A combination of esniff.c and tcpdump. It also supports a plethora of other options including DES encryption on log files, user monitoring, forwarding logs regularly to a secondary host, and NFS file handle sniffing. Will sniff on Linux, IRIX, SunOS 4.x, Solaris 2.x, BSD/386, DEC/OSF, * Digital UNIX, Ultrix 4.x, 4.x BSD, NetBSD, FreeBSD, BSDI, and HP-UX.