How do I know if a remote computer is open at one end?

Http://topic.csdn.net/u/20090105/15/9ee19e77-d848-4186-984a-542292b0d742.html

Telnet IP Port

=========http://blog.sina.com.cn/s/blog_5f2f51490100di66.html

First, how to see which ports the computer is open
1, the use of netstat command
Windows provides the netstat command to display the current TCP/IP network connectivity.
Method: Start--Program--Attachment--command prompt, enter the DOS window, enter the command Netstat-na carriage return, you can display the local connection and open port. Where local addresses represent the native IP address and the open port number, the Foreign address is the remote computer IP addresses and port number, state indicates the current TCP connection status.
2. Using port monitoring software such as security Monitoring tool vstat, it can also identify system paths and query properties in addition to all network activities in order to find files. Allows you to turn off any existing TCP and UDP connection setup and termination activities.
Second, how to permanently close some dangerous Trojan port

Each service corresponds to the corresponding port, and the service that is normally used by default is open-it is really not necessary for individual users.
A port is like a few doors in a house (server), and different doors lead to different rooms (servers provide different services). Our common FTP default port is 21, while the General WWW Web page default port is 80. But we tend to open some of the easily intrusive port services, such as 139, and some trojans, such as glaciers, BO, wide and so on are automatically open up a you do not detect the port. So, as long as we have to lock up all the ports we can't use, we will not put an end to these illegal intrusions.
1, "Control Panel" in the Administrative tools in the "services" in the configuration, disable unwanted services, the corresponding port is closed.
Reference: port services list, XP can be disabled in the service table (see the first floor)
Reminder: It is highly recommended for individual users to turn off the sever service (you can disable null connections)
2, use the TCP/IP filtering feature to limit the server's port.
Method: Local Connection Properties--internet protocol (TCP/IP)--Properties-Advanced-Advanced TCP/IP Settings--Xiangxiang--TCP/IP filtering
In the pop-up dialog box, select the "Enable TCP/IP Filtering" checkbox, and then choose "Allow only" on the left "TCP port".
3, run Gpedit.msc, in the Computer Configuration--windows Settings--Security Settings--ip Security Policy for manual settings.
Reminder: There are multiple policies that can only assign a current policy.
4. Use Ipseccmd to shield unsafe ports.
Its primary role is to set your filter rules, assign a name to it, and specify a policy name, which is a set of filter rules. For example, you want to close the TCP3333 port data two-way transceiver, using the command:
Ipseccmd-w reg-p "block default ports"-R "Block tcp/3333"-F *+0:3333:tcp-n block-x
The commonly used parameters are as follows:
The-W REG indicates that the configuration is written to the registry and is still valid after reboot.
-p Specifies the policy name and, if the name exists, adds the rule to this policy or creates one.
(Note that it is best to use the same policy name because the IP security policy for the system is last added)
-r Specifies the rule name.
-n Specifies the operation, which can be block, pass, or inpass and must be capitalized.
-X activates the policy.
-Y makes it invalid.
-O deletion.
-p Specifies the policy.
-F Sets the filter rule.
-y delete rule.
Methods: Copy the program ipseccmd to the C:\WINDOWS\system32 directory, and use the command prompt to execute it directly.
Reference: Denial of service network port filtering policy (see 2 floor)
Reference to some information, but the main body is written on their own know (probably not comprehensive, hope understanding).