Conflicting DHCP when Deco in AP mode ?
Today I ran into an issue which made me almost cringe.. as I hadn't expect this to happen, considering I've been working in the IT networking business for over 30 years..
I had recently purchased a Deco M5 mesh set with 3 nodes and setup as AP access points, because I alread have a decent router from my ISP (Zyxel EMG2926). This has been working fine for the last 6-8 weeks and nothing to complain about.
Last night, for some strange reason my router rebooted and I lost Internet connexion from everywhere, including my wired PC's which I use every day to work from home.. So getting back internet was critical to me and I tried the quick obvious options like rebooting the router and also reseting to factory the router, then reloading the configuration I had on backup.. To no avail, I wasn't able to get an functional internet, still the router diagnostic was able to ping any IP address outside my network.. Since I needed to work and support clients, I disconnected the Zyxel router and put back the Mercku M2 Hive base I had prior to the ISP router and after 5 minutes, was back into business.. (The Mercku is also a Mesh Wi-Fi system with 4 Bee nodes, albeit it wasn't working to my entire satisfaction, thus the purchase of the Deco M5).
Having spend the morning with work, I had hope the issue with the router might have been on the ISP side, so tried to set it back in action. Result was identical and nothing was really working.. Put the Mercku M2 back for the PM as I had a support call and did need internet ASAP.
At the end of the PM I got back to my router and it was so weird that I even tried to reset the Zyxel for the n-th time and start from scratch.. What puzzled me was that it was working if I forced my computer into fixed IP address, and even with DHCP Mac address reservation, the router wouldn't route my requests properly to the internet.. Looking at the IP addresses in the config made me think that router was totaly corrupt and crazy.. The router's IP is 192.168.127.1, but returns 192.168.127.102 as gateway and .254 for the DNS server, which is even crazier.. This is when I started to scan my network for rogue devices with my Android smartphone, but couldn't find anything suspicious. I've a lot of IoT devices and aside of the 3 Deco M5 AP's, there was nothing un-usual. However, the .102 IP address made me tick and look closer at the Mac Address, to finally discover that the main Deco M5 unit (the one connected by Cat5 cable to the switch) was the culprit.
For some obscure reasons my Zyxel router was thinking that the Deco M5 AP unit was the master DHCP on the network, despite TP-Link saying in their documentation that it is not the case when in AP mode.. As a proof, my Mercku M2 router had no issues at all with that and was perfectly handing over IP addresses to all devices..
Has anyone run into such a situation with another HW router ? getting conflicting DHCP server mode while the Deco M5 is in AP mode ?
I fixed my problem my disconnecting the Cat 5 cable temporarly from the switch, rebooted the Zyxel router and voilà.. after it was back as 'master' DHCP, I plugged the Deco M5 back and all was working as before.. But I'm really curious about that strange behavior.
Any comments are welcome on this.
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TP-Link wrote
Hi, I see that you also have Deco M5 which Is on firmware 1.6.0.
So when Deco M5 is working as the main Deco under access point mode, there is no need to install any beta on M4.
You could turn off the smart DHCP switch on M5, then M4 will sync with the same configuration.
Thank you.
Ok, good to know. Thank you.
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I hate to point out the obvious but you're wasting your time. This issue is now close to 3 years old. The ability to fully disable a network breaking and undocumented feature should have come within months of the initial post. But 36 months in, it's still not here.
I'd say move off of tp-link altogether but I am using, and like, their Omada product line for my APs (EAP660 HD), and they work great. I suspect it's an entirely different product team
Sell the stuff you've currently got and find something better.
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Can someone who has tried v1.6 / a beta confirm whether the new "disable smart dhcp" function works properly? I have a collection of M9s and am very frustrated by this. I'm trying to decide whether to just get rid of my M9s or wait it out a little bit longer in hopes that a 1.6 firmware will drop soon. It's a moot point if the feature to disable it doesn't work properly.
