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Linux as router

  • eth0: WAN
  • eth1: LAN

Enable IP Forwarding

sysctl
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sudo sysctl -w net.ipv4.ip_forward=1
- To make it permanent, add the following line to /etc/sysctl.conf:
sysctl.conf
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net.ipv4.ip_forward = 1
- To apply the changes, run:
sysctl
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sudo sysctl -p

IPTables Configuration

rules

iptables
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sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT
sudo iptables -A FORWARD -i eth1 -o eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT

Save/Persist iptables rules

  • To save the iptables rules, you can use the following command:
    iptables
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    sudo iptables-save > /etc/iptables/rules.v4
  • To restore the iptables rules on boot, you can use the following command:
    iptables
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    sudo iptables-restore < /etc/iptables/rules.v4
  • To make the iptables rules persistent across reboots, you can install the iptables-persistent package:
    apt
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    sudo apt-get install iptables-persistent
  • During the installation, you will be prompted to save the current iptables rules. Choose "Yes" to save them.
  • After installation, the iptables rules will be automatically restored on boot.