Such as Skype/Team viewer/Logmein etc application, which send audio/video behind NAT (behind firewall). But when i make a small tiny application which send text to another NAT location it failed to do the same.
Example:
Sender:
-> Public ip: 91.1.2.3 My lan ip is: 192.168.1.2 with port 14446 udp
-------> Data format: RTP packets
Receiver:
<------- Data received: 0 packets
-> Public ip: 92.1.2.3 Friend lan ip is: 10.0.0.2 with port 14446 udp
* same in both way
How others does this? What is the way of doing peer 2 peer application development to overcome NAT issues? Always we have public ip's and mostly it has NAT issues.
But how does then Skype works in such cases too? Do we have a audio/video port range for UDP or always UDP is open from anything? But mine does not work above range ports for UDP i also tried. What is the secret? that is making me curious!!.
Note:
My goal is audio packets handling where i believe too much filtering or firewall cause latency and delay and other issues gets involved relatively too. So i would like to know very clearly for my application that some of the ports (which port ranges?) can be used for such purposes, where it really not blocking development stress.
There are a number of types of NATs, which vary in what traffic they'll allow in.
See the Wikipedia article on NATs
For most NATs, STUN will let you open ports AND find out what port you opened (may be different than the port you sent from). In SIP and RTSP you'd typically provide the external IP and port determined by STUN to the other end.
A fully-symmetric NAT means that STUN won't let you use a 3rd-party server to prop ports via STUN, so you'll have to use UPnP (if enabled) or map ports in the router (or set up triggers), or you'll have to play evil games to make both sides think they initiated the connection. (Not easy and not guaranteed.)
See the ICE & TURN specs (RFCs) from the IETF for detailed mechanisms to traverse NATs - though note that in some cases you must use an external proxy to forward packets.
One common solution is that the client program connects outward to the server and thus establishes a connection. Most firewalls allow outward connections - the assumption being that you are trusted and can always connect to the outside. When the server then wishes to send a message to you, it responds on the open connection.
I believe the port that you use is what is usually used to determine if it should be allowed or not. Certain ports are always let through. I'm not sure of the exact ports, but that will be different for all NATs and firewalls.
Related
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 am studying the TCP hole punching technique and have got some knowledge from this article: TCP_hole_punching. But I don't understand below part:
Network Drawing
Peer A ←→ Gateway A ← .. Network .. → Gateway B ←→ Peer B
Types of NAT
The availability of the TCP-hole-punching technique depends
on the type ofcomputer port allocation used by the NAT. When
two peers, A and B, instantiate TCP connections by binding
to local ports Pa and Pb, respectively, **they need to know
the remote endpoint NAT port in order to make the connection**.
Here are some questions, could somebody help explain? Any help or suggestion will be greatly appreciated!!
Q1. Suppose we have a client app running behind NAT1 and a server app
running behind NAT2. They will have messaging and file transfer communication.
The pattern will be the server listens and accepts connection
from the client. Do they need to use the TCP hole punching to keep the tcp
connection work?
Q2. Is the TCP hole punching technique necessary only when it's peer to peer
communication and both parties are connecting to each other (e.g., 2x CONNECT(), no LISTEN(), ACCEPT(), etc.)?
Q3. In the above text, what does it mean of "they need to know the remote endpoint NAT port in order to make the connection"? Why do they need to know the remote endpoint NAT port?Don't they only need to know the local port of the other machine?
For example, suppose the pair are (ClientA, publicIPA, LocalPortA), (ClientB, publicIPB, LocalPortB). If the ClientA wants to communicate with ClientB via TCP, it may do something like this:
clientBAddr.port = LocalPortB;
clientBAddr.ip = inet_addr(publicIPB);
connect(fdA, clientBAddr,...);
why would it need to know information such as NATPortA and NATPortB? Is there any problem if the clientA and clientB don't care about the NATA and NATB?
Since this post is reopened and nobody leaves an answer until this moment, I would like to answer it myself based on this article: Peer-to-Peer Communication Across Network Address Translators
About Q1, yes. Without mechanism like hole-punching, the packets one side use to sync with the other side will be dropped by the routers.
About Q2, no exactly. Listening sockets won't work directly. You need other tricks.
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.
some guys use a firewall on their laptops which not only blocks their own local incoming ports (except those they need for their application) but also blocks messages unless they are issued from a distinct port number. We're talking about a local UDP server which is listening to UDP broadcasts.
The problem is that the remote client uses a random port, say 1024, which is blocked unless they tell the firewall to accept it.
What puzzles me is that as far as I know from using sockets in my programs is that usually the client gets its port number from the OS, whereas only when you have a server, you bind your socket to a distinct port, right?
In my literature and in tutorials and code snippets in the web I haven't found any clue that clients should be using fixed port numbers at all.
So how is this in reality? Am I probably missing a point?
Are there client applications around using fixed ports?
Is is actually useful to block remote ports with a firewall?
And if yes, what level of added security does this give to you?
Thanks for enlightenment in beforehand...
Although the default API's allow the network stack to select a local port for client connections, clients may specify a fixed port for various reasons.
Some specifications (FTP) specify a fixed port for clients. Most servers don't care if clients get this correct.
Some clients use a fixed pool of ports for egress from a LAN to the Internet. This allows firewall rules to more completely lock down outbound traffic.
Source ports are sometimes uses as a weak type of "security through obscurity".
You always get a random address and/or port when not explicitly having bound to one before sending.
Daemons are usually bound to a fixed port, so that:
you can actually contact them without having to try all possible ports or utilize a secondary resolver (remember the SUNRPC portmapping crap?)
and because a TCP socket is not allowed to listen() if it has not bound to a port, IIRC.
Are there client applications around using fixed ports?
Some can be configured so, like BIND9.
useful to block remote ports with a firewall?
No, because your peer may choose any port of his. Block him and you'll lose a customer, so to speak.
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