50%(4)2 out of 4 people found this document helpful
This preview shows page 3 - 5 out of 5 pages.
and google-public-dns-a.google.com. In this example, the DNS server google-public-dns-a.google.com provides the IP address of the host which is a web server for Drexel. Now that we have gone through a few illustrative examples, you are perhaps wondering about the general syntax of nslookup commands. The syntax is: nslookup –option1 –option2 host-to-find dns-serverIn general, nslookup can be run with zero, one, two or more options. And as we have seen in the above examples, the dns-server is optional as well; if it is not supplied, the query is sent to the default local DNS server.Now that we have provided an overview of nslookup, it is time for you to test drive it yourself. Do the following (and write down the results):For more information about google’s public dns server use this /url:1.(10 points) Run nslookup to obtain the IP address of a Web server in Asia, such as pku.edu.cn.2.(10 points) Run nslookup to determine the authoritative DNS servers for a university in Europe, such as ox.ac.uk.3.(10 points) Run nslookup using the google-public-dns-a.google.com server and query for the mail servers for Yahoo! Mail (yahoo.com). Use the option –type=MXto get the mail server information.If your query times out, just perform an nslookup mail.yahoo.com to get the ip address ofyahoo email.2. ipconfigipconfig (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 want to see all this information about your host, simply enter:ipconfig /allinto the Command Prompt, as shown in the following screenshot.ipconfig is also very useful for managing the DNS information stored in your host. In Section 2.5we learned that a host can cache DNS records it recently obtained. To see these cached records, after the prompt C:\> provide the following command: ipconfig /displaydns3
Each entry shows the remaining Time to Live (TTL) in seconds. To clear the cache, enteripconfig /flushdns Flushing the DNS cache clears all entries and reloads the entries from the hosts file.