The Journey of A HTTP Request
Example
Let’s say that one student, Bob, wants to downloads a web page(www.google.com). Then there is a lot going on:
(1) Connecting to local Ethernet: DHCP, UDP, IP, Ethernet
(2) Send HTTP Request: DNS, ARP
(3) Web Client-Server Interaction: TCP and HTTP
To summarize, in order to get the webpage content from Internet,
(1) Bob’s laptop first needs to connect to local Ethernet, during which DHCP is required for initializing the laptop’s components
including default gateway router, default DNS server, network mask, the allocated IP address to the laptop.
(2) After that, Bob types the URL and UDP is used to retrieve the IP address of the domain(www.google.com), but in order to send the
UDP packet, an ARP request is sent so as to obtain the MAC address of the default gateway router. The UDP packet wrapped in IP datagram
will be first send to the gateway router, then to the DNS server. In this way, Bob can obtain the IP address as a response from the
DNS server.
(3) With the IP address, a HTTP request asking for the content of webpage will reach the IP address navigated by the routers distributed
in network.
The PDF as follows illustrates what is going on with a HTTP request in details:
