The system property `impl.prefix` has been removed. This undocumented system property dates from early JDK releases where it was possible to add an implementation of the JDK internal and non-public `java.net.InetAddressImpl` interface to the `java.net` package, and have it be used by the `java.net.InetAddress` API.
The `InetAddressResolver` SPI introduced by [JEP 418](https://openjdk.java.net/jeps/418) provides a standard way to implement a name and address resolver.