One of the most useful one liners thought I'd put it up here for my own easy access

snoop -d nxge0 -x 0 ether\[20:2\]=0x2000

For my current place of employment this will show details that are being advertised by the switch, including name and port number , which is handy as our Network services folk often either don't record where the put you or indeed just plain lie about where they connected us.