plugin/dns64 : add support for DNS requests over IPv4 network (#4809)

plugin/dns64/setup.go

@@ -66,6 +66,8 @@ func dns64Parse(c *caddy.Controller) (*DNS64, error) {
 				dns64.Prefix = pref
 			case "translate_all":
 				dns64.TranslateAll = true
+			case "allow_ipv4":
+				dns64.AllowIPv4 = true
 			default:
 				return nil, c.Errf("unknown property '%s'", c.Val())
 			}