发布时间 : 星期五 文章Homework Chapter 2更新完毕开始阅读
《Computer Networks and Internet》
Chapter 2
1. Consider the following string of ASCII characters that were captured by Wireshark when the browser sent an HTTP GET message (i.e., this is the actual content of an HTTP GET message). The characters
GET /cs453/index.html HTTP/1.1
Mozilla/5.0 (Windows;U; Windows NT 5.1; en-US; rv:1.7.2) Gecko/20040804 Netscape/7.2 (ax)
en-us,en;q=0.5
a. What is the URL of the document requested by the browser? b. What version of HTTP is the browser running?
c. Does the browser request a non-persistent or a persistent connection? d. What is the IP address of the host on which the browser is running?
e. What type of browser initiates this message? Why is the browser type needed in an HTTP request message?
考虑以下的ASCII字符字符串被Wireshark当浏览器发送一个HTTP GET消息(即。,这是一个HTTP GET消息的实际内容)。字符< cr > < >如果是回车和换行符字符(即italized下面的文本字符串< cr >代表单一回车字符包含在这一点上的HTTP头)。回答下列问题,表明在HTTP GET消息下面你找到答案。 a。什么是文档的URL请求的浏览器? b。浏览器运行HTTP版本是什么? c。浏览器请求一个非持久性或持久连接? d。什么是浏览器的IP地址的主机运行吗?
e。什么样的浏览器启动这个消息吗?为什么浏览器类型所需的HTTP请求消息吗?
1
浏览器类型信息需要由服务器发送同一对象的不同版本,不同类型的浏览器。
2. The text below shows the reply sent from the server in response to the HTTP GET message in the question above. Answer the following questions, indicating where in the message below you find the answer.
HTTP/1.1 200 OK
3874 transitional//en”> a. Was the server able to successfully find the document or not? What time was the document reply provided? b. When was the document last modified? c. How many bytes are there in the document being returned? d. What are the first 5 bytes of the document being returned? Did the server agree to a persistent connection? 下面的文本显示来自服务器的应答发送响应HTTP GET消息在上面的问题中。回答下列问题,显示下面的消息,你找到答案。 一个。服务器能够成功地找到文档吗?文档回复提供时间是什么? b。最后修改的文档是什么时候? c。有多少字节的文档返回? d。第一个是什么5字节的文档返回?服务器同意一个持久连接吗? 3. Consider following Figure, for which there is an institutional network connected to the Internet. Suppose that the average object size is 900kb and that the average request rate from the institution’s browsers to the origin servers is 15 requests per second. Also suppose that the amount of time it takes from when the router on the Internet side of the access link forwards an HTTP request until it receives the response is 3s on average. Model the total average response time as the sum of the average access delay (that is, the delay from Internet router to institution router) and the average Internet delay. For the average access delay, use Δ/(1–Δβ), where Δ is the average time required to send an object over the access link and β is the arrival rate of objects to the access link. 2 Figure 1 Bottleneck between an institutional network and the Internet a. Find the total average response time. b. Now suppose a cache is installed in the institutional LAN. Suppose the miss rate is 0.4. Suppose hit rate increases to 0.95. Find the total response time. 考虑下面的图,有一个机构网络连接到互联网。假设对象的平均尺寸是900 kb,平均请求率从机构的浏览器起源服务器每秒15请求。还假设的时间在互联网上需要从路由器的访问链接转发HTTP请求,直到接收到响应平均3 s。模型总平均响应时间平均访问延迟之和(即延迟从互联网路由器到路由器)机构和平均网络延迟。平均访问延迟,使用Δ/(1-Δβ),Δ发送对象所需的平均时间的访问链接和β的到达率是对象的访问链接。 发现总平均响应时间。 b。现在假设一个缓存是安装在机构局域网。想错过率是0.4。假设命中率增加到0.95。发现总响应时间。 4. Print out the header of an e-mail message you have recently received. How many Received: header lines are there? Analyze each of the header lines in the message. (Allow printing of an email header file.) 打印头你最近收到的一封电子邮件。多少接受:头行吗?分析每个头线的消息。(允许打印头文件的电子邮件。) 3 5. Read RFC 5321 for SMTP. What does MTA stand for? Consider the following received spam email (modified from a real spam email). Assuming only the originator of this spam email is malacious and all other hosts are honest, identify the malacious host that has generated this spam email. 为SMTP读RFC 5321。MTA代表什么?考虑以下收到垃圾邮件从一个真正的垃圾邮件(修改)。假设只malacious这个垃圾邮件的发起者和所有其他主机是诚实的,识别malacious主机生成的这个垃圾邮件。 From - Fri Nov 07 13:41:30 2008 Return-Path: (barmail.cs.umass.edu [128.119.240.3]) by cs.umass.edu (8.13.1/8.12.6) for Received: from asusus-4b96 (localhost [127.0.0.1]) by barmail.cs.umass.edu (Spam Firewall) for Received: from asusus-4b96 ([58.88.21.177]) by barmail.cs.umass.edu for Received: from [58.88.21.177] by inbnd55.exchangeddd.com; Sat, 8 Nov 2008 01:27:07 +0700 From: \To: Subject: How to secure your savings MTA stands for Mail Transfer Agents. A mail is forwarded by a source to a MTA and then it follows a sequence of MTAs to reach the receiver’s mail reader. We see that this spam email follows a chain of MTAs. An honest MTA should report where it receives the message. Notice that in this email, “asusus-4b96 ([58.88.21.177])” does not report where it receives the email. As we assume that the only the originator is dishonest, so “asusus-4b96 ([58.88.21.177])” must be the originator. MTA代表邮件传输代理。邮件转发由源到MTA然后遵循一系列放在到达接收方的邮件阅读器。我们看到这个垃圾邮件之前放在链。一个诚实的MTA应该报告接收消息。注意,在这封邮件中,“asusus-4b96([58.88.21.177])“不报告接收电子邮件。当我们假定唯一的发起人是不诚实的,所以“asusus-4b96([58.88.21.177])”必须发起人。 6. Answer the following question, using the WHOIS Tools (such as, SmartWhois, WhereIsIP ,CountryWhois, http://whois.cndns.com/) and nslookup. a. What is a whois database? b. Use various whois databases on the Internet to obtain the names of two DNS servers. Indicate which whois databases you used. (such as, www.mit.edu, www.zaobao.com, www.yahoo.com, www.bupt.edu.cn) c. Use nslookup on your local host to send DNS queries to three DNS servers: your local DNS server and the two DNS servers you found in part (b). Try querying for Type A, NS, and MX reports. Summarize your findings. d. Use nslookup to find a Web server that has multiple IP addresses. Does the Web server of BUPT have multiple IP addresses? e. Use the ARIN whois database to determine the IP address range used by your institution (such as,. www.mit.edu, www.google.com, www.bupt.edu.cn). 回答下列问题,使用WHOIS工具(如SmartWhois WhereIsIP,CountryWhois,http://whois.cndns.com/)和网路资讯查询。 4