‘Allow 2G’ Switch in Android – How About Roaming?

As I tend to be a bit on the security conscious side of the discussion, I like the 2G-Allow switch on my Pixel 6 with LineageOS. By disabling 2G, I’m not prone to fallback attacks by network jamming and my device recovers more quickly from a loss of LTE coverage. For most of my daily usage scenario, returning to LTE more quickly is a significant benefit. But there is one catch one has to be aware of: Roaming!

Disabling 2G on the device also applies to roaming. The slight issue with that is that in case I roam into a network which does not support VoLTE Roaming with my home network operator, and the visited network did not support 3G anymore, I wouldn’t be able to make or receive any ‘traditional’ voice calls. At first I wondered if it could be possible to automatically enable 2G while roaming to fix this, but such a move would undermine the security aspect of the feature. Google aptly explains the conundrum as follows:

“When 2G is disabled for security purposes it will not be re-enabled, even if the device is roaming. Certain areas in the world depend on 2G coverage and some roaming agreements assume devices will be able to connect to 2G. In these situations, the user will not have connectivity unless they re-enable 2G. It’s not possible to reliably detect 2G roaming because of the lack of mutual authentication in 2G. Leaving 2G off despite roaming signals, prevents a FBS [Fake base station] from spoofing its network identifiers to convince a device to re-enable 2G.”

As a lot of networks have switched-off 3G by now, disabling 2G by default, particularly in Europe, would be quite problematic. Here, due to the many countries being in close proximity and the resulting frequent roaming by many people, and the fact that many network operators have switched-off 3G by now makes this a no-go in my eyes. In North America, things might look different. When I was recently in the US and Canada, I could perform VoLTE calls in all networks while roaming. So here, 2G could perhaps be disabled by default? I’m not sure about roaming into Mexico as a US or Canadian network subscriber, though, so perhaps this is still a showstopper?