I didn't get what ports does Nmap scan. Does Nmap start from zero or one when scan subnet or all the ports?
- 0/24 is it 0-255 or is it 1-255
- -p is it 0-65535 or is it 1-65535
Ask Ubuntu is a question and answer site for Ubuntu users and developers. It only takes a minute to sign up.
Sign up to join this communityI didn't get what ports does Nmap scan. Does Nmap start from zero or one when scan subnet or all the ports?
Connecting to port 0 is not possible, see
https://unix.stackexchange.com/a/180500/85039
It is a special port allowing programs to obtain random port for outgoing connection, and should not be used for incoming connections
Therefore, use -p 1-65535
for nmap
, especially if you are using TCP or UDP scans
As for /24
notation that is entirely different thing: it is called CIDR notation and used to match range of hosts on network. For instance, 192.168.0.0/24 will specify all addresses between 192.168.0.0 to 192.168.0.255
-p 0-65535
. But trying to scan port 0 is pointless - it's never open to outside world, only to programs on the host itself.
– Sergiy Kolodyazhnyy
Jan 3 '20 at 6:48
/24
, yes, address range starts at 0 and goes to 255. That's 256 hosts in total theoretically. But remember that in practice 192.168.0.255 is broadcast address for the whole 192.168.0.0/24 network. Typically it's not used for a host and ping
utility for example will throw an error, but it is perfectly valid address. On a different subnet other than /24
, it could be a perfectly valid host. See also stackoverflow.com/a/14915309/3701431 and unix.stackexchange.com/a/407395/85039
– Sergiy Kolodyazhnyy
Jan 3 '20 at 6:48
Nmap can scan all TCP UDP ports. You must to know subnetting and network knowledge. 0 port is not a standart port. For subnet if you use 24 subnetmask you will not scan 192.168.0.0 address because 24 subnetmask have a useable range for hosts. 0.0 is out of subnet useable scope. You can learn from here: http://www.steves-internet-guide.com/subnetting-subnet-masks-explained/