512 to 1,073,741,824
The value should be a power of 2.
No. The parameter can only be changed at boot time.
If you set the parameter to a value that is not a power of 2, it is rounded up to the nearest power of 2.
If the system consistently has tens of thousands of TCP connections, increase the value accordingly. With the default value, TCP performs well up to a few thousand active connections. Note that increasing the hash table size means more memory consumption so set an appropriate value to avoid wasting memory unnecessarily.