A host-based mechanism is a general purpose mechanism. It allows you to give access to a particular host, in which all users on that host can connect to the server. This is a weaker form of access control: if that host has access to the server, all users on that host are allowed to connect to the server.
The Solaris environment provides the host-based mechanism for backward compatibility. Applications linked with versions of Xlib or libcps older than OpenWindows Version 2 software or X11R4 do not recognize the new user-based access control mechanism. To enable these applications to connect to the server, a user must either switch to the host-based mechanism, or relink with the newer versions of Xlib and libcps.
If possible, clients linked with older versions of Xlib or libcps should be relinked with newer versions of these libraries to enable them to connect to the server with the new user-based access control mechanism.