I'm trying to get a BACNet scanner up on an Seimens server running the Apogee system with a BACNet interface. I've tried using BACNet4j put i get a port bind error on the LocalDevice object for test/Scan.java.
Does anyone know of any other libraries I could use or a reference to instructions for setting up a BACNet plugin to a building management system?
I have had the same problem before, i.e. the BACnet client needs to both send and receive from UDP port 47808. Since the BACnet server already uses that port to listen (and reply) my solution was to use a virtual IP (a bridge) so that my client runs on the same Ethernet card but with a different IP address. A bit convoluted, I know, but it works.
Whether or not the Apogee system supports virtual (or simply additional) network drivers is another question altogether. On my Linux and Windows machines I can run as many servers and clients as I need (I actually don't know what is the limit, I have run up to 5 servers and 3 clients without any problems).
Concerning the port bind error, you may have to configure your firewall because:
BACnet/IP is using UDP
the default port number is 47808 (0xBAC0)
Your issue might be the use of a (BACnet port #) socket that is already in-use; you have to ensure that it's not in exclusive-use - before binding to the socket, but also (slightly more) important, also ensure it's marked for reuse.
But unless you're listening for Who-Is broadcasts, I'd recommend listening for the (unicast) responses upon a different port #, e.g. 0xBAC1/47809, but still send upon the standard port # 0xBAC0/47808.
Related
The problem: In java you can create a socket on the server with ServerSocket(0) and it will choose a random port to listen on. However when you create a socket on the client to send a message with Socket(addr, port) there is no apparent way to determine which port on the server you need to send to. I couldn't find anything about this option through web searches besides the basic "if you put 0 it will chose a random port". Does anyone know or have a resource that could explain what this scenario is supposed to look like from the client end?
Some background: I am currently converting a system from UDP to TCP. The reason I need the server to listen on a random port is that my server/client do not have a strict server/client relationship. So the "server" in this situation is really an application that I need to open multiple instances of on one PC. The old way of having predetermined send/receive ports is causing only one instance to be able to open a port and all communication is being redirected to that instance. My understanding that the best way to fix this problem is for each instance to use a different port, and the best way for that is to do ServerSocket(0). Despite including this background, I do not want comments on how messed up the situation is, only answers pertaining to the problem.
If a fixed port number is not part of the server's documented setup / protocol, then the only way for clients to figure out is to have the running/active servers publish that information in some datastore, the location and details of which are documented and known by the clients, and where that datastore is reachable for the clients.
[Or have the clients run a portscan each time they want to connect. It will work but probably not as fast as your users would like.]
And your situation is indeed messed up.
Perhaps if you are on the same IP subnet with all the servers/clients, then you could use UPnP to signal which random port new instances of your application are running on, and similarly other instances could monitor UPnP to discover this new instance.
I've never implemented UPnP in Java, but suspect libraries are out there..
eg. https://github.com/jupnp/jupnp
My issue is a protocol that identifies terminals by it's sending IP. I want to manage the connections of several terminals to this server using some kind of proxy that implements that protocol.
So I have Terminal A which is identified by the server by the IP 1.2.3.4 and Terminal B which is identified by the server using the IP 5.6.7.8. Now the proxy will be in a local network with Terminal A and B.
When Terminal A wants to reach the server, it will query the proxy and the proxy needs to send the request on behalf of Terminal A using IP 1.2.3.4 to the server
When Terminal B wants to reach the server, it will query the proxy and the proxy needs to send the request on behalf of Terminal A using IP 5.6.7.8 to the server
Is it even possible to solve that issue in Java or do I have to do network voodoo on the router to achieve this?
Edit: to make things clear. I know what a network proxy is and what a router does. I also know how to solve my problem on a network level using advanced network voodoo if required. What I want to know is if my guess that the problem can't be solved using Java is correct. So the bottom line question is: can I use Java to send traffic using a specific network interface to which a specific IP has been assigned or do I have to rely on what the operating system does to route my traffic (in which case the advanced network voodoo would be required)?
Edit2: If routing of network traffic can be done in java, I'd just like a quick pointer where to look into. My own googling didn't return any useful results.
1) You already have some implementations for tcp tunelling with java. Below are some examples:
http://jtcpfwd.sourceforge.net/
http://sourceforge.net/projects/jttt/
2) Even with these existing implementations, you can still do you own by forwarding packets arriving in the proxy using java.net.Socket.
3) I still think that a better option would be a specific implementation using java.lang.Runtime.exec() and socat linux command. socat is just like the Netcat but with security and chrooting support and works over various protocols and through a files, pipes, devices, TCP sockets, Unix sockets, a client for SOCKS4, proxy CONNECT, or SSL etc. To redirect all port 80 conenctions to ip 202.54.1.5:
$ socat TCP-LISTEN:80,fork TCP:202.54.1.5:80
I'm writing a Java application like AIM where I want a lookup server to help two clients connect to each other with the ServerSocket class. Unfortunately a serversocket needs an open port or it will be blocked by your firewall. Without having the clients manually change their firewall settings is there a way I can either find an open port, open a port (it's okay if it asks for permission) I just don't want every client to manually have to change firewall settings. Thanks!
