Reserved address not applying

I have a reserved address for MAC, but its not applying. Its supposed to set that mac-address to a static ip of

The device on the MAC is a RS232-WiFi adapter, and I'm connecting it to WiFi, and every thing works except its not assigning that specific IP to that specific device.

I'm using Firebox as my dhcp server.


  • edited November 2022

    If the firewall already has a entry for this MAC addr in its ARP cache, it won't apply a different IP addr.

    Clear the ARP table on the firewall, and you should get the device to get the desired IP addr.

    You can clear the ARP cache using FSM

  • Thank you, that worked.

  • Now it goes back to dhcp when ever the device reconnects to WiFi.

  • Is the MAC addr still the one initially posted?
    Many wireless devices change MAC addrs unless an option is changed on the device.

  • For example, on my iPhone, I need to unselect Wi-Fi -> "Private Wi-Fi address" so that the same MAC addr is always used by it.

  • Yes, the MAC addr is the same. Same as before, and the same one that's labeled on the back of the device.

    I think it might be my WiFi, because the one AP the device is connecting is also disconnecting once in a while.

  • That does not explain the device getting the old IP addr again.

    What do you see in Traffic Monitor for dhcpd log messages for this MAC addr?

    If you use FSM Traffic Monitor, one can set the max log messages to keep, up to 25k.
    Settings -> Maximum Log Records
    Search for: dhcpd

  • I don't see anything for that mac-address. That device is a WiFi device, and I'm having issues with one of my AP.

  • I'm sorry, this is stupid. Someone unplugged the device so it was not turned on. Its getting the static IP now. I'm not on site, so I had no clue.

  • Yup, APs won't work without power or an Ethernet connection.

    Glad that it is working again.

  • So far, after the device was reconnected to WiFi, instead of getting the mac-addr ip reservation, it got DHCP. One time so far.

  • The firewall logs should show DHCP requests from clients and DHCP replies to them, which should show light on the issue.

    For example, the client sends DHCPREQUEST for a specific IP addr.
    If that IP addr is already associated with the MAC addr of the client, then the DHCP server will send an DHCPACK , acknowledging the request.
    If it isn't, then the DHCP server will offer an IP addr.
    If the DHCP server has a MAC addr reservation which matches, then the DHCP server offers the reservation IP addr - otherwise it offers one from its available list from the DHCP pool.

  • ok thanks again

  • You can do DNS Logging on your Windows DNS server to see what is coming to it and what it is responding.

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