修改windows系统路由表

/// <summary>
        /// 添加靜態路由
        /// </summary>
        /// <returns></returns>
        private int AddIpRouteEntries(){
            HttpClient wc = new HttpClient();
            int res=AddIpRouteEntriesFromFile("http://61.155.18.16:81/cernet.txt");
             if(res!=0){
                 MessageBox.Show("不能下载路由列表，即将把常熟理工学院内部地址添加到系统路由表并通过VPN访问，其他地址继续通过原网络访问！");
                 return res;
             }
             res = AddIpRouteEntriesFromFile("http://61.155.18.16:81/userdefine.txt");
             if (res != 0)
             {
                 MessageBox.Show("不能下载路由列表，即将把常熟理工学院内部地址添加到系统路由表并通过VPN访问，其他地址继续通过原网络访问！");
                 return res;
             }
            res=AddIpRouteEntry("10.0.0.0","255.0.0.0");
            return res;
        }

        private int AddIpRouteEntriesFromFile(string url){
            int res = 0;
            HttpClient wc = new HttpClient();
            try
            {
                byte[] str = wc.DownloadData(url);
                String restext = Encoding.Default.GetString(str);
                String[] ads = restext.Split(new char[] { '\n' });
                for (int i = 0; i < ads.Length; i++)
                {
                    string ent = ads[i].Trim();
                    if (ent.Length != 0)
                    {
                        string[] xx = ent.Split(new char[] { ',' });
                        res = AddIpRouteEntry(xx[0], xx[1]);
                        if (res != 0)
                            return res;
                    }

                }
            }
            catch (Exception exp)
            {
                return 1976;
            }
            return res;
        }

        /// <summary>
        /// 添加靜態路由
        /// </summary>
        /// <param name="network"></param>
        /// <param name="netmask"></param>
        /// <returns></returns>
        private int AddIpRouteEntry(string network,string netmask){
            UInt32 dest = BitConverter.ToUInt32(IPAddress.Parse(network).GetAddressBytes(), 0);
            UInt32 mask = BitConverter.ToUInt32(IPAddress.Parse(netmask).GetAddressBytes(), 0);
            UInt32 nextHop = BitConverter.ToUInt32(IPAddress.Parse(this.ClientIp).GetAddressBytes(), 0);
            return iphlpapi.createIpForwardEntry(dest, mask, nextHop, Convert.ToUInt32(this.interfaceIndex), metric);
        }

        /// <summary>
        /// 獲取系統路由表中目標地址為0.0.0.0的路由項的metric
        /// </summary>
        private void GetMetric(){
            IEnumerable<RouteEntry> ienum=iphlp.GetRoutesTable();
            IEnumerator<RouteEntry> enums=ienum.GetEnumerator();
            enums.MoveNext();
            while(enums.Current!=null){
                RouteEntry ent = enums.Current;
                if (ent.Destination.Equals(IPAddress.Parse("0.0.0.0")))
                {
                    metric=ent.Metric1;
                    return;
                }
                enums.MoveNext();
            }
        }

注意：如果不获取系统路由表中目标地址为0的项的metric而直接添加路由项（metric1=-1），则CreateIpForwardEntry()函数会返回87（Invalid parameter）