Ethernet not sending packets


I have reactivated my BBB that was sitting in a corner for a while and everything went well except when I tried reconnecting Ethernet. I’m using Debian with a bone kernel (because I need PRU with uio). Auto negotiation works correctly and the interface sees traffic inbound. However the switch does not even show the MAC as being connected to it. DHCP packets go out and don’t get a response. So something seems to eat the outbound packets. Is there something I could do to debug this?

Kind regards and thanks
Philipp Kern