Any attentive business or home user will quickly change their Internet Service Provider if throughput or availability is not up to scratch and yet few realise they can do exactly the same thing with the 'name servers' resolving the global Domain Name System (DNS). Doing this costs nothing and the benefits in terms of improved performance and security can be significant and yet few bother. Most users continue to take DNS for granted, unaware of the hidden bottlenecks of ISP services and potential for improvement.
Put very simply, the job of DNS name servers is to resolve public web addresses or domains to their underlying TCP/IP addresses. This sounds like a straightforward process but there are a number of variables that affect performance. The most obvious of these is simply the round trip time between the client device and the DNS server itself, which will depend on geographical proximity as well as response times from any other DNS infrastructure involved in a query.
Even meaty name servers will not cache every possible website domain and have to look that up recursively by sending a query to a remote server. This is why visits to websites in remote countries sometimes take perceptibly longer for reasons that aren't (as many assume) to do with a slow web server on the other end of the request. Another problem is that DNS name servers can become congested due to heavy use at peak times or malicious DDoS attacks causing problems behind the scenes. DNS was designed to be resilient but under stress it will still slow.
Security: DDoS attacks on DNS servers underscore the system's vulnerability - no website whose DNS servers have been overloaded will be able to conduct much business - but other security issues abound including cache poisoning (redirecting users from legitimate to fraudulent DNS servers). This was a major impetus behind the Domain Name Security Extensions (DNSSEC) security layer used to authenticate name servers for those providers supporting it.
By default, a computer will use the default DNS server of the network it is connected to, which will be provided by the service provider or ISP. The user can manually adjust that setting, either on a one-off basis or indefinitely. DNS really is a matter of preference.
Changing DNS settings: For IPv4, this can be carried out for every PC connection (separately for wired Ethernet and wireless) or for every device on a network through the network router's DNS settings panel. On Windows 10, navigate to the Control or Settings panel to the Ether or Wireless properties box and clicking on IPv4 properties. Then untick the 'obtain DNS server address automatically' and specify the correct address for the service that is going to be used. For home routers the same is achieved via the configuration interface, usually in the WAN settings under something like 'DNS settings'.
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