When a SIM card attaches to a cellular network, the network knows who the device is. But the device still needs to know where to send its data. That's the job of the APN, a short text string that points the device at a specific gateway.
This article explains what an APN is and what fields make it up. For the values to use with your Simbase SIM, see Set up the Simbase APN on your device.
What an APN is
An APN (Access Point Name) is a configuration setting that defines the network path your device takes from the cellular network to the internet. It's set on the device (not the SIM card), and a typical APN configuration includes:
| Field | What it does |
|---|---|
APN | The name of the gateway (e.g. simbase), the most important field. |
Username | Optional, for APNs that require authentication. |
Password | Optional, pair to the username. |
Authentication | The auth scheme: None, PAP, or CHAP. |
APN type | The class of traffic, e.g. internet, MMS. Most IoT APNs are internet or default. |
IP type | IPv4, IPv6, or dual-stack. Simbase uses dynamic IPv4 (DHCP). |
APN
Username
Password
Authentication
APN type
IP type
Why APNs are device-side, not SIM-side
The SIM identifies the subscriber to the operator. The APN identifies which gateway the operator should route the subscriber's traffic to. That separation is intentional:
One operator can offer many APNs (consumer internet, IoT, enterprise, MMS, etc.) and the same SIM can use any of them.
The same SIM can hand off between APNs as the device moves between use cases (rare in IoT, common in enterprise).
Operators can change gateway configurations without re-provisioning every SIM.
The practical implication for IoT: don't trust the device's auto-detected APN. Most cellular modules come with a default APN list that tries to guess based on the network MCC/MNC. The guess is often wrong, sometimes routes traffic through an insecure or unstable gateway, and is hard to debug. Always set the APN explicitly.
Public APNs
A public APN is a shared gateway used by many subscribers. The Simbase default APN, simbase, is a public APN. So is the consumer internet APN your phone uses on a normal cellular plan.
Public APNs:
Are open to any device with a SIM that's authorised to use them.
Provide internet access via the operator's standard gateway.
May apply traffic policies (filtering, throttling, port blocking) at the gateway level. Simbase doesn't apply these on
simbase, but other operators may.Often use NAT (Network Address Translation), your device gets a private IP and can't be reached from the internet by default. See Network Address Translation (NAT).
Public APNs cover 99% of IoT use cases.
Private APNs
A private APN is a dedicated gateway provisioned for a single customer. Traffic from SIMs assigned to a private APN routes through the customer's gateway, often back into the customer's own network via VPN or a direct connection.
Private APNs typically include:
Source IP allocation from a customer-controlled subnet
No public internet exposure by default
Direct routing to the customer's data centre or cloud VPC
Custom firewall, DNS, and traffic policies
Use a private APN when:
Security or compliance requires that device traffic never touches the public internet
You need fixed IP addressing that's controlled by your network team, not the operator
You need direct integration with on-premises systems via private interconnect
You operate at scale where a dedicated gateway justifies the cost
Simbase offers private APN provisioning for qualifying customers. To discuss, contact sales@simbase.com.
Which APN to use with a Simbase SIM
The APN you need depends on your SIM profile and whether the SIM has a fixed IP assigned. Some profiles also offer alternative APNs to force a breakout in a specific region, or to route through a different gateway.
For the exact value for your SIM, see Set up the Simbase APN on your device.
Common questions
Most cellular modules ship with a built-in APN list and guess based on the network's MCC/MNC. On IoT SIMs that roam between operators, the guess is frequently wrong, which is why it's worth setting the APN explicitly rather than relying on auto-detection.
Usually not. Most IoT APNs, including Simbase's, use no authentication, so leave username and password empty and set authentication to None. Only APNs that specifically require PAP or CHAP need credentials.
No. APN settings are stored on the device and persist across reboots. Once configured, they stay until you change them.
No data passes, regardless of how registration looks. The SIM may show as registered, or it may show repeated registration requests and frequent location updates. If the SIM is enabled and the account has balance but no data session ever establishes, check the APN first.
Related
Set up the Simbase APN on your device, the values to use, per profile and per Public IP state
Network Address Translation (NAT), why public APNs hide your device behind NAT
Public IPs, bypassing NAT with a routable address
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