31 Jul ist the major disadvantages with the layered approach to protocols.
ist the major disadvantages with the layered approach to protocols.
2. Let us assume that an application generates a video stream to be sent. The video data consist of multiple period data – each datum will be delivered periodically. Which services (i.e.,
TCP or UDP) are appropriate to send the video data? Explain why.
Part 2:
In part 2, you will study the Domain Name Service (DNS) and analyze DNS traffic using
Wiresharki. Provide answers for Questions 1 through 19.
Analyzing DNS
I. nslookup
In this lab, we’ll make extensive use of the nslookuptool, which is available in most Linux/Unix and Microsoft platforms today. To run nslookupin Linux/Unix, you just type the nslookupcommand on the command line. In it is most basic operation, nslookup tool allows the host running the tool to query any specified DNS server for a DNS record. The queried DNS server can be a root DNS server, a top-level-domain DNS server, an authoritative DNS server, or an intermediate DNS server (see the textbook for definitions of these terms). To accomplish this task, nslookup sends a DNS query to the specified DNS server, receives a DNS reply from that same DNS server, and displays the result.
1. Run nslookupto obtain the IP address of a Web server in USA. Provide a screenshot.
2. Run nslookupto determine the authoritative DNS servers for a university in Europe. Provide a screen shot.
II. ipconfig(for Windows) and ifconfig(for Linux/Unix) are among the most useful little utilities in your host, especially for debugging network issues. ipconfigis also very useful for managing the DNS information stored in your host. We learned that a host can cache DNS records it recently obtained. To see these cached records, provide the following command:
ipconfig /displaydns
Each entry shows the remaining Time to Live (TTL) in seconds. To clear the cache, enter
ipconfig /flushdns
Note: Ubuntu does not include DNS caching by default.
Flushing the DNS cache clears all entries and reloads the entries from the hosts file.
Let’s first capture the DNS packets that are generated by ordinary Websurfing activity.
• Use ipconfigto empty the DNS cache in your host. (For windows users)
• Open your browser and empty your browser cache. (With Internet Explorer, go to Tools menu and select Internet Options; then in the General tab select Delete Files.)
• Open Wiresharkand enter “ip.addr == your_IP_address” into the filter, where you obtain
• your_IP_address (the IP address for the computer on which you are running Wireshark) with ipconfig (or ifconfig). This filter removes all packets that neither originate nor are destined to your host.
• Start packet capture in Wireshark.
• With your browser, visit the Web page: http://www.ietf.org
• Stop packet capture.
Answer the following questions:
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