Internet went down. Tried two routers. Why did MAC Address Clone fix my internet?

[Sharpbarb]

I primarily use an AX88U. I also have a spare AC86U.

This afternoon the internet via the router stopped working all of the sudden. When I connected the router directly to my PC the internet worked fine. The router main page said "Your ISP's DHCP is not working properly" and there was a red light on the router. I rebooted the router and the modem and it didn't work. I tried different cables and that didn't work.. I factory reset the router; nothing. I installed stock firmware (was Merlin); no change. I pulled out my old AC86U and it gave me the same exact problem "Your ISP's DHCP is not working properly."

I called my ISP and they said everything looked fine on their end. I finally called ASUS Support and explained the problem. Right away they had me go into the settings under WAN and change some settings under "Special Requirement from ISP." They said to press "MAC Clone" and "Change DHCP frequency to "Normal." Boom! All of the sudden it worked. If I reverted the settings to default, it stopped working.

Why did this work? Why would doing a MAC clone suddenly make my router able to communicate with the modem?

 

[Tech Junky]

Some ISP's use what's called a sticky static IP which binds to the MAC of the attached device. Typically rebooting the ISP device sends a notification to the ISP DHCP server to get a new one when it comes back online. Sometimes this doesn't work and needs to be manually released to issue a new IP to a new MAC.

 

[Justinh]

Which MAC is being cloned from where to where? The ISP is attaching to the modem, not the router, right?

 

[Sharpbarb]

Which MAC is being cloned from where to where? The ISP is attaching to the modem, not the router, right?

The "MAC Clone" button in the WAN settings apparently will clone the MAC address of whichever device is logging into the router. In my case, it cloned the MAC address of my PC.

So the internet would work when the modem was directly connected to my PC or if I connected to modem to the router and set the router to clone my PC MAC address.

I eventually called my ISP back and explained what worked to see if they had any insight. They tried "re-provisioning" the modem and that seemed to do the trick. I was able to restore the router to the default settings and it works as it normally did.

I would really like to understand the issue so I can prevent this from happening in the future. At least now I have a temporary work around.

 

[RMerlin]

Which MAC is being cloned from where to where? The ISP is attaching to the modem, not the router, right?

The DHCP lease is tied to the MAC. That`s why with many cable providers, when you change router you also need to unplug the modem for 5-10 minutes for the ISP to forget that router's MAC/lease, and to allocate a lease to the new router.

 

[Justinh]

The DHCP lease is tied to the MAC. That`s why with many cable providers, when you change router you also need to unplug the modem for 5-10 minutes for the ISP to forget that router's MAC/lease, and to allocate a lease to the new router.

So the MAC in question is the router's and not the modem's.
I still don't know what MAC address is being "cloned" to what. Is it the old router's MAC being cloned to the new router?

Strange that it is not the modem's MAC address that the lease gets attached to.

 

[Tech Junky]

not the modem's MAC address that the lease gets attached to.

It's always the first attached device to a provider modem

 

[ColinTaylor]

So the MAC in question is the router's and not the modem's.
I still don't know what MAC address is being "cloned" to what. Is it the old router's MAC being cloned to the new router?

The "MAC Clone" button in the router's GUI populates the "MAC Address" field with that of the PC you're currently logged in with. If you want to use a different MAC address, for example one from a previous router, you can enter it manually instead.

By default the "MAC Address" field is empty in which case the MAC address of the router's WAN interface will be used.

Strange that it is not the modem's MAC address that the lease gets attached to.

The modem is operating as a network bridge so the MAC address of the router (or whatever device it is that's connected to the modem) is simply being forwarded upstream to the ISP's DHCP servers.