When enabling this flag on freebsd, all traffic is bypassed, not sure if it’s a bug :
net.bpf.optimize_writers: 0 Various programs use BPF to send (but not receive) raw packets (cdpd, lldpd, dhcpd, dhcp relays, etc. are good examples of such programs). They do not need incoming packets to be send to them. Turning this option on makes new BPF users to be attached to write-only interface list until program explicitly specifies read filter via pcap_set_filter(). This removes any performance degradation for high-speed interfaces.