Ubuntu Networking :: Script To Monitor Connection - VPN Client Disconnected

My promlem is that I wrote a few simple script to monitor the network connection as follows:

script 1 "netmonitor.sh"
#!/bin/bash
# /usr/local/bin/netmonitor.sh
HOST=www.google.hu
ping -c 1 "$HOST" > /dev/null 2>&1 .....

So it's run every 5 minutes, and it works well, when it sees host is down, it restart the connection, BUT as the log shows below, about a half an hour after using the connection (for example the ssh through the internet or the vpn clients disconnected) , br0 (probably) goes down or something and the script needs always restarting the connection...

The log:
Fri Jan 21 14:45:01 CET 2011 Network is ready! .....
Fri Jan 21 15:55:41 CET 2011 Network seems down, rechecking...
Fri Jan 21 15:56:21 CET 2011 Network is down, restarting interface br0!
Fri Jan 21 15:56:48 CET 2011 Network is ready after interface br0 restart! .....

Then if I use again, its ready... Is it possible, that if system don't use the connection after getting the DHCP lease, it close the connection automaticly? Anyway it works ok, but I don't want to owerwrite my router's flash in every 5 seconds with te new lease, my script probably defeat it soon if I don't do anything.