It's just a quick tips rather than an article, anyway, and you won't need to touch it unless there is DNS nameserver change or newly setup.

Basically, what DNS lookup does is when an application brower or any network connection go over network, it makes a request which requires a DNS lookup, such programs send a resolution request to the local DNS resolver in the local operating system, which in turn handles the communications required.

On Linux, it is configured in /etc/resolv.conf file.

# cat /etc/resolv.conf

search fibrevillage.com fibrevillage.com. ## fibrevillage.com. means any subdomains if you have
nameserver 4.3.2.1
nameserver 4.3.2.2
nameserver 4.3.2.3


Use your own nameserver ips in your working environment of course.

Here are mostly used 3 options:

nameserver Name server IP address
domain Local domain name
search Search list for host-name lookup

Other two are less used:

       sortlist
              This option allows addresses returned by gethostbyname(3) to
              be sorted.  A sortlist is specified by IP-address-netmask
              pairs.  The netmask is optional and defaults to the natural
              netmask of the net.  The IP address and optional network pairs
              are separated by slashes.  Up to 10 pairs may be specified.
              Here is an example:

                  sortlist 130.155.160.0/255.255.240.0 130.155.0.0

       options
              Options allows certain internal resolver variables to be
              modified

Internal resolver variables of options

 The syntax is

                     options option ...

Timeout

options timeout:1
‘timeout’ sets the amount of time the resolver will wait for a response from a remote name server before retrying the query via a different name server. In secs, default is 5.

Attempts

 attempts:n
  sets the number of times the resolver will send a query to its name servers before giving up and returning an error to the calling application.

Rotate

options rotate
‘rotate’ sets RES_ROTATE in _res.options, which causes round robin selection of nameservers from among those listed.

Note: If your name servers are not identificatly same, for example, nameserver #1 is for one subdomain, while server #2 is for the other subdomain, then rotate may not be the ideal option to play with

 

Check out more options in http://man7.org/linux/man-pages/man5/resolver.5.html

 

 

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