wwan: Do not change initial bearer config and properly clear unused default bearers #4401

milan-zededa · 2024-10-25T17:17:24Z

This PR addresses two issues related to cellular connectivity.

First, make sure that there are no bearers left from previous
connection attempts before starting a new connection, Otherwise, we may get
interface-in-use-config-match error from ModemManager.

Second, we should not change the initial EPS bearer settings and assume that
the same APN should be used for both the initial and the default bearer.
This is not always the case and the modem registration may fail when we
apply the same APN. However, we might want to make this user configurable
through EVE API and the controller.

Some background for understanding: LTE connection consists of two IP bearers,
the initial EPS bearer and the default bearer. Device must first establish
the initial bearer (which shows as transition from the searching to registered
state) and then it connects to a default bearer (transition from registered to
connected). Both bearers require PDP context settings (APN, ip-type, potentially
username/password, etc.).
Settings for the initial bearer are typically provided by the SIM card while
settings for the default bearer are user-configured.

It is not necessarily the case that the APNs for the initial and the default bearers
are the same. We used to make that assumption but this has led to cases where modem
was failing registration because the APN for the initial bearer was wrong. It is
better to let the SIM card provide the PDP context setting for the initial EPS bearer.
Furthermore, once these settings are changed, there is no straightforward method to
revert back to the SIM-provided configuration; for more details, see the discussion here:
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/1490#note_2628804

Users may only need to override SIM-provided settings in rather rare cases: either when
the SIM card has incorrect configuration (we have seen this only once) or when the initial
EPS bearer requires username/password authentication (also uncommon). Despite the rarity
of these cases, these settings should be user-configurable. We will do this later
(requires EVE API and controller changes).
Please note, that the same enhancement was recently implemented in NetworkManager
(used by Ubuntu and other major Linux distributions):
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1915

Also included in this PR is a documentation how to capture control-plane traffic on
Qualcomm-based modems.

…efault bearers This commit addresses two issues related to cellular connectivity. First, make sure that there are no bearers left from previous connection attempts before starting a new connection, Otherwise, we may get "interface-in-use-config-match" error from ModemManager. Second, we should not change the initial EPS bearer settings and assume that the same APN should be used for both the initial and the default bearer. This is not always the case and the modem registration may fail when we apply the same APN. However, we might want to make this user configurable through EVE API and the controller. Some background for understanding: LTE connection consists of two IP bearers, the initial EPS bearer and the default bearer. Device must first establish the initial bearer (which shows as transition from the "searching" to "registered" state) and then it connects to a default bearer (transition from "registered" to "connected"). Both bearers require PDP context settings (APN, ip-type, potentially username/password, etc.). Settings for the initial bearer are typically provided by the SIM card while settings for the default bearer are user-configured. It is not necessarily the case that the APNs for the initial and the default bearers are the same. We used to make that assumption but this has led to cases where modem was failing registration because the APN for the initial bearer was wrong. It is better to let the SIM card provide the PDP context setting for the initial EPS bearer. Furthermore, once these settings are changed, there is no straightforward method to revert back to the SIM-provided configuration; for more details, see the discussion here: https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/issues/1490#note_2628804 Users may only need to override SIM-provided settings in rather rare cases: either when the SIM card has incorrect configuration (we have seen this only once) or when the initial EPS bearer requires username/password authentication (also uncommon). Despite the rarity of these cases, these settings should be user-configurable. We will do this later (requires EVE API and controller changes). Please note, that the same enhancement was recently implemented in NetworkManager (used by Ubuntu and other major Linux distributions): https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1915 Signed-off-by: Milan Lenco <[email protected]>

QCSuper[*] allows to capture raw 2G/3G/4G (and for certain models also 5G) control-plane radio frames from Qualcomm-based modems. This can be super useful when troubleshooting registration/connection establishment issues. [*] https://github.com/P1sec/QCSuper Signed-off-by: Milan Lenco <[email protected]>

uncleDecart · 2024-10-29T15:17:32Z

pkg/wwan/mmagent/mmdbus/client.go

+		return err
+	}
+	for _, bearerPath := range bearers {
+		if !bearerPath.IsValid() {


so we will keep non-valid bearers?

This is just checking if the path itself is valid. This should be unreachable because otherwise it means we are getting some nonsense output from ModemManager. I put it there just in case (I have these path validations in multiple places across mmagent).

Maybe then we should just in case log them. If there will be some weird (faulty) modem or ModemManager will go insane. What do you think?

uncleDecart · 2024-10-29T15:22:37Z

Do I get it right that you're deleting all default bearers, which are user configured?

milan-zededa · 2024-10-29T18:30:36Z

Do I get it right that you're deleting all default bearers, which are user configured?

Yes correct.

pkg/wwan/mmagent/mmdbus/client.go

eriknordmark

LGTM

eriknordmark

Run eden again

milan-zededa · 2024-10-30T18:55:42Z

There seems to be some problem with onboarding and also pull limit was reached. I will retry and investigate tomorrow.

uncleDecart · 2024-10-31T14:01:29Z

Do I get it right that you're deleting all default bearers, which are user configured?

Yes correct.

Then what's the point of specifying default bearers?

