I recently upgraded from a Hitron CGNM-2250 to an XB6. Specifically, I received the Technicolor CGM4140COM, and have placed it bridge mode, where it is connected to a Ubiquiti ER-X SFP.

With the Hitron, I had an IPv6 tunnel with Hurricane Electric (https://tunnelbroker.net) working for years without issue. With the XB6, no such luck. While I appreciate that the XB6 is finally allowing native IPv6 connectivity (and I am making using of it via DHCPv6 PD), I would still like the Hurricane Electric tunnel as it provides a know stable IPv6 address vs the Shaw delegated prefix which makes no such guarantees.

After extensive testing and packet capture, it appears that the tunnel works in the outbound direction, with a ping reaching the target host, and is then returned, but that never makes it back to the tunnelled IPv6 address. As best as I can tell, these 6in4 protocol 41 packets are blocked somewhere by the XB6, or within whichever cloud stack that it's dealing with.

I'm seeing Comcast users with a CGA4131 (which uses the same Broadcom BCM3390 chipset as Shaw's CGM4140) seeing this same issue develop between a 3.x and 4.x firmware version (my CGM4140 is currently running CGM4140COM_4.4p8s1_PROD_sey) (https://forums.businesshelp.comcast.com/t5/Connectivity/IPv6-over-IPv4-6in4-seems-to-be-blocked/td-p...), but Comcast employees there seem to have been less than helpful.

I'm hoping that I can get confirmation that another Shaw customer is seeing this issue too, and hopefully some helpful comments from a Shaw employee, probably @corbin if he's still around.