Consider the network shown at right. Assuming: 1) that all HTTP queries originating in a com are first directed to a com’s HTTP cache, 2) that both a com’s HTTP and all DNS server caches are initially empty, and 3) that all DNS queries are iterative, answer the following questions. (a) A user at m1.a.com types the URL www.b.com/bigfile.html into a browser to retrieve a big file from www.b.com. List, in order, and in the form 1. {DNS/HTTP} {request/response} from W to X 2. {DNS/HTTP} {request/response} from Y to Z all DNS and HTTP messages generated by this browser request. (b) Immediately after the big file is delivered to m1.a.com, a user at m2.a.com requests the exact same file from www.b.com. List, in order, in the same form as displayed above, all DNS and HTTP messages generated by this request. (c) Would your answer to (a) change if the all DNS queries were recursive? If so, rework (a) in this case. How about (b)? If so, rework (b) in this case. (d) It is often said that iterative DNS queries are “less burdensome” to DNS servers than recursive DNS queries. Why?
