The grep calls were meant to be run inside the container, not on the host.
Though in any case, the issue is firewalling. You can see that your default policy for INPUT, FORWARD and OUTPUT is DROP. There are some basic rules that LXD put in place to allow DNS and DHCP to make it through but your firewall isn’t even allowing basic ICMP6 multicast traffic so route advertisement won’t make it through.
Can you try:
- ip6tables -I INPUT -i lxdbr0 -p icmpv6 -j ACCEPT
- ip6tables -I OUTPUT -o lxdbr0 -p icmpv6 -j ACCEPT
This should allow sending and receiving ICMPv6 which should unblock the router advertisements. If that does the trick, I think I’ll send a tweak to LXD upstream so we add those rules automatically like we do DNS and DHCP.