Below are the IPv6 addresses for the PDNS1-6 name servers:
pdns1.ultradns.net. = 2001:502:f3ff::1
pdns2.ultradns.net. = 2610:a1:1014::1
pdns3.ultradns.org. = 2610:a1:1015::1
pdns4.ultradns.org. = 2001:502:4612::1
pdns5.ultradns.info. = 2610:a1:1016::1
pdns6.ultradns.co.uk. = 2610:a1:1017::1