Single packet filter technology , with its flaws , cannot provide perfect security protection ; intrusion detection , as an active defense system , is a crucial supplementary to the packet technology and work as a second line of defense ; content filter supplies the gap of the information content protection that two former technologies leave and form the last barrier for security protection 單純的包過(guò)濾技術(shù)由于其自身的缺陷而不能提供完全的安全保護(hù)。入侵檢測(cè)作為一種主動(dòng)防御技術(shù),是包過(guò)濾的重要補(bǔ)充,起到了第二道防線的作用。內(nèi)容過(guò)濾彌補(bǔ)了前兩種技術(shù)在信息內(nèi)容防范方面的不足,形成了安全防護(hù)的最后一道屏障。