Dear Teltonika Networks Support,
The following report was prepared with the assistance of an AI language model. All observations, command outputs and test results have been verified by me.
Product
Device: TRB501
Firmware: TRB501_R_00.07.23.6
Firmware build date: 2026-06-12
ISP: Oister Denmark (MCC 238 / MNC 06)
The TRB501 replaced my previous Falcon/Vantiva 5G router. Initial installation was successful. The device automatically detected the correct APN and established Internet connectivity without any manual configuration.
The TRB501 is acting as router, DHCP server and DNS server.
LAN subnet: 192.168.1.0/24
Gateway: 192.168.1.1
Three TP-Link Deco BE65 units are operating in Access Point mode.
Problem summary
The TRB501 works correctly with all of my personal devices.
However, one specific managed Windows 11 laptop consistently experiences network problems when connected through the TRB501.
The same laptop works immediately if I connect it to the Internet using USB tethering through my Android phone.
Affected device
Lenovo ThinkPad T16 Gen2
Windows 11 (corporate managed)
Cisco Secure Client VPN
Other devices
Lenovo ThinkPad T15 Gen3
Windows 11
Works normally.
Phones, tablet and other LAN devices also work normally.
Symptoms
When the Lenovo T16 is connected through the TRB501:
-
Cisco Secure Client reports that Internet access is restricted and refuses to establish the VPN connection.
-
Browsers are unable to access normal HTTPS websites such as https://mail.google.com.
-
curl reports “Recv failure: Connection was reset”.
-
The problem occurs both over Wi-Fi and over wired Ethernet.
The same laptop immediately works when connected through USB tethering to an Android phone.
Tests performed
DHCP
PASS
The laptop receives:
-
valid IPv4 address
-
valid IPv6 address
-
correct default gateway (192.168.1.1)
IPv4 routing
PASS
Default route exists.
DNS
PASS
The TRB501 provides DNS service correctly.
Both IPv4 (A) and IPv6 (AAAA) records resolve normally.
IPv4 connectivity
PASS
ping -4 www.google.com succeeds.
IPv4 traceroute to Google succeeds.
TCP
A TCP connection is established successfully.
While running:
curl -4 http://example.com
netstat shows the connection in ESTABLISHED state.
After a delay, curl reports:
Recv failure: Connection was reset
This indicates that the TCP three-way handshake completes successfully, but the connection is reset afterwards.
IPv6
IPv6 was disabled on the Windows network adapter.
The problem remained unchanged.
Router reboot
During the first occurrence of the problem, I upgraded the TRB501 firmware.
After the router reboot, the affected laptop immediately started working again without rebooting the laptop.
Later, the problem returned.
I have not yet been able to reproduce this behaviour consistently.
Kernel log
The kernel log contains only the standard Linux conntrack helper message:
nf_conntrack: default automatic helper assignment has been turned off for security reasons...
No firewall, conntrack or TCP-related messages corresponding to the failed connection attempts were observed.
Radio status
Carrier Aggregation active:
-
LTE Band 3
-
NR n78
-
NR n1
Signal quality and performance are good.
Other devices achieve normal Internet performance through the TRB501.
Request
Could you please advise whether this behaviour matches any known interoperability issue involving:
-
TRB501
-
RutOS 7.23.6
-
Windows 11
-
Cisco Secure Client
-
Microsoft Defender for Endpoint or other enterprise endpoint protection
or recommend additional diagnostics that would help identify why only this managed Windows laptop experiences TCP connection resets while all other devices function normally through the same router?
Thank you for your assistance.
Kind regards,
Pekka Teräsalmi