Important Thing

this page include some important concept and component in networking

IP Address (IPv4, IPv6, Public & Private)

An IP address is a unique number that identifies a device on a network and allows it to send/receive data.
IPv4 is a 32-bit address (e.g., 192.168.0.10) written as 4 numbers (0–255) separated by dots.
IPv6 is a 128-bit address (e.g., 2001:0db8:85a3::8a2e:0370:7334), designed to handle more devices worldwide.
Private IPs are used inside local networks (e.g., 192.168.x.x, 10.x.x.x) and can't access the internet directly.
Public IPs are assigned by ISPs and used to communicate with servers on the internet (e.g., Google, YouTube).
A router uses one public IP to connect multiple devices using private IPs inside your home or office.

A MAC address is a unique hardware identifier (e.g., A1:B2:C3:D4:E5:F6) assigned to a device's network card.
It’s used for communication within the local network (LAN) to deliver Ethernet frames.
Devices don’t know each other’s MACs directly, so they use ARP (Address Resolution Protocol).
ARP helps a device ask: “Who has IP 192.168.0.1?” — the device with that IP replies with its MAC address.
Then the sender uses that MAC to deliver the packet on the LAN.

NAT allows many devices with private IPs to share a single public IP for accessing the internet.
Your router changes your private IP (e.g., 192.168.0.10) into its public IP (e.g., 122.56.77.88) before sending the packet.
It also tracks which internal device made which request using port numbers.
When a reply comes back from the internet, the router uses this mapping to forward the data to the correct device.

When your device connects to a Wi-Fi network, it sends a request asking for network details.
The DHCP server (usually your router) replies with:
- Your IP address (e.g., 192.168.0.10)
- The Subnet Mask (e.g., 255.255.255.0)
- The Default Gateway IP (e.g., 192.168.0.1)
- And DNS server IPs

So DHCP sets up everything you need to start communicating on the network and with the internet — automatically, no manual settings.

The subnet mask you get from DHCP (like 255.255.255.0) tells your device which devices are “local” (in your network).
For example, if your IP is 192.168.0.10 and the subnet is /24, you can directly talk to devices from 192.168.0.1 to 192.168.0.254.
If you try to reach an IP outside that range (like Google’s server), your system knows: "This is outside my subnet — send it to the gateway."

Your device sends packets meant for the internet (e.g., Google’s IP) to the gateway, usually your router.
The gateway handles NAT, replacing your private IP with the public IP to go out to the internet.
It also keeps track of which device requested what, so it can route the response back correctly.

Before contacting a server, your device asks a DNS server (whose IP you got from DHCP):
“What’s the IP address of google.com?”
DNS replies with the IP (e.g., 142.251.220.46), and then your device sends the actual data to that IP via the gateway.

A firewall is like a security guard for your network.
It decides which traffic is allowed or blocked based on rules (like blocking ports or IPs).
Both routers and operating systems have firewalls to protect against hackers and unwanted traffic.

A port is like a door on your device used by applications to send/receive data.
Common ports:
80 (HTTP – web),
443 (HTTPS – secure web),
22 (SSH),
25 (Email SMTP)
Protocols like TCP, UDP, HTTP, and FTP define how data is transmitted.

A switch connects multiple devices in a local network and sends data only to the intended device.
A hub broadcasts data to all devices — it’s outdated and less efficient than switches.

A router connects different networks together (e.g., your home network to the internet).
It also performs NAT, DHCP, DNS forwarding, and firewall filtering.

LAN (Local Area Network): Small area like home, office.
WAN (Wide Area Network): Large scale — the Internet.
MAN (Metropolitan Area Network): City-wide network (used by ISPs or large institutions).

Bandwidth: How much data can be transferred per second (like speed).
Latency: Time delay in sending data (measured in milliseconds, lower is better).

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