# description : 'default DNSSEC mode',
# choices : ['yes', 'allow-downgrade', 'no'],
# value : 'allow-downgrade')
+# option('default-private-dns', type : 'combo',
+# description : 'default private DNS mode',
+# choices : ['opportunistic', 'no'],
+# value : 'no')
# option('dns-servers', type : 'string',
# description : 'space-separated list of default DNS servers',
# value : '8.8.8.8 8.8.4.4 2001:4860:4860::8888 2001:4860:4860::8844')