[FS#1363] QMI does not use correct APN

[LEDE Bugs]

The following task has a new comment added:

FS#1363 - QMI does not use correct APN
User who did this - dchard (dchard)

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I can confirm this behavior.

I have a Quectel EC25 modem and in QMI mode it is not applying the APN set in the luci-protocol-qmi app. No matter what APN I set on the webui, the modem sends the default APN it was programmed in the factory ("3gnet" in my case).

I also have a small LTE test network at my disposal, so I also checked the core network, where it is clear that the modem tries to activate the default EPS bearer with APN=3gnet, while I already set "internet", also tried with "static" and "" (empty string where the modem should not send a requested APN during the attach procedure).

Another way to confirm this without a core network:

1. Set whatever APN in the luci-protocol-qmi app.
2. Open minicom and query the PDN profiles with:
AT+CGDCONT?
3. If the APN set on the luci-protocol-qmi is not matching the APN in the above query, the APN will be used is the one seen with AT+CGDCONT?

If I manually set the APN with AT+CGDCONT, then the QMI mode connection will use that APN instead of the one the user gives on the luci interface.

To elaborate why this problem is not so obvious and not affecting a lot of people:

During the default PDN activation - at least on LTE - the core network requests the subscribed profile from the HSS, and if the requested APN is not matching the "subscribed" APN, then the core network will in most cases activate the data connection with the default subscribed APn no matter what the modem requests, therefor the user will have internet.

The problem is visible when an operator allows multiple APNs like in the above example: public IP, NAT-ed, but even corporate can be part of this, so the user must specify the APN for these non-default cases.

I did not tried the above mentioned fix, I will on next monday.

None the less this is a serious issue that in QMI mode the APN setting is not applied.

I am using latest master for ar71xx for GL-MIFI and the kernel is  4.9.96.

I am more than happy to test any future fixes/patches to help fix this as soon as possible. In case needed, I can provide core network traces.
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More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1363#comment4699