public static Version fromIpAddress(String ipAddress) {
            if (ipAddress.contains(":")) return v6;
            if (ipAddress.contains(".")) return v4;
            throw new IllegalArgumentException("Failed to deduce the IP version from the textual representation of the IP address: " + ipAddress);
        }
IP version.  Can be compared with ==, !=, and equals().
node-repository/src/main/java/com/yahoo/vespa/hosted/provision/node/IP.java