I wrote a java program of TCP/IP Client which is supposed to read data from TCPIP server device.
Problem is when I give the IP and Port of the Device, java gives error of "Connection Time out". Obviously this is problem of not connecting to that Device.
I want to know if there is way to know where the problem is? Whether that TCPIP server device is not reachable (if no, then how to check it )
whether Its the router / network issue that TCPIP Client and Server has to be on same network or use same router to communicate. OR Just IP:Port is enough.
How on my computer may I know that TCPIP server device is turned on and streaming??
P.S. That TCPIP Server device can also be connected with blutooth connection. can i read streaming through blutooth in Java?? if yes what/How should I do it?
I want to know if there is way to know where the problem is? Whether
that TCPIP server device is not reachable (if no, then how to check it
)
Use telnet from the client - it will try to connect to the remote server at the port that you specify. For example telnet google.com 80 attempts to reach google.com on port 80. You could also use an IP address in place of "google.com". If you are on a windows box, you might have to enable telnet first.
You can also use netstat on the server. It should say the ports that are currently open and the state that they are in. For example, your Java server program should be listening on the port, so the state should say LISTEN.
Related
i have a three system connected in a LAN and one of the system has server program running but the client doesnt know IP of that server. Client has to detect that server and connect with that server . Is it possible to do and whether it can be done using TCP/IP
You could probably send a TCP package to the broadcast address of your network when trying to find the servers ip address.
That way every device in your network receives your package. Then just make the server listen and respond to that package. That way you can easily find your servers IP address without trying to connect to every single IP
I'm trying to build a peer-to-peer game, where each player is both a server and a client with tcp sockets. The sockets can connect fine when I'm using local ip:s, but of course fails when I'm trying to use external ip:s.
But I'm thinking that the players should be able to connect to each other if they just knew the external address + port that the router assigns to them.
Setting up port forwarding is out if the question since I don't have access to the players routers.
I'm thinking of having a server in between, just to be able to read the external address and port of the players, and tell the other player about it so that it can connect.
But I haven't found any info anywhere if that's how port forwarding works. If computer A makes a request from a local address and a port to the server, and the router assigns this address + port to an external address + port, and the server tell computer B which address + port to use. Can computer B use that external address + port to connect to the computer A and start a tcp socket with it? Is there any way to know that this external address + port stays the same when another computer makes a request against them?
The problem is that most people don't expose their PC directly to the internet. They have a router that has an external address. When you send a packet to their IP address, it is going to their router. The router doesn't know where to forward it to and what port to use without port forwarding.
So, getting everyone to enable port forwarding is out of the question, as it should be. A simpler mechanism is to have a server on the internet that you control. It has a firewall with port forwarding setup. The clients are just clients, they connect to the server on a port and send and receive info about the current status of the game. That way, everyone has real-time updates on their local game engine. Plus, this way is much easier to program and implement.
No, TCP doesn't work like that.
The source port that has been used to talk to the rendezvous server will be transient and specific to that particular initial TCP socket connection and can only be used as a destination for return traffic on the same connection from the rendezvous server, and can't be used by a third party to make new inbound connections.
The typical (only?) practical solution when NATs are involved and port forwarding is not available is to have that central server relay all messages bidirectionally between the peers.
Hole punching is what I was looking for.
https://en.wikipedia.org/wiki/Hole_punching_(networking)
When we open a TCP Listening, we use a fixed port, like "9870".
But the clients which connect to this listening, use different ports like "1024, 1025" or other. I don't know what is the name of this port, "client port", "dynamic port" or "ephemeral port"... But I need to know if is possible to change this client port.
Because, like in the second image, it shows the error "Port numbers reused", and I think this is related to this port configuration.
I think if I could configure these ports, the connections of the equipments on my network will be stabilized.
TL;TR: there is usually no need to configure the clients source ports and you can definitely not set the clients source port at the server.
The client can bind to a address+port the same way the server can do and this port is then used as the source port for the connection. But usually this is not done and instead the socket is not specifically bound and a free source port is automatically assigned by the system. The client source port can only be set by the client itself and can not be changed by the server.
Usually it is not possible that a port number gets reused by the client since the OS will not let the client do this. But what you see can happen if the client crashes . After the restart the client is not aware of any connections which were established (and never closed) before the reboot so it will happily use the same source port again. In this case it gets a RST from the server since the new data do not match the old connection.
This can also happen if the client is connected with some router doing NAT and the router crashes. After restart the router is not aware of any previous connections and will thus create new translations which might conflict with old connections.
I am having some trouble allowing my 2wire router (provided by AT&T to forward certain ports.
I have a raspberry pi running subsonic (a music server) and I would like to access it from the outside internet. I have configured the pi with a static LAN IP address and have opened the specified ports (4040 and 80) on both TCP and UDP. I have also confirmed the service is active and is listening on the specified ports via netstat.
When I attempt to connect, however, from my WAN IP I am confronted with a connection refused dialog. Checking the firewall logs on my router, I see this message
IN=br1 MAC=--:--:--:--:--:-- SRC=(my computer IP) DST=(My WAN IP) LEN=40 TTL=240 PROTO=TCP DPT=5060 Unknown inbound session stopped
It appears that my firewall is still blocking the external connection. What strikes me as odd is, although I am unable to connect I can still see that the port is open from an outside port scanner. Using the service provided from http://www.yougetsignal.com/tools/open-ports/ I have confirmed that my IP has port 4040 to be open.
Once again, I have confirmed that the service is indeed listening on the raspberry pi, setup a static LAN address and created the protocol for both TCP and UDP....
Any help on this matter would be greatly appreciated.
Thanks in advance!
Ok so for whatever reason it was working all along. Apparently it was just getting confused by me trying to connect to my own router. I confirmed this by connecting to the server via 4G on my phone.
Dumb mistake by me.
(I have not put code in this question since the actual code probably doesn't matter here. If you say it does though then I can edit the question later to put it in.)
I'm new to using winsock2 or any other networking API for that matter. I have a very simple server application and client application in which the server sends a string to the client and then disconnects.
The applications work fine when I use localhost or 127.0.0.1 as the inet_addr() argument, but when I use my "real" IP, the client application just gets WSAECONNREFUSED and the server doesn't see it. I made sure that the port was the same for both applications and that also the protocol was the same.
[Edit] I have come back to this issue after abandoning networking for a while. I think this may actually have something to with the fact I am using a router, and not something in my code.
WSAECONNREFUSED is an active refusal of the connection by the peer or by an intermediate firewall. If it was the peer who issued it, it means you got the IP address or the port wrong, or else you got it right but the server isn't actually running; anyway, nothing is listening at that IP:port. If it was the firewall, adjust it.
Did you use htons() on the port number?
inet_addr() only works with IP address strings, you have to use gethostbyname() or getaddrinfo() to resolve localhost or any other hostname string to an IP address.
WSACONNREFUSED means the connection was actively refused on the remote end that you are trying to connect to.
If the server machine is refusing, that means either there is no socket listening on the requested IP:Port, or that there is one but its queue of pending client connections is full so it cannot accept a new connection at that moment.
If a router is refusing, that usually means the router is not configured to forward inbound connections for the requested IP:Port to a machine on the router's network. If you have a server running behind a router and are trying to connect to it using the router's public IP address, then the router has to be setup for port forwarding.
If a firewall is refusing, that usually means the requested port is not open.
Either way, there is no way for the client to know in code why the connection was refused. All it can do is wait for a period of time and then try again.