I dont know why I'm having this issue but it's happenig. I am working on basic topology. Router to layer 3 switch to little trendnet L2 switch to hosts. Image attached. Very simple. For some reason, the switch in the middle, STP is blocking the port. I have no idea why. How can I fix this and why it this even blocked, there is no redundant links
interface GigabitEthernet0/4 switchport access vlan 100 switchport mode access switchport nonegotiate switchport port-security maximum 4 switchport port-security violation restrict switchport port-security aging time 60 switchport port-security aging type inactivity switchport port-security no keepaliveend
TEST_SW#sh spanning-tree blockedportsName Blocked Interfaces List-------------------- ------------------------------------VLAN0100 Gi0/4Number of blocked ports (segments) in the system : 1