But if a user has a contract with a big telco, I'd assume one way they will have connectivity through some credentials that they will be supplying to a modem. Maybe I'm not following the logic, but then the scenario is following :

I'm using my modem with default bearer to login into network, I mean I might use an operator which uses other's telco towers, so I need that particular default bearer
Then once I'm logged in you're deleting the default bearers that I specified
Modem tries to communicate with telco, not with my overlay credentials and therefore there's no connectivity

milan-zededa · 2024-10-31T14:51:02Z

Do I get it right that you're deleting all default bearers, which are user configured?

Yes correct.

Then what's the point of specifying default bearers?

But if a user has a contract with a big telco, I'd assume one way they will have connectivity through some credentials that they will be supplying to a modem. Maybe I'm not following the logic, but then the scenario is following :
1. I'm using my modem with default bearer to login into network, I mean I might use an operator which uses other's telco towers, so I need that particular default bearer

2. Then once I'm logged in you're deleting the default bearers that I specified

3. Modem tries to communicate with telco, not with my overlay credentials and therefore there's no connectivity

What you are referring to is the "initial EPS bearer", with parameters embedded in the SIM card / modem. We do not touch this bearer here (if it is connected, it stays connect even after this method). Default bearer is what user configured through zedcloud. We do not support multiple PDN contexts at the moment, so there will be at most one default bearer active at any time. I noticed that the ModemManager Disconnect method only deactivates the currently active bearer, without removing it. When we run Connect (with the same or changed args), ModemManager looks for the same (inactive) bearer and tries to activate it. However, I have seen this to fail in the past in multiple occasions. It was necessary to delete inactive default bearer(s) and let ModemManager to create a new one from scratch. So I'm thinking that is maybe better to not keep inactive bearers hanging around. But I could be wrong on this and there is no documentation on "how to do this the right way", it is mostly driven by experiments :/

milan-zededa · 2024-10-31T14:53:44Z

We are still seeing some issues on the modem tested, so I'm bringing this back to Draft. I really don't like these cellular modems :/

milan-zededa · 2024-11-23T19:59:30Z

We have some positive updates from the issue reporter. It seems that soon this PR will be moved back into the ready-for-review state. Stay tuned.

milan-zededa added the stable Should be backported to stable release(s) label Oct 25, 2024

milan-zededa self-assigned this Oct 25, 2024

github-actions bot requested a review from eriknordmark October 25, 2024 17:17

milan-zededa force-pushed the revert-eps-config branch from 5c6ca9c to da4676a Compare October 29, 2024 14:36

milan-zededa changed the title ~~wwan: Do not change default bearer config and properly clear unused dedicated bearers~~ wwan: Do not change initial bearer config and properly clear unused default bearers Oct 29, 2024

milan-zededa marked this pull request as ready for review October 29, 2024 14:42

milan-zededa force-pushed the revert-eps-config branch from da4676a to 2d6c0a3 Compare October 29, 2024 14:45

milan-zededa requested a review from uncleDecart October 29, 2024 14:53

uncleDecart reviewed Oct 29, 2024

View reviewed changes

eriknordmark reviewed Oct 29, 2024

View reviewed changes

pkg/wwan/mmagent/mmdbus/client.go Show resolved Hide resolved

eriknordmark approved these changes Oct 30, 2024

View reviewed changes

milan-zededa marked this pull request as draft October 31, 2024 14:53

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

wwan: Do not change initial bearer config and properly clear unused default bearers #4401

wwan: Do not change initial bearer config and properly clear unused default bearers #4401

milan-zededa commented Oct 25, 2024 •

edited

Loading

uncleDecart Oct 29, 2024

milan-zededa Oct 29, 2024

uncleDecart Oct 31, 2024

uncleDecart commented Oct 29, 2024

milan-zededa commented Oct 29, 2024

eriknordmark left a comment

eriknordmark left a comment

milan-zededa commented Oct 30, 2024

uncleDecart commented Oct 31, 2024

milan-zededa commented Oct 31, 2024 •

edited

Loading

milan-zededa commented Oct 31, 2024

milan-zededa commented Nov 23, 2024

wwan: Do not change initial bearer config and properly clear unused default bearers #4401

Are you sure you want to change the base?

wwan: Do not change initial bearer config and properly clear unused default bearers #4401

Conversation

milan-zededa commented Oct 25, 2024 • edited Loading

uncleDecart Oct 29, 2024

Choose a reason for hiding this comment

milan-zededa Oct 29, 2024

Choose a reason for hiding this comment

uncleDecart Oct 31, 2024

Choose a reason for hiding this comment

uncleDecart commented Oct 29, 2024

milan-zededa commented Oct 29, 2024

eriknordmark left a comment

Choose a reason for hiding this comment

eriknordmark left a comment

Choose a reason for hiding this comment

milan-zededa commented Oct 30, 2024

uncleDecart commented Oct 31, 2024

milan-zededa commented Oct 31, 2024 • edited Loading

milan-zededa commented Oct 31, 2024

milan-zededa commented Nov 23, 2024

milan-zededa commented Oct 25, 2024 •

edited

Loading

milan-zededa commented Oct 31, 2024 •

edited

Loading