ExamSim MCSE 2000: Design A Dynamic DNS Network Page 3
Answer A is incorrect because you cannot have 5 Primary DNS Servers for the same domain. If you do this, you will create a totally unmanageable DNS situation, where every DNS Server would have to be configured as a Secondary, and the risk of inconsistency in the zone database for the domain is extremely high. This is never done in the real world, and probably is never done in the fantasy world either. Another problem with this answer is that downlevel clients cannot directly register their IP addressing information with a DDNS Server.
Answer B is incorrect because if the single Primary DNS Server for the domain becomes unavailable, then none of the DNS clients will be able to dynamically register their IP addressing information. The requests could be sent to Standard Secondary servers, but the Secondary servers need to forward the registration request to a Dynamic Standard Primary DNS Server. Since the single Primary DNS Server is unavailable, no machine will be able to update information in the zone database. Not even the DHCP Server which is acting as proxy for the downlevel clients will be able to perform the Dynamic updates. Finally, the downlevel clients are not able to directly communicate with the DDNS Server.
Answer C is incorrect because although almost everything is in place, all network clients are not able to directly communicate with the Dynamic DNS Server. In order for this solution to work, you need to implement a DHCP Server that will act as a "proxy" for the downlevel clients that are not able to register their own IP addressing information.