The network in your home is a small version of the networks you will secure at work: a boundary, a router, internal devices and a wireless segment. Understanding it makes corporate network diagrams much less intimidating.
The pieces
- Modem / ONT terminates the connection from your ISP.
- Router moves traffic between your local network and the internet, and usually runs NAT, DHCP and a firewall.
- Switch connects wired devices on the same local network.
- Access point provides Wi-Fi; on home equipment it is often built into the router.
- Devices include laptops, phones, TVs, cameras and smart speakers.
Your LAN is the local side; the WAN is the ISP side. The router is the boundary between them.
NAT and port forwarding
NAT (Network Address Translation) lets many private devices share one public IPv4 address. As traffic leaves, the router rewrites the source address and tracks the connection so replies can find their way back.
NAT is not a firewall, although it hides internal addresses by default. Port forwarding deliberately opens a path from the internet to an internal device. Every forwarding rule is an exposed service; keep the list short and reviewed.
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