$2\mathrm{.}4-06.$ 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 choices

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.

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.

Yes. 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.