beamer}

\usetheme{Frankfurt}

\makeatletter
{%
\vskip-5.5ex%
\end{beamercolorbox}%
}%
\makeatother

\begin{document}
\section{Section1}
\subsection{Subsection1.1}
\frame{test}
\subsection{Subsection1.2}
\frame{test}
\section{Section2}
\subsection{Subsection2.1}
\frame{test}
\subsection{Subsection2.2}
\frame{test}
\end{document}


Option 2:

\documentclass{beamer}

\useoutertheme[subsection=true]{smoothbars}
\usecolortheme{orchid}
\usecolortheme{whale}

\setbeamerfont{block title}{size={}}

\makeatletter
{%
\ifbeamer@sb@subsection%
\vskip-8.2ex%
\else%
\vskip-7ex%
\fi%
\end{beamercolorbox}%
\ifbeamer@sb@subsection%
\end{beamercolorbox}%
\fi%
}%
\makeatother

\begin{document}
\section{Section1}
\subsection{Subsection1.1}
\frame{test}
\subsection{Subsection1.2}
\frame{test}
\section{Section2}
\subsection{Subsection2.1}
\frame{test}
\subsection{Subsection2.2}
\frame{test}
\end{document}