What is LAN?
Local Area Network
A LAN (Local Area Network) is a network connecting devices in a limited area, such as a home, office or building, usually over Ethernet or Wi-Fi.
Technically, a LAN is usually one layer-2 broadcast domain: every device on it can reach every other device directly by MAC address, and a broadcast (such as an ARP request) reaches all of them. Switches connect the devices and learn which MAC address lives on which port. A LAN normally matches one IP subnet, for example 192.0.2.0/24, and hosts reach anything outside that subnet through a default gateway, the router interface on the LAN. Many home and office LANs use private ranges such as 10.0.0.0/8 or 192.168.0.0/16 and rely on NAT at the edge. A VLAN splits one physical switch into several separate LANs, each its own broadcast domain, joined only by a router.
Engineers use the word in a few related senses: the inside network of a router (as in "WAN and LAN interfaces"), a single Ethernet segment, or more loosely a whole campus network. In routing protocols it has a narrower meaning. An OSPF interface on a LAN is normally the broadcast network type, where routers find each other with multicast hellos and elect a DR to cut down the number of adjacencies; a link with only two routers is often better configured as point-to-point. Common LAN problems are a wrong subnet mask or gateway on a host, two devices with the same address, and loops between switches, which is what STP prevents. The Switching basics lesson builds a LAN from a switch, three PCs and a router, then splits it with VLANs.
Lessons that use LAN
- Office gateway: DHCP, DNS and VRRP on VyOSBeginner · 40 min
Two VyOS routers serving one office LAN: VRRP for a gateway that survives a router failure, DHCP with split pools and a printer reservation, and DNS forwarding. Then a real failover, the DNS outage it exposed, and the fix.
- Zone-based firewall on VyOSIntermediate · 35 min
Rebuild the NAT lesson's router with a zone-based firewall: WAN, LAN, a DMZ and the router itself, with one ruleset per direction. Includes the missing-return-traffic mistake, post-NAT matching, and a full test matrix.
- Edge and core: building out a VyOS networkIntermediate · 60 min
Split one BGP router into edge routers that face the outside world and a core that carries traffic inside: loopbacks, OSPF for infrastructure, iBGP between loopbacks, next-hop-self, and what happens when a link fails. Built and broken on three real VyOS routers.
- Setting up VyOS with NATBeginner · 45 min
A VyOS router with a NAT interface for a private LAN and a public interface for a routed public subnet: plain routing, source NAT, port forwarding and the forward firewall that NAT isn't. Every output comes from a real VyOS lab.
- IPv6 on VyOS: setup and routingBeginner · 55 min
Number a site from an ISP's /48 on VyOS: WAN and blackhole routes, SLAAC with Router Advertisements, handing a /56 to a downstream router statically and with DHCPv6 prefix delegation, and the forward firewall IPv6 needs because there's no NAT. Every output comes from a real two-router VyOS lab.
- Site-to-site VPN with WireGuard on VyOSIntermediate · 35 min
Join two sites' private LANs across the internet with WireGuard on VyOS: keys and peers, the AllowedIPs mistake and what it teaches, what the internet actually sees, and the tunnel's smaller MTU.
- Setting up VyOS with basic BGPIntermediate · 50 min
Build a VyOS edge router from scratch: one upstream transit provider, one Internet Exchange route server, and the import and export policy that keeps both safe. Every command and output comes from a real VyOS lab.
- Linux Network ConnectivityBeginner · 80 min
Find out why a Linux machine can't reach something, layer by layer: interfaces and addresses, routes and ip route get, ARP and the neighbour table, ping and traceroute, DNS, and listening sockets — with real output from a three-host lab.