I have to live stream video using VLC. The streaming is done over UDP. The problem is the computer receiving the stream is in a different network.
When I stream using the public IP of the receiver, it doesn't receive the stream. What should I do?
As per your comment,
Yes, you need port forwarding. You stream to your home computer's public IP. However that IP is not you computer's; it is the IP address of the internet facing port of your router. Your router knows your computer by its local address (probably 192.168.x.x).
You need to do port forwarding to let your router know it needs to send incoming packets of a port, to a specific port of your computer. Router's web interface is likely to have such an option.
Related
I read a post on superuser.com (https://superuser.com/questions/284051/what-is-port-forwarding-and-what-is-it-used-for) that answered everything except for the port that is used. When sending out data from behind a NAT router, what port does the sending device use to send to the router and what port is used by the router once it's sent out, over the internet? I know that when a server receives this packet, it uses the port it was sent by the sending device (client) to know where to send the packet back to. But, this still doesn't answer where the NAT router came up with these two (private and public) ports originally. Do NAT routers just pick random ports and play a game of peek-a-boo with it's sending ports to make it nearly impossible for hackers to use port scanners to find an opening on random nodes on the internet? Please someone put me out of my misery.
The port stays constant across the entire spectrum unless otherwise specified. For example,
Client sends HTTP on 80, router forwards HTTP on 80 private to 80 public. Internet router recieve on public 80 and forwards to private 80.
The only thing that changes at the router (behind NAT) is the requesting IP Address. If I send a packet from my computer on port 80 to am internet site, the router changes the packet Source IP to its IP and then sends it across the globe.
Now, let's say we're on a home network. Here's how things work.
192.168.0.2 send request to router headed to 8.8.8.8 (google) on port 80. Packet gets to router. Router changes the SourceIP from 192.168.0.2 to its Public IP (64.5.5.5). It stores a record of this using various information such as the requesting MAC Address. Packet arrives at 8.8.8.8, which then changes the Destination IP from 8.8.8.8 to 172.0.0.5 (some internal web server at Google) and send the request to the server. When the server send a response, the same process happens in reverse.
I'm trying to build a peer-to-peer game, where each player is both a server and a client with tcp sockets. The sockets can connect fine when I'm using local ip:s, but of course fails when I'm trying to use external ip:s.
But I'm thinking that the players should be able to connect to each other if they just knew the external address + port that the router assigns to them.
Setting up port forwarding is out if the question since I don't have access to the players routers.
I'm thinking of having a server in between, just to be able to read the external address and port of the players, and tell the other player about it so that it can connect.
But I haven't found any info anywhere if that's how port forwarding works. If computer A makes a request from a local address and a port to the server, and the router assigns this address + port to an external address + port, and the server tell computer B which address + port to use. Can computer B use that external address + port to connect to the computer A and start a tcp socket with it? Is there any way to know that this external address + port stays the same when another computer makes a request against them?
The problem is that most people don't expose their PC directly to the internet. They have a router that has an external address. When you send a packet to their IP address, it is going to their router. The router doesn't know where to forward it to and what port to use without port forwarding.
So, getting everyone to enable port forwarding is out of the question, as it should be. A simpler mechanism is to have a server on the internet that you control. It has a firewall with port forwarding setup. The clients are just clients, they connect to the server on a port and send and receive info about the current status of the game. That way, everyone has real-time updates on their local game engine. Plus, this way is much easier to program and implement.
No, TCP doesn't work like that.
The source port that has been used to talk to the rendezvous server will be transient and specific to that particular initial TCP socket connection and can only be used as a destination for return traffic on the same connection from the rendezvous server, and can't be used by a third party to make new inbound connections.
The typical (only?) practical solution when NATs are involved and port forwarding is not available is to have that central server relay all messages bidirectionally between the peers.
Hole punching is what I was looking for.
https://en.wikipedia.org/wiki/Hole_punching_(networking)
I'm trying to send UPD packets from node A to node B, both are connected to internet through different routers.
I am able to send (and receive) UDP packets between them when they connected on the same network by giving the local destination ip adddress (192.168..) and port number.
Now I'm finding the dynamic ip address of node B using www.whatismyip.com and consider it as w.x.y.z
When I send the packets from A to this destination, I'm unable to receive them at B. I've also setup port forwarding on both the routers.
This is completely new to me. Is there is something else that needs to be done when I want to send packets to a node connected on another network? Please help!!
I can suggest something to check:
Port Forwarding in both the router are configured for the UDP protocol?
If you ping the remote address w.x.y.z, you receive a response? (check if the routers are configured to do so)
Verify also if there are firewall that block the UDP packet that arrives from the Internet (on the routers or on the target machine).
The thing that you can not receive them at B is because NAT will filter all the messages if you haven't build a connection in the netfilter's table. The way to solve the problem is to use a port mapping like UPNP or NAT-PMP. In this way, the destination node's specific port will receive any message from WLAN and send it to this node. But this needs your router support these protocols, if not, maybe you need to use ICE as a realy server to realize it.
I want to estabilish TCP connection over the internet between 2 computers which are in different local networks(wifi).
I have looked for description of TCP protocol, esspecially the structure of TCP header: http://en.wikipedia.org/wiki/Transmission_Control_Protocol#Checksum_computation
I assumed from that data that only: Source address(global ip), Destination address(global ip), Source port, Destination port are needed.
But how router in recipient's local network will know which computer in this network is recpient without MAC address or local ip address?
So the question: Is MAC address is needed to estabilish connection?
