Friday, January 10, 2020

DHCP Server addresses me with my (former) IP after ipconfig release - how does it know?

Packet #61 - my client releases the IP Address 192.168.130.173

Packet #83 - my client renewes the IP Address by sending a broadcast, trying to find the DHCP Server

Packet #85 - DHCP Server sends me the packet directly to my former Address, giving me the same address again.

I've ever seen it like this:

client to broadcast: request
server to broadcast: ack

This trace is kinda different:

client to server: release
client to broadcast: discover
server to client: offer
client to broadcast: request
server to client: ack

I wonder why that's different.

Mainly: Why does the DHCP Server directly address me with my former IP, how does my PC accept it (if it has no IP, especially not the one previously used and released).

I understand that the Server does cache the mac-ip pair in case I want to re-use the address, but I specifically tell my (windows) PC to release it, I assume release does not mean "completely forget"?

I was trying to find out how ipconfig release actually works, but I couldn't find anything so far.
Here is the filtered trace, in case you wanna check it out: https://drive.google.com/file/d/1qZPQBg_lc80zwzJvPZkAu53yy6uySOt4/view?usp=sharing



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