rdisp/sna_gateway is a SAP Parameter attribute which is used to control SNA gateway host 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 .
Name of the host on which a gateway with SNA support is running. The
name of the host must be known in the host database.
UNIX
Must be entered in the /etc/hosts file or on the domain name server.
NT
Must be entered in the file C:\WINNT\SYSTEM32\DRIVERS\ETC\HOSTS or on
the domain name server.
See SAP Parameter Documentation for full SAP documentation for this profile parameter.