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There is no such thing as a master dhcp server. Every dhcp server will answer a DHCPDISCOVER request if it has a free lease. It is entirely up to the client to decide which lease to request (DHCPREQUEST). The protocol doesn't specify how the client makes its decision. I stumbled on your post while looking for a dhcp problem I have with my Deco M5. It stops relaying answers from my dhcp server.
Deco M5 Firmware 1.5.7 Build 20210819 Rel. 43499
dhcp server log:
...
Mar 12 12:25:34 nuc dhcpd[689803]: DHCPDISCOVER from f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:34 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.151 to f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:40 nuc dhcpd[689803]: DHCPDISCOVER from f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:40 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.151 to f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:49 nuc dhcpd[689803]: DHCPDISCOVER from f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:49 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.151 to f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:51 nuc dhcpd[689803]: DHCPDISCOVER from f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:51 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.151 to f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:54 nuc dhcpd[689803]: DHCPDISCOVER from f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:54 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.151 to f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:59 nuc dhcpd[689803]: DHCPDISCOVER from f0:f0:a4:53:17:bf via eno1
Mar 12 12:25:59 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.151 to f0:f0:a4:53:17:bf via eno1
Mar 12 12:26:05 nuc dhcpd[689803]: DHCPDISCOVER from f0:f0:a4:53:17:bf via eno1
Mar 12 12:26:05 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.151 to f0:f0:a4:53:17:bf via eno1
Reboot closest Deco M5
Normal sequence {
Mar 12 12:46:25 nuc dhcpd[689803]: DHCPDISCOVER from f0:f0:a4:53:17:bf via eno1
Mar 12 12:46:25 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.151 to f0:f0:a4:53:17:bf via eno1
Mar 12 12:46:25 nuc dhcpd[689803]: DHCPREQUEST for 192.168.68.151 (192.168.68.8) from f0:f0:a4:53:17:bf via eno1
Mar 12 12:46:25 nuc dhcpd[689803]: DHCPACK on 192.168.68.151 to f0:f0:a4:53:17:bf via eno1
}
Mar 12 12:47:40 nuc dhcpd[689803]: DHCPREQUEST for 192.168.68.163 from 08:84:9d:77:8b:ed via eno1
Mar 12 12:47:40 nuc dhcpd[689803]: DHCPACK on 192.168.68.163 to 08:84:9d:77:8b:ed via eno1
Mar 12 12:47:44 nuc dhcpd[689803]: DHCPREQUEST for 192.168.68.37 from 04:0c:ce:e3:65:fe via eno1
Mar 12 12:47:44 nuc dhcpd[689803]: DHCPACK on 192.168.68.37 to 04:0c:ce:e3:65:fe via eno1
Rebooted Deco M5 requesting an IP address {
Mar 12 12:47:53 nuc dhcpd[689803]: DHCPDISCOVER from 3c:84:6a:98:53:e4 via eno1
Mar 12 12:47:53 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.10 to 3c:84:6a:98:53:e4 via eno1
Mar 12 12:47:53 nuc dhcpd[689803]: DHCPREQUEST for 192.168.68.10 (192.168.68.8) from 3c:84:6a:98:53:e4 via eno1
Mar 12 12:47:53 nuc dhcpd[689803]: DHCPACK on 192.168.68.10 to 3c:84:6a:98:53:e4 via eno1
}
Mar 12 12:48:22 nuc dhcpd[689803]: DHCPREQUEST for 192.168.68.52 from b8:27:eb:ef:d0:11 via eno1
Mar 12 12:48:22 nuc dhcpd[689803]: DHCPACK on 192.168.68.52 to b8:27:eb:ef:d0:11 via eno1
Mar 12 12:48:24 nuc dhcpd[689803]: DHCPDISCOVER from 40:a9:cf:64:0e:a3 via eno1
Mar 12 12:48:24 nuc dhcpd[689803]: DHCPOFFER on 192.168.68.152 to 40:a9:cf:64:0e:a3 via eno1
Mar 12 12:48:24 nuc dhcpd[689803]: DHCPREQUEST for 192.168.68.152 (192.168.68.8) from 40:a9:cf:64:0e:a3 via eno1
Mar 12 12:48:24 nuc dhcpd[689803]: DHCPACK on 192.168.68.152 to 40:a9:cf:64:0e:a3 via eno1
...
