I want to pass certain parameters to a desktop application remotely via the internet. I don't want my application to contact the server repeatedly, because many such applications can bring the server down easily. Is there a way to initiate the connection from the server? How can I identify the applications, as there will many of them running on many computers somewhere around the globe. I don't know where to start - I'm trying to do this in C# and ASP.NET/PHP on the server-side. Please give some advice.
Is there a way to initiate the connection from the server?
No. Not without having the client contact with the server first, informing it with the IP address, port to use etc... Which the server will need to keep for each client, hoping that they don't change (or get updated when they do change).
Long polling by the client is the right solution for what you are doing, even if you don't want to use it.
There are many different ways you could approach this, just thinking out of the box, both your app and the server could utilize a different mechanism for transferring the settings. I'm not recommending any of these methods, please don't shoot me down, they are all just ideas.
As an example, your server could connect out using FTP and output the updated settings to an FTP server on each PC. You could install something like Filezilla on each machine which runs your app. You'd obviously need to configure port forwarding on the router to allow the server FTP access.
You could use email. Setting up an email account where your server can login to send out the settings. Your app could possibly login to the same email account possibly even a single Gmail account to retrieve the settings.
Another idea would be to use a file sharing service like Dropbox, Google Drive or similar and where the settings could be shared. Obviously this would involve learning any API and I'm not sure if there are any restrictions on this approach.
The last idea and probably my preferred approach would be to host a web service and database on a remote server, both your server and the applications would connect to the same service to transfer the settings. This approach is obviously firewall/router friendly as all the clients connect out to the web service to collect the required data.
Hope this helps?
Related
Using some code from codeproject, I converted a LAN scanner into an ASP.NET web application. The app attempts to ping all ips in a given user inputted range. The app works fine locally. However, I wanted to make the app online. Using the free AZURE subscription, I put the site online. However, it does not scan the user's LAN. This might be because it is trying to scan the LAN of the server computer my app is deployed on. I would like to know if using ASP.NET, it is possible to scan the CLIENT'S LAN instead of the SERVER'S LAN. Please comment if you require the code for the webpage. The website should be online at http://nkdscan.azurewebsites.net/index . Please comment if any other info is required.
No, this is not possible using a server-based scanner, because that server has no way to access the private IP addresses used by the local network. You can only do this from the inside of a network, which means client-side code of some sort.
The problem is that your local network addresses (192.168.., 10...*, etc) are not accessible from the other side of your router. When you connect to a remote server your router does some address translations to make it look like it's sending the request. If you have lots of computers in the same LAN connecting to the same server it's going to look very much like lots of connections from the same place.
If you want build internet server applications then you need to know the basics of how the internet works, and this is one of the important ones. You don't have to know how things happen at the packet level (although that's interesting too), but some understanding of things like network address translation is essential.
I'm new to web development and I'm developing a web app in MVC 5 / C# where I want to access data from the SQL server from multiple devices (laptop, PC, iPad etc).
I've setup a small test website and SQL database on the Azure account and have been able to run CRUD operations from the website from a single device.
The problem I'm facing is when trying to access the data from another device. I'm constantly needing to manually add new IP address to the SQL firewall. To make matters worse my ISP has me on a dynamic IP.
Eventually I'm planning to provide a subscription service where clients can login via the website and access their data. Is there any way to allow multiple connections to an Azure SQL database without having to manually update the firewall?
Would setting up an Azure VPN an a VM running SQL server be the way to go?
Regards,
Marc
Might be worth taking a look at Windows Azure Mobile Services. Mobile Services provides a REST interface over your Windows Azure SQL Database automatically. Could be a good option, especially if looking to access the database from multiple devices.
http://www.windowsazure.com/en-us/documentation/articles/mobile-services-windows-store-dotnet-get-started-data/
In general, under NO circumstances should you ever make your database server directly accessible to the general public. There are far too many security risks associated with doing so- by exploiting vulnerabilities in the SQL capabilities, you (as a hacker) could quite easily take full control of the instance. That's one reason why you have to constantly update your firewall settings.
To solve your issue with the ISP re-assigning IP addresses, I would ask the ISP for a static number. It will probably cost you on the order of $10 per month, but worth the saved headache in my opinion. I am fortunate to have Comcast, and they do not reassign IP addresses randomly, but I know several other ISPs who do.
The generally-accepted way to make your data available is through a REST-based web service.
I have a windows tablet application which store some data from the users. Now i need to send this data to a server via Internet. What all options are there for me to try?? I think syncng the server and client database wont do good since multiple tablets are getting connected to the server.
I think syncng the server and client database wont do good since multiple tablets are getting connected to the server.
Why do you think that? How do you think web servers work? Databases can easily handle multiple connections.
You can either directly connect to the db server, if it supports remote connections, or you can create a webservice and communicate with db via that. Either way, be sure to set the permissions right, otherwise you might have a serious security problem.
// edit to address concerns in the comments
If you want to use a direct connection, you connect to a database exactly the same way as if it was on the same machine. How do you connect to that CE db?? You just need to alter the connection string, but everything else stays the same.
