以下关于防火墙描述，正确是（ ）。
- A.防火墙可以限制外网对内网访问，但不能限制内网对外网访问
- B.防火墙可以防止外网对内网攻击，但不能防止内网对内网攻击
- C.代理服务防火墙通常直接转发报文，它对用户完全透明，速度较快
- D.包过滤防火墙相对于代理服务防火墙有更强身份验证和日志功能
正确答案及解析
正确答案
解析
本题考查防火墙基本概念。所谓防火墙，就是在内部网与外部网之间界面上构造一个保护层，并强制所有连接都必须经过此保护层，在此进行检查和连接。只有被授权通信才能通过此保护层，从而保护内部网资源免遭非法入侵。防火墙技术已成为实现网络安全策略最有效工具之一。防火墙主要用于实现网络路由安全性。网络路由安全性包括两个方面：①限制外部网对内部网访问，从而保护内部网特定资源免受非法侵犯②限制内部网对外部网访问，主要是针对一些不健康信息及敏感信息访问防火墙可以防止外网对内网攻击，但不能防止内网对内网攻击。防火墙大体上可以划分为两类：一类基于包过滤(Packet Filter)，另一类基于代理服务(Proxy Service)。二者区别在于：基于包过滤防火墙通常直接转发报文，它对用户完全透明，速度较快；而另一类防火墙是通过代理服务器建立连接，它可以有更强身份验证和日志功能。
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