Add network interface troubleshooting guide

Document solution for IP address changes caused by dual ethernet ports:
- Identify three network interfaces (WiFi, eth left port, eth right port)
- Provide NetworkManager commands for static IP configuration
- Include step-by-step solution using "Wired connection 2" (enp4s0)
- Configure both ethernet and WiFi to use same static IP (192.168.0.100)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

troubleshooting.md

@@ -268,3 +268,45 @@ HandleLidSwitchDocked=ignore
 
 Then restart service:
 `sudo systemctl restart systemd-logind`
+
+## IP addresses keep changing
+
+Due to 3 interfaces:
+* Wifi
+* Ethernet left port (ThinkPad adapter) - Wired Connection 1
+* Ethernet right port (regular ethernet cable) - Wired Connection 2
+
+### Proposed solution
+
+* Stick with wired2
+
+● Configure static IP for "Wired connection 2" (enp4s0):
+
+  * Set static IP to 192.168.0.100
+  sudo nmcli connection modify "Wired connection 2" \
+      ipv4.method manual \
+      ipv4.addresses 192.168.0.100/24 \
+      ipv4.gateway 192.168.0.1 \
+      ipv4.dns 192.168.0.1
+
+  * Apply the changes
+  sudo nmcli connection up "Wired connection 2"
+
+  Then configure WiFi with the same static IP:
+
+  * First connect to your WiFi if not already
+  sudo nmcli connection up "Telekom-4b28df-2.4GHz"
+
+  * Set same static IP for WiFi
+  sudo nmcli connection modify "Telekom-4b28df-2.4GHz" \
+      ipv4.method manual \
+      ipv4.addresses 192.168.0.100/24 \
+      ipv4.gateway 192.168.0.1 \
+      ipv4.dns 192.168.0.1
+
+  Verify the configuration:
+  nmcli connection show "Wired connection 2" | grep ipv4
+  ip addr show enp4s0
+
+  This way both your ethernet (enp4s0) and WiFi will use 192.168.0.100, solving your dual interface IP issue.
+  Ready to run these commands?