1. Modify Netplan configuration#

1. Remove all existing Netplan configuration files:

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   sudo rm -rf /etc/netplan/*.yaml

2. Create a new base configuration file:

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   sudo nano /etc/netplan/01-netcfg.yaml

3. Add the following content to enable DHCP on the interfaces and configure a static IP address for the NIC connected to the router:

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   network:
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     version: 2
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     renderer: networkd
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     ethernets:
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       enp1s0:
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         addresses:
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           - 192.168.1.1/24
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         dhcp4: false
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         gateway4: 192.168.1.254
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         nameservers:
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           addresses:
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             - 8.8.8.8
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             - 8.8.4.4
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       enx5a5f0a205236:
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         dhcp4: true

4. Save the file and exit, then apply the configuration:

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   sudo netplan apply

2. Validate network configuration#

Run the following commands to check whether each interface has successfully obtained an IP address:

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ip addr

• Target state:

  • The configured interfaces should obtain IP addresses via DHCP.

  • The router-facing interface should be assigned a static address.

    Run the following command to check whether enp1s0 has a static IP address:

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    ip addr show enp1s0

    The output should include:

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    inet 192.168.1.1/24 scope global enp1s0

3. Configure router network sharing#

According to my network layout, the Internet connection is provided by enx5a5f0a205236 and is shared to the router via enp1s0:

4. Configure DHCP Service#

The router’s WAN needs to obtain an IP address via enp1s0, which requires configuring a DHCP service.

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sudo apt update
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sudo apt install isc-dhcp-server

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sudo nano /etc/dhcp/dhcpd.conf

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subnet 192.168.1.0 netmask 255.255.255.0 {
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    range 192.168.1.10 192.168.1.100;
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    option routers 192.168.1.1;
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    option domain-name-servers 8.8.8.8, 8.8.4.4;
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}

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sudo nano /etc/default/isc-dhcp-server

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INTERFACESv4="enp1s0"

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sudo systemctl restart isc-dhcp-server
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sudo systemctl status isc-dhcp-server

5. Validate network sharing#

1. Check NAT and IP forwarding are active:

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   sudo iptables -t nat -L -v
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   cat /proc/sys/net/ipv4/ip_forward

   • Ensure the NAT rules exist.
   • cat /proc/sys/net/ipv4/ip_forward should return 1.

2. Test network connectivity on devices connected to enp1s0:

   • Ensure devices obtain IP addresses via DHCP.
   • Test whether devices can access the Internet.