英语翻译a firewall is a deivce that filters all traffic between

英语翻译
a firewall is a deivce that filters all traffic between a protected or "inside" network and a less trustworthy or "outside" network.Usually a firewall runs on a dedicated device;because it is a single point through which traffic is channeled,performance is improtant,which means nonfirewall functions should not be done on the same machine.Because a firewall is executable code,an attacker could compromise that code and execute from the firewall's device .Thus,the fewer pieces of code on the device,the fewer tools the attacker would have by compromising the firewall.Firewall code usually runs on a proprietary or carefully minimized operating system.The purpose of a firewall is to keep "bad" things outside a protected environment.To accomplish that,firewalls implement a security policy that is specifically designed to address what bad things might happen.For example,the policy might be to prevent any access from outside(while still allowing traffic to pass from the inside to the outside).Alternatively,the policy might permit accesses only from certain places,from certain users,or for certain activities.Part of the challenge of protecting a network with a firewall is detemining which security policy meets the needs of the installation.

防火墙是一种装置,它对受保护的、“内部”网,及不值得信任的、“外部”网之间的所有通信量进行过滤.一般情况下,防火墙在专用设备上运行,因为它是疏导流量的一个接点,故性能很重要,这意味着防火墙的功能不可能在一台机器上实现.由于防火墙是可执行代码,攻击者可能会篡改该代码,并让防火墙所在设备执行.因此,代码越少,攻击者拥有影响防火墙的工具就越少.防火墙源代码通常运行在专有的或最小化的操作系统上.防火墙的功能是确保将“不好”的东西隔绝在受保护的运行环境之外.为了实现这个目标,防火墙执行针对可能发生的不好情况的安全策略.例如,该策略可能阻止任何来自外部的访问（但仍允许流量从内部通往外部）.或者该策略可能只允许来自特定地方,特定用户的访问,及对某些特定活动的通信.用防火墙保护网络通信的挑战是决定用哪一种安全策略可以满足安装需要.
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