Understanding IP Address Assignment in Cellular Networks_Static and Public IP Vs Dynamic and Private IP

Cellular Routers
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Many customers expect cellular routers to behave like wired broadband connections, where a device receives a static and public IP address by default. In reality, cellular networks assign IP addresses very differently, and misunderstanding this is one of the most common causes of remote-access issues.

In cellular networks, most SIM cards use Carrier-Grade NAT(CGNAT) and receive dynamic and private IP addresses. This prevents inbound access from the internet. If remote access to end devices is required, a static and public IP plan must be ordered and provisioned by the carrier.

1. How IP Addressing Works in Cellular Networks

In cellular networks, IP addresses are assigned by the mobile carrier, not by the router. For most standard cellular data plans, carriers use Carrier-Grade NAT (CGNAT).

With CGNAT:

  • The device receives a private IP address
  • The IP address is dynamic (it can change)
  • Multiple devices share a small pool of public IPs
  • Inbound connections from the internet are blocked

This design allows carriers to:

  • Conserve IPv4 address space
  • Improve scalability
  • Enhance security by blocking unsolicited inbound traffic

As a result, a cellular router is able to browse the internet, but cannot be accessed remotely from the public internet. This is expected behavior, not a misconfiguration. 

2. Why Remote Access Fails with a Regular SIM

If you try to remotely access:

  • PLCs
  • IP cameras
  • Industrial controllers
  • Web interfaces behind a cellular router

…it will fail when using a regular SIM because:

  • CGNAT blocks inbound traffic
  • Port forwarding on the router cannot bypass CGNAT
  • The carrier does not know which shared device should receive the inbound packet

3. When You Need a Static & Public IP

If your application requires remote access from the public internet, you must use a Static and Public IP plan provided by the carrier.

A Static Public IP plan provides:

  • A dedicated, routable public IPv4 address
  • The same IP every time the device reconnects
  • Inbound connections allowed
  • Predictable firewall and routing behavior

Typical use cases:

  • Remote device management
  • SCADA / industrial polling
  • VPN termination on the router
4. How to verify if the SIM has dynamic and private IP or static and public IP

To determine whether a SIM is using a dynamic, private IP (behind CGNAT), you can compare the IP address assigned to the router with the IP address visible on the public internet.

On the router side, check the cellular IP address assigned by the mobile network. This is the IP the carrier provides directly to the device.

  1. On IR300 serial routers and CR202 routers, go to Status=>Network Connections. At Cellular session, the IP Address is assigned by the cellular network to the router.

Then, from a computer connected behind the router, visit an external website such as whatismyip.com to view the public-facing IP address seen by the internet.

  • If the Cellular IP shown on the router and the public IP shown on the website are different, the SIM is operating behind NAT/CGNAT and is using a dynamic, private IP.

  • If both IP addresses match, the SIM is likely using a public IP, and inbound connectivity may be possible (subject to carrier policy and firewall rules).

Tips:
  1. APN(Access Point Name). Please confirm with the carrier about the proper APN value for your SIM. Carriers may have different APNs for different plans. If it's a Verizon SIM, please refer to the article below:
    1. https://help.inhand.com/portal/en/community/topic/how-to-configure-verizon-static-ip-apn