ms/max_vhost is a SAP Parameter attribute which is used to control maximum number of virtual hosts information. This is available within R/3 SAP systems depending on the version and release level.
Below is the standard documentation available and a few details of the attributes values .
Maximum number of virtual hosts that the message server can open.
Each HTTP or HTTPS port can be assigned a virtual host (addition
VHOSTIDX for ms/server_port_<(><<)>xx<(>><)>).
As soon as an HTTP request is directed to the message server through
a port of this type, only application servers that have also opened
a virtual host with this index are taken into account for the load
distribution.
A dynamic change for this parameter only takes effect on application
servers that log onto the message server after the change.
The number of HTTP, HTTPS, and virtual hosts must not exceed the
total number of ports (
See SAP Parameter Documentation for full SAP documentation for this profile parameter.