The value of the object iesIfDefaultPrimaryDnsIPv6Addr
specifies the IPv6 address of the default primary
DNS server for the subscribers using this interface.
Subscribers that cannot obtain an IPv6 DNS server addres
by other means, can use this for DNS name resolution.
The object iesIfDefaultPrimaryDnsIPv6Addr can only be set
to a nonzero value if the value of iesIfType is
'subscriber'.