luizluca:

Netifd uses a all-zero mac address when interface is not a bridge and ip6ifaceid is 'eui64'.

It happens on x86/generic and x86/64, both with Trunk (r7516-ac10975) and 18.06rc1.

root@OpenWrt:# uci set network.lan.ip6assign='64'
root@OpenWrt:# uci set network.lan.ip6prefix='fdc8:1234:5678:abcd::/64'
root@OpenWrt:# uci set network.lan.ip6ifaceid='eui64'
root@OpenWrt:# uci delete network.globals.ula_prefix #just to avoid also listing ULA addressses
root@OpenWrt:# uci delete network.lan.type
root@OpenWrt:# uci commit
root@OpenWrt:# /etc/init.d/network restart
root@OpenWrt:# ip -6 link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN qlen 1000
link/ether 08:00:27:b7:ae:8e brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN qlen 1000
link/ether 08:00:27:a7:cc:ce brd ff:ff:ff:ff:ff:ff
root@OpenWrt:~# ip -6 address show scope global
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 1000
inet6 fdc8:1234:5678:abcd:200:ff:fe00:0/64 scope global
valid_lft forever preferred_lft forever

In this case, Host ID for eth0 is ::200:ff:fe00:0, which is generated when mac is 00:00:00:00:00:00.

If type is bridge, it can read the mac address and get the correct IPv6 address.
Another workaround is to force macaddr for that interface:

root@OpenWrt:# uci set network.lan.macaddr='08:00:27:b7:ae:8e'
root@OpenWrt:# uci commit
root@OpenWrt:# /etc/init.d/network restart
root@OpenWrt:# ip -6 address show scope global
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UNKNOWN qlen 1000
inet6 fdc8:1234:5678:abcd:a00:27ff:feb7:ae8e/64 scope global
valid_lft forever preferred_lft forever

The address fdc8:1234:5678:abcd:a00:27ff:feb7:ae8e is the expected output.