We notice the traffic that Zabbix records for some of our servers is lower then the server itself reports, in magnitude 10 times or more.

The items are net.if.in["adapter"] and net.if.out["adapter"], with the data type numeric (unsigned) decimal. Store as delta (speed per second), multiplier 8.

Also, sometimes there are gaps in in the graph.

We ran into this problem earlier with snmp ifInOctets on Linux devices, which is a 32 bit counter, which wraps around 4Gb, which happens quite soon with bigger interfaces (1Gbit or 10Gbit).

Looking at the code, it appears Zabbix calls the getifentry API, which returns an MIB_IFROW struct, which uses DWORDS for the fields, which are 32 bits, confirming this is the issue.