Yum update is not working showing "gaierror: [Errno -3] Temporary failure in name resolution"

I am trying to upgrade my RHEL server (V6.4).
But getting this error as follow,

gaierror: [Errno -3] Temporary failure in name resolution
2018-03-20 09:55:19,064 [ERROR] @virt-who.py:173 - Unable to recover, retry in 60 seconds.
2018-03-20 09:56:52,129 [ERROR] @virt-who.py:212 - Error in communication with subscription manager, trying to recover:

Seems like DNS Issue, but not able to fix this.