80 lines
4.1 KiB
Markdown
80 lines
4.1 KiB
Markdown
---
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navigation: true
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title: NAT & DHCP
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main:
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fluid: false
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---
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:ellipsis{left=0px width=40rem top=10rem blur=140px}
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# Router and NAT
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::alert{type="info"}
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🎯 __Goals:__
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- Understand how port forwarding works
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- Learn how to configure router NAT
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- Learn how to issue DHCP leases (fixed IPs)
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::
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## What is a "port"?
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---
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Ports are different channels through which your router sends and receives data. This allows multiple services to run simultaneously.
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When it receives data through a port, your router forwards that data to the machine that:
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- either initiated the request,
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- or is configured to receive data on a specific port.
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Your router has over 65,000 ports available.
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Some programs and applications are designed to use specific ports. For example, when your network sends data from an HTML page, the router receives it through port 80 (non-secure) or port 443 (secure via SSL).
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So, your router acts as a data dispatcher between the internet and your local machines.
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## Port Forwarding
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---
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Forwarding a `port` means setting a rule that specifies which `source` can send data to which `port` on your router, which will then forward it to a specific `port` on a specific `machine`. The `sources` and `destination machine` are identified by their IP addresses.
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| Variable | Description | Example |
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|------------------------|---------------------------------------------------------|-------------------------|
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| `source machine` | IP of the source machine (from the internet) | `All`<br>`123.45.67.89` |
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| `source port` | Incoming port on the router | `443` |
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| `destination port` | Port on the destination machine | `3000` |
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| `destination machine` | IP of the target machine (on your local network) | `192.168.1.50` |
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According to the table:
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If we remove `All` and keep the IP `123.45.67.89`, all traffic from this IP sent to port `443` on your router will be forwarded to port `3000` on the local IP `192.168.1.50`.
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If we remove the IP and keep `All`, then all traffic from the internet on port `443` will be redirected to port `3000` on `192.168.1.50`.
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This is useful when you have a server that must be accessible from the internet. For instance, a website uses port `80` (non-secure) or `443` (SSL-secured).
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To make the website accessible, you'll configure your router to redirect the domain request to your local server.
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Assume your service runs on port `3000` locally (`http://192.168.1.50:3000`), you would redirect all traffic from port `443` on the router to port `3000` on the local server.
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::alert{type="warning"}
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:::list{type="warning"}
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- __Warning:__ If you have multiple services to expose like `subdomain1.mydomain.com` and `subdomain2.mydomain.com`, your router cannot differentiate requests and forward to different ports.
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You must use a [Reverse Proxy](../../serveex/coeur/swag) to route traffic based on the request.
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:::
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::
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## DHCP
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---
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Every time a device connects to your local network, your router assigns it an IP address using DHCP rules.
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This IP is randomly selected from a predefined pool.
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At every device reboot, the IP may change — which is problematic if you're forwarding ports, as the target IP may no longer be valid.
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To avoid this, use your router's DHCP server to assign a static IP address.
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Each device has a physical "MAC address".
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To assign a fixed IP, you must know your device's MAC address (visible in your router when it's connected), and assign it a static IP.
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This is called a "static DHCP lease."
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That way, your machine's IP never changes and your port forwarding rules remain effective.
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| Variable | Description | Example |
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|---------------|----------------------------------|---------------------|
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| `IP` | Fixed local IP to assign | `192.168.1.50` |
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| `MAC Address` | Physical address of the device | `5E:FF:56:A2:AF:15` |
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For more information, refer to your router's documentation.
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