Title: Queries
Course: CIS 208: Linux/UNIX III: Intermediate System Administration, Networking, and Security ~ For IGNITE Review > Section: Learning Modules

Queries

The DNS structure was planned to provide quick and reliable resolution of queries.  This requires management "from the top" as provided by the root servers, and it requires a distributed database which is managed by the owners of each domain.  In addition, there are caching servers which can speed up resolution but can also add a layer of complexity.

There are three steps that are needed to ensure proper resolution of a domain.

1. The first step is to verify that each authoritative server is responding and using the correct serial number.  The "host" command provides a convenient way to test a server and get its serial number.  Run "host -t soa domain.tld 1.2.3.4" replacing the domain.tld with the actual domain name and the 1.2.3.4 with the first server.  The serial number is the first number, and it should match for every server.  For example:

[carl@hal ~]# host -t soa wccnet.edu 198.111.176.4
wccnet.edu has SoA record dns.wccnet.edu dns-admin.wccnet.edu 2014100901
86400 3600 604800 604800

1. The second step is to verify that the domain is healthy if the domain is accessible from the Internet.  The IntoDNS website provides a thorough report.

http://www.intodns.com/wccnet.edu

1. The third step is to check from the client side.  Windows computers will cache records, whether good or outdated, for 24 hours.  Run "ipconfig /flushdns" and then "nslookup wccnet.edu".  If this doesn't fix the problem, run "ipconfig /all" and note the nameservers.  These nameservers will likely be forwarding or caching servers managed by the organization or its ISP.  Request assistance from the support team to further troubleshoot the forwarding or caching servers.