18.06.2 DHCP server won't assign IPv4 addresses

I'm running 18.06.2 on the Linksys WRT1900ACS.

I recently set up radio0 interface (Marvell 88W8864 802.11nac Channel: 36 (5.180 GHz)) with WPA2 PSK (CCMP) and I have the strange problem that both computers and phones are able to join the WiFi network, but the router is not assigning IPv4 addresses to either computers or phones.

In LuCI, Network-Interfaces for the LAN settings page I have the "Ignore interface" checkbox left unchecked because I don't want to "Disable DHCP for this interface." But the router seems to be acting as if this checkbox was checked.

Under the Advanced Settings tab, the Dynamic DHCP checkbox is checked because I do want to "Dynamically allocate DHCP addresses for clients. If disabled, only clients having static leases will be served."

I've left the Force checkbox on that tab unchecked as there is only this DHCP server on the network.

In the IPv6 tab, I've disabled Router Advertisement-Service and DHCPv6-Service and NDP-Proxy but I disabled these after I encountered the problem with failure to assign IPv4 addresses when I noticed that IPv6 addresses are getting assigned to clients that join the WiFi network.

When I look at LuCI's Status->Overview page, in the "Active DHCPv6 Leases" section, I see two IPv6 addresses assigned to two computers (from the time period before I disabled the IPv6 server settings), and in the "Active DHCP Leases" section, I see "There are no active leases."

On the client, I note that when I manually assign an IPv4 address and netmask and router address in a computer that has joined the WiFi network associated with the radio0 interface, I do get normal LAN and WAN access on that computer. But I do want DHCP to assign IPv4 addresses.

I looked at One wireless interface connecting and then not assigning DHCP addresses to see if my problem was related, but I don't think it is related for two reasons: (1) my router is the Linksys WRT1900ACS (theirs was the WRT3200ACM) and (2) I seem to have only two interfaces (BGN and NAC) whereas they had three interfaces; plus, I'm using my NAC (5.180 GHz) interface and seeing this problem whereas the other post author reported that "This only happens on the 2.4GHz bgn interface".

Any ideas on what is causing my problem with my router not assigning IPv4 addresses to clients that join the WiFi network?

Thanks in advance.


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I would enable logging for DHCP requests, and then check on the logs if the router receives a request and what is answering.


Great idea @eduperez . Thank you! I feel silly that I didn't think of it myself.

It looks like I can enable logging for DHCP requests in the LuCI page at Network->"DHCP and DNS" page using the "Log queries (Write received DNS requests to syslog)" checkbox which I found unchecked initially.

So is it just a matter of checking this box and then clicking the "Save & Apply" button to enable logging of DHCP requests?


After doing so, I'm seeing some entries in my syslog like these.

I'm not sure what I should be seeing, but this entry:

Mon May 20 10:49:51 2019 daemon.info dnsmasq[2607]: 75 query[PTR] from
Mon May 20 10:49:51 2019 daemon.info dnsmasq[2607]: 75 config is NXDOMAIN

is something I recognize as having originated with a computer that I assigned the ip address to manually, so it looks like something is being received by the DHCP server from clients.

Does this look correct to you? For normal DHCP logging of a fully functional DHCP server, should I be seeing something different?

Thanks again.

That log is not a response to a DHCP request.

You agree it's not DHCP too.

That is some device trying to get a reverse DNS record. It does confirm that dnsmasq is running, though. That's all.

  • Can you show your LAN sections in /etc/config/dhcp and /etc/config/network?
  • Also can you show your /etc/config/wireless ?

Good point about the log entries not being DHCP entries. That didn't really dawn on me until you pointed it out.

About the files, yes thanks for asking. I posted the entire files rather than just the LAN sections. I don't think there's anything sensitive in these, but would appreciate some feedback if I'm mistaken on that point so I can remove them from pastebin.

Here is /etc/config/dhcp (I'm pretty sure it is all defaults except for perhaps 1 or 2 changes I mentioned above).

Here is /etc/config/network

And here is /etc/config/wireless (sans sensitive details).

[Workaround] GL-AR150: No DHCP if LAN cable is not plugged during boot

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Thanks @vgaetera for the link. I don't think that issue was the problem for me, but it did give me the idea to try rebooting my router, and now magically, after rebooting my router, my DHCP server is now offering ipV4 addresses.

I should have tried this before posting. Thanks everyone for all the help. Sorry to have raised the topic before trying a simple reboot.


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