asuswrt is seeing the cable modem MAC address - in your case 00:01:5C:xx:xx:xx. It is getting the mac from the “ip neigh” command. Try running “ip neigh” on the router and see if your external (public) ip of your router (handed out by your ISP to the ASUS) is shown with the MAC address of the cable modem. This is the case with my setup.
The device tracker can detect if the cable modem is dsconnected from your router - ie - loss of the internet. So, it is a good thing.
The new release 0.82.0 with asyncssh includes some (overly) verbose logging at the INFO level showing the commands the asuswrt component is running on your router (assuming you are using ssh access to your asus - you should be).
See below. the lines with Command: show the command being executed on the router. Sorry for the double timestamp - this is from the syslog output.
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=124] Requesting new SSH session
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=124] Command: for dev in `nvram get wl_ifnames`; do wl -i $dev assoclist; done
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=124] Received exit status 0
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=124] Received channel close
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=124] Channel closed
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=125] Requesting new SSH session
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=125] Command: arp -n
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=125] Received exit status 0
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=125] Received channel close
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=125] Channel closed
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=126] Requesting new SSH session
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=126] Command: ip neigh
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=126] Received exit status 0
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=126] Received channel close
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=126] Channel closed
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=127] Requesting new SSH session
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=127] Command: cat /var/lib/misc/dnsmasq.leases
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=127] Received exit status 0
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=127] Received channel close
Nov 11 08:28:33 mondo hass[9150]: 2018-11-11 08:28:33 INFO (MainThread) [asyncssh] [conn=0, chan=127] Channel closed