Fixed IP SIM Cards – When You Need One and When You Do Not
A fixed IP SIM gives your cellular device a permanent, publicly routable IP address. It is essential for some applications and unnecessary for others. Understanding the difference saves money and avoids architectural decisions that are expensive to reverse at scale.
What a Fixed IP SIM Does
Every device on a cellular network needs an IP address. With a standard dynamic IP SIM, the mobile operator assigns an address from a shared pool each time the device connects. That address changes between sessions and sits behind the operator’s NAT – the device can initiate outbound connections but nothing external can reach it directly.
A fixed IP SIM assigns the same IP address to the device every time, permanently. That address may be publicly routable from the internet, or reachable only from networks connected to the same private APN. Either way, the device has a stable, known address that a remote system can initiate a connection to.
Do You Actually Need a Fixed IP?
Fixed IP is needed when…
A remote system needs to initiate a connection to your device. SCADA head-ends polling RTUs. Video management servers pulling camera streams. Engineers connecting directly to a router web GUI over the internet. Any case where the far end needs a stable, pre-configured address to reach your device.
Fixed IP is NOT needed when…
Your device initiates all connections outbound. Cloud-reporting sensors. Devices managed via the Milesight Development Platform or similar – both use outbound connections from the device. Devices behind a VPN tunnel. Most modern IoT architectures fit here and are better served by dynamic IP plus VPN.
Private APN – The Companion to Fixed IP
Fixed IP SIMs are almost always paired with a private APN. A private APN routes device traffic through a dedicated operator gateway onto a private connection to your own infrastructure – bypassing the public internet entirely. Devices on the APN are not reachable from the public internet, only from authorised networks connected to the APN.
For SCADA and utility applications, private APN is the difference between SCADA traffic crossing the public internet (typically unacceptable under NIS and NCSC CAF requirements) and staying on a private network path from device to control centre. For a full explanation of what a private APN is and how it is provisioned, see the private APN guide.
Use Cases Where Fixed IP Is the Right Answer
CCTV and Remote Camera Systems
A video management server needs to pull streams from cameras on cellular connections. The VMS cannot initiate a connection to a device behind NAT. Fixed IP SIM on a private APN connecting back to the monitoring centre is the standard solution for cellular CCTV backhaul.
SCADA and RTU Polling Without VPN
Where a SCADA head-end polls RTUs directly using DNP3 or IEC 104 and there is no VPN infrastructure in place, fixed IP on a private APN gives the SCADA master the stable address it needs. For new deployments, a VPN-first architecture is preferable on security grounds.
Direct Router Access Without a Management Platform
Cellular routers not enrolled in a remote management platform and needing direct web GUI or SSH access require a fixed IP to be addressable from an engineer’s machine. Enrolling in the Milesight Development Platform removes this requirement entirely.
Water and Utility Telemetry – Legacy Systems
Older telemetry master stations that poll outstations by IP address and cannot be updated to support VPN client connections. Fixed IP on private APN replicates the private network behaviour they were designed to work with.
Fixed IP SIM and Multi-Network Roaming – The Tension
Fixed IP SIM cards are typically single-operator – the fixed IP is assigned within that operator’s network. This means giving up the coverage resilience of a multi-network roaming SIM. For outdoor sites where coverage from any single MNO is not guaranteed, this is a real trade-off.
One approach to resolving this: use a fixed IP SIM on SIM 1 for the primary SCADA or access path, and a multi-network roaming SIM on SIM 2 as the failover – on a dual-SIM router like the Milesight UR35 or UR75. The primary path has the stability of fixed IP. The failover path has the coverage resilience of multi-network. The SCADA application connects via VPN or fixed IP on the primary; remote management via the Milesight Development Platform works on either path.
See the multi-network SIM guide for more on coverage resilience options and how they combine with fixed IP in dual-SIM architectures.
Costs and Provisioning
Fixed IP SIMs carry a modest cost premium over standard dynamic IP SIMs – typically a few pounds per month per SIM. For small deployments this is negligible. For large fleets, the comparison between fixed IP per-SIM cost and a VPN concentrator serving dynamic IP SIMs at scale is worth running before committing to an architecture.
Fixed IP and private APN are provisioned by the SIM supplier. When ordering, you specify the APN name, the IP range to be assigned to devices, and the method for connecting your own infrastructure to the operator’s private gateway – typically an IPsec tunnel or dedicated circuit. Minimum device counts for dedicated private APN start at around 10-20 devices depending on the provider; shared private APNs are available for smaller deployments.
- IoT SIMs – fixed IP and M2M SIM cards for UK and global IoT deployments
- Roaming SIM – when multi-network roaming is a better fit than fixed IP
- Multi Network SIM – multi-network SIM for deployments needing coverage resilience alongside fixed IP
- eUICC Explained – how eSIM remote profile switching changes the fixed IP and operator lock-in calculation
Industrial SIM Cards and M2M Connectivity
Fixed IP, multi-network, private APN and eSIM options alongside the Milesight hardware they connect.