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Old 01-02-2008, 04:04 AM
Les Cargill
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Default Re: DHCP over a dd-wrt client bridge.

Jeff Liebermann wrote:
> Les Cargill <lcargill@cfl.rr.com> hath wroth:
>
>> <snip>
>>
>> http://www.dd-wrt.com/phpBB2/viewtop...ht=dhcp+bridge
>>
>> For reference: DHCP does not work unless you use WDS.

>
> Retch. DHCP *SHOULD* work through a wireless bridge (if it will pass
> broadcast packets).


If it's a MAC layer broadcast, that could be a problem. Multicast
won't work - the firmware appears to simply hardcode a MAC address
for each port. So it's not a true transparent bridge. I don't think
plain-old ports on the switch will want to forward promiscuously. We've
kind of inverted the original intended topology of the device by making
the wireless MAC the backhaul.


Also, when I dump the arp cache on YET ANOTHER workstation :), I get the
same MAC assigned to both the IP address for the client-bridge router
(192.168.1.2) and a workstation connected to the Ethernet switch on that
router (192.168.1.49)

C:\Documents and Settings\Owner>arp -a

Interface: 192.168.1.102 --- 0x10004
Internet Address Physical Address Type
192.168.1.1 00-1c-10-b0-32-eb dynamic
192.168.1.2 00-1c-10-ae-1b-76 dynamic
192.168.1.49 00-1c-10-ae-1b-76 dynamic
192.168.1.100 00-40-ca-90-f1-0b dynamic

C:\Documents and Settings\Owner>

For clarity:

Main machine - connected wired to WAP which has a cable modem on the
WAN port. 192.168.1.100 and 192.168.1.1 respectively.

Second machine - wired to client-bridged WRT54G - 1.49 and 1.2

*Third* machine - USB 802.11G adapter elsewhere. The "arp -a" is done
from there.

Not sure that this matters. Doesn't seem very bridge-like -
a real learning bridge has no MAC address *per se*(1). Might
have one in CAM for its own purposes ( inband traffic terminating
at a CPU off the bridge... ).

(1) been a while - there may be an exception I'm missing, and
it may have been colored by the equipment I was working with.

> Using WDS seems like a band-aid or work around
> for a bug. I have a funny feeling there's some interaction with WOL
> (Wake on LAN) which also uses an all 1's broadcast packet. If the
> micro version supports WOL, try turning it on and see if it now passes
> broadcast packets.


It does. Will do.

> You can also use a WOL client to generate
> broadcasts to 255.255.255.255 to see if they make it through the
> bridge.
>
> If you get a usable answer from the DD-WRT folks, I would be
> interested.
>


I'll put a little effort into that, then. My workaround for
the moment is a static IP, but the least I can do for the
guys is due diligence to get it on the scope.

> Hmmm... I just checked the Bug Tracker and couldn't find anything
> directly related to v25 RC4 and DHCP. There are a few DHCP bug
> reports, but I'm discounting any reports without corroberating details
> (i.e. clueless bug report). I don't see anything on the most recent
> 50 bug reports:
> <http://www.dd-wrt.com/dd-wrtv2/bugtracker/view_all_bug_page.php>
>


Lemme start a thread on the website. It seems odd that this would go
unnoticed - indeed, it hasn't - maybe just not noticed by the right people.

--
Les Cargill

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