all you need is your kernel to listen to RAs
Accept Router Advertisements (default is 1)
0 -- Do not accept Router Advertisements
1 -- Accept Router Advertisements if forwarding is disabled
2 -- Overrule forwarding behaviour. Accept Router Advertisements even if forwarding is enabled
and eventually enforce them on the front-facing interface when dealing with a router (that would possibly manage a delegated prefix on its internal interface, while receiving a SLAAC address on its external interface)
nic=xenbr0
nic=eth0
echo 2 > /proc/sys/net/ipv6/conf/$nic/accept_ra
check
ls -lF /proc/sys/net/ipv6/conf/*/accept_ra
cat /proc/sys/net/ipv6/conf/*/accept_ra
ls -lF /proc/sys/net/ipv6/conf/*/autoconf
cat /proc/sys/net/ipv6/conf/*/autoconf