This read-write integer records whether a DNS server entry in the resolver's Sbelt, or safety belt, name-server list was configured manually, static, or learned automatically via dhcp or dhcpv6. An administrator checks this to know whether a listed DNS server will persist through reboots and DHCP renewals or whether it's tied to a lease that could change. For example, seeing dhcpv6 here tells the admin that server entry came from a DHCPv6 lease and will update automatically if that lease changes.