DHCP requests not logged consistently

[tomschmidt]

My Orbi log files will show "DHCP IP" entries sometimes, and not other times.  If I reboot my RBR50, then "DHCP IP" requests are logged, reboot again and they are NOT logged, reboot again and it starts logging them again.  Is anyone else seeing this issue with their Orbi log files?

Example (last octets of real MAC address changed to X's):

[DHCP IP: 192.168.1.30] to MAC address cc:50:e3:xx:xx:xx, Sunday, March 08, 2020 16:04:11

[Access Control] Device ESP_XXXXXX with MAC address CC:50:E3:XX:XX:XX is allowed to access the , Sunday, March 08, 2020 16:04:11

Reboot RBR50, check log and it only shows this entry for the device:

[Access Control] Device ESP_XXXXXX with MAC address CC:50:E3:XX:XX:XX is allowed to access the , Sunday, March 08, 2020 16:13:15

Reboot the router again and "DHCP IP" entries are logged again.

Anyone else see this bug?  I have all the checkboxes for logging selected.

[tomschmidt]

Another observation is that when it is not logged DHCP IP requests, if I go to the Advanced -> Setup -> LAN Setup page and click Apply (without changing anything), the RBR50 appears to reset the DHCP server. This process takes almost 2 minutes, and it is not a reboot of the system since uptime (seen on the debug.htm page) shows it was not rebooted.  Going back to viewing the logs, DHCP IP is again being logged.

So the I repeat this process, and go to the LAN Setup page again and click Apply without changing anything.  After almost 2 minutes, the system web page is back, so I then check the logs and DHCP IP is still being logged.  Hmm.

So then I go to the Advanced Home page and click the Reboot button.  After about 3 minutes the router is back up, I log in and check the logs and DHCP IP is no longer being logged.

Anyone else able to duplicate this?

[CrimpOn]

Interesting issue, mixing DHCP and Access Control.  My guess is that the device in question did not actually renew the DHCP lease when the Orbi was rebooted.  No renewal: no log entry.

DHCP is more complicated than I had ever imagined.  When the device receives an IP assignment using DHCP, it knows how long the lease is for.  There is no reason to ask for another until the proper time (when 1/2 of the lease time remains).

How about this test:  When the Orbi is rebooted, also reboot the device.

[tomschmidt]

I have had my systems log file not report any DHCP IP entries for days.  Then once rebooted, I would see each device make the DHCP IP entry in the log file once every 12 hours, which mismatches the 24 lease time.  That is another anomoly, anyone else seeing the "DHCP IP" entry every approximately 12 hours rather than 24 hours for each MAC address?

@CrimpOn, I have rebooted devices after rebooting the router.  When the RBR50 is not logging DHCP IP entries, the rebooted device and even any new device off for over 24 hours is not logged.

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@CrimpOn wrote:

Interesting issue, mixing DHCP and Access Control.  My guess is that the device in question did not actually renew the DHCP lease when the Orbi was rebooted.  No renewal: no log entry.

DHCP is more complicated than I had ever imagined.  When the device receives an IP assignment using DHCP, it knows how long the lease is for.  There is no reason to ask for another until the proper time (when 1/2 of the lease time remains).

How about this test:  When the Orbi is rebooted, also reboot the device.

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[FURRYe38]

Something to bring up to NG support.

@Blanca_O 

@Christian_R 

[CrimpOn]

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@tomschmidt wrote:

I have had my systems log file not report any DHCP IP entries for days.  Then once rebooted, I would see each device make the DHCP IP entry in the log file once every 12 hours, which mismatches the 24 lease time.  That is another anomoly, anyone else seeing the "DHCP IP" entry every approximately 12 hours rather than 24 hours for each MAC address?

This one I can answer.  The standard DHCP practice is for the device to request a DHCP renewal when 1/2 of the lease time has elapsed.  If not granted, the device begins asking more and more frequently until the lease expires.  At this time, the device reverts to asking for a lease (rather than a renewal). See https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol for a thorough discussion.  So, this is NORMAL.

@CrimpOn, I have rebooted devices after rebooting the router.  When the RBR50 is not logging DHCP IP entries, the rebooted device and even any new device off for over 24 hours is not logged.

Thanks for the report.  "When the RBR50 is not logging DHCP" is consistent with not seeing any specific DHCP grants.  I am now searching the forum for a problem I had 18-24 months ago when my Orbi was not logging DHCP.  There was a "fix", but now I cannot find the original post.  Will keep searching.....

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[CrimpOn]

My search of past community messages turned up two items:

• Is "Wireless Access" checked (on) on the Advanced Tab, Administration, Logs?
  I found a note that "Wireless" appears to refer to "Everything".
  Anyway, can we confirm that the "Wireless Access" is checked?
• I also found a note that disabling and re-enabling UpNP caused the log contents to change.

I also found a recommendation to do a "Factory Reset" which is sort of the "Last Resort when all else has failed."  I avoid that unless the situation is DIRE.

[tomschmidt]

Thank you @CrimpOn for digging a bit into this.  I was not aware that DHCP would start checking at 1/2 the lease time to see if the client was still alive, so that explains why I was seeing entries for the same MAC address approximately 12 hours apart.

Yes, I confirmed that all items are checked (enabled) on the Advanced -> Administration -> Logs page including "Wireless access". 

UPnP is on.  I have never changed it, and its portmap table is empty.

As for a factory reset, I did one when I first upgraded from v2.5.0.x to v2.5.1.8 to clear the mess left behind by the v2.5.0.x release.  For the most part, v2.5.1.8 had run well for me with the exception of a few quirks:

1. The DHCP log issue reported here
2. DNS resolver still not being able to resolve hostnames of local Linux hosts on the local domain (see https://community.netgear.com/t5/Idea-Exchange-For-Home/orbi-add-dns-server/idc-p/1632085#M1731 for related information)