this is my first question here, after searching and reading through many places I have not choice but to ask.
I have a C# application that receives data from a GPS device and stored in a database, I need now is to send a string that contains commands which the device should be interpreted.
This device connects to the Internet over GPRS, I haven't idea how to send this packet over TCP over GPRS because the IP is dynamic.
I hope any suggestions or ideas on how to solve this.
Best regards.
You should do it the other way around - the device should poll the server for instructions. Just make sure the server is accessible.
As you have specified that you have developed a C# application to read the GPS data through GPRS that means you are running C# application on a public/static IP.
Nwo as soon as you get a request from the GPRS client, you get the DHCP IP address of the remote endpoint too.
Once you have that endpoint and socket open, you can transmit any data to the GPS device back.
Assuming that your GPS device is having some microcontroller to drive the GSM/GPRS modem.
I'm going to make an assumption here that the 'Device' is some kind of mobile phone connected to a standard GSM network?
If it is, then the short version of the story is "Forget it" even if the IP wasn't dynamic, you simply wouldn't be talking to the IP of your device, you'd actually be talking to the IP address of your providers GGSN, and for a standard consumer connection this is going to be where the buck stops.
Now that said, IF you have the budget, and all your devices (Assuming multiple ones) are with the same carrier, then you can approach the carrier and request a dedicated APN (Access point name) essentially what this is , is the mobile network equivalent of a DNS record, or at least similar enough to use that analogy anyway.
When you set up your data connection on your device you may recall having to enter something like 'pp.vodafone.com' or 'INGhub411.o2-uk.inbound' we'll this is your actual APN, and if you have a custom one they your devices can be set up so that the IP the presents itself at the GGSN actually has a static route back to the individual device in the suppliers GSM network.
As a general rule of thumb however on consumer grade connections this is not enabled and hence there is no ingress available to the individual device.
As zmbq says, the ONLY option you have is for the device to keep polling the server on a regular basis, and yes unfortunately that is going to be very unforgiving on the battery.
of course there is one other way of approaching this, and that's to have the device open a socket directly to your server then keep that socket open. Once the socket is open, 2 way communication can be performed across the link, unfortunately your going to also have to write all the code to manage this connection including, but not limited to monitoring the connection to make sure it's still open and re-establishing it if it's not, something which is incredibly important on a mobile device.
Related
I am sorry, this is kind of a noob question, but I don't get how ports work.
I think that when I open a tcp port in C# via the TcpListener on the server, anyone can connect to it. However, I only want my application client to connect to the port and send my predefined packets. Would it be possible for any person to connect to the port and send data that might harm my computer? Or is it just possible to send random data that is then just wrongly interpreted by my packet handlers?
I hope I could communicate my question clearly. Thanks in advance
Securing a port is generally a function of the operating system or the network infrastructure (could be as simple as a software firewall). You can use something like iptables to allow incoming connections from whitelisted IP addresses only.
If you want to do it through software, the server and client can use symmetric encryption. Only clients that know the key will be able to send meaningful messages. All other messages can be safely discarded.
Is there a way to find out whether the current chat session is happening through a VPN connection programatically (using either C# or Java) ?
I don't have access to network tools to do a R&D ( first of all not sure whether it can be tracked live), hence i haven't tried anything.
Any help/pointers/directions will of great help.
Thanks
I believe it would depend on how the VPN is set up.
If the VPN is connected using a software endpoint then it will normally have a simulated network adaptor that you could most likely find the name of (the hardware drivers display name not the connection name) and compare it to a list of known VPN network adaptors.
If the VPN is connected using a hardware endpoint like a firewall or other dedicated network device then there may be no way to tell without some sort of man in the middle hardware approach.
I am developing a LAN-based database application. It involves a central "server" app to house the database, along with many "client" applications that access it.
The "server" will be a simple C#-based HTTP server that responds to GET and POST requests. However, since it is designed to be able to run from any laptop on the network, I am wondering how to establish the connection between clients and the server without knowing the IP address.
I suppose I could ping every IP address from 192.168.0.0 to 192.168.0.255, and then test those that responded to see if any are my server. But I would only do that if there is no better way. Any suggestions?
Many of these types of discovery services run by putting out some kind of beacon on either the subnet broadcast address (for 192.168.0.0/24 it would be 192.168.0.255) or by putting out a beacon on a multicast address.
Multicast is particularly interesting because in a properly configured network, it allows hosts to find the service even across subnets. Routers and switches won't generally forward broadcast packets across subnet boundaries, but multicast packets will.
The beacon would have information in it such as the port the service is running on, what type of service it is, whatever is needed to start using the service.
