tcpdump -v -i vmbr0
tcpdump: listening on vmbr0, link-type EN10MB (Ethernet), capture size 65535 bytes
09:38:37.282986 STP 802.1d, Config, Flags [none], bridge-id 8000.00:07:xx:cc:xx:46.8415, length 43
message-age 0.00s, max-age 20.00s, hello-time 2.00s, forwarding-delay 15.00s
root-id...