diff --git a/pyzkaccess/cli.py b/pyzkaccess/cli.py
index 1c1ccdb..4326135 100644
--- a/pyzkaccess/cli.py
+++ b/pyzkaccess/cli.py
@@ -4,6 +4,7 @@
 import ipaddress
 import os
 import re
+import string
 import sys
 import traceback
 from datetime import date, datetime, time
@@ -1199,17 +1200,7 @@ def connect(self, ip: str, *, model: str = "ZK400") -> ZKCommand:
             raise FireError(f"Unknown device model '{model}', possible values are: ZK100, ZK200, ZK400")
 
         if not connstr:
-            try:
-                if not isinstance(ip, str):  # python-fire may pass here int, tuple, etc.
-                    raise ValueError("IP address must be a string")
-                ip_addr = ipaddress.ip_address(ip)
-            except ValueError:
-                raise FireError(
-                    f"Bad IPv4 address: '{ip}'. Note: if you want to pass a connection string, set IP to "
-                    f"'ENV' and use the PYZKACCESS_CONNECT_CONNSTR environment variable"
-                )
-
-            connstr = f"protocol=TCP,ipaddress={ip_addr},port=4370,timeout=4000,passwd="
+            connstr = f"protocol=TCP,ipaddress={self._parse_ip(ip)},port=4370,timeout=4000,passwd="
 
         zkcmd = ZKCommand(ZKAccess(connstr, device_model=device_model, dllpath=self._dllpath))
 
@@ -1227,7 +1218,7 @@ def search_devices(self, *, broadcast_address: str = "255.255.255.255"):
         converter = TextConverter(formatter)
 
         def _search_devices():
-            devices = ZKAccess.search_devices(broadcast_address, dllpath=self._dllpath)
+            devices = ZKAccess.search_devices(self._parse_ip(broadcast_address), dllpath=self._dllpath)
             for device in devices:
                 values = [device.mac, device.ip, device.serial_number, device.model.name, device.version]
                 yield dict(zip(headers, values))
@@ -1242,11 +1233,32 @@ def change_ip(self, mac_address: str, new_ip: str, *, broadcast_address: str = "
 
         Args:
             mac_address: MAC address of a device
-            new_ip: new IP address to be set
+            new_ip: new IPv4 address to be set
             broadcast_address: broadcast network address to send
                 broadcast packets to. Default: 255.255.255.255
         """
-        ZKAccess.change_ip(mac_address, new_ip, broadcast_address, ChangeIPProtocol.udp, self._dllpath)
+        ZKAccess.change_ip(self._parse_mac(mac_address), self._parse_ip(new_ip), self._parse_ip(broadcast_address), ChangeIPProtocol.udp, self._dllpath)
+
+    @staticmethod
+    def _parse_ip(value: Any) -> str:
+        try:
+            if not isinstance(value, str):  # python-fire may pass here int, tuple, etc.
+                raise ValueError("Bad IPv4 address")
+            ip_addr = ipaddress.ip_address(value)
+        except ValueError:
+            raise FireError(f"Bad IPv4 address: '{value}'")
+
+        return str(ip_addr)
+
+    @staticmethod
+    def _parse_mac(value: Any) -> str:
+        if not isinstance(value, str):
+            raise ValueError("Bad MAC address")
+
+        if not re.match(r"^[0-9a-fA-F]{2}([:-]?[0-9a-fA-F]{2}){5}$", value):
+            raise FireError(f"Bad MAC address '{value}'")
+
+        return value
 
 
 class WriteFile(wrapt.ObjectProxy):
@@ -1271,7 +1283,7 @@ def main():
             sys.stderr.write(traceback.format_exc())
         sys.stderr.write(
             f"ERROR: {e}\n"
-            f"Please ensure that the environment is set up correctly by running the `pyzkaccess setup` command\n"
+            f"Note: You can ensure that the environment is set up correctly by running the `pyzkaccess setup` command\n"
         )
         sys.exit(2)