I have an openbsd machine that is used as a bridging firewall to my desktop machine with windows.
I am setting the rules to allow dhcp on the windows machine to work, but I don't understand a few things.

The rules are:
-allow outbound connection to port 67 UDP
-allow outbound connection to port 53 UDP
-allow outbound connection to port 68 UDP
This rules work perfectly and combined with one to allow outbound connections to port 80 TCP i'm writing this on linuxquestions.org.

My doubt is this:why is it that dhcp(in the windows machine) is unable to retrieve the ip information with no rule to allow outbound traffic to port 67. Isn't port 67 used for a dhcp server to listen to. To retrieve the ip information should there be a need for more than the 68 port? If yes, why?

Another thing that i don't understand is why it doesn't make any difference whether i have an inbound or outbound rule for the 68 port. It works either way, but shouldn't this be important? The traffic has to come from somewhere specific, right?

I hope this clears it up, it works this way.
client transmitts requests from its source port 68 to server on port 67
server sends reply from its source port 67 to client on port 68