[ubuntu] What network layer does ifconfig operate at?

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http://ubuntuforums.org – What layer does ifconfig operate at when setting a MTU. Does it set the MTU for the physical device (Network Interface Layer) or the MTU of the packet (Internet Layer)? By executing Code: ifconfig eth0 mtu 1300 it leads me to believe this is causing the Network Interface Layer to be restricted because an interface must be specified. I am not sure of this though. Can anyone confirm this for me? Furthermore, if anyone has a good source that would be great! (HowTos)