is/HTTP/virt_host_0 is a SAP Parameter attribute which is used to control Definition of virtual server for HTTP 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 .
Parameters is/HTTP/virt_host_0 to is/HTTP_virt_host_9 define the mapping
of hosts and services used to address an HTTP request on a "virtual
host". In turn, the virtual host controls request handler searches (see
transaction SICF).
When maintaining these parameters, make sure that there are no "gaps".
Otherwise, subsequent parameters will be ignored. If the parameters
../virt_host_0 to ../virt_host_5 and the parameter ../virt_host_7 have
been maintained, for example, then ../virt_host_7 will be ignored.
The definition of the virtual host begins with the highest maintained
parameter, continuing downwards. If, for example, you have maintained
the parameters ../virt_host_0 to ../virt_host_5, ../virt_host_5 is
evaluated first. If this parameter applies, it is used to define the
request handler. If not, the evaluation continues with ../virt_host_4,
and so on to ../virt_host_0.
Parameter is/HTTP/virt_host_0 sets the default host (see transaction
SICF).
See SAP Parameter Documentation for full SAP documentation for this profile parameter.