Ok story goes something like this. Big server machine ( eg. DL570G7 ) with multiple network ports, and system was “maintained” so that you have no idea which port at back of server is eth0, eth1, …. So here is simple trick how to find that out
Run
# ethtool -p ethX 60
X=0,1,2,3,..
and watch NICs LEDs, the one which correspond X will will blink very fast during 60 seconds, and you will know how is particular physical network card recognized by your system ( as eth0, eth1, … )
More information
# man ethttool
elvir's [elvir kuric] blog 