Currently zabbix agent does not provide data on interface speed. Documentation says that agent provides only current data. So for example if someone wants to create trigger on "network utilization reached 90% of interface speed" he should set the limits manually for every interface.

SNMP provides this data (IF-MIB::ifSpeed - 1.3.6.1.2.1.2.2.1.5), but I don't want to install both zabbix and snmp agents on one host.