How a device sends an HTTP request

Step 11: Device requests IP address for URL

The device is now connected to the Wi-Fi network. The user can open up the browser and enter any URL. The device must resolve fully qualified domain names (FQDN) to an IP address. This service is provided by the Domain Name System (DNS) server.

1. The device creates a DNS query message, putting the URL string in the question section of the DNS message.
2. The DNS message is placed within a UDP segment with destination port 53. DNS always runs on port 53 on the DNS server.
3. The DNS message is placed in an IP datagram with a DNS server destination IP address.
4. The datagram is routed through the gateway, in the same way as any other packet that leaves the subnet.
5. The DNS server returns the resource record that specifies the IP address for the URL.

Step 12: Device makes HTTP GET request

Before the device sends the HTTP GET request, it needs to create a Transmission Control Protocol (TCP) connection with the server using a 3-way handshake. When the device makes the HTTP GET request, the server responds with the HTTP response message that contains the requested webpage content.