2.4-06. DNS local caches. We saw that a local DNS cache will respond immediately to a client when the local DNS has the name-to-address translation in its local cache. There are millions of such local DNS caches across the Internet. For a given Internet name, will the name-to-address translation pair stored in these local caches always be the same (i.e., are the contents of the local caches synchronized)?Group of answer choicesYes.  The caches are always synchronized.  When a name-to-address mapping changes in the DNS hierarchy, the DNS hierarchy will push to new mapping to all local caches, and the local caches will not install the new mapping until all local caches commit to doing to sat the same time.No.  The caches are not always synchronized.  When a name-to-address mapping changes in the DNS hierarchy, the DNS hierarchy will push the new mapping to all local caches.  However,  it takes different amounts of time for these updates to propagate to all local caches.  Thus, all of the local caches are not always perfectly synchronized.No.  The caches are not always synchronized.  An entry in a local cache will eventually time out, and the local cache will again eventually go to the DNS hierarchy to get the name-to-address translation pair for this name.  So if the name-to-address mapping changes in the DNS hierarchy, the new mapping will eventually (but not immediately) make its way into the local cache.  Therefore, not all local caches may have the same value for name-to-address translation pair.

2.4-01a. DNS in Action. Suppose that the local DNS server caches all information coming in from all root, TLD, and authoritative DNS servers for 20 time units. (Thus, for example, when a root server returns the name and address of a TLD server for .com, the cache remembers that this is the TLD server to use to resolve a .com name).  Assume also that the local cache is initially empty, that iterative DNS queries are always used, that DNS requests are just for name-to-IP-address translation, that 1 time unit is needed for each server-to-server or host-to-server (one way) request or response, and that there is only one authoritative name server (each) for any .edu or .com domain.Consider the following DNS requests, made by the local host at the given times:t=0, the local host requests that the name gaia.cs.umass.edu be resolved to an IP address. t=1, the local host requests that the name icann.org be resolved to an IP address. t=5, the local host requests that the name cs.umd.edu be resolved to an IP address. (Hint: be careful!)t=10, the local host again requests that the name gaia.cs.umass.edu be resolved to an IP address. t=12, the local host requests that the name cs.mit.edu be resolved to an IP address. t=30, the local host again requests that the name gaia.cs.umass.edu be resolved to an IP address. (Hint: be careful!)Which of the requests require 8 time units to be resolved?

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DNS addresses are used to?

2.2-11a. Local Web Caching (a). Consider the following scenario, in which a Web browser (lower) connects to a web server (above).  There is also a local web cache in the bowser’s access network.  In this question, we will ignore browser caching (so make sure you understand the difference between a browser cache and a web cache). Assume that the total Round Trip Time propagation, queueing and object transmission delay between the browser and web server (and including TCP setup time) is 250 msec; if the object is retrieved from the local web cache, this delay is only  10 msec.Suppose that 80 percent of the time when the browser makes a request, the requested object is found in the local web cache.  What is the average time (over all requests that the browser makes to this site) from when the browser issues the initial HTTP GET request until it is able to display the requested object?Group of answer choices250 msec220 msec420 msec230 msec58 msec88 msec120 msec

Explain how names are translated (resolved) into IP address?