Unicast DHCP OFFER?

Knaack Phillip-PKNAACK1 Phillip.Knaack at motorola.com
Sun Sep 17 14:38:41 EST 2006


Greetings!

You should all ignore this message. I found that someone here had
modified the netif_rx code in a really stupid way.  I now see how it
works.

-Phil K

-----Original Message-----
From: Knaack Phillip-PKNAACK1 
Sent: Saturday, September 16, 2006 5:02 PM
To: 'linuxppc-embedded at ozlabs.org'
Subject: Unicast DHCP OFFER?

Greetings!

This isn't really a powerpc question, more of a general Linux question,
although I'm working on an embedded powerpc target board.  It's a stupid
question about DHCP.

My target is running udhcpc over a wireless (not wi-fi) interface to a
remote radio which is running a dhcp relay agent. I see the DHCP
discover sent out, and I see (at the driver level) the DHCP offer coming
back.  However, the offer is being sent unicast directly to my (new) IP
address, which I don't know yet.  As a result, the ip stack is dropping
the packet because of "no route".  So I ask myself, how can I receive a
UDP packet addressed directly to me if I don't yet know my own address?
It defies logic.
And the odd part is, it works with another version of this card on
Windows, though I wouldn't be surprised if they just hacked it up to
"just work" anyway.

Because of the nature of this wireless connection, it really needs to be
unicast.  I'm thinking of recognizing a UDP/DHCP packet in the radio
driver and hacking the iphdr source addr to be a broadcast, so the raw
socket in udhcpc will receive it, but this shouldn't be necessary.

So-- how is a unicast dhcp offer supposed to work?

-Phil K



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