If you want to use a webservice for parsing and communicating with the database, the things get a bit more complicated, but it's still fairly simple. Search the google (or SO) how to use a webservice and how to create one. There are plenty of examples and tutorials out there. It's impossible to cover it all in here I'm afraid.
Is it possible to write C# code as below and send email using mnetwork in different country?
MSExchangeWebServiceURL = mail.something.com/ews/exchange.asmx
It's a web service URL. This works great when I run the same code from home network, my friends home network anywhere around, but when I run it from my client's location in Columbia it fails.
I have a valid user name and password on that Exchange Server. Is there any configuration that I can set to achieve this?
BTW this code below works when I run it within office network and any network within any home network. I have tried it at least with five friends network in Plano, Texas. I want this code to work running from any network in another country.
My client in Columbia can connect to the web service using a browser using the same user name and password, but when I run the code above it is not able to connect to our web service.
EDIT: Based on the comments and updated post, I would wager that the client location has a proxy server or firewall that is blocking the traffic. The client probably needs to add the relevant domain to whatever "whitelist" they have.
If it works from an internal network, then the problem is most likely not the code. You need to debug it and see what error turns up when running it outside of the network. Then check the logs on the firewall and the target exchange server to see what is happening.
One possible culprit is that the DNS name is not setup outside the office network, or that the office firewall is not setup to pass traffic (or only to pass SMTP traffic) from the internet to the server in question. Another is that Exchange Web Services is not setup properly to accept requests from the outside world. That can be tested from http://www.testexchangeconnectivity.com/.
If this isn't enough for you to get there, post more info about what errors you are seeing. "It isn't working, I want it to work" kind of reminds me of the Star Trek TNG episode about the species who kept telling Geordi to "make it go".
If you are asking if the code works (which it doesn't look like you are but it's in your post) you should ask on stackoverflow. If you are wondering why it won't work from home Its likely because the edge server is not set up to relay, and if you are at home and not vpn'd into the network that's all you have access to.
You need to break this down a bit:
What's the MSExchangeWebServiceURL? I don't need to know your real URL, but is this resolvable from your home network? i.e. is it an internal DNS host (server.mycompany.local) or is it an externally-resolvable DNS host (mail.yourcompany.com)?
If it's internal, like another poster said, you'll at least need to VPN in (or replace that with the external URL).
I'm not a big C# guy, but I'm guessing it's looking for your Exchange Server hostname or FQDN, and since the type is "SMTP" it wants to establish a TCP session with your mail server. You can likely test this out by opening up your command prompt and trying to telnet <MSExchangeWebServiceURL> 25. When that works, my guess is your code will work too.
I am writing you because of a new problem I need to solve, and I have now been banging my head against a wall for too long now.
Basically, I need to create an application that can take care of the following:
A user starts an app, which sends a broadcast to the subnet, and recieves a response of all servers there with their IP (and some additional info). The user can then select what server he wants to connect to.
Making it work is simple enough, with identifying the subnet, and broadcasting with UDP, and then having a different server application recieving it and sending back a response . The problem lies with these restrictions, that I need to take into consideration:
There will most likely also be clients on the server machines in the network, meaning that we can assume that the application is present on all machines. Every machine needs to have the listener running, and every machine can launch the GUI for selecting a server.
I am only allowed to add one exception to the firewall - an exception that handles both sending out the broadcasts, recieving broadcasts, sending answers and recieving answers.
I should also only be adding one Windows Service
on a server machine, the listener should run as a windows service, so the user won't notice it. Nor will the user notice, that the response is sent back to the client.
On the client machine, the user can start an application, which will notify the application to emmit the broadcast, and will get all the server responses, so the user can choose one to connect to.
Besides from the application that the user launches in order to select a server, there should be no interaction with the user whatsoever. Not even a popup, requesting the user to allow traffic trough the firewall - it should all be automatically
It needs to work on and in between Win XP, Win Vista and Win 7.
I don't know if I am putting too many constrains on myself, but I really hope that I can make the application with these requirements.
I have a few ideas - I just need to figure out how to do it:
Should i make everything into one application, that I add to the firewall exception list, so it will take care of the traffic on both the server and the client machines?
Should I add a custom exception to the firewall, allowing UDP traffic on a specific port, and then have all traffic flow trough that?
Is there a third and better option for managing that?
It is OK to have the service running on both client and server machines. But can it take care of everything for me - like it handling both the broadcast send/recieve and answer send/recieve? And is there any way to extract the information about servers on the network from a service?
I know it is a lot, but I really hope that you will be able to help me out.
let me know if I wasn't clear enough, or if you need further explanations.
I am coding in C# .Net, and I can utilize all I want from the .Net framework. As soon as I have this functionality implemented
All the best
/Sagi
The kind of peer-to-peer networking problems become simple to the point of being trivial if you designate one machine as the master server. It should have a well-known name that all sub-servers can connect to so they can publish (and withdraw) their availability. A client can then send a query request to the same server and get a list of known servers in return.
This can also solve your firewall problem, the master server could be listening on port 80.
Look into the System.Net.PeerToPeer namespace for a p2p solution supported by the framework.
Maybe a UPnP server and client may be a solution to your problem?