try the following commands on a UNIX/linux system (such as npu1.npu.edu), or a w
ID: 3757886 • Letter: T
Question
try the following commands on a UNIX/linux system (such as npu1.npu.edu), or a web-based dig utility with a UNIQ domain name which has probably NOT been used by your classmates; and explain briefly what the outputs mean:
a). dig +short +norecurse NS domain-name
b). dig +short +recurse NS domain-name
c). dig +short +norecurse NS domain-name
### for example, here is my sample output for linkedin.com (including commands)
howard% dig +norecurse +short NS linkedin.com
howard% dig +recurse +short NS linkedin.com
pdns1.ultradns.net. pdns2.ultradns.net. pdns3.ultradns.org.
pdns4.ultradns.org. pdns5.ultradns.info. pdns6.ultradns.co.uk.
howard% dig +norecurse +short linkedin.com
pdns1.ultradns.net. pdns2.ultradns.net. pdns3.ultradns.org.
pdns4.ultradns.org. pdns5.ultradns.info. pdns6.ultradns.co.uk.
### IN OTHER WORDS, my first query got nothing with "+norecurse" option; 2nd query returns an answer, repeated the 1st query, gets the same answer as the 2nd query. WHAT HAPPENED? TRY similar "+norecurse", "+recurse" and "+norecurse" command sequence for a DIFFERENT domain-name, WITHOUT the "+short" option and explain WHY;
Explanation / Answer
The first, and the third will give the same output. Please check..as there is no logical diffrence between the two. They will both give an empty result.
dev@static:~$ dig +norecurse +short linkedin.com
dev@static:~$ dig +norecurse +short NS linkedin.com
dev@static:~$
The dig command,queries the DNS nameservers for information about host addresses, mail exchnages and much more. The result for solely the dig command is vast. In order to view just the ip-addresses of a web-site, we use the +short option. For e.g.
dev@static:~$ dig linkedin.com +short
108.174.2.129
We can also specify any record type that we are looking for, like this.-
dev@static:~$ dig linkedin.com ns +short
ns3.linkedin.com.
ns4.linkedin.com.
ns3.p43.dynect.net.
ns4.p43.dynect.net.
ns1.p43.dynect.net.
ns2.p43.dynect.net.
ns1.linkedin.com.
ns2.linkedin.com.
The recurse option enables dig command to send recursive queries, this is automatically enabled. To switch it off, we use norecurse option.
Now with 1) and 3) query, we are getting empty output, because we have disabled recursion, hence no repetitive queries, and since we are using short, the output is automatically shortened, and thus empty.
For 2) since the recursion option is ON, we are getting specific (NS) type we want, with use of short. Hence the shown output. :)
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