@Robert Cotter Thank you for your reply ！
I try the solution you given , but i didn’t work.
Maybe it’s the pf_ring that causes the problem.
When i used tcpdump, i finded the same problem of Dropped Packets.
Runtime environment:
NIC is Broadcom Corporation NetXtreme BCM5720 Gigabit Ethernet PCIe
pf_ring version is 7.1.0
bro 2.5.5
linux:centos