To head you in the right direction, what you should do is have the database server running on a specified port. Then send out a broadcast to that port from the client (the system needing to connect to the database). When the database server receives this, it will be able to respond to the sender, allowing a handshake to occur.
Of course, you will need to validate the database server's authenticity (to make it secure, unless you aren't worried about that). This can be as simple as having the client display 4 numbers which then need to be typed into the database, so that the database can send the 4 numbers back to the client proving it is the right computer (how the iTunes remote works), or you can use certificates (but that is too complex a topic for me to cover correctly).
After that the two computers will know each others IPs, and you're set!
I am currently working on a little chat utility in C#.
The problem is I can't figure out how to scan the network for a specific port on all machines. I am currently using this method
IPGlobalProperties network = IPGlobalProperties.GetIPGlobalProperties();
IEnumerable<IPEndPoint> connections = network.GetActiveTcpListeners()
.Where(x => x.Port == ConstParams.iPort);
where ConstParams.iPort is the port I want to scan (6910 here).
The problem is that the returned values are only local ports and the "0.0.0.0" ip address...
How can I scan for all open ports (6910) on the current network?
Rather than using port scanning, I suggest you to implement a simple discovery mechanism based on multicast/broadcast communication.
During the startup the application should broadcast/multicast its IP/Port information. All running instances should respond to this message with their IP/Port information. This kind of a discovery mechanism is easy to implement, and it is both faster in runtime and more dynamic than the port scanning approach.
You should consider multicast, but rather than rolling your own, rely on an existing standard with library support, like mDNS:
http://en.wikipedia.org/wiki/Multicast_DNS
Or, since you said C#, using one of its native solutions:
http://msdn.microsoft.com/en-us/library/system.net.peertopeer.aspx
Scanning ports is a poor choice, you will most likely trigger firewalls on machines in the network to display your machine as an attacker. Any Intrusion detection systems on the networks could potentially be triggered as well. It's a lot of overhead for what you need.
I would recommend doing a broadcast using UDP or a multicast to discover other clients
http://www.codeproject.com/Articles/1705/IP-Multicasting-in-C
Another option would be to have a centralized server, either on a web server (php script, asp.net page, etc) or a web service (REST) which the chat client would connect to on start up, POSTing it's listening IP/Port, and then in turn would receive a list of all recently announced IP/Ports of the other clients on the network. You'd probably want some keep alive here, IE: the client would POST to the page every 5 minutes, if an IP does not POST for 10 minutes, it would be removed from the list.
To get the public IP of the machine, you could check out this page:
http://www.whatismyip.com/faq/automation.asp
You'd just need to send a web request to it to retrieve the IP. If you want to get the non 0.0.0.0/127.0.0.1 IP of the local interface, you can check out these posts:
Get local IP address
How do I get the Local Network IP address of a computer programmatically? (C#)
GetIPGlobalProperties only returns info about your local machine (see http://msdn.microsoft.com/en-us/library/system.net.networkinformation.ipglobalproperties.getipglobalproperties.aspx ).
To find out which other machines on the network have that port open, you'd have to iterate through the a range of IPs, attempting to connect on that port. There is no central repository to query on this.
This article describes an approach: http://www.dijksterhuis.org/building-a-simple-portscanner-in-c/
I want to monitor my router to see what is currently being downloaded and what application/Software that initiate it, who is the user doing this and download speedthat user occupy
i got all credential needed for both my wireless connection and the router
any head start for sth like that in C#?
the idea
First of all: Do you even know that your router can do this? Most routers I've seen do not have this level of traffic understanding and management.
If your router does, then there is one of two ways that such data is generally made available:
1) Through a HTTP interface (password protected)
or
2) Through an SNMP interface
To retrieve the appropriate HTTP URL, you simply get it as you would any other web page. Try something like: http://www.csharp-station.com/HowTo/HttpWebFetch.aspx
To retrieve the SNMP settings, there are many options; try this question: What SNMP library for .NET makes traps, sets or gets simple?
However, most likely, your router will not actually have this information available.
So, edit: If your router doesn't support side-chaining, and doesn't support SNMP or similar statistics, then you can't do this in the general sense.
You could spin up a Linux box as the gateway for the machines, and use NAT session statistics to monitor this. The way to do this is to have two network interfaces (logical or physical), one of which gets an IP from your modem, and the other which is the default gateway for the wireless network. Turn on IP forwarding and masquerading (NAT) as well as a DHCP server for the wireless network side. Now, you can use iptables to look at active NAT sessions and how much data has been transferred. You can also use packet filters for more specific information.
Also, if you know which machine is doing the downloading, and are running Windows, you can use WMI ("perfmon.exe" to plot this) to see how much data is being transfered on the actual machine.