For my setup, the host first obtains an internet connection, then forwards and shares it with the router via an Ethernet cable. The solution is described below. PS: This configuration was performed on a fresh Ubuntu installation. If your environment contains configurations that need to be retained, back them up first to avoid losing them.
Check the Current Network Status
ip addr# 1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000# link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00# inet 127.0.0.1/8 scope host lo# valid_lft forever preferred_lft forever# inet6 ::1/128 scope host noprefixroute# valid_lft forever preferred_lft forever#2: enp1s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000# link/ether 68:1d:ef:4a:41:4e brd ff:ff:ff:ff:ff:ff# inet6 fe80::85cf:33e6:14a0:3af6/64 scope link noprefixroute# valid_lft forever preferred_lft forever#3: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000# link/ether 68:1d:ef:4a:41:4f brd ff:ff:ff:ff:ff:ff# inet 192.168.0.148/24 brd 192.168.0.255 scope global dynamic noprefixroute enp3s0# valid_lft 7094sec preferred_lft 7094sec# inet6 fe80::8590:b5db:d80c:eae8/64 scope link noprefixroute# valid_lft forever preferred_lft forever#4: wlp2s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000# link/ether bc:2b:02:7c:27:a7 brd ff:ff:ff:ff:ff:ff#5: enx5a5f0a205236: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000# link/ether 5a:5f:0a:20:52:36 brd ff:ff:ff:ff:ff:ff# inet 192.168.9.107/24 brd 192.168.9.255 scope global dynamic noprefixroute enx5a5f0a205236# valid_lft 3421sec preferred_lft 3421sec# inet6 fe80::86cb:2037:bfdc:9300/64 scope link noprefixroute# valid_lft forever preferred_lft foreverIdentify the network interfaces connected to the internet and the router.
Network Configuration
1. Modify the Netplan Configuration
- Remove all existing Netplan configuration files:
sudo rm -rf /etc/netplan/*.yaml
2. Create a new basic configuration file: shell
sudo nano /etc/netplan/01-netcfg.yaml
3. Add the following content to enable DHCP on the internet-facing interface and configure a static IP address for the network interface connected to the router: yaml
network:
version: 2
renderer: networkd
ethernets:
enp1s0:
addresses:
- 192.168.1.1/24
dhcp4: false
gateway4: 192.168.1.254
nameservers:
addresses:
- 8.8.8.8
- 8.8.4.4
enx5a5f0a205236:
dhcp4: true
4. Save the file and exit, then apply the configuration: shell
sudo netplan apply
```
2. Verify the Network Configuration
Run the following command to check whether each interface has successfully obtained an IP address:
ip addr- Expected state:
- The internet-facing interface should obtain an IP address via DHCP.
- The router-facing interface should be assigned a static address.
Run the following command to check whether
enp1s0has been assigned a static IP address:
ip addr show enp1s0
The output should include: plain text
inet 192.168.1.1/24 scope global enp1s0
```
3. Configure Network Sharing for the Router
In my network layout, enx5a5f0a205236 provides the internet connection, which is shared with the router through enp1s0:
3.1 Enable IP Forwarding
- Enable it temporarily:
sudo sysctl -w net.ipv4.ip_forward=1
2. Enable it permanently by editing the **`/etc/sysctl.conf`** file: shell
sudo nano /etc/sysctl.conf
Ensure that the following line is uncommented: plain text
net.ipv4.ip_forward=1
3. Apply the configuration: shell
sudo sysctl -p
```
3.2 Configure NAT Forwarding
- Add NAT forwarding rules:
sudo iptables -t nat -A POSTROUTING -o enx5a5f0a205236 -j MASQUERADE
sudo iptables -A FORWARD -i enx5a5f0a205236 -o enp1s0 -m state —state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i enp1s0 -o enx5a5f0a205236 -j ACCEPT
2. Save the rules: shell
sudo apt install iptables-persistent
sudo netfilter-persistent save
sudo netfilter-persistent reload
```
4. Configure the DHCP Service
The router’s WAN interface needs to obtain an IP address through enp1s0, which requires configuring a DHCP service.
4.1 Install the DHCP Service
Install isc-dhcp-server:
sudo apt updatesudo apt install isc-dhcp-server4.2 Configure DHCP
Edit the /etc/dhcp/dhcpd.conf file:
sudo nano /etc/dhcp/dhcpd.confAdd the following content:
subnet 192.168.1.0 netmask 255.255.255.0 { range 192.168.1.10 192.168.1.100; option routers 192.168.1.1; option domain-name-servers 8.8.8.8, 8.8.4.4;}Specify the interface used by the DHCP service:
sudo nano /etc/default/isc-dhcp-serverSet:
INTERFACESv4="enp1s0"4.3 Start the DHCP Service
Start the DHCP service and check its status:
sudo systemctl restart isc-dhcp-serversudo systemctl status isc-dhcp-server5. Verify Network Sharing
- Check whether NAT and IP forwarding are working:
sudo iptables -t nat -L -v
cat /proc/sys/net/ipv4/ip_forward
```
- Ensure that the NAT rules are present.
- cat /proc/sys/net/ipv4/ip_forward should return 1.
2. **Test the network connection on a device connected to **enp1s0****:
- Ensure that the device obtains an IP address via DHCP.
- Test whether the device can access the internet.
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