Wacky DHCP values that work in windows but not in FreeBSD

[David Horn]

On Mon, Oct 12, 2009 at 6:21 PM, Doug Barton <dougb at freebsd.org> wrote:
> Howdy,
>
> I usually have a wireless router connected directly to the AT&T/Yahoo
> DSL modem but last night I wanted to do some debugging so I plugged my
> laptop directly into the modem (after powering off the modem, etc.).
>
> The values I got back from DHCP not only don't make sense, they didn't
> work in FreeBSD at all. Dual-booting to Windows showed that the values
> I saw from DHCP were "correct," and somehow they managed to work.
> Taking a closer look at the router after I plugged it back in showed
> the same.
>
>        Dhcp Enabled. . . . . . . . . . . : Yes
>        Autoconfiguration Enabled . . . . : Yes
>        IP Address. . . . . . . . . . . . : 76.212.147.xxx
>        Subnet Mask . . . . . . . . . . . : 255.255.0.0
>        Default Gateway . . . . . . . . . : 151.164.184.xxx
>        DHCP Server . . . . . . . . . . . : 192.168.1.xxx
>        DNS Servers . . . . . . . . . . . : 192.168.1.xxx
>
> Can anyone tell me how they managed to get this to work in Windows,
> and suggest where to look to get it working in FreeBSD?
>
>
> Doug
>

Without seeing the actual tcpdump of the dhcp packets, I would guess
that this is the Classless Static Route option in DHCPv4 (option 121).

See:

http://www.rfc-editor.org/rfc/rfc3442.txt
http://www.iana.org/assignments/bootp-dhcp-parameters/

But tcpdump before dhclient initialization of the interface should
show what options are in play (I could be wrong on option 121)

tcpdump -vvv -i em0 port bootpc

Good Luck.

---Dave H