just noticed that there is no data from one of hosts for more then 10 minutes, found in log:
24613:20131226:134300.808 Zabbix agent item "net.if.out[eth1,bytes]" on host "inetgw-nsk" failed: first network error, wait for 15 seconds
I noticed this at 13:55 or so, so I restarted zabbix server and immediately get:
28701:20131226:135742.513 resuming Zabbix agent checks on host "inetgw-nsk": connection restored
This is definitely a bug, even f there was network problem far more then 15 seconds passed...