A customer asked today why our control panel showed their server with over 10 GB of traffic, but the ifconfig on their server showed that they had done just over 1 GB of traffic. Their server had not been rebooted for several months, so it should have accounted for all traffic during the current month.
What they didn’t realize was that the counters used by ifconfig are 32 bit counters, so they can only go as high as about 4.3 GB (technically 2^32 = 4,294,967,296 bytes) before rolling over. With 10 GB of traffic during a month, that would mean that they roll over a little more than 2 times per month, or about every 2 weeks.