Qucetel RM502-AE with TMobile 5G SA & NSA fix

[vigilant]

Hello Internet Nerds,

I want to share this post with you folks just in case there is somebody out there loosing it because their expensive RM502-AE modem fails to connect to 5G what so ever on tmobiles 5G network.

As many of you folks may have heard Tmobile has been seriously changing a crap ton of things in the back end that are breaking our mobile internet setups.

So, past week or so, my modem straight-up refused to connect to any 5G Network and would only connect when I would lock it to a 4G bands, even after me updating to the newest baseband for this modem it still didn't work.

What I noticed, when it failed to connect it just straight out refused to connect to T-Mobile's APN no matter what I tried, i tried selecting ipv6/ipv4 or IPv6 or ipv4 as my protocol it completely still didn't work.

After doing some more testing and and troubleshooting I was able to get this modem to connect to T-Mobile's 5G Network by changing the modems protocol from qmi to mbim once I did that the modem was now able to connect to a 5G Network.

It turns out T-Mobile is no longer handing out ipv4 addresses and they're forcibly forcing modems to connect using a IPv4 in IPv6 sometimes called 6in4xlat when connecting to 5G and there's a wired bug in golden orb or the modem with 6in4xlat when using QMI.

When switching over to this mode you also would want to modify your MTU settings to 1472 which I found to be the best TTL setting and my connections to my work VPN seem to be very stable now.

I'm using golden orb as my router firmware and I had to change a couple of IPv6 settings in order for the IPv4 to basically work.

I do seem to have a couple of UDP issues I have one VPN service I use and I think there might be some packet drops here and there but from my experience doing icmp pings I haven't seen any packet drops there. I was able to do some UDP rtsp video feeds test and it seemed to work just fine.

The only thing I noticed now is that my bufferbloat is pretty high now I'm not sure if it's because of the 5G bands or I'm uploading too much saturating my bandwidth but it might just be me or my antennas.

Anyways I hope I hope that this helps somebody out there.

Thanks,

[Didneywhorl]

... modify your TTL settings to 1472 ....

1472?

One Thousand Four Hundred Seventy Two?

Are you sure? That's crazy high. Not that I would be too surprised, but... wow.

[mtl26637]

It turns out T-Mobile is no longer handing out ipv4 addresses and they're forcibly forcing modems to connect using a IPv4 in IPv6 sometimes called 6in4xlat when connecting to 5G and there's a wired bug in golden orb or the modem with 6in4xlat when using QMI.

This is interesting as I'm currently using a WRT32X running OpenWrt with ModemManager and have the ICMP issue still so not sure its a fault of the GO firmware? Also, my RM500Q-AE works just fine running GO firmware? What brought you to the conclusion that it is a GO bug?

When switching over to this mode you also would want to modify your TTL settings to 1472 which I found to be the best TTL setting and my connections to my work VPN seem to be very stable now.

I assume you meant MTU=1472 rather than TTL? I did see that thread on quectel forum but still don't see how internal wifi is causing all of these problems as they suggest.

I will most definitely give MBIM I try. Pretty sure I've tried it and ECM mode but its been a minute since I've really wrestled with this problem. Its been happening since early/mid summer for me. Thanks for the info and I'll give status update once I have a chance.

[Didneywhorl]

MTU 1472 that makes more sense, lol.

[mtl26637]

I fold. Spent all weeekend on trying to get my WRT32X and RM502Q-AE in USB sled working with no luck. I have literally tried everything I can think of and still have ICMP or connection without internet issues. Seems I'm the only one that still posting on this so I guess I may have some type of hardware issue. It's getting shelved until ATT or VZW gets 'real' 5G in my area.

[vigilant]

I fold. Spent all weeekend on trying to get my WRT32X and RM502Q-AE in USB sled working with no luck. I have literally tried everything I can think of and still have ICMP or connection without internet issues. Seems I'm the only one that still posting on this so I guess I may have some type of hardware issue. It's getting shelved until ATT or VZW gets 'real' 5G in my area.

I see, I see,
I understand that you get connect to the 5g network and I assume that you see that your modem connected to the TMO APN but still no internet.

If it helps, I had to change my local networks "IPv6 ULA-Prefix" to be blank. Mind you im on golden orb. Once I did that I was then able to access the internet. (IPv4)

If you can check, to see if your modem is able to ping IPV6 addreses. It could be that your modem is indeed connected to the internet but IPV4 isn't quite working in your router because of that awful new tech 464XLAT.

[Esoteric]

Have you guys been able to get IPv6 Only to work? Whenever I try to go that route it seems like im running against dns issues where only some sites work but i otherwise can ping and have internet. Im currently back to IPv4 Only but i still get drop outs(momentary) about every 2-3 hours, where before they made whatever changes i was on IPv4/IPv6 and would never experience the need for the modem to reconnect.

[Orlimar1]

I started having this issue with this modem on a Cudy P5 I bought from WH. It has the 502 modem in it. Cudy put out some tips to get it to connect again. If you search for Cudy p5 T-mo issues the link should pop up. I don't want to post it here even though I bought via WH. I had to turn on IPV6 and increase my ttl on both high and low to 65. I finally did connect again. But now, I'm getting throttled into oblivion on a pc's4people sim. I'm using a vpn to get around it on a Fire Cube. But I hate having to use a vpn.