This concept of interface allows the Linux kernel to use networking functions without knowing much of the real implementation made by the driver.

Author : Pjmdef21

Publish Date : 2021-01-09 18:46:42

Studying network programming, I understood how to use Linux sockets in order to communicate with other systems/computers. I also studied a lot of higher level technologies built on top of sockets such as http, ssh, ftp.
I wrote this blog post while improving my understanding of Linux kernel networking features, from a socket to a NIC.
Plan
I) The Network Interface Controller (NIC)
II) The Network Interface
III) From socket to NIC
IV) Network interface functions
I) The Network Interface Controller (NIC)
According to Wikipedia; a NIC is a hardware component connecting a computer to a computer network.
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An ethernet NIC
If your computer doesn’t have a NIC, you cannot communicate with other computers.
Indeed you are isolated from the rest of the world (private and public networks).
So the first thing to do is to plug a NIC on the motherboard.
(If you want to connect to the internet thanks to wifi, you’ll need to plug a second NIC: a wifi NIC).
NICs are connected to the computer thanks to the PCI ports of the motherboard.
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PCI ports on a motherboard
On this Linux computer I only have 1 NIC plugged (wireless):
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The ‘lspci’ command shows hardware connected to PCI ports
The command above shows us that a NIC device (also called adapter) is plugged on the motherboard.
It is not possible to use it directly for the moment. A network driver must be installed and activated on our computer.
II) The Network Interface
“Linux Network Interface” is a category of drivers made for networking communications.
The Linux network interface defines a set of functions which must be implemented by the driver in order to be used by the kernel as a network driver.
This concept of interface allows the Linux kernel to use networking functions without knowing much of the real implementation made by the driver.

Among every existing drivers, most implement either:
The “char device interface” (e.g: mouse, keyboard).
A driver implementing this interface is available as a special file located somewhere in the “/dev” folder.
The “block device interface” (e.g: disks).

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A driver implementing this interface is available as a special file located somewhere in the “/dev” folder.
The “network device interface” (the interesting one in our case).
A driver implementing this interface is different from the previous ones as it doesn’t have a “file” entry in our filesystem.
Network drivers have to implement the Network device interface to be considered as “network interfaces” by the OS.
The “ifconfig” linux command shows our current activated network interfaces.

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This concept of interface allows the Linux kernel to use networking functions without knowing much of the real implementation made by the driver.

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