I recall reading an article about a proposed way to do this. If I recall correctly, the researchers successfully created a connection to a client on another network without port forwarding by sending HTTP packets to each other (Alice pretends that Bob is an HTTP web server while Bob pretends Alice is a web server).
I'm not sure if that makes sense, but does anyone know where I can find the article or does anyone have any other ideas how to connect two clients together without a central server or port forwarding?
Is it even possible?
Edit: I would know the IPs of both computers and port the program listens on.
It is possible. I see at least 2 parts to your question. (It is not going to be HTTP packet. It is a lot more complex than that.)
First off, I believe you might be talking about a concept called decentralized P2P network. The main idea behind a decentralized peer-to-peer network is the fact that nodes conjoint in such a network will not require central server or group of servers.
As you might already know, most common centralized peer-to-peer networks require such centralized system to exchange and maintain interconnectivity among nodes. The basic concept is such, a new node will connect to one of the main servers to retrieve information about other nodes on the network to maintain its connectivity and availability. The central system gets maintained through servers constantly synchronizing network state, relevant information, and central coordination among each other.
Decentralized network, on the other hand, does not have any structure or predetermined core. This peer-to-peer model is also called unstructured P2P networks. Any new node will copy or inherit original links from the "parent" node and will form its own list over time. There are several categories of decentralization of such unstructured networks.
Interestingly enough, the absence of central command and control system makes it solution of choice for modern malware botnets. A great example could be Storm botnet, which employed so-called Passive P2P Monitor (PPM). PPM was able to locate the infected hosts and build peer list regardless whether or not infected hosts are behind a firewall or NAT. Wikipedia's article Storm botnet is an interesting read. There is also great collaborative study called Towards Complete Node Enumeration in a Peer-to-Peer Botnet, which provides excellent conceptual analysis and techniques employed by Storm botnet network.
Second of all, you might be talking about UDP hole punching. This is a technique or algorithm used to maintain connectivity between 2 hosts behind NATed router/gateway using 3rd comment host by means of a third rendezvous server.
There is a great paper by Bryan Ford, Pyda Srisuresh, and Dan Kegel called Peer-to-Peer Communication Across Network Address Translators.
As answered, a peer-to-peer connection requires establishment of a connection between two (presumably) residential computers, which will necessitate punching holes through both of their firewalls. For a concrete example of hole punching, see pwnat: "The only tool to punch holes through firewalls/NATs without a third party". The process, put simply, goes like this:
The "server" (who doesn't know the client's IP address, but the client knows the server's) pings a very specific ICMP Echo Request packet to 1.2.3.4 every 30 seconds. The NAT, during translation, takes note of this packet in case it gets a response.
The client sends an ICMP Time Exceeded packet to the server, which is a type of packet that usually contains the packet that failed to deliver. The client, knowing in advance the exact packet that the server has been sending to 1.2.3.4, embeds that whole packet in the Data field.
The NAT recognizes the Echo Request packet and happily relays the whole Time Exceeded packet, source IP and all, to the correct user, i.e. the server. Voila, now the server knows the client's IP and port number.
Now that the server knows the address, it begins to continually send UDP packets to the client, despite the fact that the client's NAT did not expect them and will therefore ignore them all.
The client begins sending UDP packets to the server, which will be recognized by the server's NAT as a response to the server's packets and route them appropriately.
Now that the client is sending UDP packets to the server, the server's stream of UDP packets starts getting properly routed by the client's NAT.
And, in 6 easy steps, you have established a UDP connection between a client and a server penetrating two residential firewalls. Take that, ISP!
Related
I am making a multiplayer game that is UDP with node.js (dgram for UDP) and unity as the client (uses c#'s sockets). I originally had a web-socket server, but remade it to be UDP for more competitive response times.
It works perfectly at my house and between my and my friends, but when I try it at school it doesn't work (both LAN and WAN). With non-local hosting nothing works (expected because my school has a whitelist), but with LAN (not localhost) The client sends and initial join packet (exactly the same way of sending as everything else) but then just doesn't send any more packets. My server logs the join message but then the client gets timed out from not sending any more messages after that.
Additionally, the client freezes during the second message and has to be shut down from task manager, which gives me the idea that it's message is being blocked over the network.
Is there a way around my school wifi blocking my server messages, and if there isn't what should I ask my school's tech person for (probably won't work but worth a shot)
Thanks in advance (:
Well, there is nothing you can do to solve certain situations like this by bypassing alone.
If your school remotely controls what protocols (TCP, UDP) that is allowed or blocked, it is better and the right thing to ask them to lift the ban up for traffic between UDP connections.
Also, the firewall can be the main one to blame. By default, many firewalls block UDP traffic because essentially, it is an unsolicited network traffic and may be used to do malicious exploitation since it doesn't care whether or not it has the server's permission to communicated in between and it can't do it doesn't support ACK (Can even cause DDOS in that manner).
