Debian / Ubuntu

ifupdown

Edit /etc/network/interfaces:

# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d
source /etc/network/interfaces.d/*

auto eth0
iface eth0 inet static
        address <Your IPv4 address>/32
        gateway 100.100.0.0
        pointopoint 100.100.0.0
        dns-nameservers 23.143.176.176 23.143.176.177

iface eth0 inet6 static
        address <Your IPv6 address>/64
        gateway fe80::1

And delete /etc/network/interfaces.d/eth0

RouterOS

/ip address add address=<Your IPv4 Address> interface=ether1 network=100.100.0.0
/ip route add distance=1 gateway=100.100.0.0

/ipv6 address add address=<Your IPv6 Address>/64 interface=ether1 advertise=yes
/ipv6 route add gateway=fe80::1%ether1