Socket Server with SSLStream some times refuses new connections from clients.
I used the telent hostname port, and it says Connecting To host...
Could not open connection to the host, on port 6002: Connect failed
I used netstat -a , and I see TCP status as
TCP 0.0.0.0:6002 host:0 LISTENING
I also see the service as listening in tcpview too.
The error I see on client side is connection refused with error code 10061.
The same socket server was accepting new connections and just runs fine without any issues.But after some time the above issue happens.its random.
When I restart the sockets it just works fine and accepts conenctions, which I don;t want to do it frequently.becasue this disconnects clients, who are already connected.
Could somebody help me to trouble shoot this?
Thanks.
Where are you running netstat? On the server?
Try connecting to the socket from localhost (from the server itself) using the destination IP address 127.0.0.1
Do the same test with the network IP of the server.
My guess is that the firewall is preventing external access or a router in between is preventing the connection.
It works for a while and then stops. Few options I can think of:
Some firewall on the way does some kind of throttling
You open and close too many connections too quickly. In this case you exhaust the ephemeral ports on the client (usually) and/or on the server. If you do netstat -a you will see a lot of sockets in TIME_WAIT state, try this both on client and server. Solution here is to reuse connections (best). Or increase the number of ephemeral ports (registry setting). But this will take you only so far.
You have a bug in your server and it stops accepting new connections after a while.
Related
I created a multi-threaded client/server application that can send messages to each other at real time. Everything works perfectly, but I want to be able to send messages over the Internet. From what I understand, I need to do port forwarding to be able to make my server reachable for the clients. I then set up my port forwarding options by providing a port (9991) and then my Macbook Air's IP Address (192.168.0.1).
I then tried to connect to my server using my public server IP (let's say 197.132.20.222) and it didn't work. I then tried to see if the port forwarding worked by using this website: https://www.yougetsignal.com/tools/open-ports/ and I realized that the connection was closed. I also tried the command nc -vz 197.132.20.222 9991 while running my application and the connection is refused.
I'm using a JavaFX application, and for my server side I use a ServerSocket with port 9991. For the client side, I use a Socket and set the IP Address to my public router IP Address, and I tried to connect with another PC using mobile data to use a different network.
My firewall settings are turn off, so I really don't know what is blocking my application to connect to that port. Could it be my ISP is blocking connections? I just don't understand why my ports are blocked even with no firewalls enabled.
The Preamble
I start up my local SSH terminal at work behind a firewall, and connect to a remote server all the time without any problem.
The way Xdebug works, correct me if I'm wrong, is that it sends an "unsolicited" request to my network's port 9000. I actually initiated that action by sending the remote server an HTTP request through my browser with a POST/GET/COOKIE variable instructing xdebug to start up. But my network doesn't know that. All it knows is that it is getting a request on port 9000 from the internet. It doesn't know which computer in its private network to forward it to (without setting up port forwarding on the router), and can only ignore the request.
So if you can't do port forwarding, another option (and a much better one from what I can tell), is SSH tunneling. My computer sends the SSH request, the server responds. My router knows which computer in its network to route these responses to. Piggybacking on that SSH connection allows those "unsolicited" port 9000 requests from the remote server to get to me.
I think I understand that much.
I finally got tunneling to work, thanks to stackoverflow, but how it works is still fuzzy to me.
On the remote server, I tell Xdebug to connect to localhost (not to my ip via xdebug.remote_host=173.123.45.56, and not to xdebug.remote_connect_back=1 which also would end up at my IP) on port 9000. Connecting to localhost seems a bit weird, since I picture that as the server sending messages to its own IP address, as if it is sending messages into itself (but I think that connecting to localhost is probably fundamentally different than connecting to any other IP... I don't think the message gets routed out and back in to localhost).
On my computer at work, I open up an SSH connection on port 22, specifying a tunnel to/on port 9000, and remote port 9000. I've seen some explanations of the various settings here but still don't understand them. Some even seem to involve three machines. What seems to be happening though, is I'm connected as usual via port 22, but I've told the remote machine that I want to receive its port 9000 communications. I've specified "localhost" in my tunnel, and I suppose that might need to match the localhost in my xdebug.remote_host value. I wonder if I specified my IP address in both places (i.e. xdebug.remote_host=173.123.45.56 on the remote server, and same IP in my SSH terminal), would that work too?
So Xdebug on the remote server sends me a request to initiate a debug session. It comes through my port 22, but my SSH tunnel somehow makes it seem that it is coming in on port 9000. So my IDE that is listening on port 9000 receives the request and sends a response (also on 9000), which my SSH tunnel intercepts somehow and sends back to the remote server on port 22, where it is similarly spoofed into looking like port 9000 to xdebug.
The Crux
So what I'm really not clear on is, what exactly is the localhost in my SSH tunnel configuration referring to? Does it relate directly to the xdebug.remote_host=localhost value? Can I change them both to my IP address?
