A WAN (Wide Area Network) is the network connection that links a local network to the wider internet or to another remote network. In an industrial IoT deployment, the WAN is what carries device data from a site back to a cloud platform, corporate data centre, or monitoring system.

In short: In cellular IoT, the WAN is typically the 4G or 5G mobile network, with a SIM card in the router providing the connection. Some deployments use Ethernet or fibre as the primary WAN and cellular as a backup (failover) link. Others run cellular as the only WAN, particularly at sites where fixed-line broadband is unavailable, slow to deploy, or commercially impractical.

Industrial routers usually support multiple WAN interfaces simultaneously. A Teltonika RUTX12, for example, can hold two active SIMs across two modems, allowing dual-cellular WAN operation with automatic failover between them. RUT series routers often have one cellular WAN, one Ethernet WAN, and a Wi-Fi WAN option, giving operators flexibility to specify whichever combination matches site conditions and budget.

The WAN side of the router is where security policies are most important. The WAN interface is the device's exposed surface. This is why private APN, fixed IP, firewall configuration, and VPN tunnels all matter most on the WAN interface.