Is anyone familiar with any free/open source software that can generate arbitrary volumes of valid but fake ethernet packets on a network? I'm working on an analysis system that uses pcap/tcpdump to sniff traffic, but there are logistical/policy issues about sniffing real networks. It'd be real sweet if the contents of those packets (balance of IP vs. other traffic, specific IP protocols/ports. etc.) were configurable to provide an interesting mix of traffic, but that's not essential at this point.