Until now the study of computer forensics has been focused only system forensics which carried on keeping, processing and collecting the remained evidence on computer. Recently the trend of forensic study is proceeding about the network forensics which analyze the collected information in entire networks instead of analyzing the evidence on a victim computer. In particular network forensics is more important in Automated Computer Emergency Response System because the system deals with the intrusion evidence of entire networks. In this paper we defined the information of network forensics that have to be collected in Automated Computer Emergency Response System and verified the defined information by comparing with the collected information in experimental environments.