WRT32X running 21.02.3 unable to grab WAN DHCP IP

Hello all,

I've been running OpenWrt stable on this device for probably the better part of the last 2 or 3 years, running on the 19.07 for quite a bit and doing incremental updates as they happened without issue.

With the 21.02 release, I did see that it was recommended to start fresh, so I flashed back to stock firmware and reset the config before doing a clean upgrade fresh to 21.02.3. I was able to apply it and upgrade without issue.

My problems start when I attempted to get the device up and online, I was unable to pull a WAN / Public IP Address from my ISPs Modem (Charter Spectrum - Modem is a Modem Only and not a Modem/Router combo). I haven't had to do anything silly or complicated in the past to get this to work either, it is a fairly dumb / simple configuration on my end where I simply plug the WAN/Internet port of a router into my ISP modem and receive a public IP.

But for whatever reason I was unable to pull one even after attempting to restart the interfaces, reboot the device several times, reboot the modem and reset it, even replug in every single cable. Eventually I had to call it and swap back to an older Buffalo DD-WRT router just for the sake of getting online while I troubleshoot this further in spare time.

If anyone has any recommendations, advice, or request more information please let me know as I'd love to get to the bottom of this. I have not tried going back to 19.07 to see if that fixes anything, as I didn't have the right tools to flash it back and get the older images when I was without an internet connection.

Two possible causes come to my mind:

  • Your modem requires to use a specific VLAN.
  • Your modem requires to use a specific MAC address.

Is the configuration on the DD-WRT router the same as the OpenWrt router?

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The configuration of the Buffalo DD-WRT is essentially out-of-the-box factory reset, I have actually never used it before on my current ISP (or home that I am currently living in) so nothing about it should be unique or have properties that are required by my ISP

(And if there are values / specifics required by my ISP, I have never know them and have interchanged routers in the past without issue here for example coming from a Netgear R7000 (Tomato Firmware) to a Linksys WRT32X (OpenWrt) without issue in the past.

Copy the WAN MAC of the Buffalo, and set it (MAC override) on the WRT32s WAN port.

Internet should start working.


I will try changing the WAN IP in a bit and report back (currently working / in meetings so need internet)

Is there something that is causing newer versions of OpenWrt to change the MAC Address that I should be aware of?

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There was a swap of LAN / WAN MACs between those releases, but given that you rebooted both devices, and apparently dropped in a completely different device, I don't think that explains what you are seeing.

Not IP, but MAC.

Your ISP could be caching the last MAC used, and not issuing any new IPs until the DHCP lease attached to that MAC expires.

A way around it is to let the ISP think your device haven't changed, which is done by cloning the WAN MAC.

Another option is obviously to wait, over night, perhaps, the current lease should expire, and you will (hopefully) be able to use a different MAC.

Apologies, I did mean WAN MAC* (Work brain)

But I was wondering if OpenWrt, either has been doing this or in the later versions - changes the factory MAC Address that would cause this from doing upgrades, going back to stock, etc.

Still plan to get around to testing a bit later and will report back after I do.

i expereinced a similar problem with my son's charter-spectrum account (modem only) after upgrading a router that caused its WAN MAC to change. it took mnay hours of spectrurm modem in power off state to get the spectrum system to 'forget' the previous WAN MAC.
if you can force a reset of your spectrum modem by using their management tool, it might speed up this process.
?? let us know

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Wan/lan MAC swap is probably comming from this
or here

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Apologies on the delay here as I was unavailable to change it yesterday, but I changed the "wan" interface in the web interface of LuCI to that of my Buffalo Routers WAN MAC Address and was able to swap it right back in and got right up and going, so it did work.

It is interesting to know that Charter Spectrum appears to be holding onto the MAC Address and taking sometimes hours to change. I was unable to find anywhere in their web portal where to release it or force a refresh, but also in the event of being offline - it is a bit of a hassle to do anyways.

I have taken note and am now aware of the MAC Snafu for the future. It does worry me a bit about the possibility of needing to put in a new device in the future and if I'll run into the same issue again, thankfully it seems multiple advanced user interfaces allow changing of MAC Addresses.

Also thank you very much @dr191 for the commit history of the swap. I guess I just had some bad timing on when I went to get the latest firmware, that I was hit by that and my ISP had started to do some level of MAC history.

Anyways, thanks all - TL;DR: ISP (Charter Spectrum) remembers MAC History of LAN device connecting to modem, and an upgrade from OpenWrt 19.07 to 21.02 which included a commit/change of the WAN/LAN MAC Addresses caused a MAC update that brought me offline.

If you're lucky, it may be sufficient to power off modem and router over night, for the existing lease to time out and for your ISP to accept a new MAC (the exact timespan varies and may take from 5-10 minutes to several hours - or it might require manual intervention (phoning them)).

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Thanks, I will try that when I get a new device. Again totally not an OpenWrt problem at that point, more of an issue with the ISP which sucks. But is appreciated!

I have been dealing with Spectrum (pka Brighthouse) for about 10 years now.

They run a warped headend that sets a cable-side ARP age of what appears
to be about an hour.

They are blind to device disconnection while this ARP entry is in the
table and while the modem is running, the modem will cache and re-supply
this MAC address to the headend even if the modem device is changed and
rebooted numerous times.

Stacked on that bad-dog conduct they have a 1 DHCP per modem constraint

So what happens is that when you disconnect the current device from the
modem and replace it with a new device, they will not issue another DHCP
address to you until the cable-side ARP entry expires, and for that to
even occur the modem must be power cycled removing it from the modem's

In order to do a device transition you either need to brace for the
anywhere from a minute to an hour of expiration time and you must power
cycle the modem after the new device is connected to it. This will
reliably resync, and will acquire a new IP address within an hour.

The only other alternative is to clone the MAC of the existing
router/host which will reconnect almost immediately but will retain the
previously assigned IP address.

The critical point is that if you make a device change, connect and
bring up the new modem/host device first, then power cycle the modem,
otherwise I am not sure it will ever see the new device.

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