I have a dumb AP setup to forward wireless clients to the router. It's working except that I'm seeing numerous dhcpinform and dhcpack requests similar to Syslog flud (LEDE)

This only happens on clients connected to the dumb ap, which points to it being related somehow. The dumb ap does not have an ip address nor internet access (and no ntp). Any reason this would occur?

Just for clarification: you are seeing those messages on the main router, right? and the wireless interface on the AP is bridged to the wired interface, yes?

Could this be a connectivity issue (bad cable, or too much interference)?

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Yes. Main router -> Dumb AP -> client. Clients connect to Dumb AP SSID and are given an IP address from the main router. Dumb AP is basically a wireless switch. No local ip access, or lan of its own.

Main router does DHCP and logread reports multiple DHCPINFORM, DHCPACK requests. The timing varies, but on average is from 2-10 minutes between requests. Only for clients on Dumb AP. All other clients are normal.

I have not seen any connection issues on the clients (see note at bottom). Internet seems to work ok. I should investigate cabling / interference further, though.

note: Technically, today the wifi dropped out for some 15-45 minutes. However, I can't say whether this is related to the inform / ack requests or not. These requests have been going on for at least a couple of days, and only today did any dropouts or internet connectivity issues appear... The dropout might have been due to something else (e.g. hvac motor turning on).

Things I will check so far:

  1. cabling issues
  2. different OS performance for clients. (i.e. Android client vs GnuLinux vs Windows. Are they all affected?)

DHCPINFORM is sent by the hosts and DHCPACK is the response from the server.
I don't see how the dumbAP affects that.

If the AP drops packets in one direction, the clients could be missing part of the exchange, and repeating the requests.

Sure, but there is no evidence or log for that allegation.

I've tested an android and iphone today, and did not see any DHCPINFORM or DHCPACK messages. It appears this error is related only to Windows (laptops).

An unrelated error I saw was due to the previous AP which had a different subnet. Hosts are asking for the previous routed AP's (same SSID/psk) IP range, and are getting confused. I tried 'forget network' on mobile and re-added the SSID to resolve this.

Regardless, the windows client is not having internet connectivity issues, so this may be a superfluous warning. I'm going to check ipconfig/all to see what that says about the lease time. Which according to https://kb.wisc.edu/helpdesk/page.php?id=562 should tell me whether its a 10 minute lease or if something else is occuring. It's supposed to be a default 12h lease.