unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, IdBaseComponent, IdComponent, IdUDPBase, IdUDPServer, StdCtrls,idsockethandle;

type
  TForm1 = class(TForm)
    Button1: TButton;
    IdUDPServer1: TIdUDPServer;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var ok:boolean ;
tempport:integer;
asockethandle:tidsockethandle;
begin
tempport:=idudpserver1.DefaultPort;
repeat
try
idudpserver1.Active:=true;
ok:=true;
except
  on EIdCouldNotBindSocket do
    begin
      IdUDPServer1.Active:=false;
      IdUDPServer1.Bindings.Clear;
      ASocketHandle:=IdUDPServer1.Bindings.Add;
      tempport:=tempport+1;
      ASocketHandle.Port:=tempport ;

    end;
end;
until ok;
showmessage(inttostr(idudpserver1.Binding.Port));
end;

end.