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Devices connect to WiFi but is assigned no IP address

FlyingCodeMonke
Contributor
Contributor

Hi all,

I've had this issue for a long time and really hoping someone can help as it's driving me and my family crazy.

I have a Smart Hub 7 Pro and because it's an ancient house with thick stone walls, we need  3 WiFi extenders for full coverage. They all have ethernet backhaul to the Smart Hub (upstairs where the line comes into the house), although the extenders are daisy-chained because of the ridiculous way the house was wired (room to room, rather than each room direct to the attic!).

At various different times, the devices in the house keep dropping offline for no apparent reason. I eventually figured out that they're managing to connect to the WiFi network with a strong signal but aren't receiving an IP address via DHCP. After about 5 minutes (or turning WiFi off and on again on the device) it'll connect and obtain an IP address properly.

I've tried increasing and decreasing the DHCP lease time, which hasn't helped. I've tried assigning fix IP addresses via DHCP, which didn't help. I've even tried disabling the DHCP server on the Smart Hub Pro and configured my desktop computer (always online and connected via ethernet) to act as a DHCP server, but I've still got the same issue.

That said, now that I'm running my own DHCP server, I can see the full log output, and it's showing up something odd. Because the device knows about the server, it skips the DISCOVER message and goes straight to sending a REQUEST message to extend/renew the lease. Fine. The server replies with the ACK message - acknowledging the request and supplying all the configuration data, but it's like the device never receives the ACK message. It just keeps firing REQUEST messages. Then, it starts sending out DHCP DISCOVER messages, to which the server replies with the appropriate OFFER message...only to receive another DISCOVER message from the device.

Eventually, something I see DISCOVER, OFFER, REQUEST, ACK in the logs and then there's silence in the file because the device gets its IP address and can access the internet.

Once the device has connected, there is no packet loss on the network, so I don't think it's that. And other devices can be connected and working properly at the same time.

Also it's not always the same device that has trouble - sometimes it's my laptop, sometimes it's my wife's laptop or one of the kids' iPads, or the printer, or something else, or several not working at the same time...or sometimes miraculously everything is working fine. It's absolutely driving me bonkers that I can't figure it out.

WiFi devices upstairs have no problem getting online. It only seems to be the ones downstairs.

Can anyone help me at all please?

Thanks.

11 REPLIES 11
FlyingCodeMonke
Contributor
Contributor

Hi @bobpullen  Thanks for the suggestion. Sorry it took a while to get back to you - I had to get a couple of longer ethernet cables so I could swap things around and have the Playroom extender plugged directly into the Kitchen, and the other device into the switch.

Sadly that didn't help. I also tried switching off the Playroom extender completely, but all that did was knock all the devices at the back of the house offline!


@FlyingCodeMonke wrote:

I also tried switching off the Playroom extender completely, but all that did was knock all the devices at the back of the house offline!


Including the Kitchen devices? Bizarre if so!

Your diagrams look sound and I think we can assume basic network routing is OK as manually configuring the DHCP info is working. Have you managed to work out of devices connected to either the Playroom or Kitchen extender exhibit the problem. It would be helpful to determine a demarcation point for where the problem is actually occurring.

My next step would probably be to run a Wireshark capture on an affected device and capture the DHCP exchange, compare it with the Windows server, and try to establish what's 'going missing where' - certainly not for the faint of heart though.

I assume the Playroom needs to be wired somewhere and can't be switched to wireless backhaul to see if there's any change?