I'm writing a program on Windows using winsocks that can send messages to another computer. The client connects with the server in the other computer and begin exchanging data.
It works fine on my local network using local addresses(192.168.1.*), but I can't communicate with public addresses (216.185.45.129); not even my own. I can successfully connect to a website on port 80, but not to my laptop at home using its public IP address, regardless of what ports I use (unreserved ports).
So I did research online and the only solution that seems to work is port forwarding.
-But is there absolutely no other way to achieve this?
-How do other programs like Teamviewer connect to other computers on the network then?
-Is there an already open but typically unused port that I can use?
-At the very least, can I forward the ports on my router but not have the client do anything? Or maybe have my program forward the ports automatically.
The main problem is, that every router is using NAT to distinguish different computer in your lokal network against the WAN. He need to do this, because you got only one IP in the internet, but several devices in your home. To archive this, he uses groups of ports. That means, if you use to send maybe from port 2048 to a webserver in internet with two devices, the router gives one device another port (like 2049). The response has the Port of the requester, so the router can map it back. Unfortunately most router always map ports so you never now which port you have from the internet side.
There are two common ways to work around and archive your goal.
Port Fowarding
You can force most router not to map special ports but bind them to unique MAC addresses. You can use UPNP to config most router to do that, but I do not recommend that for security reasons and also it does not work in many enviroments where Router do not allow UPNP manipulation.
Most router have port forwarding abilities for gaming reasons (mostly it is used in P2P networks)
It works with TCP and UDP.
NAT Traversal
The common way is NAT traversal, also known as NAT hole punching. I will describe it in short for UDP. You can find a wiki explanation here for TCP and for UDP here. Unfortunately you need a server in the internet both clients can reach. Here the steps:
Both clients contact the server. The server now know IP and PORT of both clients.
Server send back the information to the clients.
Both(!) clients send now packages to each other on the known address.
It is necessary that both client send a UDP package and have to accept that the first package get lost. The reason is the router. Most router only accept packages from a source on a mapped PORT if a client has send a package to that source before.
UPDATE
Regarding to a comment of Remy Lebau I changed the Firewall piercing part to NAT Traversal as it was partly wrong.
I have made a simple Jetty server using this tutorial here, http://www.seas.upenn.edu/~cis550/jetty.html
Now that I have the initial steps completed, I can succesfully connect to my server by entering localhost:8080/hello or 127.0.0.1:8080/hello in my browser. Everything is going great up until this point. The servlet is working properly.
I am now interested in connecting to the server using "Machine B". I want to build a server that can be connected by any browser, anywhere.
My IP is XX.173.XXX.216, parts hidden for obvious privacy reasons. On my "Machine B" I try and enter XX.173.XXX.216:8080/hello into the browser URL. The website cannot be found. From experience I questioned my port mapping and opened my 8080 port.
After a few google searches and a while of reading, I give up. Does anyone know a possible solution to my problem? Are there any further steps I need to do in the setup of the Jetty server to make it accessible from external machines?
It is usually not hard getting from the inside of a firewall and out. It is much trickier to get from the outside and in (just have a look at the hoops Skype jumps through to be able to get two computers each behind a firewall to talk to each other directly).
First of all you need to ensure that Jetty listens to the right network devices.
Identify the IP-number of the computer running Jetty (not 127.0.0.1) and see if you can connect to "http://that-ip-number:8080" from the machine itself. If this doesn't work, fix your jetty configuration. Then put another computer on the same network and connect to "http://that-ip-number:8080" too. This MUST work before you go any further. If this doesn't work, fix your firewall configuration on the computer running Jetty.
When the above works,then you can start thinking about exposing the port through your router. The router most likely has a web interface where you can configure this, but the easiest way to do that is to use a uPNP tool (if your router supports that) which can redirect an external port to a specific host and port on your internal network. I use "Port Map" under OS X which has a very simple interface.
Good luck
I have two applications. One is the server app and the other is the client app. The server app listens for connections and then feeds messages to all connected clients.
So far all my testing has been done by running both applications on the same machine, and this is working fine. Now though I am trying to test the server running on one machine and the client running on a different machine.
