Description
On some Windows systems, the kOS telnet server listens successfully but clients can never connect. The connection hangs indefinitely at "Trying 127.0.0.1..." with no error or rejection.
Root Cause
When TcpListener binds specifically to IPAddress.Loopback (127.0.0.1), third-party software that hooks the Windows loopback network interface can intercept the traffic before it reaches the application. The most common culprit is Npcap (bundled with Wireshark and Nmap), which installs its own "Npcap Loopback Adapter", but firewalls and other network drivers can cause the same issue.
Steps to Reproduce
- Have any software installed that hooks the loopback interface (e.g. Wireshark/Npcap)
- Enable the kOS telnet server in loopback mode
- Attempt to connect via telnet to 127.0.0.1 on the configured port
- Connection hangs indefinitely
Expected Behavior
Telnet client connects to the kOS terminal server.
Environment
- Windows 10/11
- KSP 1.12.x
- kOS 1.5.1.0
Related
Likely the same root cause as #2937 which was closed as a firewall issue.
Description
On some Windows systems, the kOS telnet server listens successfully but clients can never connect. The connection hangs indefinitely at "Trying 127.0.0.1..." with no error or rejection.
Root Cause
When
TcpListenerbinds specifically toIPAddress.Loopback(127.0.0.1), third-party software that hooks the Windows loopback network interface can intercept the traffic before it reaches the application. The most common culprit is Npcap (bundled with Wireshark and Nmap), which installs its own "Npcap Loopback Adapter", but firewalls and other network drivers can cause the same issue.Steps to Reproduce
Expected Behavior
Telnet client connects to the kOS terminal server.
Environment
Related
Likely the same root cause as #2937 which was closed as a firewall issue.