@Cepheus0815 

Cepheus0815 wrote

Hi everyone,

 

when I add a new device, my gateway (controlled by a OC 200) gives a new IP address from the default VLAN via DHCP to it. So far, so clear. If I then change the IP address to a fixed IP, nothing happens (the record is added in the DHCP reservations list though). I would have expected, to get the new IP address right away. So I unplug the new device and plug it back to the network, still the old IP address. Even restarting the gateway does not change anything. Only if I completly shut off the power to the gateway, the switches, the controller and so on, it gets the new IP address. Is this the expected behaviour?

 

Thanks, Rainer

 

P.S.: I use the managed switches, not the easy managed ones.

No, DHCP does not work in that way.

How Does DHCP Work? Common Questions and Solutions

I think you might have a cache on the controller or misconfig somewhere. 

Try to run show arp to learn more about the current status and compare. 

Hi @Clive_A 

Thank you for your answer. Unfortunately your link states exactly what I did: "You should replug your Ethernet cable when you assign a new IP to it. This equals a reboot to your device." Plus I even have the phenomenon, that sometimes devices already have the correct IP (through DHCP) and get a new one, which is not the hardcoded one. Again, the only thing that helps, is powering everything off (Gateway, controller, switches, EAP) and then it works again. Any ideas how I can ensure, that the correct IP address is assigned? I turned the DNS cache off, as it stopped working since one of the last firmware updates. I tried to run show arp on the gateway through terminal in the network tools, but I get a error message: Error: Invalid command "show". Any help is appreciated. 

One other question (maybe I need to open another thread for that): a possible solution would be to rely on DNS (Using FQDNs instead of IP addresses). I found on the Omada website that there should be LAN DNS tab. Unfortunately I am missing that tab in the UI. Any ideas?

Thanks, Rainer

  @Cepheus0815 

Cepheus0815 wrote

Hi @Clive_A 

 

Thank you for your answer. Unfortunately your link states exactly what I did: "You should replug your Ethernet cable when you assign a new IP to it. This equals a reboot to your device." Plus I even have the phenomenon, that sometimes devices already have the correct IP (through DHCP) and get a new one, which is not the hardcoded one. Again, the only thing that helps, is powering everything off (Gateway, controller, switches, EAP) and then it works again. Any ideas how I can ensure, that the correct IP address is assigned? I turned the DNS cache off, as it stopped working since one of the last firmware updates. I tried to run show arp on the gateway through terminal in the network tools, but I get a error message: Error: Invalid command "show". Any help is appreciated. 

 

One other question (maybe I need to open another thread for that): a possible solution would be to rely on DNS (Using FQDNs instead of IP addresses). I found on the Omada website that there should be LAN DNS tab. Unfortunately I am missing that tab in the UI. Any ideas?

 

Thanks, Rainer

Not sure of your network level skills. Is that possible with Wireshark?

See if you can get results where the router sends the wrong IP. 

And, show arp should be run in privilege mode. 

en

show arp

DHCP has nothing to do with the DNS. 

And your firmware is not up to date if you are missing the tabs. Please refer to the release note on the global official website.

Hi @Clive_A ,

Thanks for your reply. According to the Controller, my Firmware is up-to-date: 

But you are correct, on the website there is a newer one! I will install it.

Regarding running arp, thanks for your help. It worked. I got a table with IP addresses and MAC addresses. It basically shows me, what I can see in the clients list. The point is, it shows IP addresses for devices, that should have a different one, according to the DHCP reservation list. For example:

Thanks, Rainer

  @Cepheus0815 

Cepheus0815 wrote

Hi @Clive_A ,

 

Thanks for your reply. According to the Controller, my Firmware is up-to-date: 

ER707-M2 v1.20

1.2.3 Build 20240822 Rel.52946

 

But you are correct, on the website there is a newer one! I will install it.

 

Regarding running arp, thanks for your help. It worked. I got a table with IP addresses and MAC addresses. It basically shows me, what I can see in the clients list. The point is, it shows IP addresses for devices, that should have a different one, according to the DHCP reservation list. For example:

 

 

Thanks, Rainer

The device is an IoT?

Did you check the IoT device? Reset or anything?

An IoT device is notorious for having a slow chipset, which might cause a delay or prevent it from properly getting the DHCP IP. 

And after you upgrade your firmware, does this behavior exist on any modern device except for an IoT device? 

What's the DHCP lease time you set for this VLAN interface? 

 Hi @Clive_A,

Sorry, for my late reply. Although you are correct in this case, that this is currently affecting IoT devices, I have seen the same behavior also with Omada switches and Omada AP. I don't undertand how a client can get himself a different IP address, if the DHCP server is forcing an IP address on the device. Anything other I can do, than reboot everything?

After the firmware update nothing changed.

The DHCP lease time for this VLAN interface is the default one (120 min), never changed it.

Thanks, Rainer

  @Cepheus0815 

Cepheus0815 wrote

 Hi @Clive_A,

 

Sorry, for my late reply. Although you are correct in this case, that this is currently affecting IoT devices, I have seen the same behavior also with Omada switches and Omada AP. I don't undertand how a client can get himself a different IP address, if the DHCP server is forcing an IP address on the device. Anything other I can do, than reboot everything?

 

After the firmware update nothing changed.

 

The DHCP lease time for this VLAN interface is the default one (120 min), never changed it.

 

Thanks, Rainer

Wireshark and provide the capture of the DHCP interaction.

I would not comment on the reason or give suggestions as everything we've tried so far does not seem to fix it.

You insist that the device is getting the wrong IP but the only way to verify it is to see where that DHCP IP comes from and who assigned it. 

That's the thing that matters now. 

https://www.tp-link.com/en/support/faq/3235/

How Does DHCP Work? Common Questions and Solutions

  Hi @Clive_A ,

thank you for your prompt answer! You wrote "Wireshark and provide the capture of the DHCP interaction.". I do know whireshark, but I am not sure, how I can intercept the traffic between the gateway and any given device. May I kinldy ask you for a description, how I can capture the traffic between the gateway and the client from my PC (which is in the same network)?

Thank you so much,

Rainer

  @Cepheus0815 

Cepheus0815 wrote

  Hi @Clive_A ,

 

thank you for your prompt answer! You wrote "Wireshark and provide the capture of the DHCP interaction.". I do know whireshark, but I am not sure, how I can intercept the traffic between the gateway and any given device. May I kinldy ask you for a description, how I can capture the traffic between the gateway and the client from my PC (which is in the same network)?

 

Thank you so much,

Rainer

See the link 1.

You mirror the PC to the port where your AP is connected. Then use the filter to see the results. dhcp is the filter you should use. 

Port mirroring guide can be found in the User Guide. 

  @Cepheus0815 I find that whenever I change IP addressing in DHCP reservations, frequently those changes don't take affect until I reboot the gateway (in my case an er8411, but I'd image the same across the lineup).  after the router reboot, the new IP address change takes affect as soon as the device renews it's IP address.  not really sure why that is, but it seems to be a glitch in the router's DHCP server.  inconvenient but not intolerable...