环境：一台Zabbix服务器，一台Zabbix Agent服务器，服务器运行正常，但是从Zabbix Frontend上看到agent的状态为红色。显示报错信息如下：
Received empty response from Zabbix Agent at [10.0.0.201]. Assuming that agent dropped connection because of access permissions.
检查了agent服务器的服务状态都是正常，但是发现配置文件不正确。

vim  /etc/zabbix/zabbix_agentd.conf
### Option: Server
#       List of comma delimited IP addresses, optionally in CIDR notation, or DNS names of Zabbix servers and Zabbix proxies.
#       Incoming connections will be accepted only from the hosts listed here.
#       If IPv6 support is enabled then '127.0.0.1', '::127.0.0.1', '::ffff:127.0.0.1' are treated equally
#       and '::/0' will allow any IPv4 or IPv6 address.
#       '0.0.0.0/0' can be used to allow any IPv4 address.
#       Example: Server=127.0.0.1,192.168.1.0/24,::1,2001:db8::/32,zabbix.example.com
#
# Mandatory: yes, if StartAgents is not explicitly set to 0
# Default:
# Server=

Server=127.0.0.1

Server的IP需要设置成Zabbix服务器的IP地址，并重启agent服务。

Server=x.x.x.x
systemctl restart zabbix-agent

再检查Zabbix监控页面已经恢复正常。

参考文档:
http://www.ttlsa.com/zabbix/received-empty-response-from-zabbix-agent/