Troubleshooting DNS resolution issues

Question:

It seems that the Appliance is not capable of reaching another server. How can I verify that the DNS requests are properly working?

Answer:

An Appliance is relying on the DNS infrastructure for many aspects of the Nexthink Solution. Here is a non-exhaustive list of some of them:

Access to Active Directory servers
Access to the Nexthink Library
Access to the Nexthink Central License Manager (CLM)
Access to the Nexthink Update Repository
Access to other Nexthink Servers

As the underlying system powering the Nexthink Server Components is Linux, you have at your disposal several tools. Here are some ideas on how to troubleshoot issues with DNS queries.

Using "nslookup" command

nslookup is the basic command to quickly get the IP address associated with any fully qualified domain name.

Command:

CODE

nslookup

Here is a sample output:

CODE

Server:         10.10.10.10  
Address:      10.10.10.10#53  
Non-authoritative answer:  
Name:     Address: 176.31.63.214

10.10.10.10 is the DNS server that answered my request. Below this information you get the “A Record” (IP Address) of the server behind “library.nexthink.com”.

Using "dig" command

dig has the same purpose as the preceding command but provides a richer output.

Command:

CODE

dig

Sample output:

CODE

; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.23.rc1.el6_5.1 <<>>   
;; global options: +cmd  
;; Got answer:  
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14611  
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 9, ADDITIONAL: 11  
;; QUESTION SECTION:  ;application-library.nexthink.com. IN   A  
;; ANSWER SECTION:  application-library.nexthink.com. 9923 IN A     87.98.150.251  
;; AUTHORITY SECTION:
.           69      IN      NS      ns2142.dns.dyn.com.  
.           69      IN      NS      a.ns.zerigo.net.  
.           69      IN      NS      d.ns.zerigo.net.  
.           69      IN      NS      f.ns.zerigo.net.  
.           69      IN      NS      e.ns.zerigo.net.  
.           69      IN      NS      b.ns.zerigo.net.  
.           69      IN      NS      ns3146.dns.dyn.com.  
.           69      IN      NS      ns1195.dns.dyn.com.  
.           69      IN      NS      ns4145.dns.dyn.com.  
;; ADDITIONAL SECTION:  
.        12035   IN      A       64.27.57.11  
.        12035   IN      AAAA    2607:fc88:1001:1::4  
.        18933   IN      A       174.36.24.250  
.        18933   IN      AAAA    2607:f0d0:1004:82::4  
.        5843    IN      A       72.20.45.70  
.        5843    IN      AAAA    2607:fc88:1001:1::4  
.        5300    IN      A       119.81.89.172  
.        5300    IN      AAAA    2607:f0d0:3001:90::4  
.        34663   IN      A       208.76.58.195  
.        34663   IN      A       208.76.59.142  
.        118980  IN      A       208.76.61.145  
;; Query time: 1 msec  
;; SERVER: 10.10.10.10#53(10.10.10.10)  
;; WHEN: Tue Apr 29 09:38:03 2014  
;; MSG SIZE  rcvd: 475

The first section starting with “; <<>>” displays a bunch of information like the version number, the global options and other parameters used by dig.

The second section labelled QUESTION displays what was asked to the DNS.

The third section labelled ANSWER is the information the Appliance received from the DNS query.

The fourth section labelled AUTHORITY displays the available name servers for the nexthink.com domain.

The fifth section labelled ADDITIONAL lists the IP addresses of the name servers listed in the preceding section.

The very last section displays stats regarding the query. An important one to look at is the time the query took.