How does a Client Verify if the DNS server is Alive or down

[Phil Mayers]

On 20/10/15 07:26, Harshith Mulky wrote:
> Hi All,
>
> How can a Client verify if the DNS Server is Running(named service is
> Running) or Down?

By the presence or absence of a reply to a query.

> Does it periodically send any messages to the server.

No. It just sends a query when it has one, and waits for a reply; if it 
doesn't get one, it tries another DNS server (if it has one)