A public IP makes a SIM addressable from the internet, but only once three things line up: the IP is assigned, the device is using the fixed IP APN, and nothing on the device is blocking what you send. Most reports come down to the second or third.
1. Is the IP assigned, and is the SIM in session?
Open the SIM in the dashboard and confirm a public IP is listed against it, and that the SIM is currently in session. An IP cannot answer anything while the device is offline. See Public IPs.
If the SIM is not in session at all, go straight to check 2. An IP assigned while the device is still on the standard APN stops the SIM connecting entirely. If the APN is already correct, continue with Connectivity issues.
2. Is the device using the fixed IP APN for its profile?
This is the most common cause. The fixed IP APN is different from the standard one, and it differs by profile.
| SIM profile | ICCID range | Fixed IP APN |
|---|---|---|
Black, Red, Green | 89103* | fixedip.us or fixedip.eu |
Blue, Yellow, Cyan | 89445* | fixedip.m2m |
Black, Red, Green
Blue, Yellow, Cyan
On 89103* profiles, pick the breakout that matches where the device is deployed. See Set up the APN.
3. Has the device reconnected on the new APN?
Assigning a fixed IP ends the SIM's current session. The device only comes back online once it connects using the fixed IP APN.
Reboot the device, or use Reset connection in the dashboard, then check that the SIM returns to in session with the assigned IP.
4. Is the device's firewall blocking inbound traffic?
The most common device-side cause. Many routers and modems block unsolicited inbound traffic by default, which is sensible security but stops exactly what you are testing.
Check that the device's firewall allows the traffic you are sending, and that any port you need is open and forwarded to the right internal host.
5. Are you testing the right thing?
Ping and reachability are not the same. A device can refuse ICMP while happily answering on a TCP port, so a failed ping does not prove the device is unreachable.
Test the service you actually care about, on its own port, before concluding the IP is dead. If the service answers and ping does not, the device is simply dropping ICMP, and nothing is wrong.
6. Is the device running the latest firmware?
Older modem firmware sometimes handles fixed IP addressing badly, particularly around holding the session open. If everything above checks out, update the firmware and test again.
Still not reachable
Contact support with:
The SIM's ICCID
The APN currently configured on the device
What you are testing with, ping or a specific port
Where you are testing from
The device make and model, and its firewall configuration
Whether the IP has ever been reachable, or has never worked since it was assigned
Common questions
The device is likely trying to connect on the standard APN. A SIM with a fixed IP can only connect when the device uses the fixed IP APN for its profile.
Yes. The charge runs daily for as long as the IP is assigned, regardless of whether the SIM is in use. Remove the IP if you no longer need it.
Not reliably. A released IP goes back to the top of the queue, so re-assigning within a few minutes usually returns the same address, unless another customer requested one in between. Nothing is reserved, so don't depend on it.
Only as far as you need to. An open firewall on a public IP means inbound scanning traffic reaches the device and is billed to you, so allow the specific ports you use rather than everything.
Related
Public IPs, assigning and removing public IPs
Set up the APN, the fixed IP APN for your profile
Connectivity issues, if the SIM isn't connecting at all
Private networks, reaching devices without exposing them to the internet
Data usage and overages, why inbound traffic counts
© 2026 Simbase Connect. All rights reserved.