Thanks for the response - no particular issue, just trying to get my head round how it all works.
I have a typically cheap and nasty ISP supplied router, so was having trouble accepting that it could be intelligent enough to act as a DNS server.
The product specs that I could find said absolutely nothing about DNS cache - only where I could enter the address of the DNS servers (Google etc.).
Then when I happened to run Speccy on my pc, the network detail page listed my router's address as the preferred DNS server.
So I was confused.
Edited by HTTP404 (Tue 10-Feb-15 11:20:52)