gw/nibuf_max is a SAP Parameter attribute which is used to control number of entries in network hostname buffer 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 .
Number of entries in the host name buffer. If the parameter value is not
set, the default value of the network layer is used (100).
Host names and service names are saved in this buffer since it can
otherwise take considerable time to retrieve the names.
The buffer contents can be displayed in the gateway monitor.
If the number of entries is changed, the current entries are deleted.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.