[PaulGo]

I usually use IPv6 with Verizon FiOS and had no problems. However, I decided to try it with Comcast. I am running New Build - 10/01/2022 - r50308 on my Netgear R7000P. Using Comcast with vCMTS I need to put in the following commands:

Fix (added this to startup Firewall Commands):
ip6tables -F
ip6tables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
ip6tables -A INPUT -p icmpv6 -j ACCEPT
ip6tables -A INPUT -s fe80::/64 -j ACCEPT
ip6tables -A INPUT -p udp --dport 546 -j ACCEPT
ip6tables -A INPUT -i lo -j ACCEPT
ip6tables -A INPUT -i br0 -j ACCEPT
ip6tables -A INPUT -j DROP
---------------------------------------------------------------------------------------------------

Use dnsMasq for the LAN (additional dnsmasq options):

quiet-dhcp
quiet-dhcp6
quiet-ra
enable-ra
dhcp-range=::10,::1ff,constructor:br0,ra-names,slaac,64,24h

No need for either radvd or dhcp6s.

In the past using previous builds of several months ago it worked. However, now it did not. I then disabled IPv6 and I then got a IPv6 address. When I again enabled IPv6 the IPv6 address disappeared. I check this with my browser at an IPv6 test site to confirm this. It appears now with the above changes the IPv6 toggle has the opposite effect.

[PaulGo]

I tried rebooting the router, and it left the router in an unstable condition that would not connect to the internet and I had no access to the router. I reset the router and it is working properly. So the additions I previously made to gain access to Comcast's IPv6 no longer works.

[PaulGo]

I got it working with Comcast vCMTS by only using the firewall rules and NOT using "Use dnsMasq for the LAN (additional dnsmasq options)".

Also, be sure to change Prefix Length to 64.