网络防火墙功能与防护威胁类型.pdfVIP

Thepurposeofanetworkfirewallistoprovideashell

定语从句

aroundthenetworkwhichwillprotectthesystems

connectedtothenetworkfromvariousthreats.Thetypesof

定语从句

threatsafirewallcanprotectagainstinclude:

●Unauthorizedaccesstonetworkresources—anintruder

maybreakintoahostonthenetworkandgain

unauthorizedaccesstofi.

●Denialofservice—anindividualfromoutsideofthe

networkcould,forexample,sendthousandsofmail

messagestoahostonthenetinanattempttofill

availablediskspaceorloadthenetworklinks[1].

●Masquerading—electronicmailappearingtohave

originatedfromoneindividualcouldhavebeenforged

byanotherwiththeintenttoembarrassorcauseharm[2].

?1●Whatisnetworkfirewall?

?2●Describerthreetypesofthreatsafirewallcan

protectagainst

Afirewallcanreduceriskstonetworksystemsby

filteringoutinherentlyinsecurenetworkservices.Network

FileSystem(NFS)services,forexample,couldbe

preventedfrombeingusedfromoutsideofanetworkby

blockingallNFStraffictoorfromthenetwork.

Thisprotectstheindividualhostswhilestillallowingthe

非限定性定语从句

service,whichisusefulinaLANenvironment,onthe

internalnetwork.Onewaytoavoidtheproblemsassociated

withnetworkcomputingwouldbetocompletelydisconnect

anorganization’sinternalnetworkfromanyotherexternal

system.This,ofcourse,isnotthepreferredmethod.Instead

主语从句时间状语从句

whatisneededisawaytofilteraccesstothenetworkwhile

stillallowingusersaccesstothe“outsideworld”.

?3●Whatmethodcanreduceriskstonetwork

system?

Inthisconfiguration,theinternalnetworkisseparated

fromexternalnetworksbya