work(),systemsthateffectivelyisolateanorganization'sinternalnetworkstructurefroman(请作答此空)network,suchastheINTERNETisbecomingincreasinglypopular.Thesefirewallsystemstypicallyactasapplication-layer()betweennetworks,usuallyofferingcontrolledTELNET,FTP,andSMTPaccess.Withtheemergenceofmoresophisticated()layerprotocolsdesignedtofacilitateglobalinformationdiscovery,thereexistsaneedtoprovideageneral()fortheseprotocolstotransparentlyandsecurelytraverseafirewall.
A.exterior B.Internal C.center D.middle正确答案A