Creating a ServerSocket is what opens the port on the server end (assuming the port is NOT also blocked on the firewall). On many systems, port numbers <1024 are not blocked by the firewall, and therefore often don't require custom configuration. However, since many ISPs have been more and more stringent with what ports they block within their network, many pieces of software have moved to operating over port 80. Why port 80? It's the port used for HTTP, and therefore pretty much open (at firewalls) 100% of the time for any service that operates on the web.
To answer the question of how to find an open port, port scanners perform this function. Basically all they do is try to establish a connection on a range of ports (say port 1-1024). When a connection is successful (in Java you would see this as a good connection over a Socket), you can consider that port "open". You don't need to exchange any data in order to make the connection, you just need to establish the connection, and then close it.
Also, if there is no server software of any kind running on the server, it won't appear "open", even if it isn't blocked. Without a successful Socket (TCP) connection, you won't know what ports are not blocked by user's firewall.
To reiterate, I'm switching back and forth between two related, but separate concepts. Firewalls can block/open ports, or have port forwarding. That's not the same as a port being "open" for connections on a given machine. In order for a machine to accept connections on a given port, there must be a piece of software listening for a connection on that port, otherwise no connection can be made.
I would suggest to look at a couple of alternative solutions that are less cumbersome - scanning for open ports can take quite some time, can cause panicky reactions from firewalls that feel attacked, and so on. There are a couple of techniques that are in active use and have been developed exactly to solve the problem of servers behind firewalls.
UDP Hole Punching, zero user side configuration needed. Simple explanation on how Skype uses this technique can be found here
UPnP / IGD could be used as an alternative, though less devices support it out of the box nowadays due to security problems.
STUN with a Java implementation of client and serverside called JSTUN
Whatever solution you choose, test it thoroughly with different internet service providers, there's a plethora of limitations you can expect wrt blocked ports.
I created a game and I want to put it on online. I want to buy a website (I'll probably use goddaddy to buy a domain name and use them as the web host) to use as the server to handle game play. Because I would need a separate server for each game, I would need each game's server to exists on different ports. So this leads to my question, is is possible to access these ports on my future web server? (I wrote the program in Java, so I would assume that I would access the ports from the server side by choosing a port for a ServerSocket, and from the client side by using the IP address from the website and the chosen port for a Socket)
(note: also, I am aware that it may be easier to simply use one port and run the servers on different threads instead, but I am just curious to have my question answered)
thanks a lot,
Ian
Technically it is possible to use different ports, but I don't think that a webhoster like goddaddy will let you run a java process that binds to a special port.
If you mean that you are going to create your own TCP server you obviously can create as many instances of your server and configure them to listen to different ports. But it is year 2011 now. This solution was OK in early 90s.
I'd suggest you to use Restful API that works over HTTP. In this case you can forward calls to server side of each application using URL, e.g.
http://www.lan.com/foo/login?user=u123&password=123456 - log in into application foo
http://www.lan.com/bar/login?user=u123&password=123456 - log in into application bar
In this case you need only one server (the web server) that is listening to socket (port 80).
Your server side implementation could be done using various web techonlogis (php, java, asp.net etc) on your choice.
Yes, that should work. The security manager permits connections to a different port on the same IP address that the applet was loaded from.
You can run a Java server on whatever port you want. Each server will accept incoming requests on one port.
The correct way is simply run on one port and each connection will instantiate a new servlet instance (which happens to run in its own thread) that can then service that request. You usually don't need to run separate ports or worry about concurrency, especially if all the stuff that's shared between connections (e.g. multiple players in one game) is handled through database read/writes.
Your host (GoDaddy) will have to allow you use of those ports, but if they are providing proper hosting (not virtual hosting) and given you your own IP there's no reason why you shouldn't be able to.
Your solution may work theoritically, and I like AlexR's solution. But providers like godaddy doesnt let you run a java server, on ANY port. You will need to find out somebody who does. What I found is the cost goes up from $5/mo to about $20/mo, but you get a much better (read faster) machine. Good wishes, - MS.
I have written a simple Java application that interacts with multiple instances of itself using sockets. The first instance automatically takes on the role of the server, listening on a specific port, and all subsequent instances connect to it.
The problem I'm faced with is that Windows Firewall pops up asking me if I want to unblock the program from "accepting incoming network connections". The thing is: it doesn't matter if you leave the application blocked, because the instances of the application are always on the same machine, so it will always work.
Can I inform Windows somehow that I don't even want incoming network connections to be accepted?
Use the three parameter constructor of the ServerSocket class to specify the IP address as well that the server it should listen on. That way you can restrict the server to listen only on 127.0.0.1, unlike the default of 0.0.0.0. See this related Stack Overflow question, for more details.
It is preferable to use InetAddress.getByName(null) to obtain the local address.