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TCP friendsTCP friendsPosted 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.
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TCP friends Posted Aug 18, 2012 0:00 UTC (Sat) by intgr (subscriber, #39733) [Link]
> tcpdump hasn't reliably shown 'packets on the wire', even for physical devices, since checksum offload was implemented
The lack of checksums is a very trivial issue. The lack of segmentation is also irrelevant -- it appears as an interface with an infinitely large MTU. The packets captured on "lo" are still basically valid TCP packets.
Not seeing any packets and being unable to debug network interactions *at all* is a huge deal compared to these.
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