VB.NET Server Does Not Receive Connection Requests from Remote Clients
A VB.NET server application does not see connection requests from another client on the network (i.e. with a different IP address). However, it does see connection requests from the client application running on the same computer as the server.
The listening socket is created with the following parameters
System.Net.Sockets.AddressFamily.InterNetwork
System.Net.Sockets.SocketType.Stream
System.Net.Sockets.ProtocolType.IP
We have experimented with the preceding without success.
The endpoint to which the listening socket is bound specifies the local IP address and a specific port number.
The wait-for-connection code is textbook asynchronous:
thelistener.Listen(10)
thelistener.BeginAccept(New System.AsyncCallback(AddressOf targetofaccept), thelistener)
If the client that attempts connection is on the same computer as the listener, then targetofaccept is run successfully. If the client that attempts connection is on some other computer on the network, then targetofaccept is not run.
The behavior occurs for any other client on the network (i.e., not just one).
Thinking that there was some firewall issue, we created VB6 servers and clients using the same addresses and ports. The VB6 server will receive connection requests regardless of the client system.
There is no other issue with communication between clients and the server, as far as we can see. The network architecture has not been modified for a number of years.
We are debugging the code as a VB.NET console application.
Any tips on how to diagnose appreciated.
Before calling Listen() you need to bind your listener socket to the address 0.0.0.0 (in .NET IPAddress.Any) so that it listens to connections from any IP address.
This can be done using the Socket.Bind() method:
Dim listenerEndpoint As New IPEndPoint(IPAddress.Any, <your port>)
thelistener.Bind(listenerEndpoint)
thelistener.Listen(10)
Thank you.
Issue WAS firewall. Fixed by finding exact location of the IDE (devenv.exe), opening "Windows Firewall" in the control panel, selecting "Allow a program or feature through firewall", selecting "Allow another program...", browsing to the exact location and selecting the executable, then ensuring "Home/Work (Private)" column is checked for that "Name".
Related
I am new to WCF Services, I have developed a WCF service library hosted within a Windows Service. The service end point is http://servername:9980/ApplicationServer/ServiceName.
When I run this service on local system and try to connect using my application, everything works fine.
The problem starts when I deploy this service on server system, none of my application can use this service, even the browser says page not found. Though, if I remove the specific port number from the endpoint all works well.
I have already opened all the ports in Windows Firewall including Client and Server. Also proper exceptions are made to the router firewall, still I am not able to host the service on specific port. I have even tried by switching firewall off on both client and server system.
Thank you in advance.
-Ashish Sharma
When you remove the specific port number it defaults to port 80.
So there is something that is blocking the other port.
Try using the Telnet command to check if the port is open (you may have to enable telnet)
As you have allready checked the firewalls, it could be urlscan or a network device.
I have created a simple tcp client-server application in vb.net. Everything works fine when i set local host (127.0.0.1) as the ip address. I wish to make a connection to a remote machine (keeping client at my machine and server on the other - or vice versa).
EDIT:
ok, the code of interest is as follows:
the server:
Dim server As TcpListener = New TcpListener(IPAddress.Any, port)
the client:
Dim theip As IPAddress = IPAddress.Parse(TextBox1.Text)
client = New TcpClient(theip.ToString, port)
Now, what should i enter in "TextBox1.Text" if i have my client on a remote machine (connected over internet) and server at a different computer (whose external IP address is known)?
Can i enter the external IP address of the machine running the server directly in the text box? Also, do i need to take care of things like "port forwarding" / "let firewall allow the connection" and all? If yes, can you please guide me or link a tutorial so that my application does this automatically or is there an alternative approach to achieve this and so that port forward is not required? Thanks a lot!
You say the other machine has an external ip address. This implies it also has a local ip address; ie it is behind a NAT firewall or similar. In this case, you will have to configure the firewall to allow communication to take place, eg by setting up port forwarding.
Applications such as MSN Messenger, VOIP clients etc have elaborate mechanisms to negotiate this automatically, but they're often not very successful.
I'm planning on using a wsDualHttpBinding for a WCF service with callbacks. The clients will be a windows form application communicating to the service over the internet. Obviously I have no control over the firewall on the client side, so I'm wondering what is the proper way to set the ClientBaseAddress on the client side?
Right now in my intiial testing I'm running the service and client on the same pc and i am setting the binding as follows
Dim binding As System.ServiceModel.WSDualHttpBinding = Struct.Endpoint.Binding
binding.ClientBaseAddress = New Uri("http://localhost:6667")
But I have a feeling this won't work when deploying over the internet because "localhost" won't translate to the machine address (much less worrying about NAT translation) and that port might be blocked by the clients firewall.
What is the proper way to handle the base address for callbacks to a remote client?
some one tell me if i do not specify ClientBaseAddress then WCF infratructure creates a default client base address at port 80 which is used for the incoming connections from the service. Since port 80 is usually open to firewalls, things should just work.
so just tell me when win form wcf client apps will run then how can i open my custom port like "6667" and also guide me what library or what approach i should use as a result response should come from client side router
to pc and firewall will not block anything. please discuss this issue with real life scenario how people handle this kind of situation in real life. thanks
The proper way is to use TCP transport instead of HTTP transport. Duplex communication over HTTP requires two HTTP connections - one opened from client to server (that's OK) and second opened from server to client. This can work only in scenarios where you have full control over both ends. There is simply too many complications which cannot be avoided just by guessing what address to use like:
Local Windows or third party firewall has to be configured
Permission for application to run - listening on HTTP is not allowed by default unless UAC is turned off or application is running as admin. You must allow listening on the port through netsh or httpcfg (windows XP and 2003) - that again requires admin permissions.
