The following are the protocol steps required in downloading a Web page from the PC when the DNS server contains no data:
1. Connect the PC to the network using an Ethernet cable.
2. Using the DHCP (Dynamic Host Configuration Protocol) the PC obtains its IP address. The following are the steps to be followed for obtaining IP address with in a given amount of time:
• The PC first creates a special IP datagram with the destination address 255.255.255.255 in the server discovery step of DHCP.
• The datagram is then placed in an Ethernet frame send then broadcasted in the network.
• The DHCP server present in the Ethernet then allows the PC a list of IP addresses of the routers with one hop, the subnet mask and the subnet where the PC resides and the address of DNS server if they exist.
3. The ARP cache for the PC is initially empty. So, the PC uses the ARP protocol to obtain the MAC address of first-hop routers and the local DNS server.
4. The PC first obtains the IP address of the Web page that the user wants to download. When the local DNS server does not contain any IP address, then the computer uses the DNS protocol in order to obtain the IP address of the Web page.
5. After obtaining the IP address of the Web page, then the PC will send out the HTTP request by using the first-hop router.
6. If the Web page is not found in a local Web server then the HTTP request message will be segmented and encapsulated into TCP packets, which are further encapsulated into IP packets, and then finally encapsulated into Ethernet frames.
7. The PC then sends the Ethernet frames destined to the first-hop router.
8. The first-hop router when it receives the frames, it passes the frames up to the IP layer and then checks its routing table. The router then sends the packets to the right interface out of all of its interfaces.
9. The IP packets are then routed through the Internet until they reach the Web server.
10. The server hosting the Web page will send back the Web page to the PC by using the HTTP response messages.
11. These messages are then encapsulated into TCP packets and then further into IP packets.
12. The IP packets then follow IP routes and finally reach the first-hop router.
13. The router then forwards these IP packets to the user PC by encapsulating them into Ethernet frames.