More information and references about UDP: Link
However it is more of an overstatement but know that firewall in general do block all incoming traffics by default. TCP is usually accepted, and maybe your school blocked all UDP connections because of the details said above.
I'm trying to follow the code given here to implement NAT hole punching in Node.js. I'd like to know if the server is strictly necessary. Having read about hole punching, I am under the impression that the purpose of the server is to allow the clients to exchange some information (including but not limited to their addresses and ports they want to communicate on) so that they can proceed to talk directly. Assuming the clients already had each other's information (again, including but not limited to their addresses and ports), would the server still be necessary? If so why and if not, how could this be implemented?
For instance, say one were to build an application where client_A prints out all information that would have been transmitted to the server for user_A to read, who then sends this to user_B, who then submits this info to client_B (this could be done via email for example). Wouldn't this avoid the need for a server?
Here is another explanation of why I think it might be possible to remove the server in the middle:
In NAT hole punching (assuming I understand it correctly), the communications begin when client_A sends a message to the server. The message contains some information that the server then passes on to client_B when client_B contacts the server. After this point, client_A and client_B are able to communicate directly without the need for the server. I am under the impression that once a direct connection between client_A and client_B has been established, the server could go offline and the two clients would still be able to communicate directly with one another. If this is the case, then I would imagine that any information that is being used to maintain this connection (be that addresses, ports, or any other kind of info) could be exchanged through any other channel (eg: email, a handwritten letter, a voice call, etc) at the beginning of the protocol, and then the connection could be established without ever needing the server.
Regarding 'tricking' the router
As manishig pointed out to me in a comment (thanks), NAT hole punching also requires tricking the router. If I understand correctly (please correct me if not) the router is tricked by having the router store the info for directing incoming packets from the server to client_A, however, these packets are actually coming from client_B after the initial phase of the protocol. If this is a correct description of the problem, is there a way to trick the router that doesn't require using a server?
There are ways to communicate between two remote computers over the internet without an intermidiate server, but IMO it is not the preferred way.
Why an intermidiate server is needed?
If client_A and client_B are both in the same LAN (e.g your home/office network) you can make sure (configure on the clients side and/or the router) that they will have a static ip address over this LAN and they can just talk freely.
E.G: If client_A is listening on port 8080, client_B can create a connection to client_A_ip on port 8080
Over the internet any packet sent is passed through NAT usually at least twice. One time after going through your LAN (e.g your home/office router) and at least once over an ISP endpoint. Which means you have no controll over the public ip and port assigned to your packet.
Now not only that you don't have controll over your packet's assigned public ip and port, these are also not static. They won't change while you have an active TCP connection, but you don't have any other guarantee from your ISP regarding your assigned public ip and port.
The intermediate server`s purpose is to dynamically update each client with it's peer info and also keeping the tcp connection open, so that peer to peer comunication will be available.
Alternative solution to an intermidiate server (Not recommended)
If you want your clients to communicate without an intermidiate server you can buy a public static ip from your ISP (if they support it) and then there are ways you can make (with some config) that one of your clients have a public static ip and port that the other client can connect to.
But I wouldn't recommend it, since it requires some understanding in IT and security risks.
Also if both client's are portable and connect to different networks all the time it's not a valid solution
How we can share any type of data over the two separate networks without violating security mechanisms using UDP ?
There are a few things you'll have to remember:
Every network has its firewall, and it depends on the firewall rules, whether to allow your traffic into the network or not. First, ask your client or receiver to make changes in the firewall so that it accepts your IP address and also remember most of the systems have an edge firewall too.
Be clear with the type of connection i.e., p2p (or) server & client. It's better if it is a client & server type connection.
UDP by definition is NOT a connection-oriented protocol, so there is no state to keep track of as far as OSI layers 2-4 are concerned. All incoming UDP connections are treated as "new" or the same.
Also, see that none of the systems is under NAT connection, as the router will remember the IP and port of the device just for a while. And if there is any delay in response from client-side then the system under NAT will not know the IP or the port of the device, where it is supposed to send the traffic.
I'm writing a piece of P2P software, which requires a direct connection to the Internet. It is decentralized, so there is no always-on server that it can contact with a request for the server to attempt to connect back to it in order to observe if the connection attempt arrives.
Is there a way to test the connection for firewall status?
I'm thinking in my dream land where wishes were horses, there would be some sort of 3rd-party, public, already existent servers to whom I could send some sort of simple command, and they would send a special ping back. Then I could simply listen to see if that arrives and know whether I'm behind a firewall.
Even if such a thing does not exist, are there any alternative routes available?
Nantucket - does your service listen on UDP or TCP?
For UDP - what you are sort of describing is something the STUN protocol was designed for. It matches your definition of "some sort of simple command, and they would send a special ping back"
STUN is a very "ping like" (UDP) protocol for a server to echo back to a client what IP and port it sees the client as. The client can then use the response from the server and compare the result with what it thinks its locally enumerated IP address is. If the server's response matches the locally enumerated IP address, the client host can self determinte that it is directly connected to the Internet. Otherwise, the client must assume it is behind a NAT - but for the majority of routers, you have just created a port mapping that can be used for other P2P connection scenarios.
Further, you can you use the RESPONSE-PORT attribute in the STUN binding request for the server to respond back to a different port. This will effectively allow you to detect if you are firewalled or not.
TCP - this gets a little tricky. STUN can partially be used to determine if you are behind a NAT. Or simply making an http request to whatismyip.com and parsing the result to see if there's a NAT. But it gets tricky, as there's no service on the internet that I know of that will test a TCP connection back to you.
With all the above in mind, the vast majority of broadband users are likely behind a NAT that also acts as a firewall. Either given by their ISP or their own wireless router device. And even if they are not, most operating systems have some sort of minimal firewall to block unsolicited traffic. So it's very limiting to have a P2P client out there than can only work on direct connections.
With that said, on Windows (and likely others), you can program your app's install package can register with the Windows firewall so your it is not blocked. But if you aren't targeting Windows, you may have to ask the user to manually fix his firewall software.
Oh shameless plug. You can use this open source STUN server and client library which supports all of the semantics described above. Follow up with me offline if you need access to a stun service.
You might find this article useful
http://msdn.microsoft.com/en-us/library/aa364726%28v=VS.85%29.aspx
I would start with each os and ask if firewall services are turned on. Secondly, I would attempt the socket connections and determine from the error codes if connections are being reset or timeout. I'm only familiar with winsock coding, so I can't really say much for Linux or mac os.
How can an application be designed such that two peers can communicate directly with each other (assuming both know each other's IPs), but without outgoing connections? That's, no ports will be opened. Bitorrent for example does it, but multiplayer games (as far as I know) require port forwarding.
I'm not sure what you mean by No Outgoing Connections, I'm going to assume like everyone else you meant no Incoming Connections (they are behind a NAT/FW/etc).
The most common one mentioned so far is UPNP, which in this context is a protocol that allows you as a computer to talk to the Gateway and say forward me this port because I want someone on the outside to be able to talk to me. UPNP is also designed for other things, but this is the common thing for home networking (Actually it's one of many definitions).
There are also more common and slightly more reliable ways if you don't own the network. The most common is called STUN but if I recall correctly there are a few variants. Basically you use a third party server that allows incoming connections to try and coordinate a communication channel. Basically, what you do is send a UDP packet to you're peer, which will open up you're NAT for a response, but gets dropped on you're peer's NAT (since no forwarding rule exists yet). Through the connection to the intermediary, they are then told to do the same, which now opens up their NAT, and matches the existing rule in you're NAT. Now the communications can proceed. Their is a variant of this which will allow a TCP/IP connection as well by sending SYN and SYN-ACK messages with some coordination.
The Wikipedia articles I've linked to has links to the relevant rfc's for these protocols on precisely how they work. Essentially it comes down to, there isn't an easy answer, as this is a very network centric problem.
You need a "meeting point" in the network somewhere: the participants "meet" at a "gateway" of some sort and the said "gateway function" takes care of the forwarding.
At least that's one way of doing it: I won't try to comment on the details of Bittorrent... I am sure you can google for links.
UPNP dealt with this mostly in the recent years, but the need to open ports is because the application has been coded to listen on a specific port for a response.
Ports beneath 1024 are called "registered" because they've been assigned a port number because a company paid for it. This doesn't mean you couldn't use port 53 for a webserver or SSH, just that most will assume when they see it that they are dealing with DNS. Ports above 1024 are unregistered, so there's no association - your web browser, be it Internet Explorer/Firefox/etc, is using an unregistered port to send the request to the StackOverflow webserver(s) on port 80. You can use:
netstat -a
..on windows hosts to see what network connections are currently established, including the port involved.
UPNP can be used to negotiate with the router to open and forward a port to your application. Even bit-torrent needs at least one of the peers to have an open port to enable p2p connections. There is no need for both peers to have an open port however, since they both communicate with the same server (tracker) that lets them negotiate and determine who has an open port.
An alternative is an echo-server / relay-server somewhere on the internet that both peers trust, and have that relay all the traffic.
The "problem" with this solution is that the echo-server needs to have lots of bandwidth to accomodate all connected peers since it relays all the traffic rather than establish p2p connections.
Check out EchoWare: http://www.echogent.com/tech.htm