Normally DNS is on port 53, but if your ISP is preventing you from DNS requests to servers other than theirs on port 53 you can use the other one. 'DNSSEC' mea

Normally DNS is on port 53, but if your ISP is preventing you from DNS requests to servers other than theirs on port 53 you can use the other one. 'DNSSEC' means DNSSEC is supported by the server if your resolver can use it - it's a digital signature regime to prevent DNS forgery (disclaimer: look up criticisms of it as well as selling points).