# ifconfig ib0 192.168.0.5 netmask 255.255.255.0
# tail -7 /var/log/messages

Feb  2 18:55:35 schizo kernel: ib_init entered
Feb  2 18:55:35 schizo kernel: ib_start entered
Feb  2 18:55:35 schizo kernel: ib_encap entered
Feb  2 18:55:35 schizo kernel: DHOST ff ff ff ff ff ff
Feb  2 18:55:35 schizo kernel: SHOST  0 c0 ee 22  3 14
Feb  2 18:55:35 schizo kernel: txeof entered
Feb  2 18:55:35 schizo kernel: txeof exiting

(I've modified ping.c to add extra debug messages about the length of the packet sent)
$ ping 192.168.0.1
PING 192.168.0.1 (192.168.0.1): 56 data bytes
packets sent: -1
ping: sendto: Invalid argument
packets sent: -1
ping: sendto: Invalid argument
packets sent: -1
^C

I am dropping the IFF_DRV_OACTIVE flag as soon we reach ib_txeof (line 761) but ib_start() still doesn't start more than one time.

full source code is available here www.freebsd.az/if_ib_4.c