What alternate DNS servers can I use ?
Since many connectivity issues are eventually traced to DNS problems, you can add to, or even replace your ISP's nameservers with other free public ones. Your ISP automatically assigns their default DNS servers when your computer, or router connects to the internet. The problem is, their DNS servers can sometimes be congested, and cause connectivity issues, catching problems, or delays in name resolution.
Below is a list of the better free public DNS servers you can use instead of the ones assigned by your ISP. Just configure your network adapter (or your router) to use the following IPs as your DNS servers:
Alternatives include 18.104.22.168, 22.214.171.124, 126.96.36.199, 188.8.131.52, 184.108.40.206, 220.127.116.11.
IPv6: 2001:4860:4860::8888 and 2001:4860:4860::8844
OpenDNS (25 datacenters worldwide)
IPv6: 2001:67c:28a4:: and 2a01:3a0:53:53::
dnsadvantage (Neustar cloud-delivered DNS)
IPv6: 2620:74:1b::1:1 and 2620:74:1c::2:2
Comodo Secure DNS
Some of the free DNS services above may filter DNS results to keep you "safe" from malicious sites, phishing, even scam/adult content and may use aggregate data collected from you (Google, OpenDNS, Norton ConnectSafe) while others will not alter content and most likely not log your queries (Level3, Comodo, Verisign, UncensoredDNS).
There are other alternatives to the US government DNS root zone, which cover some new TLD listings that many nameservers don't yet include. Check here for more information: Alternative DNS root.
It is a good idea to choose a DNS server that is geographically close to you, or ones with global presence.
You can choose to replace both, only one, or add to your ISP's DNS servers. Under Windows, the "Advanced -> DNS" tab allows to specify more than two DNS servers, and the order of DNS servers used for resolution.