Client PCs   |--------|
  Windows-----|        |                |----------------|
   Linux(1)---| Switch |-------------(2)| Server (18.04) |(3)-------Internet
  Printer-----|        |                |----------------|
 Other PCs----|        |
              |--------|

eth0  Link encap:Ethernet  HWaddr 00:19:66:82:61:f7
      inet addr:192.168.1.126  Bcast:192.168.1.255  Mask:255.255.255.0
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:37 errors:0 dropped:0 overruns:0 frame:0
      TX packets:82 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000
      RX bytes:4829 (4.8 KB)  TX bytes:8871 (8.8 KB)
      Interrupt:23 Base address:0xa800

lo    Link encap:Local Loopback
      inet addr:127.0.0.1  Mask:255.0.0.0
      UP LOOPBACK RUNNING  MTU:16436  Metric:1
      RX packets:142 errors:0 dropped:0 overruns:0 frame:0
      TX packets:142 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0
      RX bytes:10976 (10.9 KB)  TX bytes:10976 (10.9 KB)

network:
  version: 2
  renderer: NetworkManager
  ethernets:
    enp5s0:
      dhcp4: no
      dhcp6: no
      addresses: [192.168.1.2/24]
      nameservers:
        addresses: [8.8.8.8,8.8.4.4]
    enp0s31f6:
      dhcp4: no
      dhcp6: no
      addresses: [192.168.0.5/24]
      gateway4: 192.168.0.1
      nameservers:
        addresses: [8.8.8.8,8.8.4.4]

sudo iptables -t nat -A POSTROUTING -s 192.168.1.0/24 ! -d 192.168.1.0/24 -j MASQUERADE

sudo apt install iptables-persistent