verifique a estrofe "nameserver".
nameserver
IPv4 address (in dot notation) or IPv6 address (in hex-and- colon notation) of a name server that the resolver should query. Scoped IPv6 address notation is accepted as well (see inet6(4) for details). A non-standard port may be specified using [host]:port syntax. When a non-standard port is specified the host address must be enclosed in square brackets. For example:
nameserver [10.0.0.1]:5353 nameserver [::1]:5353
Você pode conseguir usar os colchetes, mas acho que o código foi alterado para torná-lo esperado para endereços ipv6. Talvez alguém possa confirmar isso.