\setbeamercovered{transparent}
  \only<presentation>{\frametitle{Ein Firewall-Beispiel}}
  %
  \begin{Verbatim}[fontsize=\scriptsize,frame=single,framesep=1ex]
/interface list
   name=WAN
/interface list member
   add interface=ether1 list=WAN
/ip firewall nat
   add action=masquerade chain=srcnat comment=''defconf: masquerade'' \
   ipsec-policy=out,none out-interface-list=WAN

  \end{Verbatim}


