The thewall tunable

The thewall network tunable option sets the upper limit for network kernel buffers.

The system automatically sets the value of the thewall tunable to the maximum value and in general, you should not change the value. You could decrease it, which would reduce the amount of memory the system uses for network buffers, but it might affect network performance. Since the system only uses the necessary number of buffers at any given time, if the network subsystem is not being heavily used, the total number of buffers should be much lower than the thewall value.

The unit of thewall tunable is in 1 KB, so 1048576 bytes indicates 1024 MB or 1 GB of RAM.