Hello
This is indeed an unusual behavior, and here are some suggested solutions to this problem:
Check DHCP client Settings:
Make sure the DHCP clients in your operating system are configured correctly and are not incorrectly requesting or caching these routes.
In Windows, you can check the DHCP Settings of your network adapter by Changing Adapter Options in the Network and Internet Settings.
Router configuration:
Check your router configuration to see if there are any Settings or scripts that might cause routes to be automatically added under certain conditions.
Try updating your router's firmware to the latest version to see if that fixes the problem.
Custom scripts or policies:
If your operating system or network environment uses custom scripts or policies to manage routes, check whether these scripts or policies may add routes at inappropriate times.
Conflicts between static routes and DHCP routes:
If you use both static and DHCP assigned routes on your network, make sure there is no conflict between them.
Third-party software or drivers:
Check for any third-party network management software or drivers that may affect routing table updates.
Network monitoring and logging:
Check the system and network logs for any error or warning messages related to route addition.
If none of the above methods solve the problem, you need to use network monitoring tools to capture and analyze network traffic to better understand how routes are added to the routing table.