ultradns.biz has been down as well.

Animats · on Oct 21, 2016

"ultradns.biz" is not responding to pings, but their DNS servers are responding to DNS queries properly:

    nslookup
    > server pdns196.ultradns.biz
    Default server: pdns196.ultradns.biz
    Address: 156.154.66.196#53
    Default server: pdns196.ultradns.biz
    Address: 2610:a1:1015::e8#53
    > pornhub.com
    Server:		pdns196.ultradns.biz
    Address:	156.154.66.196#53
    Name:	pornhub.com
    Address: 31.192.120.36

Right now, if your site is in trouble, I'd suggest getting UltraDNS service and AWS DNS service, and some obscure service as well, and put them them all in your domain registration. DNS service is cheap. Get some redundancy going. We have no idea how long this DDOS attack will last. It's not costing the attackers anything. They might leave it running for days.