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[SLUG] eth0 kernel message?

before logging in just now, i found this as well as two other similar 
looking nasty message:

Suspect short first fragment.
eth0 PROTO=6 L=20 S=0x00 I=7444 F=0x4000
T=116 (#0)

two questions arise:

First, what does it mean?

Second, how would I find out what this or any other such message means
without having to ask the erudite denizens of SLUG?