英语论文网

网络安全

摘要：
因特网使用率越来越高使得电脑时常暴露存在的安全隐患。像防火墙等目前常用的解决网络安全问题的方法并不能抵挡来自外部精心设计的侵入，同时也缺乏保障安全的综合方案。本文将介绍一个更具综合性和灵活性的网络安全体系，他的设计和应用加强了网络的强制存取控制策略，它和网络流量的操作关系密切。

简介：
在给定的网络里，显然给定的数据包是通过TCP三路握手过程、网络基本输入输出系统和SMB（服务器信息块）进行转储的。深入分析将向大家说明，前三个数据包是通过TCP三路握手过程实现，而第4、第5个数据包是基于网络基本输入输出系统会话服务实现，剩下的第6-11个数据包利用够了服务器信息块进行转储。

TCP三路握手过程：
TCP三路握手过程是建立一个TCP联系的程序。TCP三路握手是会话的开始。第一步，会话发起人向另一台主机发出信息，请求他们发起会话。第二步，目标主机发回信息，表示同意建立联系。最后一步，会话发起人再发一个信息，确认建立联系。TCP三路握手用于建立TCP/IP通信。

Network security
Published: 23, March 2015

摘要——Abstract:
The use of networks is growing continuously, constantly increasing the vulnerability of the computer systems that can use them. Current solutions for network security such as firewalls cannot support sophisticated trust relationship with external entities and lack a comprehensive approach to security. This work deals with the design and implementation of a more comprehensive and flexible network security architecture that enforces a mandatory access control policy on network related operations on a network traffic.

简介——Introduction:
From the given network dump it is clear that the packets given are based on TCP Three Way Hand Shake, NetBios and SMB (Server Message Block). Further analysis explains that the first three packets are TCP Three Way Hand Shake structures , packets 4 and 5 are based on NETBIOS Session Services and the remaining packets 6 to 11 are Server Message Blocks structures.

TCP三路握手——TCP THREE WAY HAND SHAKE:
The TCP Three way Hand Shake is the process for establishing a TCP connection. A conversation is started with a three way hand shake. In the first step of this process, the initiator of the conversation send packet to the other host requesting that they start a conversation. In the second step, the destination host sends back an acknowledgement that agrees to set up the communication. In the final step, the initiator sends back one more packet that is a confirmation of the connection. The Three way Hand Shake is used to set up the TCP/IP communication

The TCP level of the TCP/IP protocol is connection oriented. Connection oriented is that before and data can be transmitted, a reliable connection must be obtained and acknowledged. TCP level data transmissions, connection establishment, and connection termination maintain specific control parameters that govern the entire process. The control bits of Transmission Control Protocol are:

URG: Urgent Pointer field Significant

ACK: Acknowledgement field significant

PSH: Push function

SYN: Synchronize sequence numbers

FIN: No more data from sender.

The two scenarios where a Three way handshake will take place are Establishing a Connection (an active open) and Terminating a Connection (an active close).

Packet 1:
In the first packet, it is clear that a TCP SYN packet was sent from a source system 193.63.129.192 on port 1843 to a destination system 193.63.129.187 on port 139 with TCP types of service with routine precedence, normal delay, normal throughput, normal reliability and TCP option Maximum Segment Size (MSS) set to 1460 byt