Linux LAN Routing for Beginners

Linux is a real networking operating system, and always has been, with network functionality built-in from the beginning. Building a LAN router is simple compared to building a gateway router that connects your LAN to the Internet. You don’t have to hassle with security or firewall rules, which are still complicated by having to deal with NAT, network address translation, an affliction of IPv4. Why do we not drop IPv4 and migrate to IPv6? The life of the network administrator would be ever so much simpler.