hostmask

A hostmask is a string used in multi-user online networks, particularly Internet Relay Chat (IRC), to identify a user on a server. It typically comprises a nickname, an ident (username), and a host (the network-visible address), in a form such as nick!ident@host. On many networks the host portion may be a hostname or an IP address, and some servers may mask or alter parts of the address for privacy or display purposes. A user’s hostmask may be shown in server notices, logs, or channel activity.

In moderation and access control, hostmasks are used by operators to recognize and manage users. A hostmask can be exact or wildcarded to match a range of users. Common ban and access-control patterns are expressed as masks, for example, nick!ident@host, *!*@host, or *!*@*. Operators apply bans, exemptions, or mode changes using these mask expressions. This allows network staff to enforce rules across a user’s connections even if the nickname changes.

Privacy and host masking practices are common on many networks. Some servers offer vhosts or cloak services that replace a user’s real host with a generic or assigned domain to reduce exposure of identities and locations. Conversely, legitimate users may reveal more of their host in non-moderated channels. The exact format and availability of hostmasks, and the level of masking, can vary between IRC networks and other systems using similar identification concepts.