M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP

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M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP

This thread has been locked for further replies. You can start a new thread to share your ideas or ask questions.
M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP
M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP
2019-06-05 18:13:16
Model: Deco M9 Plus  
Hardware Version:
Firmware Version: 1.2.8 Build 20190403 Rel. 43515

This is a new (2-day old) installation of two Deco M9 Plus, in AP mode behind a home router.  Both Decos are updated to 1.2.8 Build 20190403 Rel. 43515, and I'm using the iOS app version 1.8.6.  The Decos say "V1.2" on the bottom labels.

 

The symptom I'm seeing is that sometimes a Windows laptop will show connected to WiFi with no internet access.  The problem also happens to other WiFi devices including TP-Link HS110 smart plug, which will become unavailable through Kasa while still showing a solid internet connection on the device status light.  So far the problem seems to happen only when the slave Deco is connected.

 

The laptop problem occurs when waking from sleep, or can be triggered by turning its wireless off and back on.  This Win7 laptop with Intel(R) WiFi Link 5100 AGN is known-good and has been working with my previous WiFi setup without problems.  When the problem occurs, the laptop shows connected to the SSID but has a link local IP address, not a DHCP one on the LAN.  When the problem occurs, both Decos show green LED lights and good health status in the Deco app.  During the probem, other WiFi and wired clients of either Deco are functioning normally and can communicate with each other.

 

During the problem, packet capture on the laptop shows it receiving broadcast traffic (MDNS, ARP, TIPC, etc.).   If I then use the app to reboot the slave Deco (or remove power from it), the laptop will immediately broadcast DHCP dicover and successfully join the LAN while the slave Deco is rebooting.  The laptop will then continue to work until sleep/wake, or until the Wifi connection is manually disconnected and reconnected.

 

If the slave Deco is powered off, the laptop will work normally across sleep cycles when reconnecting to the master Deco.  All testing has been done with the laptop in and Decos in fixed positions. 

 

So it looks to me like intermittently DHCP is not propagating to WiFi clients of the slave Deco.  I have not yet seen this problem with wired clients of the slave Deco.  I have not seen this problem with clients of the master Deco.  During the problem with either the laptop or an HS110, other clients of both Decos are behaving normally.  Again, during the problem both Decos show green LED and "healthy" status.  During the problem, turning off the slave Deco will allow WiFi clients to automatically and successfully connect to the main Deco.

 

Any help would be appreciated.  Please let me know if I can gather any other useful troubleshooting information.

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#1
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6 Reply
Re:M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP
2019-06-06 02:36:23

That's interesting.

To locate the issue, would you please provide more details?

1. Who is your Internet Service Provider? 

2. Please provide a network topology. It would be better if you could draw a picture which shows how you connect your network devices together. 

3. 'When the problem occurs, the laptop shows connected to the SSID but has a link local IP address, not a DHCP one on the LAN. ', what do you mean by this 'link local IP address'? Is it 127.0.0.1? Or any other IP addresses? 

4. Please try to exchange the master Deco and slave Deco to see how they work. 

5. If possible, please provide more details about the packet capture. 

 

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#2
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Re:Re:M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP
2019-06-06 22:06:55

Thanks for the response.  I'll try to address your questions briefly and do more testing.

1. ISP is Comcast/XFinity.  Longtime solid connection here, should be a non-issue.  (My router is using Cloudflare's DNS, also working fine for a long while.)

2. I'll have to draw something better, but it's:

cable modem->(cat5)->home router WAN

home router LAN->(cat5)->main Deco->(wifi)->slave Deco

slave Deco->(wifi)->laptop and other clients

slave Deco->(cat5)->hub->entertainment stuff + Arlo

Is this a supported configuration?  (Basically I've dropped a Deco in place where I had a wifi client bridge (but no AP) before.  To be clear, the old configuration was solid and known-good.  The only change is using the Decos.)

3. When DHCP requests fail on WiFi re-connect, the laptop assigns itself a non-routed address, in this case 169.254.17.195.

4. I will try swapping Decos.  Should I use the app to properly remove them first, and then re-add them?  Or just physically swap them and let them figure it out?

5. Using wireshark on the laptop you can see the failed DHCP requests asking for the existing leased LAN IP.  The requests get no response from the home router (sole DHCP server).   You can see in this screen capture below what a failed DHCP request looks like on the laptop in wireshark:

 

I've scrolled the expanded part of the DHCP Discover packet so you can see that the laptop is requesting it's former LAN IP of 192.168.1.143.  In this case the lease is not expired.  (You can't tell from the image but the requests with source IP 0.0.0.0 do indeed belong to the MAC address of the laptop.)

 

Here's a later segment of the same session capture in which the DHCP request is successful.  In this case because the Deco has rebooted.  In this test I disabled laptop WiFi and waited until the reboot was complete, I'm 95% certain the success happened through the same slave Deco:

 

However in today's testing I see that the problem isn't just with DHCP.   Later (after successfully getting its DHCP address) the laptop seemed to drop off the internet.  Packet capture shows that packets just aren't making it out past the client Deco to reach the home router:

What you see here is traffic from three Decos (.215, .250, and .230).  (I added a third Deco to the mix.)  The laptop is using it's DHCP-assigned address, but gets no response to its ARP request for the home router.  At that point I can only ping the connected Deco's IP, but not the other Decos or the home router.  And yet you can see there is incoming broadcast traffic from the other two Decos.

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#3
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Re:M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP
2019-06-08 20:59:25

For the record I did try swapping the Decos, with identical results.  (So I really don't think it's an individual Deco hardware problem.)

 

Also it's clear at this point that my thread is misnamed - the loss of DHCP is just a symptom of losing all outbound communication between the satellite deco's wifi client and anything beyond the satellite.  IOW, I can ping other clients of the same satellite, but can't ping the main deco or the router.  Yet I still see (at the satellite deco's wifi client) broadcast traffic arriving from the main deco and the router.  It's as if the wireless backhaul uplink from satellite to main deco is dead, but the downlink is Ok.

 

It's a bit frustrating that during this time both deco's show happy green LEDs and the Deco app shows each deco is healthy.  There's no other diagostic information available from the decos.

 

Also this thread is not visible when I visit the deco community forum. Is it hidden or quarantined for some reason?

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#4
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Re:M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP
2020-07-28 04:08:16

@MeshedPotato Did you end up getting this resolved with newer firmware?

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#5
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Re:M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP
2020-07-28 17:57:51

@LG86 I spent a solid week at it and in the end returned the set.  I got zero indication of what the problem was (or could be).  Good luck to you!

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#6
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Re:M9 Plus in AP mode - WiFi clients of slave Deco sometimes lose DHCP
2020-08-26 09:06:53

@MeshedPotato thanks for sharing your post.  It appears there are numerous posts in the community forums regarding issues with DHCP and connectivity.  After the last firmware update, I'm literally having rolling outages for devices throughout the house and the system logs are showing numerous errors with IP addresses being handed out and/or cleared.  Although I've had the Deco M9's for a year or so, I'm going to do the same thing as you and take them back.  Thank goodness for Costco's legendary return policy!  TP-Link really needs to read a customer service manual. There have been bug reports on some of these issues over a year ago. Terrible! 

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#7
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