512 to 2,147,483,648
It should be a power of two.
No. This 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 two.
If the system consistently has tens of thousands of active TCP connections, increase the value accordingly. With the default value, the system 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.