How does application running on arbitrary port get packets from Internet? - node.js

while I was studying Internet Protocols, a question just occurred to me. Typically, we could assign any ports that are not for typical usage (e.g. 80 for HTTP, 443 for HTTPS) to our applications. For example, when I use Node.js Express to build a simple server, I could assign port 5000 to this process like below.
const express = require('express')
const app = express()
const port = 5000
// some code to configure server
app.listen(port, () => {
console.log(`Server is now running on port ${port}`)
})
My Node.js application will listen to port 5000. If my ip is for example 10.10.10.10, then my application will get a request if anyone hits 10.10.10.10:5000. However, if that's a HTTP/HTTPS request, shouldn't the packets come from port 80 / 443? Can someone tell me why it's not the case or why application listening to different ports can receive packets if they indeed come from 80 / 443.
Thank you.

When a packet leaves your computer it went through all the layers of the OSI model. It contains basically six specific information.
The destination and source IP address (the IP address of the server and your IP address respectively), the destination and source port (the port it is destined to at the server and the port it uses on your machine) and the destination and source MAC address (the MAC address of the machine it is destined to (locally) and the MAC address of your computer).
In a simple configuration (the computer behind a router), when you send this packet, it will be rerouted to the router using it's MAC address. The OS keeps a routing table which has the info on what to do with what IP address. Whether it is "On-Link" or if it needs to send the packet to a default gateway. You can print the routing table of your computer by typing route print in Windows CMD. If you are joining an outside server then the packet will be sent to the default gateway. It may need to do an ARP request in order to get the MAC address of the default gateway (or not depending on your computer's ARP table at that moment). You can see the ARP table by typing arp -a on Windows (in CMD).
Once the packet reaches the router, the router strips off the source IP (your internal network IP) and replaces it with the IP of it's external interface (your public IP). It does the link between those two addresses using the NAT table:
It also strips off the internal port and replaces it with a random available port (to the right). It means that 2 different machines accessing the same website can share the same local port. The destination port stays the same.
In the end if you receive a request from outside your router. Your router doesn't have a NAT table entry for that packet because it wasn't initiated by you. You'll need to use port forwarding to tell your router to forward incoming packets (destined to a certain port) to a certain internal IP.
Some routers (like mine) don't support specifying an external port AND an internal port. So both of these are the same (you cannot specify a different external vs internal port so you can't forward external 80 to internal 5000). In your case, you would need to specify an external port of 80/443 and an internal port of 5000 destined to 10.10.10.10 for your configuration to work. Otherwise, it should not work.

Related

Why doesn't my Node.js express Server work on other devices?

I have started my Node.js express server running on port 3000 and it works on my local computer the server is running on. Then I have forwarded the port 3000 to the IPv4 adress of my computer in my router but I still cannot connect to the server on other devices.
HAs it something to do with the protocol? Do you know why it doesn't work.
To connect to a server on your own local LAN, you need the following things:
The local IP address of the server. It would typically be something like 192.168.1.x, but in some cases it might be of the form 10.0.0.x.
You need to make sure the computer the server itself is on does not have any local firewall that is blocking incoming http connections. On Windows 10, there is a local firewall that by default blocks incoming http requests so you would have to enable incoming http requests on the desired port in that firewall configuration.
You can then connect to that server from somewhere else on your local network with a URL of the form http://192.168.1.x:3000/ where the 192.168.1.x is the actual local IP address of your server computer and the 3000 is the port the server is running on.
You need to make sure your other devices are actually ON your local network. For example, if it's a phone, you need to make sure it's actually connected to your local network via WiFi and not connected to the visitor's connection that can only reach the internet, not your local network.
You do not need to do any port forwarding in your router. That's something that would be done when connecting to your server from outside your network (like from the internet). I that case, you'd have to connect to your public IP address and have that safely port forwarded to your server. But, since you said you're trying to connect to the server from within your LAN, you don't need any port forwarding on your external firewall.

How to expose tornado websocket from local machine

I have built a d3.js dashboard that ties into a tornado websocket. Everything works perfectly locally. I now would like to have the ability to share the websocket with a few friends, nothing production. Is there a way to do this without a big deployment on Heroku or other similar service? I've googled and can't seem to find an answer. Thanks
Not specific to Tornado. This is more of a networking question.
What you want to do is:
Run your server on your computer.
Connect to the internet.
Note down your public IP address.
Give your IP address to your friends.
Certain things you need to take care of:
Run your server on a higher, non-standard port (e.g. 8000 would be good) because ISPs block traffic to port 80 and other standard ports.
The IP address assigned to you by your ISP will most probably be dynamic. That mean, every time you diconnect and reconnect to the internet, your IP address will change.
Turn off your computer's firewall to let in the traffic at whichever port your server is running.
Finally, you'll need to configure port forwarding on your router. What that means is all the incoming HTTP requests will arrive at your router at your public IP address. But your computer where you'll be running your server will have an internal IP address assigned by your router. So, you'll need to forward incoming requests to your computer's internal IP.

how to connect to a server running on computer using computer's IP address?

