The Domain Name System (DNS) maps hosts within domains to IP addresses, and vice-versa. the owner of a domain name or IP block designates certain servers (often third-party) as authoritative for a domain (zone). The authoritative servers host a zone file containing host names and their corresponding IP addresses. The rest of the internet is able to see which servers are authoritative, and by querying an authoritative server learns which IP address that name translates to. Similarly, the owner of a block of IP addresses can also designate an authoritative server whose zone file will translate an address to a host name. A network or ISP is likely to contain a local DNS server which caches this information, saving users the latency of querying an authoritative server again and again for information which is unlikely to change often. Various networks purge these local caches at different intervals, but in a day or three most of the internet is likely to be able to receive an updated name-address translation for their users.