Re: DHCP over a dd-wrt client bridge.

Jeff Liebermann wrote:
Les Cargill <lcargill@xxxxxxxxxx> hath wroth:

<snip>

http://www.dd-wrt.com/phpBB2/viewtopic.php?t=23683&highlight=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
.

Relevant Pages

  • Re: DHCP over a dd-wrt client bridge.
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    (alt.internet.wireless)
  • Re: Rouge APs at Work - How to locate them?!
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  • Re: iptables, broadcast from own IP in log file?
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    (comp.security.firewalls)
  • Re: TCP/IP Issue
    ... Well then if it's a bridge, and all packets are forwarded then everything is ... on the same IP subnet and all computers should be able to see each other ... > because of Broadcast, if so, and if i made each company to work with its ...
    (microsoft.public.windows.server.networking)
  • Re: Two Netgear WGT624 models will not communicate
    ... dramatically increase the leve of complexity of wireless. ... Security in a WDS network is marginal. ... the WAP54G wireless bridge has a similar problem. ... As I see it, the MAC address in the configuration is ...
    (alt.internet.wireless)