Every service provider has their own DNS server, most of the time the browsing is fast and there are no problems, but sometimes just due to the DNS server settings the browsing can become slow. Most users do not know about DNS settings and do not think that changing the settings can help the websites load faster.
Apart from the DNS server settings provided by the service provider, many people who Google DNS settings which are:
Preferred DNS server 8.8.8.8
Alternate DNS server 8.8.4.4
After changing your DNS settings to the above Google ones you will see a considerable difference in the time it takes for a webpage to load, although the settings dont actually affect the broadband speed.