本文的主要內容是防火牆的功能，最初，防火牆的功能是通過訪問控制列表的acl來執行的。這些通常出現在路由器上。從本質上講，acl是用來確定是否需要為特定IP地址提供網絡訪問權的規則。例如，ACL可以有一行說明不應該授予來自126.96.36.199 IP的每個流量訪問權，以此類推(Vasu和Sudarsan 92-107)。有一個優勢與這些ACL有關,因為他們更高的執行能力和可伸縮性,但他們沒有能力讀過去的頭包只提供信息的基本的自然流量(Rhodes-Ousley 2)。因此,ACL的信息包過濾本身沒有能力保持遠離網絡系統的威脅。本篇幫寫論文文章由英國論文人EducationRen教育網整理，供大家參考閱讀。
Initially, the function of firewall was performed through the ACLs known as Access control lists. These were often present over routers.
Essentially, ACLs are rules written out for determining whether the access to network needs to be given or not for a particular address of IP. An ACL, for example could have a line stating that every traffic from 188.8.131.52 IP should not be granted access and so on (Vasu and Sudarsan 92-107). There is an advantage associated with these ACLs because of their higher performing ability and scalability but they do not have the ability to read past the headers of packet which only provides information of rudimentary nature over the traffic (Rhodes-Ousley 2). Therefore, the packet filtering of ACL itself does not have the capability of keeping threats away from the networking systems.
These are responsible for acting as middle ware as they are able to accept every request of traffic coming within the network through true traffic recipient impersonation across the network. After inspecting, if the system decides on granting access then the firewall proxy sends the data to the destined computer (Kaur and Rao 77). The reply of the destination computer then is sent towards the proxy who in turn repackages the data with the proxy server source address. With this process, it becomes possible for the proxy firewall to stop the connection taking place between two devices so as to ensure that it is the key machine over the networks talking about the external world (Kaur and Singh 200-204). These firewalls can indulge in completely inspecting content and making decisions of access depending upon information’s granular level and specificity.
Such a nuance is attractive for administrators of network but every application requires its individual proxy at the level of application (Jadhav and Agrawal 753-756). Networks with proxy firewall further suffer degraded performance of traffic and various limitations within the support of application and generalized functions. This leads ultimately towards issues of scalability which makes it easy to implement the pull-offs. For such reason, this type of firewall is not adopted by many people. As a matter of fact, even at the proxy firewalls popularity times, the issues of scaling and performance caused limited ability towards adopting this.