以下关于代理服务器功能描述最为正确的是()。
- A.提高客户端访问外网的效率
- B.隐藏企业内部网络细节
- C.节省IP开销
- D.以上答案都正确
正确答案及解析
正确答案
解析
代理服务器的主要功能如下：
(1)设置用户验证和记账功能，可按用户进行记账，没有登记的用户无权通过代理服务器访问Intemet网。并对用户的访问时间、访问地点、信息流量进行统计。
(2)对用户进行分级管理，设置不同用户的访问权限，对外界或内部的Intemet地址进行过滤，设置不同的访问权限。
(3)增加缓冲器(Cache)，提高访问速度，对经常访问的地址创建缓冲区，大大提高热门站点的访问效率。通常代理服务器都设置一个较大的硬盘缓冲区(可能高达几个吉字节(GB)或更大)，当有外界的信息通过时，同时也将其保存到缓冲区中，当其他用户再访问相同的信息时，则直接由缓冲区中取出信息，传给用户，以提高访问速度。
(4)连接内网与Internet，充当防火墙(Firewall)：因为所有内部网的用户通过代理服务器访问外界时，只映射为一个IP地址，所以外界不能直接访问到内部网；同时可以设置IP地址过滤，限制内部网对外部的访问权限。
(5)节省IP开销：代理服务器允许使用大量的伪IP地址，节约网上资源，即用代理服务器可以减少对IP地址的需求，对于使用局域网方式接入Intemet，如果为局域网(LAN)内的每一个用户都申请一个IP地址，其费用可想而知。但使用代理服务器后，只需代理服务器上有一个合法的IP地址，LAN内其他用户可以使用10．*．*．*这样的私有IP地址，这样可以节约大量的IP，降低网络的维护成本。
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