"You have been hired as an assistant to the head network administrator in an ISP (Internet service provider)...." to ensure that the appropriate security measures have been taken you use a root guard. Option C. This is further explained below.
Generally, a root guard is simply defined as on a port-by-port basis, root guard is an STP characteristic that prevents a specified port from being the root of the network.
In conclusion, In order to guarantee that the proper security measures have been performed, you utilize a root guard as an assistant to the chief network administrator in an ISP.
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