Taking part of connection string from xml file

I've tried to build a connection string to a firebird db based on some xml file containing server ip address.

public class globals
{
    static string _serv;
    public static string serv
    {
        get
        {
            return _serv;
        }
        set
        {
            _serv=value;
        }
    }
    public static XmlDocument xmld = new XmlDocument();

    public static void serv_check()
    {
        xmld.Load("ustawienia.xml");
        globals._serv = xmld.GetElementsByTagName("ip").Item(0).InnerText;
        if (globals._serv.Length<=0)
        {
            MessageBox.Show("Nie zdefiniowano servera");
            Server_Deff sdf = new Server_Deff();
            sdf.ShowDialog();               
        }
    }

    static string db_user = "SYSDBA";
    static string db_pass = "masterkey";

    public static string cstr=
                "User=" + globals.db_user + ";" +
                "Password=" + globals.db_pass + ";" +
                "Database=db_kanc;" +
                "DataSource=" + globals.serv +
                "Port=3050;" +
                "Dialect=3;" +
                "Charset=NONE;" +
                "Role=appka;" +
                "Connection lifetime=15;" +
                "Pooling=true;" +
                "MinPoolSize=0;" +
                "MaxPoolSize=50;" +
                "Packet Size=8192;" +
                "ServerType=0";

    public static FbConnection conn = new FbConnection(globals.cstr);
    public static FbTransaction transaction;


    public static void openConnection() // Open database Connection
    {
    conn.Open();
    transaction = conn.BeginTransaction();
}

For some reasons neither when the ip address is defined in xml file nor when it's not variable serv seems to be null. I can get the value through message box but not as a proper Datasource in connection string.

While trying to connect to db I'm getting error like this:

FirebirdSql.Data.FirebirdClient.FbException: Unable to complete network request to host "Port=3050". ---> FirebirdSql.Data.Common.IscException: Unable to complete network request to host "Port=3050". w FirebirdSql.Data.Client.Managed.Version10.GdsConnection.Connect() w FirebirdSql.Data.FirebirdClient.ClientFactory.CreateManagedDatabase(FbConnectionString options) w FirebirdSql.Data.FirebirdClient.ClientFactory.CreateDatabase(FbConnectionString options) w FirebirdSql.Data.FirebirdClient.FbConnectionInternal.Connect()

Any ideas?

Thanks in advance!