Dns_resolver_rootroot_servers are the root servers.
a_records is a list of names and bindings (A records) for the root servers.
aaaa_records is a list of names and bindings (AAAA records) for the root servers.
ips ip_proto is a list of ip addresses of the root servers.
val reserved_zones : Dns.Rr_map.t Domain_name.Map.treserved_zones is a domain-name map of reserved zones specified by RFCs (6303, 6761, 6762). The values are stub SOA records.
val reserved : Dns_trie.treserved is a trie with all reserved_zones.