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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Thank you very much for your explanation, Alexandre.
It is the router that kept changing the IP address but It seemed like Deco caused some conflict, which it shouldn’t;
In order to locate the problem, could you please help me check the following issue;
- May I know the model number of your main Huawei router?
- Can I have a picture of your network topology?
- When the Deco is powered on and connected to the main router, what would be the IP address on the Deco, and did it work fine when the main router has changed to 192.168.9.xxx?
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haha, this made me nearly choke on my breakfast when I saw you responded.
Great that you're looking into someone's specific case, but could you please fix the issue this thread was created for and is impacting lots more people.
Confirm when you are going to release a firmware that allows your "smart DNS" features to be fully disabled.
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Hi, in case it serves a purpose I'll play but the history on this thread suggests this is a problem with the firmware.
1. H112-370
2. No, but i will describe it : router going in to switch by ethernet cable, sharing connection that way and wirelessly. House is networked with cat6 cable. Decos are connected physically by ethernet cable at different outlets. There is one other router on the network - a netgear in AP mode , I've checked that isn't part of the problem (by having it on when the decos aren't, reproducing the problem with it off etc.). Other devices on the network include printers, smart doorbell, tvs, cameras, mix of linux and windows pcs and laptops. Normally non-wired devices are connecting to the deco mesh, a couple do go straight to the router if physically close.
3. 192.168.8.x - with 192.168.8.1 being the gateway / router address. When router has changed to 192.168.9.x they stay on the 8.x range and show no internet connection in the app. If i go to the router and attempt to force DHCP back onto the 8.x range it fails. If I turn off the decos then try, it works, and on restart of the router it goes back to that range.
I don't think it could be much clearer that the decos are at fault and other posts in the thread give pretty clear explanations of the problems. WIthout breaking out wireshark or similar it would look like the decos are somehow blocking the router using the 192.168.8.1 address in this situation. In this state their lights are flashing red. they have 8.x IP addresses (not 8.1 and I believe unchanged) and they show devices connected but no internet connection.
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Hi, thanks for your detailed information.
As for the smart DHCP issue, there would be a separate on/off switch on the firmware 1.6.0 which would be released on the Deco M5 very soon(for other models, it might be a little bit longer);
Actually recently, we are optimizing the IP-conflict detection mechanism on Deco;
So after seeing your post, I am quite curious about the Huawei IP conflict detecting rules why it would detect Deco in AP mode causing conflict since even though Deco enabled its own DHCP, they are still within the main router range;
Previously, I might be only focused on Deco why it would randomly start its own DHCP and we found that if it lost connection from the main router temporarily or boot up before the main router, smart DHCP would start since it did not detect any DHCP server, but did not pay much attention to how the main router behaved.
As for your case, I have forwarded it to the senior engineers, and let’s see what they could find for us;
Thank you very much for your time and cooperation.
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@TP-Link Thanks : can you give a timescale on the 1.6 firmware ? If within a month, I'll wait for it , if not I'm planning to send the decos back to Amazon within the return window.
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winter98 wrote
In your particular case, it is both companies that are at fault: TP-Link and Huawei. Based on your description of a problem, I can summarize it as following:
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There is Deco mesh running in AP mode connected to Huawei router
Huawei router goes offline, Main Deco assumes role of default gateway, DHCP server and DNS server
Main Deco distributes IP addresses in the same IP range Huawei router used to, which is 192.168.8.x
Huawei router comes back online, realizes there is another DHCP server running that gives IP addresses in same 192.168.8.x
Huawei router switches its DHCP server to a different range, 192.168.9.x
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I have no way to test that, so it is based on your words.
If my summary is true, it means that if either of these two systems, TP-Link Deco or Huawei router, were not too smart for their own good, that problem you experience on your home network would not have happened.
I have Hitron CODA router, it is dumb: when it starts back it just assumes DHCP role without checking anything. That makes my home network, which also has Deco mesh in AP mode, recover automatically and almost instantly. No matter what I tried, and I did run multiple tests to trigger the issue.
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From Networking point of view, what Deco mesh does in AP mode when router goes down is a sin. Deco mesh in AP mode should just go down with the rest of home network when ISP router goes down.
From same Networking point of view, what Huawei does with their router is a mortal sin. It is OK to run multiple DHCP servers on a network. It is not OK for DHCP server to switch to different IP range just because it sees another DHCP server on the network. It is really, really NOT OK.
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TP-Link admitted they have an issue and promised fix. All we have to do is wait.
What I would like to ask is for you to join Huawei support forums, share that story there and ask there if it is known issue. If it is, are there any mitigation options (such as configuration settings in router) and if not - how Huawei plans to address it. Because, you know, based on what you said that Huawei router "IP address conflict avoidance" feature can be triggered by any DHCP server running on home network, not just Deco.
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@TP-Link something new for this issue? I have this problem with my Deco M4 in AP mode. Thank you
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Hi, Please have a check of the private message and feel free to let me know whether it worked or not.
Thank you.
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@TP-Link i have the same issue for years.
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