A massive DDoS (distributed denial-of-service) attack against a popular cloud-based DNS provider Dyn.COM took down major websites. The DYN.COM confirmed it on twitter:

Dyn

✔@Dyn

We are aware of the ongoing service interruption of our Managed DNS network. For more information visit our status page.

 

Following sites are having issues due to DNS problems:

  1. Twitter
  2. SoundCloud
  3. Spotify
  4. Netflix
  5. Reddit
  6. Disqus
  7. PayPal
  8. Basecamp
  9. Business Insider
  10. CNN
  11. Esty
  12. Github
  13. Guardian.co.uk
  14. Imgur
  15. HBO Now
  16. Pinterest
  17. Recode
  18. The Verge
  19. Wired and more

You can verify NS with the following standard Unix command:
$ host -t ns twitter.com

twitter.com name server ns2.p34.dynect.net.
twitter.com name server ns1.p34.dynect.net.
twitter.com name server ns4.p34.dynect.net.
twitter.com name server ns3.p34.dynect.net.

From the official announcement:

This attack is mainly impacting US East and is impacting Managed DNS customers in this region. Our Engineers are continuing to work on mitigating this issue. Services have been restored to normal as of 13:20 UTC on 21/Oct/2016. But, I’m still seeing problems.

This DDoS attack may also be impacting Dyn Managed DNS advanced services with possible delays in monitoring. Our Engineers are continuing to work on mitigating this issue. — Oct 21, 2016 – 16:48 UTC

See the “DDoS Attack Against Dyn Managed DNS” update page for up to date information.