NWA50AX - %DHCP-I-OPTNWRNGVAL: Value 548 received in DHCP option 57 from MAC is lo

papu

Full warning message is: %DHCP-I-OPTNWRNGVAL: Value 548 received in DHCP option 57 from MAC ****  is lower than standard 576 

I am getting these messages from my Cisco switch (SG350), which acts as L3 router with DHCP server, and all apply from the NWA50AX access points only.

Still no problem; they do get their IP and connect through DHCP, but just curious why only Zyxel NWA50AX access points are showing this warning; ALL other dhcp clients do not show this warning.

Zyxel_Nami

Hi @papu

Thank you for reaching out.

We've analyzed the DHCP packet, the 548-byte figure represents the total frame size (590 bytes) minus the combined header lengths, resulting in 548 bytes for the DHCP payload in the NWA50AX packet as below screenshot. Also, we've noticed that other APs (NWA210AX, WAX650S,...) show a DHCP Option 57 size of 548 bytes as well.

Therefore, we are currently investigating why the switch specifically highlighted the message for NWA50AX and will need some time to find out the reason.

Please kindly wait for our feedback.

Zyxel_Nami

Hello @papu

Still no problem; they do get their IP and connect through DHCP, but just curious why only Zyxel NWA50AX access points are showing this warning; ALL other dhcp clients do not show this warning.

⇒ We would like to understand more about the other DHCP clients you referenced earlier. Could you please list some of them?

Also, are there any other APs, including those from Zyxel or other brands, connected to the same switch?

Your input would be greatly appreciated.

papu

above a screenshot of recurring messages on the Cisco SG350. Next to the two NWA50AX also a NWA210AX is showing the same warning.

Beside these Zyxel DHCP clients (the only Zyxel's I have), other clients are dozens of Android/Apple phones/pads, multiple Windows laptops and PC's, as well as a dozen of IOT devices, which do not show these warnings. All in one flat subnet.

Sorry no time to do some wireshark packet analysis at this time.

Could be an issue with this Cisco model. No priority as we do not encounter any issues; just message logging.

papu

To specifically answer your questions: no other access points beside NWA50AX/NWA55AX/NWA210AX in my network.

Clients through these access point do not show this DHCP warning. Wired clients directly connected to the switch do not show these DHCP warnings.

In a previous setup without Cisco SG350 in L3 mode; never had these warnings.

I suspect false positives from the Cisco DHCP server.

Zyxel_Nami

Hello @papu

Thank you for your update.

We conducted tests with our local DHCP server interacting with the AP/end devices and didn't encounter the mentioned warning. It appears the DHCP process functions smoothly, and the issue might be specific to the interaction with the Cisco switch.

We will continue to investigate to ensure compatibility and performance remain consistent, and we will get back to you with our findings.

Zyxel_Nami

Hi @papu

We've conducted tests on many end devices and APs, including other brands that do not have DHCP Option 57, and confirmed that the DHCP process functions normally without it. This issue typically does not trigger any operational problems. However, we can apply a specific date code that removes this DHCP option to prevent your Cisco switch from logging these warnings. Would you be willing to try this update?

Please let us know your thoughts.