I am working on IOT project in which I have to change some variables(fans speed, lights, etc). So just as a starter, I created a node.js server and tried to send requests to the server through a local network using local IP as
http://localhost:7000/users=mandar?lights=OFF
or
http://192.168.43.248:7000/users=mandar?lights=OFF
and it works fine.
Now I want to do the same over the internet. So I got Computer's IP address from https://www.google.co.in/search?q=myip and tried to send a request to the following URL:
http://(IP_address):7000/users=mandar?lights=OFF
This time it keeps on loading and finally shows this site can't be loaded.
So what is the right way to connect to the server through the internet?
Thank you.
You have to do port forwarding.
The IP address you get from the google search is the out-facing IP address of your router. However, your router knows your computer by your local IP address (i.e. 192.168.x.y).
You have to configure your router to send packets coming from internet destined to port 7000(or any other port) to your computer's port 7000.
Check your router's documentation on port forwarding. Likely there is a settings page on the web interface of your router that you can do the desired port forwarding. After configuring the router, there are several tools online to test if the port forwarding is actually working. I suggest you use one of those tools to verify the configuration before testing with your project.
You also might want to check if your router has a firewall. You can add an exception to the firewall such that a specific port number is reachable from the internet.

Node server fails to listen to public IP

I am trying to get my Node.js server to listen to a public IP so that I can access it on a different network than my home network.
I've purchased a domain and used a DNS host - right now I'm using No-IP and have downloaded their client to push my IP to their servers.
When I set the IP on No-IP configuration to my local IP I can use the domain name and hit my server on another computer on my network. But if I change this to my public IP and use the domain, the request hangs for about 10 seconds and then fails. I've set up port forwarding (I believe correctly) and opened inbound / outbound traffic on the port I'm listening to (not 80 right now). I even pulled my firewall completely.
I tried changing server.listen(4444) to server.listen(4444, '0.0.0.0') as I've seen all over the web. But this doesn't work.
Anyone have ideas out there? I feel like maybe my ISP is blocking it somehow? I'm fairly new to networking, so maybe I'm missing something critical?
Thanks!
server.listen(4444) should be fine. As long as you don't have multiple active network connections in your server, you don't need to specify an IP address. Port forwarding from your router (if configured correctly) will direct the request that came from to public IP address to the actual local IP address of your host.
Note that for port forwarding to work reliably, you will have to give your host a fixed private IP address (not a DHCP assigned address) so the IP address will not vary. Then, you configure port forwarding to that fixed IP address.
Then, you need to do some network debugging. From a computer outside your own network (e.g. something out on the internet), you should do a couple commands to your public DNS name:
ping yourserver.net
tracert yourserver.net
If your DNS entry is not working, ping should tell you immediately that it didn't find yourserver.net.
If the DNS entry is working, but the IP address can't be reached, then ping will tell you that the server is unreachable. At that point, you will know you have a networking issue with connecting to your public IP address from the internet.
If ping is initially finding your server, but packets aren't flowing properly, then either the ping results or the tracert results should give you an idea where to look next.
If ping and tracert are finding your public IP and packets are flowing to/from it, but you still can't connect to it with the browser, then you either don't have the IP address set correctly (so you're not connecting to the right server) or your node.js server isn't listening appropriately or you aren't using the right ip/port in the browser that represents the actual node.js process. If you suspect this to be the case, then back up and make sure you have everything working purely on your own private network where the browser tries to connect directly to the local IP address and port. When that is working, you will know the node.js server is working appropriately and you can move back to working on the public IP.
FYI, if you tell us what the public DNS name and public IP address is, we here can do a few steps of this debugging from our computers.
It may be that your router can only forward a port to a computer on your network, but not change the port when forwarding. If that's the case, then you have these options:
Put everything on port 4444. Have your server listen to 4444, specify 4444 in the port forwarding in the router and then put 4444 in the URL like http://thecastle.ninja:4444.
Set up the port forwarding for port 80, put your server on port 80. Change the port forwarding to port 80. Change your server to listen to port 80 (if your server is Unix, you will need elevated privileges to listen to port 80 directly). You should then be able to use a URL like http://thecastle.ninja.
Set up the port forwarding for port 80, put your server on port 4444 and use ip table settings to route 80 to 4444 on your server. This allows your server to run in the less privileged 4444 port, but lets the end-user use the default port 80. I have a node.js server on a Linux Raspberry Pi configured this way. You should then be able to use a URL like http://thecastle.ninja
Run a proxy on your server that will route port 80 to port 4444. This is probably more than you need, but nginx is a popular one and it can do port forwarding on the server.

Connecting to at-home server from web

I have a CentOS server at home that I'm trying to put a website on. I put the index.html in the /var/www/html/ folder and can access it from another computer on the local network (with 'http://192.168.etc'). The problem comes when I try to access it from the web with my ip (http://34.52.xx.xx). I turned off iptables when I tried to access it to rule out a firewall issue with no success. I use Comcast and read that they sometimes block port 80 so I edited the /etc/httpd/conf/httpd.conf to listen on port 8000 in addition to 80 incase port 80 was blocked (httpd restarted after changes). When I enter 'http://myIP:8000' with iptables down I still don't get my page to show up.
What am I missing?
Thanks!
You surely have one public IP address let say 34.52.01.01 and you surely have “several” private IP addresses 192.168.1.1/192.168.1.2 ...
Between both worlds there’s a layer in your router call NAT (Network Address Translation) that
allows a request started from let say 192.168.1.2 to reach the external world (let say google.com), when the external world provides an answer for such a request it's your router NAT who knows that that answer must be routed back to 192.168.1.2
But if you have a request originated in the exterior world pointing to 34.52.01.01 you do not have an HTTP server
on that address then you need in your router some forwarding rule saying let say if you receive a TCP request in port 80 route it to 192.168.1.5 that is the internal address of your HTTP server…
You need to add port forwarding to your router…

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