net.dns key fails while resolv.conf contains both ipv4 and ipv6 nameservers and machine haven't configured ipv6 connection correctly, even if I try to reach explicitly named ipv4 NS):

[root@ns1 ~]# cat /etc/resolv.conf
options timeout:1
nameserver 217.11.224.1
nameserver 2001:1528:1::1
nameserver 217.11.224.2
nameserver 2001:1528:1::2

[root@ns1 ~]# zabbix_agentd -t net.dns[8.8.8.8,google.com]
net.dns[8.8.8.8,google.com][8.8.8.8,google.com] [u|0]

strace says:
socket(PF_INET6, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = -1 EAFNOSUPPORT (Address family not supported by protocol)

When I comment ipv6 nameservers in resolv.conf check works okay:

[root@ns1 ~]# cat /etc/resolv.conf
options timeout:1
nameserver 217.11.224.1
#nameserver 2001:1528:1::1
nameserver 217.11.224.2
#nameserver 2001:1528:1::2

[root@ns1 ~]# zabbix_agentd -t net.dns[8.8.8.8,google.com]
net.dns[8.8.8.8,google.com][8.8.8.8,google.com] [u|1]
[root@ns1 ~]#