Update hyperv.py

lisa/tools/hyperv.py

@@ -307,10 +307,8 @@ def create_nat(self, name: str, ip_range: str) -> None:
         )
 
     def add_nat_mapping(self, nat_name: str, internal_ip: str) -> int:
+        # get next available NAT port
         external_port = self._get_next_available_nat_port()
-        if self.get_nat_mapping_id(external_port):
-            raise LisaException(f"Mapping for port {external_port} already exists")
-
         # create a new NAT
         self.node.tools[PowerShell].run_cmdlet(
             f"Add-NetNatStaticMapping -NatName {nat_name} -Protocol TCP "
@@ -551,7 +549,7 @@ def _get_next_available_nat_port(self) -> int:
         # Start checking from the external forwarding port start and
         # find the first available one
         port = self._external_forwarding_port_start
-        while port in self._assigned_nat_ports:
+        while self.get_nat_mapping_id(port):
             port += 1
         self._assigned_nat_ports.add(port)  # Assign this port
         return port