To increase the capture buffer size, open Network Monitor. On the Capture menu, click on Buffer Settings. Enter a value in ther Buffer Size (in MB) box and click OK. If you enter a number that is larger than available memory, you receive:
The buffer size you have requested may cause frames to be dropped due to swapping. Are you sure you want to allocate a buffer of this size?
Decrease the size of the capture buffer.
If you still have problems capturing data, and your buffer is at max, try decreasing the frame size.