One of our clients has changed their ISP and also upgraded their broadband to ADSL 2+. The new ISP supplied a new router, which they maintain remotely. Since the change (and upgrade) broadband speeds have been slower than they were but the ISP said that everything looked normal so far as they could see.
Today, we went in and connected a laptop directly to the router. As the router is not acting as a DHCP server, we manually added the ip, sm, dg and dns addresses. For DNS, we used the Google free DNS of 220.127.116.11 and the broadband speed measured on the laptop was much faster. We then changed dns on the DHCP server to the ISP’s own dns servers and tested the workstations and they were all much faster. It probably isn’t a good idea to leave the ISP’s DNS server addresses in DHCP as our client could have a problem should these ever go down, so we would like to put DHCP back to how it was – pointing to the internal DHCP server.
The question is this: would changing ISP have an effect on the internal DNS Server? If so, what should we have done to prevent this from happening?