xuk.ru is a domain controlled by two nameservers at
xuk.ru themselves. They are on different IP networks. Incoming mail for
xuk.ru is handled by one mailserver also at
xuk.ru.
xuk.ru has one IP record.
mx.xuk.ru,
ns3.xuk.ru,
www.xuk.ru,
ns1.xuk.ru,
ns2.xuk.ru and at least one other host are subdomains to this hostname.
ru is a domain controlled by six nameservers. All of them are on different IP networks.