Posted Aug 16, 2012 23:12 UTC (Thu) by BenHutchings (subscriber, #37955)
In reply to: TCP friends by paravoid
Parent article: TCP friends
tcpdump hasn't reliably shown 'packets on the wire', even for physical devices, since checksum offload was implemented. The loopback device already skips checksum generation, TCP segmentation and UDP fragmentation.
But you can turn most of these offloads/optimisations off if you want (though you can't force checksum generation for loopback). The same goes for tcp_friends.