## 计算机代写|计算机网络代写computer networking代考|COS461

2022年10月8日

couryes-lab™ 为您的留学生涯保驾护航 在代写计算机网络computer networking方面已经树立了自己的口碑, 保证靠谱, 高质且原创的统计Statistics代写服务。我们的专家在代写计算机网络computer networking代写方面经验极为丰富，各种代写计算机网络computer networking相关的作业也就用不着说。

• Statistical Inference 统计推断
• Statistical Computing 统计计算
• (Generalized) Linear Models 广义线性模型
• Statistical Machine Learning 统计机器学习
• Longitudinal Data Analysis 纵向数据分析
• Foundations of Data Science 数据科学基础
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## 计算机代写|计算机网络代写computer networking代考|The Bad Guys Can Attack Servers and Network Infrastructure

Another broad class of security threats are known as denial-of-service (DoS) attacks. As the name suggests, a DoS attack renders a network, host, or other piece of infrastructure unusable by legitimate users. Web servers, e-mail servers, DNS servers (discussed in Chapter 2), and institutional networks can all be subject to DoS attacks. The site Digital Attack Map allows use to visualize the top daily DoS attacks worldwide [DAM 2020]. Most Internet DoS attacks fall into one of three categories:

• Vulnerability attack. This involves sending a few well-crafted messages to a vulnerable application or operating system running on a targeted host. If the right sequence of packets is sent to a vulnerable application or operating system, the service can stop or, worse, the host can crash.
• Bandwidth flooding. The attacker sends a deluge of packets to the targeted host-so many packets that the target’s access link becomes clogged, preventing legitimate packets from reaching the server.
• Connection flooding. The attacker establishes a large number of half-open or fully open TCP connections (TCP connections are discussed in Chapter 3 ) at the target host. The host can become so bogged down with these bogus connections that it stops accepting legitimate connections.

Let’s now explore the bandwidth-flooding attack in more detail. Recalling our delay and loss analysis discussion in Section 1.4.2, it’s evident that if the server has an access rate of $R$ bps, then the attacker will need to send traffic at a rate of approximately $R$ bps to cause damage. If $R$ is very large, a single attack source may not be able to generate enough traffic to harm the server. Furthermore, if all the traffic emanates from a single source, an upstream router may be able to detect the attack and block all traffic from that source before the traffic gets near the server. In a distributed DoS (DDoS) attack, illustrated in Figure 1.25, the attacker controls multiple sources and has each source blast traffic at the target. With this approach, the aggregate traffic rate across all the controlled sources needs to be approximately $R$ to cripple the service. DDoS attacks leveraging botnets with thousands of comprised hosts are a common occurrence today [DAM 2020]. DDos attacks are much harder to detect and defend against than a DoS attack from a single host.

We encourage you to consider the following question as you work your way through this book: What can computer network designers do to defend against DoS attacks? We will see that different defenses are needed for the three types of DoS attacks.

## 计算机代写|计算机网络代写computer networking代考|The Bad Guys Can Sniff Packets

Many users today access the Internet via wireless devices, such as WiFi-connected laptops or handheld devices with cellular Internet connections (covered in Chapter 7). While ubiquitous Internet access is extremely convenient and enables marvelous new applications for mobile users, it also creates a major security vulnerability-by placing a passive receiver in the vicinity of the wireless transmitter, that receiver can obtain a copy of every packet that is transmitted! These packets can contain all kinds of sensitive information, including passwords, social security numbers, trade secrets, and private personal messages. A passive receiver that records a copy of every packet that flies by is called a packet sniffer.

Sniffers can be deployed in wired environments as well. In wired broadcast environments, as in many Ethernet LANs, a packet sniffer can obtain copies of broadcast packets sent over the LAN. As described in Section 1.2, cable access technologies also broadcast packets and are thus vulnerable to sniffing. Furthermore, a bad guy who gains access to an institution’s access router or access link to the Internet may be able to plant a sniffer that makes a copy of every packet going to/from the organization. Sniffed packets can then be analyzed offline for sensitive information.

Packet-sniffing software is freely available at various Web sites and as commercial products. Professors teaching a networking course have been known to assign lab exercises that involve writing a packet-sniffing and application-layer data reconstruction program. Indeed, the Wireshark [Wireshark 2020] labs associated with this text (see the introductory Wireshark lab at the end of this chapter) use exactly such a packet sniffer!

Because packet sniffers are passive-that is, they do not inject packets into the channel – they are difficult to detect. So, when we send packets into a wireless channel, we must accept the possibility that some bad guy may be recording copies of our packets. As you may have guessed, some of the best defenses against packet sniffing involve cryptography. We will examine cryptography as it applies to network security in Chapter 8 .

# 计算机网络代考

## 计算机代写|计算机网络代写计算机网络代考|坏人可以攻击服务器和网络基础设施

• 漏洞攻击。这涉及向目标主机上运行的易受攻击的应用程序或操作系统发送一些精心设计的消息。如果将正确的数据包顺序发送到易受攻击的应用程序或操作系统，则服务可能会停止，更糟糕的是，主机可能会崩溃。
• 带宽泛洪。攻击者向目标主机发送大量的数据包——太多的数据包导致目标的访问链路阻塞，阻止合法的数据包到达服务器。
• 连接泛洪。攻击者在目标主机上建立大量半开或完全开的TCP连接(TCP连接将在第3章中讨论)。

## 计算机代写|计算机网络代写computer networking代考|The Bad Guys Can smell Packets

. The Bad Guys Can smell Packets . The Bad Guys Can嗅包

## 有限元方法代写

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## MATLAB代写

MATLAB 是一种用于技术计算的高性能语言。它将计算、可视化和编程集成在一个易于使用的环境中，其中问题和解决方案以熟悉的数学符号表示。典型用途包括：数学和计算算法开发建模、仿真和原型制作数据分析、探索和可视化科学和工程图形应用程序开发，包括图形用户界面构建MATLAB 是一个交互式系统，其基本数据元素是一个不需要维度的数组。这使您可以解决许多技术计算问题，尤其是那些具有矩阵和向量公式的问题，而只需用 C 或 Fortran 等标量非交互式语言编写程序所需的时间的一小部分。MATLAB 名称代表矩阵实验室。MATLAB 最初的编写目的是提供对由 LINPACK 和 EISPACK 项目开发的矩阵软件的轻松访问，这两个项目共同代表了矩阵计算软件的最新技术。MATLAB 经过多年的发展，得到了许多用户的投入。在大学环境中，它是数学、工程和科学入门和高级课程的标准教学工具。在工业领域，MATLAB 是高效研究、开发和分析的首选工具。MATLAB 具有一系列称为工具箱的特定于应用程序的解决方案。对于大多数 MATLAB 用户来说非常重要，工具箱允许您学习应用专业技术。工具箱是 MATLAB 函数（M 文件）的综合集合，可扩展 MATLAB 环境以解决特定类别的问题。可用工具箱的领域包括信号处理、控制系统、神经网络、模糊逻辑、小波、仿真等。