is/hostbuffer_timeout_valid_entry is a SAP Parameter attribute which is used to control Set NI hostname buffer timeout for valid entries (internal DNS cache) 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 .
A function of the SAP Network Interface (NI) is the host name buffer,
which acts as a cache for the mapping between host names and IP
addresses.
This includes forward lookups (host name to IP) and reverse lookups (IP
to host name). Both valid entries, that is, previously successful
queries to the operating system, and invalid entries, if queried again,
are answered from this buffer.
You can use the parameter is/hostbuffer_timeout_valid_entry to define
the period of time (in seconds) after which valid entries (positive
cache) are deleted from the cache.
The value 0 deactivates the cache (positive and negative caches).
See SAP Parameter Documentation for full SAP documentation for this profile parameter.