Alternate way of TCP/ IP communication protocal.
I am using TCP/ IP communication protocol to connect device and communicating with one device to another.
But sometime ping is not reliable especially in firewalls environments.
Let me know the any another way to find out the connection status of the connected devices.
What do you mean with it is not reliable in firewall environments? Do you get a timeout on your ping-request or what? Then something is wrong with your routing on your firewall.
To your question: There's actually just the way over dns () so if there's a DNS in your network you should be able to ping with his net-name. But there's really no difference between this and an IP. You can't ping a MAC-Address (Layer 2).
Now the question, whats the point of this question (Any errors?)
Related
That's essentially my question. Isn't the network portion in a computer's IP address so that, when it is sent, other computers can look at that network portion and know where to send it back to? So why do routers have their own IP address?
The router needs to be a node on the same network as the computer using it. When your PC tries to communicate with a system on a different network, it consults it's routing table to figure out which router (there can be several) has the route to the destination. Without an IP on the router, there would be no way to send packets to the router, and thus no way to get out of your network.
I suppose the IP protocol could have been designed to use broadcasts to find the route out, but that would have caused issues with traffic congestion. Thankfully it wasn't designed like that.
I'm trying to develop an applicaton for p2p communication between two android devices. In order to punch a hole through my NAT(s), I'd need to know my external ip address and port.
To that end, I've developed a java server on GAE to report my "remote" ip address and port. The problem is that on GAE I can get my ip address, but not my port. Without it, I'm unable to successfully punch the hole.
So, my question is what's the best, free method to find out my external IP address and port?
That's a question that has no answer with TCP.
Here's the problem: your "port" is not a fixed value. You don't have "an" external port. You typically get one dynamically assigned for each outbound connection.
As answers you should see from the test sites posted in another answer clearly indicate, it's a moving target (though it may stay stationary for a short time due to the browser using HTTP/1.1 keepalives and actually reusing the same connection, not just the same port)... but if you hit the site repeatedly, you'll see it either drift around randomly, or increment. Trying it from two different web browsers on the same machine, you'd never see the same port number -- the port corresponds to the specific source connection, not the machine sourcing the connection.
Sometimes, you may find that it's the same port number as the port your machine's stack opened for the outbound connection, but even when it is, it doesn't matter, because no traffic should be able to return to your machine on that port unless it is from the IP address and port of the machine to which you made the outbound connection. Any decent network address translating device would never accept traffic from another source IP address and/or port, other than the one you addressed in the outbound connection.
There is no standard, simple, predictable, reliable, or consistent way to punch a hole in TCP NAT and then exploit that hole for a peer-to-per connection. To the extent that such things are possible in a given NAT implementation, that is an implementation that is shoddy, broken, defective, and insecure.
See also: https://www.rfc-editor.org/rfc/rfc5128
Sounds like your app could use a STUN server to get its external address.
I know that ipchicken.com will tell you your router's ip address and the port it is using for your connection. But can this information be obtained "locally"? (Without relying on a website).
What I want it for is establishing a connection between two random hosts...without a "dedicated server" in the middle. My problem is to reach through the NAT. I think the best bet is a kind of TCP hole punching, where both hosts connect somewhere and then just tell each other (it can be by phone or chat or similar) the current ip address and the port number their routers are using. It should trick the routers into forwarding the packets to the hosts, albeit coming from a different source than they originally connected to.
Is it possible to find the port number your router is using to patch you through in a more local manner than ipchicken.com?
Are there any ideas on other possible approaches to this problem?
EDIT: Setting port forwarding on the router is not an option in this case, as many people (including me) do not have admin powers over their routers and I do not want to impose such a task on the "users" of my application
The router would use a different source port for every outgoing connection, so checking based on an outgoing connection will not work for your use case.
For an incoming connection, i.e., if you want to reach a specific machine behind a NAT device (like a home router), you'll have to explicitly open up some ports on the router and set up forwarding rules. The router would then listen for incoming connections on that port and forward it to a machine:port based on the configured rule.
How you do this would depend on the specific router make/model. Search the web or logon to the admin interface and look around, it should be easy to find. However make sure you understand the security implications of opening up a port on your router!
UPDATE based on edited question:
Without port-forwarding and if both devices are behind NAT, your only solution is to have an intermediary server! If only one of them is behind NAT, you can have that machine initiate the connection.
You could use a Stun server as the external globally reachable server.
Good Day,
I basically have a laptop connected to the internet with a fixed IP Address. I need to have a way for a server possibly though a PHP script, send data/string to the laptop and it is able to receive it.
Now, if I was within a local network, i could do that. But what if I wanted to send from an external network? Do devices have a particular address that I can access from any internet connection?
Do devices have a particular address that I can access from any
internet connection?
No, it does not, unless you do use external IP for your laptop (doubtfully).
The easiest and fastest solution I could think of is to do the other way round: open TCP or UDP socket on your server and use laptop to connect and request data from the server. Of course, it is not suitable for all scenarios, but in many cases it works. Write more information (what is the purpose of this? What are the requirements and limitations?) so more specific answer may be provided.
OK, to make things easier to explain, let's say:
- Your router's public IP address is 10.10.10.10
- Your laptop's private IP address is 192.168.0.1
- You want to communicate via port 80 (since you mentioned PHP)
What you need to do is configure your router so that it forwards packets destined to 10.10.10.10:80 to 192.168.0.1:80. This is the simplest form of NAT.
Then from anywhere else with an Internet connection, you can send packets to your laptop by sending packets to 10.10.10.10:80.
I've noticed recently that I don't have to forward ports for mmorpg's that I play.
I'm thinking about working on a game that people can play online and had a question.
Why is this the case given its a two way socket connection that is constantly sending data back and forth? Doesn't their server need to get through my firewall in order to connect to me?
TCP crash lesson: TCP is a two-way protocol. The challenge is that at least one host needs to initiate. Since within an MMORPG, your own computer is never acting as a server, nobody has to connect to it. All the information about game state is passed through the company's public facing servers that have public facing IP addresses (and hey, maybe they actually use port forwarding there, just to confuse my explanation... but you never have to see their pretty network internals, proxies, and other wizardry.).
Anyway, when you connect to Stackoverflow, you're making one outbound connection that requests data from the server, and then over that same connection you're receiving it back. Same exact scenario, only with a webserver instead of a game.
UPnP allows you to tackle many routers. There's also NAT Punch-Through if you have access to a third party that isn't behind a router.
Either way, port forwarding is only necessary if you wish to act as a server (or the sender in a P2P relationship). A client does not need to forward ports.
You don't need to forward ports to access the web either, despite data coming in as well.
When you make an outgoing TCP connection, your NAT router puts the connection in a table, so that when data comes in, it knows what machine in your LAN to send the packet to.
Everyone mentions TCP, but NAT works for UDP as well: The first outgoing UDP packet associates that source port with the internal IP address, and your NAT device will forward incoming traffic to that port to the correct host on the internal network.
In other words, if your computer requests the connection (outbound) first, the router opens up the port automatically, on the assumption that you're going to want data back. But if you want remote users to connect to your computer without your computer requesting it, the router would normally drop the packets since it wouldn't know where to send them (they were unsolicited). So instead, you need to tell the router to deliver any unsolicited packets at port N to your computer.
Sorry to add another answer so late, and I know one was already accepted, but I personally found the other answers to be more confusing than this simple explanation.