Network Access Layer
Now that we have examined the structure of the network subsystem in the Linux kernel, we turn our attention to the first layer of the network implementation — the network access layer. This layer is primarily responsible for transferring information between computers and collaborates directly with the device drivers of network cards.
It is not my intention to discuss the implementation of the card drivers and the associated problems9 because the techniques employed are only slightly different from those described in Chapter 6. I am much more interested in the interface made available by each card driver and used by the network code to provide an abstract view of the hardware.
By reference to Ethernet frames, I explain how data are represented ''on the cable'' and describe the steps taken between receiving a packet and passing it on to a higher layer. I also describe the steps in the reverse direction when generated packets leave the computer via a network interface.
9 Even though this may be quite interesting — unfortunately not for technical reasons but for product policy reasons.
Continue reading here: Representation of Network Devices
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