scan hung?

[aessem]

during scan if I add a subnet there are plenty of messages like:

 

10.xx.xx.251 was not added - it is already contained in 10.xx.xx.0/23

 

i am not sure how it works, but often this process is never finish and stuck in one of ip (the subnet consist of 512 ip range)

any thought how can we effectively use scan to prevent hanging/stuck?

 

thanks