I've been using IPv6 on Comcast for years now, and my prefix has been stable during that entire time. Double check that your DHCP client is not sending a new UU

I've been using IPv6 on Comcast for years now, and my prefix has been stable during that entire time. Double check that your DHCP client is not sending a new UUID for each lease request. The UUID should be stable so that the DHCP server knows to give you the same prefix each time. I've got a /60 with multiple VLAN's running without issues.