Description of problem:
MRTG determines 0 bytes of traffic when the counter is over 32bit value.
When the traffic counter is under 32bit value it will graph it correctly.

The key is here that the values must be over 32bit range, if they are
not, it will work. So when reproducing it, check that your interface
counters are big enough or debug with own script.

Version-Release number of selected component (if applicable):
mrtg-2.14.5-2

How reproducible:

/etc/mrtg/mrtg.conf:
#traffic
Options[eth0]: growright
Target[eth0]: `/usr/local/bin/mrtg-script-eth0`
MaxBytes[eth0]: 2621440
Title[eth0]: Traffic Analysis
PageTop[eth0]: <H1>Traffic stats</H1>

/usr/local/bin/mrtg-script-eth0:
#!/bin/sh

cat /proc/net/dev | grep eth0 | sed s/eth0://g | tr -s " " | awk '{print $1;}'
cat /proc/net/dev | grep eth0 | sed s/eth0://g | tr -s " " | awk '{print $9;}'
uptime|sed -e 's/.*up \(.*\),.*[0-9]* user.*/\1/'
hostname


Steps to Reproduce:
1. Configure
2. Wait
3. Watch the result
  
Actual results:
0 bytes of traffic if the counter value is over 32bit

Expected results:
Normal traffic graph

Additional info:

Workaround to this problem is to modulo the values to under 32bit:

/usr/local/bin/mrtg-script-eth0:
#!/bin/sh

echo $[`cat /proc/net/dev | grep eth0 | sed s/eth0://g | tr -s " " | awk '{print $1;}'` % 2147483648 ]
echo $[`cat /proc/net/dev | grep eth0 | sed s/eth0://g | tr -s " " | awk '{print $9;}'` % 2147483648 ]
uptime|sed -e 's/.*up \(.*\),.*[0-9]* user.*/\1/'
hostname

.. But it would be nice that this wouldn't be needed, took some time
to debug this and confirm it.