for Yahoo! mail. What is its IP address? 2. ipconfig ipconfig (for Windows) and ifconfig (for Linux/Unix) are among the most useful little utilities in your host,especially for debugging network issues. Here we’ll only describe ipconfig, although the Linux/Unix ifconfig is very similar. ipconfig can be used to show your current TCP/IP information, including your address, DNS server addresses, adapter type and so on. For example, if you all this information about your host simply by enteringipconfig \all into the Command Prompt, as shown in the following screenshot
ipconfig is also very useful for managing the DNS information stored in your host. We learned that a hostcan cache DNS records it recently obtained. To see these cached records, after the prompt C:\> provide the following command:ipconfig /displaydns Each entry shows the remaining Time to Live (TTL) in seconds. To clear the cache, enter ipconfig /flushdns Flushing the DNS cache clears all entries and reloads the entries from the hosts file.
3. Tracing DNS with Wireshark Now that we are familiar with nslookup and ipconfig, we’re ready to get down to some serious business. Let’s first capture the DNS packets that are generated by ordinary Web-surfing activity.Use ipconfig to empty the DNS cache in your host. 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 Wireshark and enter “ip.addr == your_IP_address” into the filter, where you obtain your_IP_address with ipconfig. 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: Stop packet capture. Answer the following questions.Whenever possible, when answering a question below, you should takea screen grab of the packet(s) within the trace that you used to answer the question asked.4.Locate the DNS query and response messages. Are then sent over UDP or TCP? 5.What is the destination port for the DNS query message? What is the source port of DNS response message? 6.To what IP 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? 7.Examine the DNS query message. What “Type” of DNS query is it? Does the query message contain any “answers”? 8.Examine the DNS response message. How many “answers” are provided? What do each of these answers contain? 9.Consider the subsequent TCP SYN packet sent by your host. Does the destination