09/09: DNS Cache

Category: Technologies
Posted by: bagheljas
DNS Cache is critical part of the whole process of mapping a site domain and/or internet service address to IP address. It is created to improve performance and reduce the DNS queries served by the ROOT Name Servers, Top Level Registrars and DNS Authoritative servers and DNS caching supported the design and it is cached at every hop involves in the process.

The minimum hops for resolving a site domain suchna.com are ROOT Name Servers, Top Level Registrars, DNS Authoritative Servers, DNS Name Resolvers and Client Machines.

The Time To Live(TTLs) settings at the DNS Authoritative Server or also referred as Master DNS Server / SOA owner for a site domain and/or internet service address recommends the client machines and DNS name resolvers for refreshing intervals for a name to IP address mapping.

The settings at the client machines sometime don’t honor the DNS TTLs recommendations made by the DNS Authoritative Servers that causes an unexpected user experience. The solution to this problem is to force the client machines to clear the local DNS cache as given below:

MS Windows:
a. Go to Start > Run
b. Type: cmd [enter]
c. At the prompt type: ipconfig /flushdns

MAC:
a. Open a terminal window
b. Type: lookupd –flushcache

LINUX / UNIX: It depends on the DNS caching software used on the client machines.

Restart NSCD
sudo /etc/init.d/nscd restart, OR
service nscd restart

Restart DNSMASQ
sudo /etc/init.d/dnsmasq restart, OR
service dnsmasq restart

Restart BIND
/etc/init.d/named restart, OR
service named restart

Don’t forget the power and use cases of /etc/hosts file on client machines that is by default overrides the external DNS name to IP address mapping.

Disclaimer

The views expressed in the blog are those of the author and do not represent necessarily the official policy or position of any other agency, organization, employer, or company. Assumptions made in the study are not reflective of the stand of any entity other than the author. Since we are critically-thinking human beings, these views are always subject to change, revision, and rethinking without notice. While reasonable efforts have been made to obtain accurate information, the author makes no warranty, expressed or implied, as to its accuracy.