Quick question regarding DHCP lease list

Ro berto

Regular Contributor
Hi all, just a curious question.

I have a smart bodyscale that has WiFi and connects to the router everytime I step on it to measure my weight and other parameters.

I reserved a static IP to it, but I don't see the bodyscale in the DHCP lease list under System Log, eventhough I can see that it connects and disconects in the System Log.

I thought that every device that connects to the router will appear on the DHCP lease list, am I wrong?

Or is it because it connects just for a short time that it doesn't require an ip lease??

Code:
Mar 19 08:04:21 wlceventd: wlceventd_proc_event(527): eth5: Auth 00:24:E4:D9:91:C2, status: Successful (0), rssi:0
Mar 19 08:04:21 wlceventd: wlceventd_proc_event(556): eth5: Assoc 00:24:E4:D9:91:C2, status: Successful (0), rssi:0
Mar 19 08:04:27 wlceventd: wlceventd_proc_event(508): eth5: Disassoc 00:24:E4:D9:91:C2, status: 0, reason: Disassociated because sending station is leaving (or has left) BSS (8), rssi:0

Have a nice weekend all

Ro berto
 

Martinski

Regular Contributor
Code:
Mar 19 08:04:21 wlceventd: wlceventd_proc_event(527): eth5: Auth 00:24:E4:D9:91:C2, status: Successful (0), rssi:0
Mar 19 08:04:21 wlceventd: wlceventd_proc_event(556): eth5: Assoc 00:24:E4:D9:91:C2, status: Successful (0), rssi:0
Mar 19 08:04:27 wlceventd: wlceventd_proc_event(508): eth5: Disassoc 00:24:E4:D9:91:C2, status: 0, reason: Disassociated because sending station is leaving (or has left) BSS (8), rssi:0
What's the output of the following commands typed in a terminal window (e.g. via an SSH session) connected to the router?
Bash:
cat /proc/net/arp | grep -i "00:24:E4:D9:91:C2"
cat /var/lib/misc/dnsmasq.leases | grep -i "00:24:E4:D9:91:C2"
 

Ro berto

Regular Contributor
This is the output:

Screenshot_20220319-112138_JuiceSSH.png
 

Martinski

Regular Contributor
This is the output:
...
OK, the lack of output from the 1st command indicates that there is *no* current IP address leased to the device with MAC address 00:24:E4:D9:91:C2 most likely because its lease time has already expired, and the device has not requested another IP lease since it was disconnected. So the "DHCP leases" table shown on your router's GUI is correct, at least at that particular point in time.

The result from the 2nd command shows that the ARP table/cache has an entry for the device & it's marked as "incomplete" which, AFAIK, basically means that the device is currently not found up and running within the network (e.g. it's not responding to an ARP request).

I have a smart bodyscale that has WiFi and connects to the router everytime I step on it to measure my weight and other parameters.
Does the device connect to WiFi only when triggered by stepping on it?
Does it then disconnect itself from the WLAN after being idle for some time (e.g. a specific timeout is reached)?
Does it go perhaps into some kind of "energy saver" mode where it doesn't respond at all until someone again steps on it?
Does it have a very short lease time?
Is this lease time shorter than the interval between each use?

There could be other factors involved that I'm not aware of, but, for now, I'd say that it's very likely that the lease time has expired so you don't see the device in the "DHCP leases" webpage.
 
Last edited:

Ro berto

Regular Contributor
Does the device connect to WiFi only when triggered by stepping on it?
I think it does, not sure if it connects at a random time to sync or something.

EDIT: I found that it also connects around 3am, 1am, midnight
Does it then disconnect itself from the WLAN after being idle for some time (e.g. a specific timeout is reached)?
From what I have seen, it disconnects as soon as I step out of the body scale.
Does it go perhaps into some kind of "energy saver" mode where it doesn't respond at all until someone again steps on it?
I think it does, they say its batteries last for 18 months (AAA x4).
Does it have a very short lease time?
Is this lease time shorter than the interval between each use?
I forgot to mention the leasing time, it's the maximum allowed, 7 days (604,800 seconds). And I have had the body scale for less than a week. So that's why I found strange not seeing the body scale on the DHCP Lease time list. I reserved IP 192.168.1.33 for the body scale. I reserved that IP before connecting the body scale for the first time so it connects with that reserved IP (OCD of mine hehe)

