Question

Dear all, i'm facing a big issue with my TCR100. Until now I was quite happy but the following issue blocks further usage of the router for me.

I have to connect to my company via L2TP/IPSec PSK VPN tunnel from my windows 11 client laptop -> TCR100 is connected via LTE.

Connection is established but a lot of packets are lost. Amaz** website us working. Websites like "how is my ip" are not working.

I'm able to ping goo**.de and some clients in the network behind the vpn in the companys lan. But many many packets get lost.

I tried a lot of different things which were recommended here in the forum. Without any success.

I also tried several factory resets, firmware updates, different sim cards. No improvement.

No issue in other wifi networks or with mobile hotspot from my cell phone.

TCR100 is running on latest TCR1_R_00.07.02.7 firmware.

I'm really looking forward to your help to unblock the usage of the TCR100 also for my work.

Thanks

Answer 1

Hello,

Please note that the following should be tried only if you have local access to the router, as there is a risk of complete mobile connectivity loss.

Mobile interface MTU is known to cause issues - this is universally true and it's not related to just Teltonika devices, but service provider and/or default modem manufacturer settings. In some cases, reducing or increasing mobile interface MTU can resolve strange issues such as the ones you've listed. 

Note - if you don't see such navigation options, it might be necessary to switch mode from "Basic" to "Advanced" in the top right corner, by clicking on the "Basic" selection after logging into the device.

To reduce mobile interface MTU, login to the TCR100 router via WebUI, then navigate to Network > Interfaces > [Edit mob1s1a1 interface] > Advanced Settings > Override MTU [Set custom MTU value] > Save & Apply settings

It might take a few tries to get this right, but the following values should be tested in general:

• 1500
• 1420
• 1380

If changing MTU doesn't resolve your issue, it might be related to another part of overall configuration, either on Teltonika or UniFi device. If that's the case, please remember to reset MTU value by simply deleting any entry in the "Override MTU" field.

Comments

Hi Tomaspr,

thanks you for your response! You made my day!

Changing the MTU size to 1500 fixed the issue immediately! Since months I'm trying to find the root cause of my issue and now just with one click the whole thing is done!! I'm very happy now, thank you very much!

Side note: with MTU size 1420 and 1380 the issue still exists

Best regards,

xmace

Answer 2

Hello,

I would like you to attach a troubleshoot file to your question. Please, replicate the issue, then access router's WebUI, go to System -> Administration -> Troubleshoot section and download troubleshoot file from there.

If you could install TCPdump from Services -> Package manager section and enable traffic monitoring for mobile interface in System -> Administration -> Troubleshoot section, that may also help to find the issue.

What is the device/vendor of equipment your company uses?

Best regards,

Comments

Hi, thanks for your fast response.

Troubleshoot file attached.

File from TCP Dump is not possible to upload because of the 2mb limit.

Device/Vendor of the VPN of my company is unifi. Misconfiguration could be disregard in my opinion. Connection via every other wifi hotspot is possible without issues.

looking forward to your response.