Joining the network
A phone, a laptop and a TV are hosts: devices that send and receive data. A few boxes connect them to each other and to the internet. Let's follow the phone as it opens a web page.
The phone joins the Wi-Fi by radio. The box it talks to is the access point (AP): it links wireless devices into the home network. The Wi-Fi password lets them set up encryption.
The router runs DHCP, a service that lends each device an address. The phone gets 192.168.1.23, a private address that only works inside the home. It also learns to send everything bound outside to the router.
Out to the internet
The phone sends its request for the page. It goes by radio to the AP, then over a cable to the router: the box that joins your home network to the internet.
Private addresses don't work on the public internet. So the router swaps the phone's address for the home's one public address, 203.0.113.45, and notes the swap in a table. This is NAT, network address translation.
The modem turns the router's signal into the kind your provider's line carries: signals on a TV cable, tones on a phone line, or pulses of light on fibre, where the box is called an ONT.
The line leads to your ISP, the internet service provider you pay. Its network carries the request on, through other networks, to the web server at 198.51.100.80.
Back home
The web page comes back addressed to 203.0.113.45, through the modem to the router. The router checks its NAT table, sees the phone made this request, and swaps in 192.168.1.23 again.
The router passes the page over the cable to the AP, and the AP sends it by radio to the phone. The page appears on the screen.
The other boxes
The laptop and TV use cables instead of radio. Their cables plug into a switch, which joins wired devices and passes each message to the right port. The laptop's request reaches the router the same way.
In most homes the AP, the switch and the router sit in one 'home router' box. It also answers the devices' name lookups (DNS) by asking the ISP. Some boxes hold the modem too.
What is going on, line by line
;; step 1/11 · hosts · local ;; at the phone home network (LAN) 192.168.1.0/24 (RFC 1918 private range) phone 192.168.1.23 MAC 00:00:5e:00:53:23 Wi-Fi laptop 192.168.1.10 MAC 00:00:5e:00:53:10 cable TV 192.168.1.11 MAC 00:00:5e:00:53:11 cable router 192.168.1.1 MAC 00:00:5e:00:53:01 (LAN side) (addresses are explained in later lessons)
Before the request the phone asked the router for www.example.com's address (DNS); the router passed the question to the ISP's resolver. The DNS lesson follows that trip. With IPv6 each device usually gets its own public address, so home routers do not need NAT for it; this lesson uses IPv4.