Network discovery really not accurate (asuswrt, nmap)


I have a hard time trying to get an accurate status of my network.

My situation:

  • I have a main Asus router (with Merlin firmware).
  • I have an Asus repeater (on the other side of my house) configured in Express way mode.
  • devices can use the repeater, the router or switch between the two.

Asuswrt device tracker component is working mostly fine for the router: all devices are detected but devices actually connected on the repeater are reported not_home (offline).
If I add another asuswrt component for the repeater, I get mixed results but mostly wrong.
I tried NMAP but found a big limitation as it won’t report most devices if not run as sudo:

(homeassistant) homeassistant@raspberrypi:/home/pi $ arp -n
Address                  HWtype  HWaddress           Flags Mask            Iface             ether   30:5a:3a:5c:88:34   C                     eth0
(homeassistant) homeassistant@raspberrypi:/home/pi $ ping -c 1
PING ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=64 time=2.52 ms

--- ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 2.526/2.526/2.526/0.000 ms
(homeassistant) homeassistant@raspberrypi:/home/pi $ nmap -sn
Starting Nmap 7.40 ( ) at 2018-06-27 10:58 EDT
Stats: 0:00:01 elapsed; 0 hosts completed (0 up), 1 undergoing Ping Scan
Ping Scan Timing: About 50.00% done; ETC: 10:58 (0:00:01 remaining)
Note: Host seems down. If it is really up, but blocking our ping probes, try -Pn
Nmap done: 1 IP address (0 hosts up) scanned in 3.02 seconds
(homeassistant) homeassistant@raspberrypi:/home/pi $ exit
pi@raspberrypi:~ $ sudo nmap -sn
Starting Nmap 7.40 ( ) at 2018-06-27 10:57 EDT
Nmap scan report for TPLink1 (
Host is up (0.0073s latency).
MAC Address: 30:5A:3A:5C:88:34 (Asustek Computer)
Nmap done: 1 IP address (1 host up) scanned in 0.46 seconds

So homeassistant can ping the host (a tplink switch) but nmap will only report it up with sudo.

As anyone got the same kind of problem?