Firewall :
ifconfig eth1 inet6 add 2000::1/64
ifconfig eth4 inet6 add 5000::1/64
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PC (Linux):
The external interface of PC connect with the eth4 interface of Firewall,
ifconfig eth0 inet6 add 5000::2/64
if we want this PC could send traffic to the interface 1 of Firewall, we need to add route in this PC:
ifconfig ip -6 route add 2000::/64 via 5000::1 dev eth0 metric 1