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1、DNS实验报告一、 实验内容1、 利用nslookup工具允许主机向指定的DNS服务器查询某个DNS记录;2、 熟悉ipconfig命令,用它来查看TCP/IP信地址、DNS服务器的地址、适配器的类型等信息3、 熟悉并掌握Ethereal的基本操作利用ethereal分析DNS二、 实验条件联网的pc;装有操作系统Win7;Ethereal等软件。三、 实验步骤及分析 Nslookup进行DNS查询1) Run nslookup to obtain the IP address of a Web server in Asia.分析:首先出现的是默认名字服务器及其IP地址,即本地DNS服务器,该
2、处在查看过程中,出现非权威应答的情况,出现此提示表明该域名的解析是从本地的缓存中直接读出来的。在返回的信息里前两项是cname(别名)记录,有两个IP地址,说明该别名DNS 服务器架立了基于俩个不同 IP 虚拟主机。最后是目标域名,并注明了是别名(Alias)。2) Run nslookup to determine the authoritative DNS servers for a university inEurope.分析:nslookup type命令用于查询的资源记录类型,NS声明命名区域的每台 DNS 名称服务器。在这里我是运行nslookup确定英国剑桥大学的权威DNS服务器
3、,由nslookup的应答可以知道剑桥大学有七台域名服务器,它们都是剑桥大学里主机的权威DNS服务器。最后应答还返回了其中一台权威服务器的IP地址。3) Run nslookup so that one of the DNS servers obtained in Question 2 is queried forthe mail servers for Yahoo! mail.分析:在这里,我们是想通过DNS服务器bitsy.mit.edu查询,而不是我们开始默认的本地DNS服务器。DNS服务器bitsy.mit.edu返回了雅虎邮箱的IP地址信息,由信息我们可以知道我们所查询的目标域名是别
4、名。 Ipconfig指令查看本机TCP/IP信息分析:运行了ipconfig指令后,我们得到了本机的IP地址:115.157.220.91,DNS服务器地址:202.197.96.1,以太网适配器为Broadcom NetlinkGigabit Ethernet等等。 用ethereal分析DNS(1)利用ipconfig/flushdns命令清空你的主机上的DNS缓存。启动浏览器,并将浏览器的缓存清空。(2)启动Ethereal,在显示过滤筛选说明处输入“ip.addr=your_IP_address”(如:ip.addr=10.17.7.23),过滤器将会删除所有目的地址和源地址都与指定
5、IP地址不同的分组。(3)开始Ethereal分组俘获。(4)在浏览器的地址栏中输入:http:/www.ietf.org(5)停止分组俘获。按上步骤所示,进行俘获,截图如下所示:Screenshot for DNS query:Screenshot for DNS response:(6)开始Ethereal分组俘获。(7)在www.mit.edu上进行nslookup(即执行命令:nslookup www.mit.edu)。(8)停止分组俘获。运行后截图如下:Screenshot for DNS query:Screenshot for DNS response:(9)重复上述操作,运行n
6、slookup type=NS mit.edu指令,进行分组俘获,截图如下:(10)重复上述操作,运行nslookup www.aiit.or.kr ip_address_of_bitsy.mit.edu指令,截图如下:四、 实验问题解答在这个实验中我选择Tracing DNS with Ethereal中的第一个小部分visit the Web page: http:/www.ietf.org俘获分组里的七个问题根据如下截图进行回答:Screenshot for DNS query:Screenshot for DNS response:Answer the following questi
7、ons:1. Locate the DNS query and response messages. Are then sent over UDP or TCP?答:UDP2. What is the destination port for the DNS query message? What is the source port of DNS response message?答:The destination port for the DNS query is 53 and the source port of the DNS response is 53.3. To what IP
8、address is the DNS query message sent? Use ipconfig to determine the IP address of your local DNS server. Are these two IP addresses the same?答:Its sent to 202.197.96.1 .It is the same as the IP address of my local DNS servers.4. Examine the DNS query message. What “Type” of DNS query is it? Does th
9、e query message contain any “answers”?答:Its a type A Standard Query and it doesnt contain any answers.5. Examine the DNS response message. How many “answers” are provided? What do each of these answers contain?答:There is only one answer containing information about the name of the host, the type of
10、address, class, the TTL,the data length and the IP address,like below:Answers www.ietf.org: type A, class IN, addr 12.22.58.30 Name: www.ietf.org Type: A (Host address) Class: IN (0x0001) Time to live: 30 minutes Data length: 4 Addr: 12.22.58.306. Consider the subsequent TCP SYN packet sent by your
11、host. Does the destination IP address of the SYN packet correspond to any of the IP addresses provided in the DNS response message?答: The first SYN packet was sent to 12.22.58.30 that corresponds to the first IP address provided in the DNS response message.7. This web page contains images. Before retrieving each image, does your host issue new DNS queries?答:The host doesnt issue new DNS queries.五、 实验心得学习了如何用一些指令,如nslookup,ipconfig查询相关DNS服务器的信息,同时掌握了利用ethereal分析DNS,在阅读实验文档的过程中,英语阅读能力有了进一步的提高,这实验报告也太长了,上一个DNS的实验报告就写了19页,哎,同时也培养了我做事的耐心,也终于是完成了。