Most IoT SIM cards give your device an IP address that changes every time it reconnects. That is fine for devices that only send data outbound. The moment you need to reach the device from outside – for remote management, SCADA polling, CCTV viewing, or VPN termination – a dynamic IP becomes a problem.
A fixed IP SIM solves this. Your device gets a permanent public IP that stays the same regardless of which mast it connects to, whether it has been offline for a week, or whether it has roamed to a partner network.
Fixed IP SIMs are essential for any IoT deployment where something external needs to initiate a connection to your device. Outbound-only devices work fine on standard SIMs.
How fixed IP SIMs work
When a standard SIM connects to a mobile network, the Gateway GPRS Support Node (GGSN) or Packet Data Network Gateway (PGW in 4G/5G) allocates an IP from a shared dynamic pool. With a fixed IP SIM, the operator maintains a static mapping between your SIM IMSI and a specific IP address. Every time the device authenticates, the gateway assigns the pre-allocated address.
When you need fixed IP
Fixed IP is necessary for:
- CCTV and video surveillance – NVR access, live view, and clip retrieval all require incoming connections
- SCADA remote access – Modbus TCP, DNP3 and IEC 61850 sessions are typically initiated from the control room towards the field device
- Remote router management – SSH, HTTPS admin and Teltonika RMS all benefit from a known endpoint
- VPN server termination – if the cellular device is the VPN server endpoint, it needs a stable reachable address
The security requirement
A fixed public IP means your device is reachable by anyone on the internet. Automated scanners will probe for open ports and default credentials within hours of a device coming online. This is not a reason to avoid fixed IP SIMs – it is a reason to harden the device properly before deployment.
Documented cases exist of routers deployed with default credentials on fixed IP SIMs being compromised within 24 hours. Default credentials on a public IP is not a theoretical risk.
| SIM Type | IP Type | Internet Reachable | Best For |
|---|---|---|---|
| Standard dynamic | Dynamic private | No | Outbound-only telemetry |
| Fixed IP | Static public | Yes | CCTV, SCADA, remote access |
| Private APN | Static private | Via corporate network only | Large fleets, compliance |
Choosing a provider in the UK
Fixed IP SIMs are available from specialist IoT SIM providers. Key factors: which network does the SIM use, does the fixed IP persist on roaming, what are the contract terms, and what data bundle pricing applies. Typical cost is £2-8 per SIM per month.
For current UK provider recommendations, see the IoT Portal fixed IP SIM guide.