Roli
The DNS settings on the DNS-323 are there so that the device can use DNS - domain name services - to locate any other device that is required, for example an ntp (network time protocol) server - if there is no DNS server at the ip address you specify, you might as well leave it blank.
Just in case you hadn't noticed - the details that you provide for your network don't match the scenario that Rodent listed - specifically your DNS settings point to a public DNS server, probably that of your ISP - whilst his point to his router - which as I have said already is perfectly normal