Problems with DHCP, routing after changing service address

[piperd]

I've been running various Rogers modems in bridge mode since at least 2005, and have always used Cisco gear as my router/firewall.  Most recently I have been running a Cisco 921-4P router connected to a Hitron CGN3 in bridge mode.  Service was 150u non-Ignite, and I was successfully using IPv4 and IPv6.

We moved about a month ago and had to go to an Ignite Internet plan - still 150u - and I was dismayed to find that my Cisco router would no longer work with the XB6 in bridge mode.  I seemed to be getting a public IPv4 address and could access the XB6 admin page at 10.0.0.1, but could go no further.  After a lot of dead-ends with Rogers tech support I discovered that I could get IPv4 working if I disabled IPv6 support.

I'm at a bit of a loss to understand what's happening.  Assuming that the IPv6 prefix at the old and new service addresses would be the same, then part of me thinks that something in Rogers network has associated my router's unique global IPv6 address to the old service address.  But this doesn't necessarily explain why IPv4 is affected.

I'm throwing a hail mary on this post and hoping that somebody says "Oh yes, I had problems with IPv6 when I moved too - here's what I did".

Thanks.

[stepy2015]

I use pfSense and I haven't even enabled IPV6, I don't really see a point. Is there a reason you need IPV6?

Anyway you might want to look at this 

https://communityforums.rogers.com/t5/Internet/Rogers-IPv6-Status/m-p/373238/highlight/true#M36710

and I don't think the modem is supposed to be accessible from 10.0.0.1 after bridging, (I could be wrong) I still have the Hitron modem and after bridging it, it is accessible from 192.168.100.1 so I would assume the new modem might change ip's too 

try factory resetting and re-bridging

https://www.rogers.com/customer/support/article/how-to-bridge-your-rogers-ignite-modem

[piperd]

Thanks for the reply. IPv6 is not strictly required, however I have provisioned some Google Assistant services on the basis of an IPv6 hostname. And - IPv6 is the future, I would like it to be enable.

The most troubling thing about this is why enabling IPv6 messes up my IPv4 routing even this exact same router config worked for about a year on the Hitron.

[Linuxguru]

You could bypass the modem [ no bridge mode]and hook up the modem to your router through the wan port connected to the router then reset your router any way you need it. Thats what I use. It is now a dual network setting. I can can connect online to either device.