No, MAC addresses are not needed for that.
What you´re asking is called port forwarding:
The router of the server side must be configured that way
that incoming connections on port x are connected to local PC y.
(This could maybe be automated with UPNP, depends on the router etc.)
At the client side, after the client send something to the server,
the router "remembers" where to forward the incoming answer
If I have two internal computers connecting to the same external IP address through a NAT router, how is the router able to get the traffic to the correct internal computer? It is my understanding that NAT forwards incoming packets to the computer that recently sent outgoing packets to the [incoming packet's] sender's IP address. Since both computers are sending to the same address, does the router forward the packet to both? If that is the case, is it the responsibility of the client software to determine which packets are relevant?
Is it possible if both computers are attempting to connect to the same port?
When you open a socket, you need to address a port of the destination system and open a conjugate listening port on your own system to receive any response. You have to send the destination system your listening port.
Having more than one system using the same modem
When you start a web browser, and go to www.google.com:80, your browser obtains/searches for a free non-system conjugate port from the system for listening. Let us say, the conjugate port is 10000. The listener port is for receiving the http stream back from google.
Then your kid sitting next to you incidentally also browses www.google.com:80 and his/her google session of the play station or xbox-whatever also incidentally is assigned conjugate port 10000.
Both of you are sitting behind a cable modem, and behind the cable modem is your wireless router. And both of your systems are behind the wireless router - All sitting in that sequence, network topology-wise.
To prevent port address collision on the router/modem
Let us say that your cable company DHCP assigns your modem ip4 adress 72.72.72.72. But your wireless router DHCP assigns 192.168.0.10 to your system and to 192.168.0.11 to your kid's system.
When the frame carrying the information of your listener ports passes thro your NAT router, it would translate either one or both listening- ports. Let's say port 15000 for your page and port 16000 for your kid's page.
Your wireless router then sends your requests to google server as coming from 72.72.72.72:15000 and 72.72.72.72:16000.
The google server then responds individually to 72.72.72.72:15000 and 72.72.72.72:16000 and when you wireless router encounters the response, it reaches into the mapping that it has stored and translates 72.72.72.72:15000 to 192.168.0.10:10000 to reach your system but translates 72.72.72.72:16000 to 192.168.0.11:10000 to reach your kid's system.
Running web/game/ftp/etc servers
But what if you have a web server or an ftp server running on your system. What if you have two systems and both have a web server and both web servers are listening on port 80?
Let us say the local ip addresses registered/assigned with your wireless router of your first web server system is 192.168.0.30 and your second web server system is 192.168.0.40.
The wireless router would have a configuration web page usually by default 192.168.0.1:80, unless you changed it. There would be a tab to on the page where you could define/reserve application port mappings.
You could register with your wireless router to reserve the mapping
192.168.0.30:80 => outgoing port 8080
192.168.0.40:80 => outgoing port 8088
So that you have to phone your friends your web/game servers are addressable through
72.72.72.72:8080 and 72.72.72.72:8088 respectively,
where the wireless router would preclude its port 8080 and 8088 from its own dynamic NAT usage.
Of course, 72.72.72.72 is as good as only before your ISP DHCP decide to renew the ip4 address of your modem to say, 72.72.90.200. After which you would have to phone/email your friends and say
Hey, the servers' addresses have changed to 72.72.90.200:8080 and 72.72.90.200:8088 respectively. Or you could subscribe to dynamic dns (ddns) service to use a named domain where the ddns service will need you to install a simple heartbeat utility on your system to help them monitor the address variation. DDNS translation is a separate issue/strategy.
NAT modems
Newer ISP contracts supply you with a modem that has NAT. If so, you have to switch off either the one on your modem or the one on your wireless router. You should not use both - what's the point in translating twice because NAT is simply to prevent address collision. When you switch off NAT from your wireless router, it can operate as a hub switch and not a router anymore so that you could connect it to the modem using one of its LAN socket instead of thro its WAN socket.
The router manages "source" ports that are separate for each computer. While you may be connecting to port 80 on the "destination" the router may assign the source port to some high number port.
Wikipedia sums it up as
Network address translation involves
re-writing the source and/or
destination IP addresses and usually
also the TCP/UDP port numbers of IP
packets as they pass through the NAT.
Checksums (both IP and TCP/UDP) must
also be rewritten to take account of
the changes.
Already good answers are provided, but here is another example:
HOST A addr HOST B addr
10.1.0.2:4040 10.1.0.3:4040
-----------------------------------------
NAT 200.50.50.28:4040 200.50.50.28:4041 (what external host sees)
200.50.50.28 is router's global (internet) IP.
Every port number is unique in the NAT table. And of course the router does all the dirty job of modifying the source and destination addresses transparently.
It uses different ports for incoming external traffic, and the NAT then routes the packets on one port to one internal IP address, and the packets from the other port to the other internal IP address... The iniital request from each internal computer, when it goes through the NAT on the way out, establishes which port will be used for the incoming traffic from the external ip address, and it tells the external server what port to send it's traffic back on for that connection.
RFC3022 provides a lot of information on how this works
Since public facing or external IP Address that was given by Internet Service Provider (ISP) has been discussed, I would like to add on this.
You can ask your ISP to have your public IP Address not change. It will become static, so that you do not have to inform your friends to change the IP Address if they want to access your server inside your Network Address Translator (NAT).
As of this writing, static IP Address cost around 100 bucks. Most of the ISP they call it business account.
You can determine your public facing IP Address by googling "what is my ip address".