$2\mathrm{.}4\mathrm{.}10$ DNS in Action $(4).$ 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 address

How many time units are needed for the DNS request made at t$=1$ to be resolved?

Question $24$ options:

$2$ time units

$4$ units

$6$ time units

$8$ time units

$10$ time units