you can utilize this feature to add systems on your network that you dont want
$ nmap 192.168.1.0/24 --exclude 192.168.1.1-100
Starting Nmap 6.47 ( http://nmap.org ) at 2015-01-13 19:57 CST
[...]
Nmap done: 156 IP addresses (5 hosts up) scanned in 48.79 seconds
Excluding a range of IP addresses from a scan
In the example above, 256 addresses are specified using CIDR and a range of 100 addresses are excluded, which results in 156 addresses being scanned.
Exclude Targets Using a List
The --excludefile option is related to the --exclude option and can be used to provide a list of targets to exclude from a network scan.
$ cat list.txt
192.168.1.1
192.168.1.5
192.168.1.100
Text file with hosts to exclude from a scan
The example below demonstrates using the --excludefile argument to exclude the hosts in the list.txt file displayed above.
Usage syntax: nmap [targets] --excludefile [list.txt]
$ nmap 192.168.1.0/24 --excludefile list.txt
Starting Nmap 6.47 ( http://nmap.org ) at 2015-01-13 20:01 CST
Nmap scan report for 192.168.1.101
Host is up (0.0098s latency).
Not shown: 995 closed ports
PORT STATE SERVICE
3689/tcp open rendezvous
5000/tcp open upnp
7000/tcp open afs3-fileserver
7100/tcp open font-service
62078/tcp open iphone-sync
[...]
Nmap done: 253 IP addresses (5 hosts up) scanned in 81.09 seconds
Excluding a list of hosts from a network scan
In the above example, the targets in the list.txt file are excluded from the scan. You can utilize this feature to add systems on your network that you dont want to disturb while open?id=1Hu6wPIDsAedCaAAEAAOsgFAXB6IKNCWeL3n9zfhw0_w">performing an audit.