2.4-02. DNS: time to resolve query.  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 web.cs.umass.edu be resolved to an IP addressHow many time units are needed for the DNS request made at t=1 to be resolved?Group of answer choices6 time units.8 time units.4 time units.2 time units.10 time units.

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.

Question #1What is TTL within the context of DNSa time period when DNS query results are cacheda time period for DNS maintenancea time period when DNS is not answering requests

Question 2During the name resolution process, which server does a local recursive server contact first? 1 pointCaching name serverTop level domain (TLD) serverRoot name serverAuthoritative name server

A unique, comprehensive, accurate & free Windows (and Linux/Wine) utility to determine the exact performance of local and remote DNS nameservers . . .“You can't optimize it until you can measure it”Now you CAN measure it!

What is the function of the Domain Name System (DNS)?