Summary of "İnternet Nasıl Çalışır 1. Bölüm 🌍"

This video explains the fundamental workings of how a computer connects to the internet, focusing on the roles of hardware addresses, IP addresses, and network protocols. It takes the viewer step-by-step through the process starting from powering on the computer to sending data packets over the internet.

Main Ideas and Concepts

Starting the Connection:
- When the computer is turned on, the operating system boots and immediately communicates with the Ethernet card to initiate network connectivity.
- The Ethernet card (also called Network Interface Card or adapter) is a hardware component enabling communication over a network.
MAC Address (Media Access Control Address):
- A unique, physical hardware address embedded in the Ethernet card by the manufacturer.
- It is 48 bits long (12 hexadecimal characters) and acts like a permanent “citizenship number” for the device.
- The MAC Address cannot be permanently changed by software; only temporary changes are possible until a hard reset.
- Essential for direct communication between devices on the same local network.
IP Address (Internet Protocol Address):
- A logical address assigned to devices, similar to a “home address.”
- Unlike the MAC Address, the IP Address can change (e.g., when moving networks).
- Both MAC and IP addresses are necessary for proper network communication.
Obtaining an IP Address:
- Two methods:
  1. Manual assignment: User sets IP Address manually.
  2. Automatic assignment via DHCP (Dynamic Host Configuration Protocol): Most common method where the Modem/router acts as a DHCP server.
- DHCP server inside the Modem listens for broadcast requests from devices and assigns available IP addresses from a predefined range.
- The device accepts the offered IP and subnet mask, which are then configured on the Ethernet card.
- The Modem maintains a table mapping MAC addresses to assigned IP addresses.
Private vs Public IP Addresses:
- IPv4 addresses are 32-bit, allowing about 4.2 billion addresses.
- Many IPs are reserved for private networks (e.g., 192.168.x.x) and cannot be used directly on the internet.
- Devices inside a home or office use private IPs to communicate locally.
- To access the internet, devices must use a public IP Address assigned by the Internet Service Provider (ISP).
Default Gateway and Routing:
- The Modem/router acts as the default gateway (main door) for devices to access the internet.
- Devices send data packets to the gateway’s IP Address to reach external networks.
Address Resolution Protocol (ARP):
- Used to map an IP Address to a MAC Address on the local network.
- When a device wants to communicate with another device’s IP, it sends a broadcast ARP request asking “Who has this IP?”
- The device with the matching IP responds with its MAC Address.
- ARP caches these mappings to avoid repeated requests.
Network Address Translation (NAT):
- Since private IPs cannot access the internet directly, NAT translates local IP addresses to the public IP Address assigned by the ISP.
- All devices in a local network share a single public IP for internet access.
- NAT keeps a table of outgoing connections, mapping internal IP and port pairs to the public IP and port.
- When responses return, NAT uses this table to route packets back to the correct internal device.
- This allows multiple devices to share one public IP without confusion or data mix-up.
Port Numbers and NAT Table:
- Each outgoing connection is assigned a unique source port.
- The NAT table tracks source IPs, source ports, destination IPs, and destination ports.
- Incoming packets are matched to the correct device based on this mapping.

Step-by-Step Process of Connecting and Communicating on the Internet

Power on computer and OS boots up.
Ethernet card activates and identifies itself by its MAC Address.
Device requests an IP Address:
- Sends a DHCP Discover broadcast frame.
- Modem’s DHCP server responds with an available IP and subnet mask.
- Device accepts and configures its network settings.
Device uses ARP to find the MAC Address of the default gateway (Modem/router).
Device sends data packets to the Modem to reach external internet addresses.
Modem performs NAT:
- Translates local private IP and port to public IP and port.
- Maintains a NAT table to track connections.
Incoming internet packets are routed back through the Modem to the correct device using the NAT table.

Speakers / Sources Featured

Narrator / Main Presenter: Explains concepts, protocols, and hardware functions throughout the video.
No other distinct speakers or external sources are mentioned in