Each of these machines are within my own home network. That network is behind a router with a firewall. From what I have read, my problem might have to do with port forwarding not setup on my router. Does that sound likely?
Is this something I can fix with just my code? Do I really have to require all my users to manually open the port on their firewalls? I have used plenty of other commercial applications that connect to servers and don't require me to open ports on my firewall. What is different about those applications and mine?
Then again, maybe I am barking up the wrong tree here. Maybe there is some other problem preventing my code from working in this situation?
I can provide any code snippets that might help, but I am unsure as to where to start looking and I don't want to just post my entire solution :)
Thank you in advance
You need to bind to 0.0.0.0 (simplified version) in order to accept connections not coming from the local machine. Have you checked that you don't bind to 127.0.0.1?
When you bind to 0.0.0.0 you actually bind to all current and future addresses of the current host and so will be able to accept connections from everywhere, you can also bind to just the address of one of the network interfaces.
I have written a client/server code.
The server program executes on a terminal which plainly receives text data from the client and the client is a GUI where in you could specify the IP address of the machine where the server would be running.
However this works only in a closed Network(LAN).
I have just learnt TCP IP and have written a few codes that run on a LAN.
I wanted to make this program work across the network(over the internet).
But I have some basic doubts like,does one need the permission of the local ISP for such programs to execute across the internet.Does it involve buying a domain or some kind of permissions?
Can some one please help me on,what should I be doing,or where should I start from?
Listener have to have IP port opened in some way. If you are behind router, you should set proper port forwarding on router and if ISP provides its own subnet, you should know how to setup such link. (i do not know what kind of tehnology ISP might use for this).
For beginning you do not need you own domain name but you should be able to address by ip. If you need domain, register own domain name or create subdomain for free (i was using http://freedns.afraid.org/ )
If your server is behind a router which creates a LAN, you have to configure the router that it will forward the packages from your client to the server.
You have to forward all the incoming packages at the specific port to the local ip of the server.
We have a product we are deploying to some small businesses. It is basically a RESTful API over SSL using Tomcat. This is installed on the server in the small business and is accessed via an iPhone or other device portable device. So, the devices connecting to the server could come from any number of IP addresses.
The problem comes with the installation. When we install this service, it seems to always become a problem when doing port forwarding so the outside world can gain access to tomcat. It seems most time the owner doesn't know router password, etc, etc.
I am trying to research other ways we can accomplish this. I've come up with the following and would like to hear other thoughts on the topic.
Setup a SSH tunnel from each client office to a central server. Basically the remote devices would connect to that central server on a port and that traffic would be tunneled back to Tomcat in the office. Seems kind of redundant to have SSH and then SSL, but really no other way to accomplish it since end-to-end I need SSL (from device to office). Not sure of performance implications here, but I know it would work. Would need to monitor the tunnel and bring it back up if it goes done, would need to handle SSH key exchanges, etc.
Setup uPNP to try and configure the hole for me. Would likely work most of the time, but uPNP isn't guaranteed to be turned on. May be a good next step.
Come up with some type of NAT transversal scheme. I'm just not familiar with these and uncertain of how they exactly work. We have access to a centralized server which is required for the authentication if that makes it any easier.
What else should I be looking at to get this accomplished?
Is there no way this service can by hosted publicly by you or a hosting provider rather than with the customer?
I had a similar situation when I was developing kiosks. I never knew what type of network environment I'd have to deal with on the next installation.
I ended up creating a PPTP VPN to allow all the kiosks to connect to one server I hosted publicly. We then created a controller web service to expose access to the kiosks that were all connected via the VPN. I'm not sure how familiar you are with VPN's but with the VPN connection I was able to completely circumvent the firewall in front of each kiosk by accessing the kiosk via the VPN assigned IP.
Each kiosk node was incredibly easy to setup once I had a VPN server setup. It also brought management benefits and licensing revenue I originally didn't think about. with this infrastructure I was easily able to roll out services accessible via mobile phones.
Best of luck!
Solutions exist to "dynamically" access a software on a computer behind a NAT, but usually mostly for UDP communication.
