Thank your answer, Mr. Paxon!
However, I am still can't understand why all the status of connection not from/to my host is "S0", which means "no answer", while my host's connections were all right. In my network, my computer was running Redhat7.3, others windows. As I known, Bro is a network IDS, I think it should moniter all packets in my network. It is unbleveable that all other connections were not finished succesfully.
Waiting for your answer. Thank you!

Anderson Lee