very long connection times

[Igor Zbirka]

I would like to ask you for some advice.
I'm using free BSD server in my local network as a rooter. Connection 
to internet is done over ISDN.

During last months our connection time became rapidly too big. There 
were several connections over 12 hours and sometimes over the night I 
can see that the modem is on for a long time. Even though it shouldn't.
I would like to know if there is somewhere a log file, which would show 
me from which computer was generated the request to connect to 
internet? If yes where is it.

Sincerely yours

Igor Zbirka