The UDP hole punching technique is one of them. However, this isn't guranteed to work in every possible situation. If both sides of the communication are behind a "Symmetric Cone NAT" it won't.
You obivously can reduce the probability a client can't communicate using UPnP as a backup (or even primary) alternative.
I don't know Web Services enough and don't even know if using UDP for your webservice is an option (or if it is even possible).
Using the same technique for directly TCP is likely to fail (TCP connections aren't stateless - that causes a lot of problems here).
An alternative using the same technique, would be to set up some VPN based on UDP (just like OpenVPN), but as you stated, you'll have to manage keys, certificates, and so on. This can be automated (I did it) but still, it's not really trivial.
===EDIT===
If you really want to use TCP, you could create a simple "proxy" software on the client boxes which would serve as a relay.
You would have the following schema:
Web Service on client boxes, behind a NAT
The "proxy" software on the same boxes, establishing an outgoing (thus non-blocked) TCP connection to your company servers
Your company servers host a WebService as well, which requires a something like a "Client Identifier" to redirect the request to the adequate established TCP connection.
The proxy program interrogates the local WebService and send back the response to the company servers, which relay the response to the originate requester as well.
An alternative: you might ask the proxy software to directly connect to the requester to enhance performance, but then you might encounter the same NAT problems you're trying to avoid.
It's things like this that are the reason people are tunneling everything over http now, and why certain hardware vendors charge a small fortune for Layer 7 packet filtering.
This is a tremendous amount of work to fix one problem when the customer has at least three problems. Besides the one you've identified, if they don't know their own password, then who does? An administrator who doesn't work there anymore? That's a problem.
Second, if they don't know the password, that means they're almost certainly far behind on firmware updates to their firewall.
I think they should seriously consider doing a PROM reset on their firewall and reconfiguring from scratch (and upgrading the firmware while they're at it).
3 birds, one stone.
I had to do something similar in the past and I believe
the best option is the first one you proposed.
You can do in the easy way, using ssh with its -R option, using
publick key auth and a couple of scripts to check for
connectivity. Don't forget the various keep alive and timeout
features of ssh.
Don't worry about the performances. Use unprivileged users and ports
if you can. Don't bother to setup a CA, the public key of each remote
server is easier to maintain unless you are in the thousands.
Monitoring is quite simple. Each server should test the service on the
central server. If it fails either the tunnel is down or there's no connectivity.
Restarting the tunnel will not harm in any case.
Or you can do it at the network level, using IPsec (strongswan).
This can be trickier to setup and it's the option I used but I will
use SSH the next time, it would have saved me a lot of time.
+1 for going with a SSH tunnel. It's well known, widely available and not too hard to configure.
However, as you point out, you are running SSL already, so the SSH encryption is redundant. Instead of SSH you could just use a regular tunneling proxy, that provides the tunnelling without the encryption. I've used this one in the past, and it has worked well, although I didn't load test it - it was used with just a handful of users.
Here's a blog from someone who used the tunnelling proxy to access his webcam from outside his firewall.
Set up an Apache in front of your Tomcat. This Apache should be visible from the internet, where the Tomcat should not.
Configure Apache to forward all traffic to the Tomcat. This can easily be accomplished using mod_proxy (check out the ProxyPass and ProxyPassReverse directives).
Have your SSL certificate located in the Apache, so that all clients can talk HTTPS with the Apache server, which in turn talks plain HTTP with Tomcat.
No tunneling or other nastyness + you will be surprised how easy it is to configure Apache to do this.
If you want to have a RESTful integration to the client server, a tunnel to the central server that works as a proxy, seems the best approach.
But if this is not a hard requirement, you can let the central server handle the RESTfull stuff and integrate the central server and client server with other middleware. Good candidates would be RMI or JMS. For example, a RMI connection initiated by the client allows the server to do RMI calls to the client.
You could try to connect to an pc/ server and tunnel all the data via hamachi (Free VPN Software) because this tool you can install and it will create a reverse connection (from inside your nat to outside) so you can connect to it
site: http://hamachi.cc/