Zywall 2 suddenly stops working with Comcast cable modem?!

Zywall 2 suddenly stops working with Comcast cable modem?!
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anon @ 23rd Sep 08:16PM:
Zywall 2 suddenly stops working with Comcast cable modem?!

For the past 2 years, I've been using this configuration:

cable --> cable modem --> Zywall 2 Plus ---> PC

where "cable modem" == Comcast's Motorola surfboard (model: SB5101)

Today, while VPN'd in to work, I suddenly lost all connectivity.
At first I thought the VPN had dropped.

But it turned out I'd actually lost all connectivity.
After 5 hrs of troubleshooting and rebooting in various permutations, it looks like the problem is that (for some strange reason) my Zywall 2 Plus will no longer talk to the Comcast cable modem?!

Ie, the only way the PC will connect to the cable modem is if I remove the Zywall 2 Plus, and have this setup:

cable-->cable modem-->PC

Comcast tech support was useless.

Any suggestions?
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meowBB @ 28th Sep 07:38PM:
Re: Zywall 2 suddenly stops working with Comcast cable modem?!

Can you still login to the Zywall 2 Plus? If you can, you should call Comcast and ask them to reset the modem for you.
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switchman @ 1st Oct 06:52AM:
Re: Zywall 2 suddenly stops working with Comcast cable modem?!

These are the steps I would try:

1 - Does the modem/Zywall appear to sync up by looking at the lights. - If not, change cable with known good cable. If still no indication of Sync then possibility that you WAN port has gone out.

2 - Power down all of you equipment and power up in this order: Modem - Router - PC's

3 - Go to »192.168.100.1/RgConfig.asp on the Modem and select Restore Factory Defaults

4 - Log into router if possible and capture any specific rules/configuration information. Go to MAINTENANCE - Configuration and select the RESET button.

5 - If still not working, do a hard reset of the router using the reset button, look up how in the instructions, I think there is a special sequence to do a hard vs soft reset.

6 - As last resort I would try and load new firmware, it is possible your firmware got corrupted.
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JJJohnson @ 5th Oct 04:38PM:
Re: Zywall 2 suddenly stops working with Comcast cable modem?!

I have a Z2+ and Motorola SB5120 on Comcast and haven't seen this problem. But I have been losing connectivity a lot lately for about 30-60 seconds each time. Comcast is doing a lot of network work in my area in upgrading to DOCSIS 3.0 and (apparently) this behavior is typical while they're upgrading. What I typically see is that the SB5120 cable modem will become unavailable at »192.168.100.1 while the connection is lost. The connection tends to come back up much quicker if I just leave things alone rather than trying to reset the cable modem or mess with the Z2+.
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