Recently, I have seen this a lot in windows environments; my follow windows admins try to solution DNS issues by putting their domain controllers in the environment in the forwarders tab.
The forwarders tab is for non-authoritative requests or queries for external addresses. Now in truth, I am simplifying this article. This really about a very basic domain or domains.
The are many types of forwarders, this config is just external DNS look-up. When end-users generally talk about the internet being slow, it is usually base the DNS servers by the ISP is slow and overload with a request.
This is the config I use for my dc’s forwarders in AD has saved a lot of headaches and complains about slow internet.
I hope it is helpful.
Forwarders should only really be used for external DNS lookup and if the root server is an unavailable and/or non-authoritative request.