Question

The following information was obtained from a host:

IP address……………205.133.127.8/24

Default Gateway…… 205.133.127.1

DNS Server………….139.100.110.10

HOSTS file entries: 140.20.10.55 www.myut.utoledo.edu

140.20.10.55 myut.utoledo.edu

127.0.0.1 www.cnn.com

127.0.0.1 cnn.com

Describe the sequence of events (in detail) that would occur if this host attempts to:

a) Load the Web Site of the following Domain Names using a Web Browser.

http://www.utoledo.edu

http://www.cnn.com

Answer 1

For http://www.utoledo.edu:
1. The host types "http://www.utoledo.edu" in the address bar of the web browser from its own IP address "205.133.127.8/24".
2. The browser checks the cache for a DNS record for the IP address(140.20.10.55) which corresponds to "http://www.utoledo.edu".
There are 4 caches where the DNS record is searched for:
   a) Browser cache: It keeps the records of DNS entries previously accessed for a certain amount of time.
   b) OS cache: If not found in the browser cache, search in the OS cache.
   c) Router cache: If not found in the OS, search in host system's router.
   d) ISP cache: If all 3 above don't yeild any result, ISP cache is the final checkpost.
As in our case, we notice that there are host entries agains this website, so we find it in browser cache itself.
Hence the server knows the domain name server and name server and retrieves the matching IP address.
3. After the browser receives the correct IP address, it will build a TCP connection via a three-way-handshaking protocol, with the server that matches IP     address to transfer information.
4. Once the TCP connection is established, it starts transfering data. The browser sends a GET request requesting for web page with name "utoledo.edu".
5. The server contains a web server which receives the request handler to read and generate a response for the request. The request handler is a module that reads the requests from the hosts, the header information and cookies (if any), then it creates a response in JSON,XML or HTML format.
6.The server response contains the web page you requested as well as the status code, compression type , cache-control, cookies, privacy information, etc.

For http://www.cnn.com:
1. The host types "http://www.cnn.com" in the address bar of the web browser from its own IP address "205.133.127.8/24".
2. The browser checks the cache for a DNS record for the IP address(127.0.0.1) which corresponds to "http://www.cnn.com".
There are 4 caches where the DNS record is searched for:
   a) Browser cache: It keeps the records of DNS entries previously accessed for a certain amount of time.
   b) OS cache: If not found in the browser cache, search in the OS cache.
   c) Router cache: If not found in the OS, search in host system's router.
   d) ISP cache: If all 3 above don't yeild any result, ISP cache is the final checkpost.
   As in this case, we find that there are no host entries for "http://www.cnn.com", there fore the subsequent caches are checked for.
3. If the requested URL is not in the cache,as in our case, ISP's DNS initiates a DNS query to find the correct IP address for the website.
   a)ISP's DNS server will contact the root name, here ".com" domain name server.
   b)".com" domain name server will redirect it to "cnn.edu" name server.
   c)"cnn.edu" name server will find the matching for the IP address "127.0.0.1" in its' DNS records and send it back to the browser.
4. After the browser receives the correct IP address, it will build a TCP connection via a three-way-handshaking protocol, with the server that matches IP     address to transfer information.
5. Once the TCP connection is established, it starts transfering data. The browser sends a GET request requesting for web page with name "cnn.com".
6. The server contains a web server which receives the request handler to read and generate a response for the request. The request handler is a module that reads the requests from the hosts, the header information and cookies (if any), then it creates a response in JSON,XML or HTML format.
7.The server response contains the web page you requested as well as the status code, compression type , cache-control, cookies, privacy information, etc.