Port can be already used by another application. In case of 80 it can be used by any local web server - for example IIS.
Private networks and network devices - if your client machine is behind the NAT the port forwarding must be configured but what if you have two machines running your application on the same private network? You cannot forward from the same incoming port to two machines.
All these issues can be avoided mostly only when you have control over whole infrastructure. That is the reason why HTTP duplex communication is useful mostly for intranet scenarios and why for example Silverlight offers another implementation where the second connection is not created and Silverlight client instead polls server continuously to check if there is any callback available.
TCP transport requires only single connection from client to server because TCP protocol is natively duplex so the server can call back the client through the same connection. When you deploy a public service you usually have control over infrastructure on the server side so you can make necessary changes in configuration to make it work.
I think this also answers your previous question.
Here's the scenario: A client machine has connected to the 'Work network' via VPN (Cisco VPN Client). The work network hosts a machine that has a WCF service with nettcp binding. The client tries to connect to this service and gets an exception as follows:
Could not connect to
net.tcp://workMachine:2010/SomeService.
The connection attempt lasted for a
time span of 00:00:01.3180754. TCP
error code 10061: No connection could
be made because the target machine
actively refused it workMachine:2010.
Things I tried:
Changed the Workgroup of the client
machine to the work network
workgroup
Added domain/username/password for the Windows Networking Password vault, so that it can be used to connect
Changed the wcf service path with an IP address instead of the workMachine name
Checked client machine firewalls and added to allow the wcf client through it
All above failed and didn't work.
Has anyone encountered similar issues?
The client machine is on Windows 7
SecurityMode of the WCF service is set to NONE - so that shouldn't be an issue.
Any insights will be helpful
You may need to supply client credentials explicitly through your proxy object.
Assume that the proxy object in the code below implements one of the ClientBase interfaces.
proxy.ClientCredentials.Windows.ClientCredential.UserName = "clientaccount";
proxy.ClientCredentials.Windows.ClientCredential.Password = "S3cr3t1337Pwd";
Could you - just for testing purposes - expose the same service on the same machine using a HTTP endpoint, and try to connect to that one from your VPN client?
NetTcp is an excellent choice behind the corporate firewall - just don't know how the Cisco VPN client might cause troubles here, that might not show up when using an http-based protocol. Just a wild guess for now, but if you have nothing else to go on, give it a try!
Marc
Just another thought to assist with debugging of these kind of issues, using CMD execute "netstat -a" (you can append the -o switch and find the related process id also) and see if the port in question is currently open, if it isn't you may have an issue with the SMSvcHost.exe (this is the Windows process for managing an IIS hosted TCP Service).
I've had this issue before and rectified it by restarting the following services (obviously you'll need to carefully consider this if you are dealing with a live production system):
NetTcpActivator (Net. Tcp Listening Adapter)
NetTcpPortSharing (Net. Tcp Port Sharing Service)
and possibly if relevant:
NetMsmqActivator (Net. Pipe Listener Adapter)
NetPipeActivator (Net. Pipe Listener Adapter)
Hope this helps someone!
J.
I need to create a self-hosted WCF service.
I need secure duplex connection between client and server through Internet.
I read some documents of WCF and found that the netTcpBinding is suitable for intranet application, because the SSL is only point 2 point. If it is an internet application, the connection must not be point 2 point, am I correct? so SSL in transport security with netTcpBinding is not suitable?
so what combination should I use to create a secure duplex internet application?
thank you very much.
I have tried http://www.codeproject.com/KB/WCF/WCFWPFChat.aspx
this tutorial use netTcpBinding and endpoint localhost
I change the endpoint localhost to a name based url, forward a port in my router to my development PC, open the same port at Windows firewall.
The client program can chat with each cients program in different machines, BUT the callback connection will lost after one minute.
I also tried changing the binding to wsDualHttpBinding, the clients program can chat with each clients in the same machine and kept the callback connection in the reliableSession inactivityTimeout setting. However another client program in another machine cannot join the server, if I turn off Windows firewall on that machine, the client program can connect.
It seems that tcp binding can let the client program connecting to the server with Windows firewall turn on. but callback connection lost.
and the wsDualHttpBinding can keep the callback connections. but cannot connect to server if Windows firewall on.
Is there a way to kept the netTcpBinding callback connection as in the wsDualHttpBinding?
It sounds like you have two issues- duplex connection and security.
If you truly need a duplex connection (eg, server-initiated callbacks), neither of these will work very well over the internet unless you have very fine control over the firewalls on both ends (the client still has to expose a publicly accessible HTTP endpoint for the server to call back). The best way would be to use the new relay services with .NET 4.0- this allows for a mimic'd server-initiated connection through firewalls.
EDIT: this is now called AppFabric, and is part of the Windows Azure infrastructure
On the security front, you can always use message security over the service bus, but I don't see a reason why transport security would be a problem either.
To answer user248724,
The client program can chat with each
cients program in different machines,
BUT the callback connection will lost
after one minute.after one minute.
You need either have the client or the server to ping each other at least every minute to keep the connection socket alive.