I was wondering how tools like teamviewer work. I'm not using the words server and client because I am not quite sure who is who. So I will talk about local and remote.
I have a tool installed on a remote machine behind firewalls and NAT, so only port 80 is okay for outbound connections. Now the local machine wants to connect to the remote machine. The only way I can image connection to work, is if the remote polls the local machine to check if it wants to connect, and then the remote establishes a connection to the local machine.
Teamviewer uses the same mechanism only with one entity in the middle, so the remote doesn't have to know the local in advance? So the remote always polls the entity in the internet?
Is that the way this kind of connection works? It seems quite a wast, always having to poll the local or some dealer-webserver. Especially if the connection has to work quickly, the polls must happen every second?
Am I missing something?
If someone is to scared to answer, a simple yes or no does the trick :-)
The hole punshing approach, so it's a yes.
Related
Guidance on how to connect to SQL Server 2012 needed.
I am on Windows 10 Home Edition
I have set up SQL Server Express to allow remote connections on my database machine to serve up data to three client machines.
Firewall has been set for ports - check
Allowed mixed mode logins - check
Setup IPs through SQL Configuration Manager - check
The server is something like 192.168.1.40,1433 and I can login successfully through SQL Server Express on my client machines. I had a long LAN cable running along the floor which is not optimal. So, I went to the store and bought a router so that I could connect wirelessly but have limited experience in networking.
After, installation of the router I can no longer connect to SQL Server. This makes sense since there is another piece of hardware in the chain.
After doing an IP config on the command line I see that the IPV4 address has changed. I assume I am not picking up the private IP address of the router rather than the modem that I was initially connected to.
Should I be port forwarding?
What are my options?
I explored what I thought may be reasonable leads to get this working.
First, I tried to create a virtual server (I also assume this is how to port forward on my particular router). I didn't really know what to put in five fields that were given other than server name and Protocol TCP or if I was on the right track at all.
The other three fields consist of:
External Port, Internal IP, and Internal Port
If this is a reasonable solution can you let me know what to put in these fields and any changes to the SQL Server configuration or firewall might be?
Should I VPN ?
After exploring this option on google I also notice people saying, "set up a VPN is the correct way to go." However, I don't really know how to do this. The only VPNs I know of are external VPN providers. It seems that I would be setting up a VPN server if I am not corrected(maybe on the server computer) and connecting via my client machines.
Any clarification or direction would be greatly appreciated. I am sure I have missed the mark on many things here but still would like to make ground.
I'm trying to establish a TCP connection between a client machine and a guest VM running inside an ESXi server. The trick is that the guest VM has no network configured (intentionally). However the ESX server is on the network, so in theory it might be possible to bridge the gap with software.
Concretely, I'd like to eventually create a direct TCP connection from python code running on the client machine (I want to create an RPyC connection). However anything that results in ssh-like port tunneling would be breakthrough enough.
I'm theorizing that some combination of VMWare Tools, pysphere and obscure network adapters could be possible. But so far, my searches don't yield any result and my only ideas are either ugly (something like tunneling over file operations) and/or very error prone (basically, if I have to build a TCP stack, I know I'll be writing lots of bugs).
It's for a testing environment setup, not production; but I prefer stability over speed. I currently don't see much need for high throughput.
To summarize the setup:
Client machine (Windows/Linux, whatever works) with vmware tools installed
ESXi server (network accessible from client machine)
VMWare guest which has no NICs at all, but is accessible using vmware tools (must be Windows in my case, but a Linux solution is welcome for the sake completeness)
Any ideas and further reading suggestions would be awesome.
Thank you Internet, you are the best!
It is not clear the meaning of 'no NICs at all on guest'. If I can assume that, there is no physical NICs assigned for the guest is what is meant here. The solution is easy as a vmWare soft NIC can be provisioned for the guest VM and that will serve as the entry point to the guest netstack.
But if the soft NIC is also not available, i really wonder how and what can serve as the entry point to the netstack of guest, be it Linux/Windows. To my understanding, if thats what you meant, then you might need to make guest OS modifications to use a different door to access the guest netstack and to post/drain pkts from it. But again, when you do a proper implementation of this backdoor, it will become just another implementation of softNIC which vmware by default support. So, why not use that?
It's a bit late but a virtual serial port may be your friend. You can pick the serial port on the outer end via network or locally depending on your options. Than you can have some ppp stuff or your custom script on both ends to communicate. You could also run some tool to create a single socket from the serial link on the guest end if you want to avoid having a ppp interface but still need to tunnel a TCP connection for some application.
This should keep you safe when analyzing malicious code as long as it's not skynet :-) You still should do it with the permission of the sysadmin as you may be violating your company's rules by working around some security measurements.
If the VM 'intentionally' has no network configured, you can't connect to it over a network.
Your question embodies a contradiction in terms.
The Standard TCPServer and TCPClient don't work on my machine for some reason, but Teamviewer manages to make a connection between two machines, and I would guess that the actual remote desktop session isn't going through their servers as it would probably be quite heavy.
Could someone explain to be how this is possible, because I've tried every TCP server/client code I could find and it still cannot connect recieve information from the outside world.
TeamViewer uses a technique called UDP Hole Punching.
This allows to connect two nat'd peers without make data pass through a server.
I found a tutorial that shows you how to create server and client programs, and make them communicate over a network.
http://www.win32developer.com/tutorial/winsock/winsock_tutorial_1.shtm
I can make a client program connect to, for example, 192.168.0.4 on my local network, and I can make it connect to 74.125.225.96. But what if I wanted to make it communicate with 192.168.0.4 on the network of 74.125.225.96, instead of just the default server on 74.125.225.96? I'm having a difficult time finding the answer with Google.
Is there even a way to do this? If not, then how are Gnutella and Bittorrent, able to connect computers directly together to share files?
To do what you are asking, 74.125.225.96 would have to be assigned to a router that is configured to forward inbound connections on the target server port to the machine that is running 192.168.0.4.
BitTorrent and other file sharing apps use various techniques, like NAT traversal, hole punching, etc to get connections through routers and firewalls. For example, if one party is behind a router/firewall and the other party is not, then the two apps first try to connect to each other in one direction, and if that fails then they reverse roles - client becomes server and server becomes client - and they try again. If that still fails, they could then connect to a middleman server that both parties have access to, and let it delegate the connections.
Did you use teamviewer? (comic question i know... Who doesn't use it?)
Do you have any idea how does teamviewer make connection even if i am behind the router, firewall, switch and my local firewall..?
I'm trying to imagine a connection that is between remote machinge and my computer. Remote machine is sending the packets (and its header (for instance, destination IP, message body)) to me but it only knows my id number(which is given by my local teamviewer application).
And this packets are reaching to my computer even if there is a juniper firewall (and also my windows firewall).
What kind a message body is recieving by computer? (of course it is not like xml, text, html, excel :)
Do you have any idea?
PS. Please share your knowledge like you are explaining to beginner level user.
The software is communicating with a central server, and has made an outbound connection. When you start TeamViewer, it will try to make a direct connection, but if both directions fail that (ie. firewall or NATting at both places), then it will fall back on communicating through a server.
This is basically the same approach most online games use. Changes at one end is sent to a central server, and is then relayed back to other connected computers.