The advertiser can exclude impressions that originate from specific DNS hostnames. Hostnames can be used to identify individual network operators.
Example: a typical hostname for devices connected to the internet via the Deutsche Telekom network would be: *.t-ipconnect.de. If this hostname is selected, the advertised page will no longer be displayed on the affected devices.
What is a Hostname?
Every network-capable device is reachable via a unique IP address (example: 192.168.0.254). A hostname is a label for this IP address. Instead of an arbitrary sequence of numbers, the server receives a label under which it can be reached on the internet. This makes identification easier. In short: the hostname (plural: hostnames) is the label of a device by which it is addressed in a network.
A hostname is not the name of a domain. Domain names and hostnames follow similar patterns, which is why it is very unlikely that a hostname and a domain name follow the same syntax or pattern (digits, letters, and hyphens that do not begin or end with a hyphen). A hostname is primarily used in electronic data exchange (email, server, FTP).
Since When Have Hostnames Existed?
The translation of IP addresses into alphabetical hostnames was implemented shortly after the introduction of ARPANET in the late 1960s. Even then, the need to assign meaningful names to numeric, semantically insignificant IP addresses was recognized.
In the 1970s, however, the underlying network infrastructure was still based on numeric addresses, so each website maintained a hosts.txt file that provided a mapping between hostnames and relevant network addresses in a series of simple text records that could be easily read by a person.
