Internet Service and Protocols\\ Consider a web page for a mythical company dogm

Question

Internet Service and Protocols

Consider a web page for a mythical company dogmyth.com that contains the following embedded URLs (i.e., the following URLs are contained in the HTML source for the dogmyth.com home page):

http://www.dogmyth.com/logo.gif

http:// www.ads.dogmyth.com/dog-banner.jpg

http://www.ads.cat.biz/meow-add.jpg

http://www.ads.bird.biz/chirp-add.jpg

http://www.cat.biz/happy-cat.jpg

http://www.dogmyth.com/happy-dog.jpg

http://www2.dogmyth.com/cookie.crumb

Consider the DNS name resolution that is required for a browser to locate and request all components of this web page beginning with the home page URL http://www.dogmyth.com. Assume there is no browser cache of web objects, no web proxy server, and the browser’s resolver does not cache any DNS results. In answering the following questions you may assume:

• The cache for the local authoritative DNS server is initially empty and no other resolvers attempt to use that server until all these HTTP requests are completely satisfied.

• The local authoritative DNS server always sends iterated queries.

• For the domain names in the above URLs, there is a different authoritative DNS server for each unique domain in the name hierarchy. Domain names with a prefix of “www” are all assigned to host machines.

(a) Show the contents of the cache on the local authoritative DNS server used by a browser accessing the dogmyth.com home page after the page has been entirely fetched. For each entry in the cache, show only the values of the name and type fields for the entry.

(b) How many DNS query/reply protocol message exchanges with other DNS servers are processed by the local authoritative DNS server during the process of fetching all components of the dogmyth.com home page? Explain how you obtained your answer.

Explanation / Answer

a. The content of the cache will be the hostname and the IP address fo the site "dogmyth.com" and some other setting TTL (time to live) so that if we are making the same request again on the same browser we will give the results from the local cache instead of actual ISP.

b. All query can be understood by below points.

so around normally 9 DNS query happens to get the answer.

Note- (NS- Name server)

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