T-Mobile Wi-Fi calling issue

[ameshkov]

http://forum.adguard.com/showthread.php?7658-WiFi-Calling

User:

My carrier is T-Mobile. Feedback sent - Ticket ID #YLO-859-91874.
I also turned on pref.vpn.bypass.ipv6. No joy. 2nd log file sent.

[ameshkov]

I see UDP traffic to port 4500. Seems like they are trying to do NAT Traversal.

More information about this:
https://support.t-mobile.com/docs/DOC-4950

[ameshkov]

I have prepared two test builds and I'd be very grateful if you check how it works.

Here is an instruction.

0. Preparation
Uninstall existing Adguard app to make sure that you have default settings.

1. Empty routes build
Link: https://static.adguard.com/android/release/adguard_issue233_empty_route.apk

Important note: this build does not filter ads at all.
What it does: it establishes a local VPN connection with empty routes.
Purpose: we are checking if Wi-Fi calling goes down simply because of existing VPN.

2. Bypassing T-Mobile network

Link: https://static.adguard.com/android/release/adguard_issue233_tmobile_excluded.apk

What to do:

1. Install, go to "Settings" - "Advanced" - "Low level" - turn on "pref.vpn.ipv4.force.complex"
2. Set "Logging level" to "Record everything"
3. Start Adguard protection, disable and then enable Wi-Fi calling
4. Send us a feedback message with app logs

What it does: This option turns on special VPN routes where T-Mobile network is excluded. According to the https://support.t-mobile.com/docs/DOC-4950#subhead8 they are using 208.54.0.0/17 addresses for Wi-Fi calling. Plus, according to the log.
Purpose: According to the log, they are trying to do a so called "NAT Traversal".

This means that there is a process, listening for connections from that IP block. By default enabled VPN does not allow any incoming connections.
If I am right, we have two possible options.

First: use special routes with "excluded" T-Mobile ips.
Second: find the process listening for incoming connections and exclude this exact process.

We'll try the second way if this build does not help.

[ameshkov]

        // TODO: TEMP START https://github.com/AdguardTeam/AdguardForAndroid/issues/233
        // Exclude T-Mobile subnet:
        // https://github.com/AdguardTeam/AdguardForAndroid/issues/233
        ranges.put(IpAddressUtils.ipToLong("192.168.255.255") + 1, IpAddressUtils.ipToLong("208.54.0.0"));
        ranges.put(IpAddressUtils.ipToLong("208.54.127.255") + 1, lastIp);
        // TODO: TEMP END https://github.com/AdguardTeam/AdguardForAndroid/issues/233

[ameshkov]

Excluding T-Mobile subnet helps. We'll do this in the next update.

This exclusion may not work in some Wi-Fi networks (depends on network complexity).
To force it user should turn on pref.vpn.ipv4.force.complex in Settings - Advanced - Low Level.