Are all of the remote server's outgoing communications on port 9000 being forwarded to me, or just some of them? E.g., if someone in Chattanooga initiates a debug session in their browser, will I receive Xdebug's response?
Are all of my outgoing communications on port 9000 being forwarded to that server? I.e. can I debug two applications on two different servers at the same time, with some of my port 9000 communications going one way and some the other, or would I need one port per local application? (I can use Google Chrome and Firefox browsers at the same time, both on port 80, for example.)
The tunnel consists of an SSHD listening to port 9000 (as well as 22) at your end and an SSHD listening to port 22 at the other end. When you connect your XDebug to your local 9000, the SSHDs intercommunicate and the remote SSHD connects to port 9000 at the remote. Thereafter your local port 9000 behaves identically to the remote port 9000: all data written to either end appears at the other end.
I establish a TCP connection between my server and client which runs on the same host. We gather and read from the server or say source in our case continuously.
We read data on say 3 different ports.
Once the source stops publishing data or gets restarted , the server/source is not able to publish data again on the same port saying port is already bind. The reason given is that client still has established connection on those ports.
I wanted to know what could be the probable reasons of this ? Can there be issue since client is already listening on these ports and trying to reconnect again and again because we try this reconnection mechanism. I am more looking for reason on source side as the same code in client sides when source and client are on different host and not the same host works perfectly fine for us.
Edit:-
I found this while going through various article .
On the question of using SO_LINGER to send a RST on close to avoid the TIME_WAIT state: I've been having some problems with router access servers (names withheld to protect the guilty) that have problems dealing with back-to-back connections on a modem dedicated to a specific channel. What they do is let go of the connection, accept another call, attempt to connect to a well-known socket on a host, and the host refuses the connection because there is a connection in TIME_WAIT state involving the well-known socket. (Stevens' book TCP Illustrated, Vol 1 discusses this problem in more detail.) In order to avoid the connection-refused problem, I've had to install an option to do reset-on-close in the server when the server initiates the disconnection.
Link to source:- http://developerweb.net/viewtopic.php?id=2941
I guess i am facing the same problem: 'attempt to connect to a well-known socket on a host, and the host refuses the connection'. Probable fix mention is 'option to do reset-on-close in the server when the server initiates the disconnection'. Now how do I do that ?
Set the SO_REUSEADDR option on the server socket before you bind it and call listen().
EDIT The suggestion to fiddle around with SO_LINGER option is worthless and dangerous to your data in flight. Just use SO_RESUSEADDR.
You need to close the socket bound to that port before you restart/shutdown the server!
http://www.gnu.org/software/libc/manual/html_node/Closing-a-Socket.html
Also, there's a timeout time, which I think is 4 minutes, so if you created a TCP socket and close it, you may still have to wait 4 minutes until it closes.
You can use netstat to see all the bound ports on your system. If you shut down your server, or close your server after forking on connect, you may have zombie processes which are bound to certain ports that do not close and remain active, and thus, you can't rebind to the same port. Show some code.
We have written an application in which client-server communication is used with the IOCP concept.
Client connects to the server through wireless access points.
When temporary disconnection happens in the network, this can lead a CLOSE_WAIT state.This could indicate that the
client properly closed the connection. But the server still has its socket open.
If there are too many instances of the port (to which the server and client were talking) were in CLOSE_WAIT state then at the highest peak ,server stop functioning thus rejecting the connection.That is totally frustrating.In this case, user has to restart the server to wipe out all the close_wait state by clearing the memory.When server restart,client again try to connect to the server.Server calls accept command again,But before accepting a new connection ,previous connection should be closed at server side,How can we do that ?
How can we remove close_wait state of the socket without restarting the server ?
Is there any alternate way to avoid server restart ?
We also came to know that,If all of the available ephemeral ports are allocated to client applications then the
client experiences a condition known as TCP/IP port exhaustion. When TCP/IP port exhaustion occurs, client port
reservations cannot be made and errors will occur in client applications that attempt to connect to a server via TCP/IP sockets.
if this is happening then we need to increase the upper range of ephemeral ports that are dynamically allocated to client TCP/IP socket connections.
Reference :
http://msdn.microsoft.com/en-us/library/aa560610%28v=bts.10%29.aspx
Let us know if this alternate way is useful or not ?
Thanks in advance.
Regards
Amey
Fix the server code.
The server should be reading with a timeout, and if the timeout expires it should close the socket.
I have a simple TCP socket client and server application. They are communicating using IP = localhost and port = 33367.
I'm using SocketSniff to examine my packets going through localhost. While sniffing the client app, I noticed that every time I'm sending a packet to the server in the same process, the "local port" is changing, while remote port is always 33367.
So, is it possible for the client apps to send their data through a fixed port (if so, how in C#?) or do they have to get assigned a different port each time?
You can bind the socket before calling connect.