66U B1 with Xfinity and Arris T25 Modem...cannot get ip address after modem restart

[jplw]

I have had this probem across many firmware versions, including the latest. I have a RT-AC66U B1 and Xfinity internet with an owned Arris T25 modem. If I restart the modem (by power cycling), or Xfinity reatarts it (by sending a restart signal), the 66U cannot get an IP address from the modem thereafter. I have tried these things:

1. Power cycling the router.
2. Rebooting the router via uts GUI.
3. Having the router on and connected when the modem restarts.
4. Having the router off when the modem restarts, then turning it on.
5. Having the router on but disconnected when the modem restarts, then connecting it.

In none of the cases does the router get an IP address from the modem.
If I plug any other router into the modem I immediatelty get an IP address...telling me that the ASUS router is the problem.

The only way I can fix it is to factory reset and reconfigure the router (quite a pain).

Does anybody know what is wrong and how I can fix it short of factory reset?

 

[bbunge]

First do not reboot the modem. If you have to, power down both modem and router. Then power up the modem for 10 or more minutes. Then power up the router. Comcast can be a pain with some modems. A small UPS is a good investment to prevent problems!

 

[jplw]

Thanks. I tried that except that I waited only 5 minutes after restarting the modem. USP is s good idea...in fact I have one. I have to restart the modem when Comast performs service in my area and the speed drops way down. But why would restart effect only the Asus router? Other routers work find after restarting the modem.

 

[wouterv]

What is the Router WAN Connection Type?
I assume with the Arris modem it is Automatic IP.
In the Network Map page, open the Internet status and try to toggle the Internet Connection ON / OFF.
There is also a "DHCP query frequency" setting in the WAN page that you may try to alter.

 

[andyross]

There are several threads on the Comcast forums of similar issues with Asus routers. One of the most common fixes is to call in and have Comcast re-provision the modem. I'm guessing this clears the DHCP assigned to your router as a side-effect? You can alter the MAC address of the router to force a new IP address. If that works, try waiting a few weeks then letting it use it's default again and see if it then works.

 

[jplw]

Reprovisioning works, but Comcast has removed that option from their agents. I used to do that.