I want to wake up and see the devices connected on my local network, using NMAP.
So I execute this command :
sudo nmap -sn -PU -PE 10.11.204.1/24
(extract from the man page :
- sn: Ping Scan - disable port scan
- PS/PA/PU/PY[portlist]: TCP SYN/ACK, UDP or SCTP discovery to given ports
- PE/PP/PM: ICMP echo, timestamp, and netmask request discovery probes)
So, NMAP finds perfectly devices. But lets say device A is found, if I disconnect A from the network (airplane mode), and execute the exact same NMAP command : NMAP will continue to find A. If I keep executing the command, A will be found as online ("Host is up (0.0047s latency).") during some time, and after 2/3 minutes it will not be found anymore by NMAP. And what is really strange is that I have information about latency overtime even when I have manually disconnected A.
It appears that there is somewhere a timeout, maybe the arp-timeout ? And one thing I dont understand, even if there is a timeout why does NMAP gives me a latency when A is physically disconnected ?