Ethernet not working properly when wifi interface is on

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Ethernet not working properly when wifi interface is on

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Ethernet not working properly when wifi interface is on
Ethernet not working properly when wifi interface is on
2021-04-21 09:13:19
Model: Deco M5  
Hardware Version: V3
Firmware Version: 1.5.3 Build 20210203 Rel. 68223

Hi! 

I recently bought a Deco M5 to extend my wifi network. At first, I was using it with my existing router, using Access Point Mode, pretty much without problems but then I decided to switch it to Router Mode and replace my old router with the Deco. 

Almost everything works now but there is a very strange problem on my desktop machine (Mac mini) which sits beside the main Deco and is connected to it via ethernet through a switch. In this switch, I have also plugged in a Philips Hue bridge and a Zyxel NAS box. The Hue bridge works fine but the Zyxel does not. I can see that it gets an address, can ping it and even telnet into it. But the SMB and NFS volumes it's sharing don't work. If I run 

 

showmount -e <zyxel> 

 

it shows me the NFS shares. But when I mount them and try to read them, it just hangs. When I try logging into the Zyxel web interface, I get the login page but when I try to log in, that also just hangs.

 

The weird thing is that I have two laptops in the house that connect via Wifi to the Deco and they can access the Zyxel without problems! It's only the Mac mini, which sits in the same switch as the Zyxel, that can't. And it gets weirder. I tried turning off the ethernet interface on the Mac Mini and turning the wifi interface on and then everything worked!

 

So, there's something strange about the ethernet connection of the Deco. Almost like there's a separate firewall on it. I don't want to only use the Mac mini on wifi for obvious reasons. Don't want to settle for Wifi speed when the ethernet is right there. 

 

Before all this, I updated the firmware to the newest version so there's nothing more I can think of doing. My cables are all Cat6, brand new.

 

Hope someone can shed some light on this. 

 

Thanks,

  Gísli

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Re:Ethernet not working properly when wifi interface is on
2021-04-22 06:32:35

@Gisli 

Thank you very much for your feedback.

I would like to forward your case to the senior engineers for further assistance and please have a check of your email box.

 

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#2
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Re:Ethernet not working properly when wifi interface is on
2021-04-28 22:13:37

After some network probing and talking to TP-Link support, I found out what the issue was. My results were subsequently confirmed by the TP-Link engineers. The Deco M5 units are always using 1500 bytes for MTU for LAN traffic. This is not user configurable. The solution in my case was simply to lower the MTU setting of the ethernet interface on my Mac Mini to 1500 and the problem went away. I do hope this will be fixed in future versions of the firmware as the issue is not apparent for outbound ethernet traffic. I was able to send bigger packages to external sites but everything wired to the deco on my LAN was always using 1500 bytes as MTU.

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