Let's say we have a wifi at home. When I google "whatsmyip", it gives me public IP address, which is essentially IP address of my router on the internet.
Now lets say I have two machines (A and B) both hosting a web server. I want to reach to a web-server on my machine 'A' from outside my local network (from some other corner of the world), how I can ping to that specific machine to my network. I understand for outgoing requests from my machine we have NAT, but what about incoming request to a specific machine? How router resolves it?
How I can check that IP(for incoming requests) in my windows/linux machine?
e.g let's say I have a tomcat server running on port 8080 on machine A. Now if I do localhost:8080/home, it displays "Hello World". Now one of my friend in let's say in Europe wants to access "/home" end point. What ip would he use?{IP}:8080/home. Means how he'll identify my machine, as to the internet only router's IP address is visible
To be able to reach your comptuer on the LAN behind your router you will need to do a port forward.
All connections to your public x.x.x.x:p ip/port address are forward to y.y.y.y:p
You can't forward different connections with the same port to a different machine in your lan, you will have to implement a more sophisticated approach to be able to do that, like a load balancer and apply a rule's base on the domain etc.
To be able to ping, you have to forward ICMP request to your lan machine.
Related
I'm trying to wrap my head around networking and the internet. This is a very big subject, and it is not my goal to understand all of it. However, I want to know how to use it for... stuff... which right now means I want to find a specific computer. I'm going for my home computer. I know the IP adress is alpha and omega when it comes to finding something online, so I have looked it up, by typing "my ip" into google. So far, so good.
However, I did the same on my phone, which is connected to the same wireless router, and lo and behold, it has the same IP address, according to google. So, if I am on a different computer, on a different network, and I try to ping that IP address, my best bet is that I'll reach that wireless router and that's that (I've checked in the router settings that that is indeed my router's IP address as well). How can I send a ping (as in, using the sommand ping, either on linux or windows) from somewhere else that goes out on the internet, and specifically finds my computer, instead of just the router controlling my home network?
Your home router has a single IP address. The router's job is to use a network address translation (NAT) to figure out which computer or device on your home network sent which requests so that all the devices on your router can use the same external IP address.
The router also has port forwarding settings that you can look up so you can, for example, set up a game server or web server that directs all outside network traffic trying to use that port to that one specific computer. You can also DMZ a specific computer but that leaves that device open to attacks.
To keep it simple: the devices in your home network do have an IP address, but it is a private IP address. In order to be able to reach your phone from the internet, it should have a public IP.
Unless you try to mess with the router, you can't reach any device from outside your network.
Your PC lives underneath the router on a smaller network called your LAN. The internet cannot see it, it can only see your router, which in this case is serving as a gateway.
Pinging is difficult behind a router depending on whether your router uses PAT or NAT. In order to forward traffic to a specific port you can change a setting in your router to forward incoming traffic on that port to the local machine.
I use a static IP connection, Configured to TPLINK router.
I have a local server running which i can access from my network, but i want it to be accessed outside network.
So I did port forwarding. and its Successfully running.
Now the problem is :: The IP address of my WAN is also a private address like 10.10.X.X, so when am entering http://10.10.X.X, i can access my site, but not outside my network. Please guide me how to fix this?
If your WAN address is a private address, your ISP is using CGN. This is becoming more common since the RIRs have, or soon will, run out of public IP addresses to assign to ISPs. It sounds like your ISP has run out of public addresses and needs to use private addresses for its residential customers, reserving its remaining public addresses for its business customers which are willing to pay for public addresses.
Basically, your ISP is using NAT, too. You would need to have the ISP forward your port on its NAT router, but the odds of that are zero since it probably has a policy you agreed to to not host servers on your residential LAN (buried in the fine print of the ISP agreement). This situation will play out more and more over time.
You have to use the "Virtual Server" settings. Port triggering is used for.
Once the modem router is configured, the operation is as follows: 1. A local host makes an outgoing connection to an external host using a destination port number defined in the Trigger Port field. 2. The modem router records this connection, opens the incoming port or ports associated with this entry in the Port Triggering table, and associates them with the local host. 3. When necessary, the external host will be able to connect to the local host using one of the ports defined in the Incoming Ports field.
It is not used for incoming connections which are triggered from outside!
Of course, to have it working you have to have an application listening on that port not only having the firewall on Windows allowing the port.
After you set up the "Virtual Server" a port scanner should show you the port is open (even without having a running application listening) - it will try to port forward it. I use ShieldsUp for testing.
I'm having a static IP address, say:127.254.x.x
Is it possible to access my web application from some other place by just replacing the local host with my IP???
Also, what will I replace the local host with if Ithe server is on a wifi network.? I.e. The router assigns a different ip to my server(because of dhcp) other than my original static ip. In this case should it be
192.x.x.2:8090
Or
127.254.x.x
Any help is appreciated.
I'm having a static IP address, say:127.254.x.x Is it possible to access my web application from some other place by just replacing the local host with my IP???
Yes, provided you configure it correctly.
Normally, you have a broadband modem/router which talks to the outside world, and provides a NAT network range to your devices. So you have an external IP address (the one the modem/router uses to talk to the outside world), and probably several internal IP addresses (for your phone, your laptop, your other laptop, your Kindle, etc.).
So to access a web server on your internal network from the outside world, you have to do two things:
Configure your modem/router to "forward" traffic it receives on the desired port (port 80 for HTTP) to the server on your network. How you do this depends on your modem/router. Look for "port forwarding."
When trying to access the app from the outside world, use your external, not internal, IP address.
So for instance, if your external IP address is 222.111.222.12, and the IP address of the machine you're using as your web server is 127.154.0.23, then you tell your modem/router that whatever traffic it receives on port 80 it should forward to 127.154.0.23 (this configuration may be by IP address, or may be by the MAC address of the network card in your web server machine; it depends on the modem/router). Then to view your app from outside your network, you go to http://222.111.222.12 (or whatever name you assign that IP address to in DNS).
I'm making an XNA game. When I started, I had a broadband connection with real IP, so I could host servers of any kind without any problem, but now I don't have that connection any more and I want to be able to let players from outside my local network connect to my server again. How do I do that? How do big guys at studios do that?
Cheap option:
Configure your home router (it does have real, but probably dynamic, IP address) to forward connections on some port of your liking to your server on the local network. Read up on Network Address Translation - that's the trick routers use to hide a network behind a single routable IP.
Setup a DDNS account somewhere, so people can find your game server by name instead of changing IP address.
Expensive options:
Buy static IP package from your ISP (not always available).
Deploy your game at a Hosting Service.
Generally there are two ways to connect two clients:
Give each client other client's IP address and let them connect to each other.
Give each client a mid-server's IP address and tunnel the traffic through it.
First way assumes each client has a real IP address and they both can be a server to one another. Second way is for when one or both clients don't have real IP address.
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".