For 1½ years I have been telling QNAP, that their interface counters were wrong, when queried with SNMP, at least on a TS-419P. It was off by strange factor, that didn’t really fit with anything.
Then today I noticed the command
watch in Linux) and I did a
cmdwatch -n5 snmpget -v 2c -c secretstring qnapnas IF-MIB::ifInOctets.4
Then I saw it, of course. The counter was fluxuating up and down. Silly me. I had upgraded all my network equipment to gigabit speed, but I had missed the fact, that a 32 bit counter will wrap within the 5 minute intervals of MRTG querying.
So I had to Google how to query 64 bit counters in MRTG and it was pretty simple, just append
:::::2 to the Target line.
I have written to QNAP support and offered them my apology