Linux operating system startup interface revealing DHCP protocol implementation process

I particularly like the hint of a line on the screen when Linux starts. It tells us everything that the system is doing, unlike Windows, which gives us a progress bar when we're done, and we don't know what's behind it.

The DHCP protocol part implementation process is as follows

The ①:DHCP server passively opens UDP port 67, waiting for the client to send the message.

The ②:DHCP client sends a DHCP discovery message from UDP Port 68.

③: Every DHCP server that receives DHCP discovery messages sends DHCP-provided messages, so DHCP clients may receive multiple DHCP-provided messages.

④:DHCP the customer selects one of the several DHCP servers and sends a DHCP request message to the selected DHCP server.

⑤: The selected DHCP server sends a confirmation message DHCPAck, enters the bound state, and begins to use the resulting temporary IP address.

We all feel a bit obscure in writing, although the explanation is quite clear.

But a few days ago, I started Linux, I noticed this small detail, Linux startup process step by step in the screen output, I think can let us see more intuitive, cut a picture, hehe.

The following figure:

In this diagram, I said above from steps 2nd to 5th are very clear (the first step is the service side, we do not see), Port, MAC, state these are clearly marked.

DHCPDiscover on eth0 to 255.255.255.255 port interval 4//2nd step, send DHCP discovery message

DHCPOFFER from 192.68.116.254//step 3rd, receive DHCP delivery message

DHCPRequest on eth0 to 255.255.255.255 port 67//step 4th, send DHCP request message

DHCPACK from 192.168.116.254//step 5th, receive DHCP confirmation message DHCPACK

Bound to 192.168.116.128-renewal in 826 seconds//bound, 826 seconds should be 0.5T, that is, half of the IP lease period, and then resend the request to update the lease time

Done.

Linux is really a good thing.