AP (no DHCP server) serving IP's while main router (DHCP server) is not available?


I have a problem and it looks like my openwrt setup is to blame.

I'm using a central router (21.02) which also is the only dhcp server in the network. Also there is two wired AP's (21.02) and two external repeaters (21.02 and 19.07) configured via WDS.

When the system is shut down (for example because the RCD is tripped or there is a power outage) it happens that devices connected via the repeaters having IP's that are not served from the routers DHCP server. All my devices are dhcp only configured (no manual IP's at all) and the IP's the devices "get" isn't the old/cached one they had before.

The only thing I can think of is that the repeaters could serve IP's as long as the DHCP server is not reachable. Can that be possible?

It is a big problem because it leads to IP conflicts and it's quite annoying to first identify and than fix it with rebooting devices that are not having a DHCP lease.

Any ideas what happens or how to avoid in the future?

Have you told the DHCP server on the satellite devices to ignore the LAN (br-lan) interface?

Network > Interfaces > LAN (br-lan) > Edit > General Setup > DHCP Server > Ignore Interface?

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What's the IP you receive, the IP of the server and MAC of the server?

Your descriptions are quite vague, and it doesn't seem you actually identified a device yet.

What @eas said, at most one DHCP server should ever be active in your network-- and it is almost always the main router. When configuring the repeater units also set the IPv6 DHCP to disabled.

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Indeed I did this:



  • The "proper" lease from the dhcp server (router .1) for the old client was .133 (turquoise)
  • After the power outage (after midnight) the ip the device used was .253 (orange) but this wasn't a dhcp lease from the router. I expect it to have been "served" by the wds repeater the device connected to at the time (and properly the router wasn't fully up then or the repeater was not yet connected to it :question:)
  • Around midday I connected a new client and the dhcp server actually served the .253 for that device (that's were the conflict :boom: were present, grey)
  • After restarting the old client it was finally served a lease from the dhcp server .127 (lila)

(all devices in my network have a unique mac)


This is exactly my setup. I just rechecked again and all DHCP Servers (incl. IPv6) are disabled on all repeaters and AP's.

Which doesn't answer the question.

The point was to identify the device supposedly issuing DHCP leases, not keep "playing" and guessing about DHCP or blaming OpenWrt (or any other device) without proof.

Next, your picture makes more questions, is that OpenWrt displayed?

Not sure if this was supposed to mean something. If so, I didn't understand.

Thank's for your reply @lleachii and sorry I did confuse you with the information given. Maybe I try to put it into a general question so it might be easier to answer for you.

What happens if a WDS repeater gets dhcp request from a connected client but the (upstream) dhcp server is not (yet) reachable :question:

  • Then your device would keep requesting until it's avaliable
  • BTW...maybe you should simply fix the problem that causes the unavailability

(Hence you haven't discovered a rogue DHCP server yet.)

I'm not confused...and you still haven't answered the question(s) that could easily clear DHCP server/lease discrepancies. I suppose you dont see how the questions are relevant; or this is a kind of troll?

Are these devices set up to default to .253?

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That it what I would have also thought in the first place.

I actually checked my device side in depth already but at is has a "read only" flash it can't even keep it's DHCP information cached when turned off hard (this it what probably happen, at least my wifi went down while most lights survived the outage which was roughly a second).

So my assumption was therefor that my WDS repeater was "faster" available then my main router which does dhcp.

Thank's for the tip but that will not be possible on a short run. Power outages (even if they are only very short) are quite common in my area. I rather want to make my system resilient so that it can handle such ungraceful situations.

My old setup with WDS repeater + router with stock firmware didn't had such problems so I'm quite confident this can be solved in software/configuration.

Could be the WDS repeater configured that they just spawn an AP when the uplink connection is established (because then the upstream DHCP server will be available too)?


That's the DHCP server on the router. So .111 to .254 should be served?

When the main router is down (and with it, the DHCP server), what is one of your clients showing for the following:

  • IP address
  • Subnet mask
  • Gateway
  • DNS

(you may need to force this situation -- take your main router offline for this test and then force one of the hosts to renew its DHCP lease)

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Does this also means you refuse to find the rogue DHCP server, or explain what software is recording these IPs?

I'mma stop responding til you answer the simple questions that would resolve the problem immediately:

  • MAC of server
  • IP of server
  • What's recording these IPs with turquoise and orange (it seems to stay online and keep its IP in order to record other devices - this is why I'm asking about it)

(If you identify this, you no longer have to guess or play about where the lease is coming from. You not answering these questions lead me to think you're not serious.)

Why does your WDS repeater have a DHCP server enabled!?!? :point_left: This is the problem!

Disable this - problem solved.

It does not have a DHCP server enabled like already stated in this thread :warning:

How do you come up making such a false assumption?

That would be very nice of you. Your posts here always contain this destructive notes and I'm not entirely sure what your intentions really are. All other people in the thread can help and advise without being passive (or active) aggressive.

Thank's, that sounds like a plan. I will do this, probably even make a little test setup for it so I can get logs from my client and logs from openwrt. Maybe something interesting is there to find :mag:

Well, since you edited the exact sentence, and it still implies that there's a DHCP server:

No matter how you word it, it would help if you explained htis.

Why won't you just tell us:

"when I connect a device, it gets an address, and the DHCP server has x IP and y MAC"


I would be really grateful if you would stick to your words and

in this thread. Thank you for all the effort and thoughts you provided.

I have some news as the same problem occurred again and this time I could identify the roaming of the client and the IP's it was served:


  • first row: client IP that was served via DHCP
  • second row: connection status to a internal server
  • third row: bssid of the wifi ap the device is connected to

Turns that the ap (lila bssid) which is powered by poe actually can overcome short power outages while the main router (brown bssid) will turn off right away and with it it's DHCP server.

Still I have no idea why the ap (which doesn't have any dhcpv4/6 server enabled) is even able giving away DHCP leases(:question:) as with my configuration intended it should only "delegate" this work to the configured gateway (the main router) :thinking:

Some configs of that ap (21.02.2) which only has one lan interface:


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