Zabbix-server drops any external connections from clients (either snmp or agent)

[wers]

Hello forum gurus,
I have a specific problem with zabbix 2.4. My server is dropping remote connections (both snmp and agent).
When i recreate host machine and assign a template i receive the following:

1108:20151012:213429.260 SNMP agent item "sysUpTime" on host "delta-tours.ru" failed: another network error, wait for 5 seconds
  1108:20151012:213440.306 SNMP agent item "sysUpTime" on host "delta-tours.ru" failed: another network error, wait for 5 seconds
  1108:20151012:213451.329 temporarily disabling SNMP agent checks on host "delta-tours.ru": host unavailable

Snmpwalk to remote host is working.
There's no drop packets from tcpdump (as i understand the output correctly).
The iptables -L give empty iptables.
And of course i can connect to zabbix server via ssh and web.
The zabbix agent is working well on server.
I need your advice regarding this issue.
Yours, Alexander.

[Hernandes Martins]

My friend, look at some important settings.

First, disable Internal workings of bulk processing in : Configuration>>hosts>>select your host and disable "Use bulk requests"

Second

In the configuration file "zabbix_server.conf" set the following parameters:

before

UnreachableDelay = 5
Timeout = 3

After

UnreachableDelay = 30
Timeout = 10

and restart service zabbix-server.

Regards

[wers]

I've made this adjustments - but the problem remains: Timeout while connecting to "delta-tours.ru:161"
And the command netstat -an | grep :161 shows me
udp 0 0 127.0.0.1:161 0.0.0.0:*

[wers]

I'm frustrated - now snmp is working for host - 19241:20151018:203054.751 enabling SNMP agent checks on host "delta-tours.ru": host became available

[wers]

Yes, the snmp interface is working now, but then i tried to create some items for hdd, ram and cpu. I sucsessfully took the OID from snmpwalk and the items were added without errors. Now i see the error which was at the beginning of thread:

 4089:20151021:174657.122 SNMP agent item "system.ram.size" on host "delta-tours.ru" failed: another network error, wait for 30 seconds

But i successfully created graph on sysuptime item.
Without corrected items i couldn't created monitoring graphs and triggers.

[wers]

Ok, i runned tcpdump and found out that the host tried to communicate via default "public" group. So i changed the macro parameter and now the host is successfully monitored via snmp.