Thanks for taking the time to answer @Martinski
 
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Martinski

Regular Contributor
I forgot to mention the leasing time, it's the maximum allowed, 7 days (604,800 seconds). And I have had the body scale for less than a week. So that's why I found strange not seeing the body scale on the DHCP Lease time list. I reserved IP 192.168.1.33 for the body scale.
Next time when the device is in use & still connected to WiFi, go & check the "DHCP leases" webpage as soon as you can. Note the remaining lease time on the left-most column ("Time Left"), and compare the value to the lease time that you think it should be - just to be sure. The difference would be a few seconds to a few minutes if the device just connected to the router and got a new IP lease. AFAIK, the IP address lease should remain in effect until the lease time expires, even if the device disconnects & connects at random times during those 7 days.

For example, all my wired devices at home (TVs, NAS, Ethernet switches, mini desktops, laptops, etc.) have a lease time of 5 days, and even when some may not be connected for a day or two (for some reason), I can still see the entries in the "DHCP leases" webpage, with their corresponding lease time counting down.

If this is not the case for your body scale, perhaps something else might be going on that is affecting the IP lease, and I have no idea what that would be.

Good Luck.
 
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Ro berto

Regular Contributor
AFAIK, the IP address lease should remain in effect until the lease time expires, even if the device disconnects & connects at random times during those 7 days.
yeah, that's correct, that's why I have this doubt.

When it connects, it only does for 5 seconds, I didn't see its IP lease.
 

Martinski

Regular Contributor
When it connects, it only does for 5 seconds, I didn't see its IP lease.
No IP lease?? That certainly seems like very odd behavior.

In the system log /jffs/syslog.log which DHCP messages (e.g. DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, DHCPACK/DHCPNAK) with the body scale's MAC address do you see when the device "connects" to the network?

What indications do you have that the connection was indeed successful?

After the "5-second connection" do you see any "DHCPRELEASE" message in the system log?

Under normal circumstances, a client device always tries to hold on to its existing IP address for as long as possible via the IP lease "renewal process" using a couple of IP lease renewal timers (at 50% & at 87.5% of total lease time) to trigger a lease renewal before the IP lease actually expires. This mechanism effectively extends the device's IP lease indefinitely as long as it remains connected to the network. However, I suppose it's possible (although I've never seen, read, or heard of a network client device automatically doing this by itself without the user's intervention) that the body scale itself is automatically releasing its IP address lease before terminating its connection, perhaps as part of its "energy saver" mode. If so, this would be highly unusual, but not entirely impossible.

If the device is in fact terminating the IP lease this early every time, it would explain the behavior that you described where the body scale simply "disappears" from the network after the "5-second connection."
 

Ro berto

Regular Contributor
In the system log /jffs/syslog.log which DHCP messages (e.g. DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, DHCPACK/DHCPNAK) with the body scale's MAC address do you see when the device "connects" to the network?
I don't see any DHCP messages under system log, I just see the messages that I posted on post #1.
What indications do you have that the connection was indeed successful?
I can see my body parameters on my cellphone after I use the bodyscale, I made sure I am not connecting directly to the scale. Also the messages under post #1.
After the "5-second connection" do you see any "DHCPRELEASE" message in the system log?
Nope, no DHCP messages under System Log, the only message with the word DHCP in System Log is regarding my OpenVPN Server:
Code:
Mar 21 15:40:53 ovpn-server1[2296]: client/192.168.1.20:36125 SENT CONTROL [client]: 'PUSH_REPLY,route 192.168.1.0 255.255.255.0 vpn_gateway 500,dhcp-option DNS 192.168.1.1,redirect-gateway def1,route-gateway 10.85.0.1,topology subnet,ping 15,ping-restart 60,ifconfig 10.85.0.2 255.255.255.0,peer-id 0,cipher AES-256-GCM' (status=1)

If it helps it is a Body Scale from Withings, it's the Body+ model (https://www.withings.com/de/en/body-plus)
 

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