Identify the correct sequence in which the following packets are transmitted on the network by a host when a browser requests a webpage from a remote server, assuming that the host has just been restarted.
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Answer: C
When a host has just been restarted, its local DNS cache is empty. To fetch a webpage from a remote server, the host must perform the following steps in sequence:
- DNS Query: The browser first needs the IP address of the remote server corresponding to the domain name (e.g.,
www.example.com). Since there is no cached entry, it transmits a DNS query packet to resolve the domain name. - TCP SYN: Once the IP address is obtained, the host must establish a TCP connection with the remote web server. This connection setup begins with the TCP three-way handshake, where the host transmits a TCP SYN packet.
- HTTP GET Request: After the TCP connection is successfully established, the browser can send the application-layer request, which is the HTTP GET request, to fetch the webpage.
Thus, the correct sequence of packet transmission is: DNS query → TCP SYN → HTTP GET request.
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