IPv6 connectivity stopped working, so I rebooted my Comcast router (Comcast provided SMC), and when it came back up, my LAN IPv6 range had changed. As a result, I then had to go around all the equipment on my LAN that supports IPv6 and manually renew DHCP leases or reboot it to pick up the new LAN IPv6 range. This is the second time this has happened.
Why is my IPv6 range changing? Or how is a change of IPv6 range expected to automatically propagate to my router, and then all the equipment behind it, without either lengthy IPv6 outages (could be up to a week with the default 10080 minute IPv6 address lifetime!), or time consuming manual intervention that requires me to be physically present?
As I (and others) have stated on this forum in the past the SMC has bugs with IPv6. You have run into one. You have 2 choices:
1) Buy a lamp timer (one of those devices you plug your living room lamps into that turn them off and on when you are away so the burglars think you are at home) and set it to turn off your SMC and turn it back on maybe at 2am.
2) Have Comcast replace the SMC with a Netgear.
Your SMC router shouldn't be locking up under IPv6. That is a defect. You cannot expect equipment that has defects to act in a normal fashion. This defect was filed with SMC over 2 years ago and they have done nothing. I don't even think that Comcast offers the SMC anyore to new users.
My SMC isn't locking up. IPv4 connectivity is still working fine, and I can still access the SMC via the administrative interface. The problem I'm seeing seems to be only due to my LAN IPv6 range being renumbered and the SMC and all my equipment behind it not automatically picking up the renumbering.
Your modem's IPv6 address is obtained via DHCP. As long as the Comcast IPv6 DHCP server continues to get renewal requests from your SMC modem, the IPv6 address your modem has won't change. (at least that is what I and many others have observed)
Your problem is the SMC's IPv6 is buggy and periodically it's IPv6 will stop reissuing the re-lease requests. When this happens Comcast assigns your IPv6 address to someone else. That is why I said you need to reboot your SMC modem periodically. As long as not a lot of time is allowed to elapse from when the IPv6 DHCP allocation expires and when the re-lease request comes in from your modem, you will be fine.