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Hi, in case of any misunderstanding since I wasn't good at reading logs, could you please help me confirm the following details:
1.Deco is working on the access point mode,right?
2.what you are trying to say, the client sent the DHCP request and main ISP router answered, but Deco in between did not relay DHCP answers from main router to clients?
By the way, May I know the model number of your main router?
Can I have a full picture of your network layout?
Thank you very much.
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Hi,
just to be sure i understood correctly... i have 4 M4 in AP and Ethernet Backhaul.
My will is now to get rid of the DHCP server from the box, so i can change ISP with full transparency....
If i buy a M5, add it to the 3 M4, make it as main, and activate smart DHCP on it, it will sync to all Deco, even the M4 not having the smart DHCP (cause being on old firmware), and i can shut down DHCP server from my box.
Have I understood correctly ?
Edit : rereading the posts, i'm not sure i understood.... moreover, it is not interesting for me i think, as i need the M4 play DHCP server role, but need to be able to create static IP for some devices.... so not sure it will help, i need a router between my box and the M4 to play this role I guess.... but this is another box... and can find anything cheap, small, for that...
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I replied to the notification email but apparently the response didn't get forwarded to the list. Here is my original response:
Here are the requested details (and then some):
Switch is a tp-link t1600g-28ts 3.0 with software version 3.0.6 Build 20200805 Rel.55968, flash version 1.3.0 with 802.1Q vlans 1 untagged and 591 tagged, dhcp service/relay/L2 relay/filter disabled.
Router is Cisco RV325 with latest firmware (v1.5.1.13 (2020-10-27, 13:37:43)) with ip address 192.168.68.1, dhcp is deactivated, directly connected to t1600g-28ts port 24.
DHCP server is directly connected to t1600g-28ts port 8 native vlan 1 with address 192.168.68.8, CentOS 8 ISC DHCP.
3 x Deco M5 in AP mode, firmware 1.5.7 Build 20210819 Rel. 43499.
deco M5 Main directly connected to t1600g-28ts on port 21 with ip address 192.168.68.10 obtained via dhcp, native vlan 1 and tagged vlan 591 for guest network.
deco M5 Living room directly connected to t1600g-28ts on port 23 with ip address 192.168.68.11 obtained via dhcp, native vlan 1 and tagged vlan 591 for guest network.
deco M5 Office connected to a tp-link tl-108ge 5.0 switch, firmware 1.0.0 Build 20191021 Rel.53360 on port 7 with address 192.168.68.12 obtained via dhcp, native vlan 1 and tagged vlan 591 for guest network.
tl-108ge port 8 directly connected to t1600g-28ts port 22, native vlan 1 and tagged vlan 591 802.1Q for guest network.
client is an Amazon blink camera with latest firmware, MAC address f0:f0:a4:53:17:bf attempting to get an ip address from the dhcp server, associated to Deco Main ssid "Wall-e" (2.4GHz and 5GHz) when the problem occured.
Network traffic captured from dhcp server. We can see the DHCPDISCOVER and the DHCPOFFER but no DHCPREQUEST. So either the DHCPOFFER or the DHCPREQUEST is not relayed or the client didn't DHCPREQUEST the DHCPOFFER.
Rebooting Deco M5 Main solved the problem. The problem has occurred a few times.
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There is one scenario I can think of that would involve the router. I will make the appropriate setup later this week and see if I can reproduce the problem. This time I will capture the traffic from the t1600g-28ts by mirroring the Deco ports (gigabitEthernet 1/0/21-23) to a network analyser (on gigabitEthernet 1/0/1). I'll open a ticket if I find that the router is not at fault.
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Thank you very much and that would be very helpful.
By the way, the official firmware 1.6.0 for Deco M5 has been released today and it supports turning off DHCP on AP mode.
Maybe you could try to update to the latest version and turn off the DHCP first.
Thank you very much.
Best regards.
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