I learned today that netstat -g for multicast group membership seems to be a SysV-ism and BSDs (at least netbsd and freebsd) seem to use the root-only ifmcstat command. This isn't a big deal, but ifmcstat isn't mentioned in the netstat or ifconfig man pages AND reading the output is a lot more difficult than netstat -g found on solaris or linux. "netstat -ai" may do some of what you want.
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