APN automatically resets to China Telecom "ctnet" on Fairphone 5 / iodéOS 7.5

Apps & Core Settings
1

Device

  • Fairphone 5

  • iodéOS 7.5

SIM / Carrier

The issue occurs (reproducible) while roaming in the Netherlands on Vodafone NL, with a Lebara Germany (physical SIM). During roaming/network re-registration, the APN is remapped to the read-only China Telecom ctnet entry.

Problem description

The device repeatedly switches the active APN back to a read-only APN entry with the following values:

  • APN: ctnet

  • Username: ctnet@mycdma.cn

This appears to be a China Telecom APN. When this APN becomes active, mobile data stops working. The issue is especially reproducible while roaming in the Netherlands on Vodafone NL.
During roaming/network re-registration, the APN is remapped to the read-only China Telecom ctnet entry.

Important observations

  • The ctnet APN entry is greyed out / read-only.

  • I cannot modify or delete it.

  • A manually created APN works correctly.

  • However, after certain events, the device switches back to the ctnet APN automatically.

Triggers

The APN reset most commonly happens:

  • after leaving Wi-Fi

  • after network re-registration

  • after crossing country borders / roaming events

  • sometimes after reconnecting to mobile data

Expected behavior

The manually selected APN should remain active and the system should not automatically switch to an unrelated China Telecom APN.

Actual behavior

iodéOS appears to remap the carrier/APN configuration during network re-registration and activates the read-only ctnet APN again.

Additional notes

This looks like a carrier configuration / APN database mapping issue affecting Lebara Germany MVNO detection.

It may originate from:

  • CarrierConfig

  • APN database mapping

  • MVNO matching logic

  • inherited LineageOS telephony configuration

The issue is reproducible.

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1 Like
2

This seems to be one of the more “aggressively inaccurate APN settings” I have heard about. The fact that your manually created APN, after being selected and used is then deselected and reset back to the “clearly wrong” one is really bad.

It must be that MCC / MNC is shared by the China telecom and Lebara. The easiest way to see the MCC / MNC is under the older “Phone Information” (not V2) from *#*#4636#*#* under the “All Cell Measurement Info” section. If you could get those 2 numbers then we can look at the LineageOS Vendor APN Config source here (organized now per country): GitHub - LineageOS/android_vendor_apn · GitHub

3

Hi rik, thanks for the tip. I’d switched to the other SIM card for a while (dual SIM mode) and have now switched back to this one. Demo effect. It shows MCC 204 MNC 4, which stands for Vodafone Libertel B.V., Netherlands. Funnily enough, the APN is set to the Chinese CTNET and I have working internet. Is there anything else we can do with this information? Otherwise, wait until the error occurs again….

1 Like
4

Honestly I am not sure. It is a very strange issues, as in the CN.xml file I can find the APN settings you had, but all entries there are for mcc="460" so I have no idea how it was selected for you. The LineageOS issue tracker may have something on that, but in order to submit a bug report you would need to confirm the issue on stock LineageOS or it will get immediately closed.