NAT

Включаем форвардинг:

sudo nano /etc/sysctl.conf

Раскомментируем строку:

net.ipv4.ip_forward=1

Применяем настройки форвардинга:

sudo sysctl -p

/etc/default/ufw

DEFAULT_FORWARD_POLICY="ACCEPT"

В /etc/ufw/before.rules вставляем:

# nat Table rules
*nat
:POSTROUTING ACCEPT [0:0]

# Forward traffic from eth1 through eth0.
-A POSTROUTING -o enp3s0 -j MASQUERADE

# don't delete the 'COMMIT' line or these nat table rules won't be processed
COMMIT

sudo ufw disable && sudo ufw enable