Ethernet connection drop on Raspberry Pi

From time to time internet connection to my Raspberry Pi disappears (AFAIK it is well known feature of Pi). Removing and reconnecting the ethernet cables did not work, so one has to reboot by pulling the plug (risking to corrupt file systems from improper shutdown).

To reconnect I use the following bash script (found here):

#!/bin/bash
# Check if Internet connection is still alive *** 
# Insert into crontab at *.16
LOGLOG="/home/pi/Logs/Cron/Reboot.log"
WLAN=eth0

if /sbin/ifconfig $WLAN | grep -q "inet addr:" ; then
  echo "Network connection up!"
else
  echo "Attempting reconnect [`date +%Y%m%d%H%M`]" >> $LOGLOG
  /usr/bin/sudo /sbin/ifup --force $WLAN
fi

Note: use ifconfig -a to identify relevant interface (WLAN):

pi@raspberryberrystar ~ $ ifconfig -a ifconfig -a
eth0      Link encap:Ethernet  HWaddr b8:27:eb:f5:9a:d7  
          inet addr:192.168.1.146  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

My other Pi is connected to internet not through a cable but with WiFi dongle. The relevant interface is:

pi@blackberrystar ~ $ ifconfig -a
wlan2     Link encap:Ethernet  HWaddr 10:fe:ed:12:ef:2c  
          inet addr:192.168.1.144  Bcast:192.168.1.255  Mask:255.255.255.0

The connection is checked every 20 minutes with the following crontab entry:

## Check Internet connection every 7th, 27th, 47th minute:
7,27,47 * * * * /home/pi/bin/chk_www_alive.sh > /dev/null 2>&1