Why so we see DNS requests when accessing a service, when using tcpwrappers, while we only use IPs in the tcpwrappers config?

Issue

"ALL:[::1]" was defined in the first line of /etc/hosts.allow. When the "snmpwalk -v 1 -c public " command was executed, name resolution to DNS server occurred.

We think that name resolution to DNS server should not occur because we defined only IP address(IPv6) in /etc/hosts.allow. When we defined only IP address(IPv4) in /etc/hosts.allow, the request did not occur.

Please tell us the reason why name resolution to DNS server occurred when only the IP address(IPv6) was defined in /etc/hosts.allow.

# cat /etc/hosts.allow
ALL : [::1]