A fixed IP SIM card gives your IoT device a permanent, reachable public IP address on the mobile network. Most SIM cards use dynamic IP allocation – the network assigns a new address each time the device connects. A fixed IP SIM changes this permanently.
Why IoT deployments need fixed IP
Any application requiring remote access to the device – CCTV, SCADA polling, remote router management, VPN termination – needs a known, stable endpoint. Dynamic IP makes this difficult without DDNS, which introduces its own failure modes.
Fixed IP does not mean you choose the address. The operator assigns it from their IP range. It is permanent for the SIM lifetime, but it is their address, not yours.
Fixed IP vs private APN
Fixed IP SIM gives a public IP reachable from the open internet. Private APN gives devices non-routable private IPs accessible only through a dedicated network connection. They solve related but different problems.
A public IP SIM is visible to the whole internet. Automated scanners will probe it within hours. Never deploy with default credentials on a fixed IP SIM.
Getting a fixed IP SIM in the UK
Fixed IP SIMs are available from specialist IoT SIM providers. Typical cost is £2-8/month. For current UK provider recommendations see the IoT Portal connectivity guide.