networking - Network disconnect with netgear router

I buy a netgear R6250 for my home.

I have more than 10 devices connected by wifi, so it seem be good to this.

But, I have a problem with it:

I lost internet connection some times. I need to disconnect the wifi on my mac and reconnect to retrieve it. When I do a traceroute, I get a "could not resolve google.com hostname" like if the router have a poor dns.

The dns server configured now is the modem's dns used to provide internet.

What can be wrong in the router config which be cause this problem ?

Thanks.