[SPAM] Re: Fw: DHCP Fails to Pass Through HostAP AP

Wed Apr 29 02:51:29 EDT 2009

Hi Jouni,

Thanks for the reply.  Here are answers:

> Have you verified whether the client is able to receive broadcast frames
> when configured with a static IP address?

Yes, when configured statically network broadcasting works: the client is 
able to discover and authenticate against an MS Active Directory domain.

> I would expect this combination to work and I have noticed issues in my
> tests. Though, most of the time I do not use bridging, but when I do,
> Windows XP clients has been able to receive an IP address using DHCP.

How do you setup an access point without ethernet bridging?

> I would suggest running a test with simpler configuration, e.g.:
>
> wpa=1
> wpa_pairwise=TKIP
>
> and then another one with:
>
> wpa=2
> wpa_pairwise=CCMP

I tried both configurations but neither succeeded.

> DHCP should work fine without any additional configuration. The only
> thing that I can think of as a reason would be some kind of problems in
> delivering broadcast frames to the clients. I'm assuming that the DHCP
> server is sending out the responses using broadcast frames in this case.

The following tests revealed some interesting results:

* When connecting to an ISC DHCP server through hostapd (DHCP server 
residing on the same machine as hostapd), the XP clients work out of the 
box.  Vista clients require a registry workaround to function (setting 
'HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Interfaces\{GUID}\DhcpConnEnableBcastFlagToggle' 
to '1)

* When connecting to an MS DHCP server (XP and Vista, registry workaround or 
not) through hostapd DHCP continues to fail: the client's requests pass 
through the AP, but fail and the client assumes the auto-configuration IP 
address.  Following is a tcpdump of this scenario (192.168.8.20 is the IP 
address of the MS Windows DHCP server):

...
02:25:24.722406 IP 192.168.8.20.bootps > 255.255.255.255.bootpc: BOOTP/DHCP, 
Reply, length 311
02:25:37.413180 IP 192.168.8.20.netbios-dgm > 192.168.8.255.netbios-dgm: NBT 
UDP PACKET(138)
02:25:53.552388 IP 169.254.42.56.netbios-ns > 169.254.255.255.netbios-ns: 
NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
02:25:53.552381 IP 169.254.42.56.netbios-ns > 169.254.255.255.netbios-ns: 
NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
02:25:54.315056 IP 169.254.42.56.netbios-ns > 169.254.255.255.netbios-ns: 
NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
02:25:54.315049 IP 169.254.42.56.netbios-ns > 169.254.255.255.netbios-ns: 
NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
02:25:55.078701 IP 169.254.42.56.netbios-ns > 169.254.255.255.netbios-ns: 
NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
02:25:55.078695 IP 169.254.42.56.netbios-ns > 169.254.255.255.netbios-ns: 
NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
02:26:02.681809 IP6 fe80::7539:17f5:ed25:2a38.65460 > ff02::1:3.hostmon: 
UDP, length 24
02:26:02.681875 IP 169.254.42.56.65387 > 224.0.0.252.hostmon: UDP, length 24
02:26:02.681804 IP6 fe80::7539:17f5:ed25:2a38.65460 > ff02::1:3.hostmon: 
UDP, length 24
02:26:02.681874 IP 169.254.42.56.65387 > 224.0.0.252.hostmon: UDP, length 24
02:26:02.785702 IP6 fe80::7539:17f5:ed25:2a38.65460 > ff02::1:3.hostmon: 
UDP, length 24
02:26:02.785772 IP 169.254.42.56.65387 > 224.0.0.252.hostmon: UDP, length 24
02:26:02.785696 IP6 fe80::7539:17f5:ed25:2a38.65460 > ff02::1:3.hostmon: 
UDP, length 24
02:26:02.785771 IP 169.254.42.56.65387 > 224.0.0.252.hostmon: UDP, length 24
02:26:02.988551 IP 169.254.42.56.netbios-ns > 169.254.255.255.netbios-ns: 
NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
02:26:02.988545 IP 169.254.42.56.netbios-ns > 169.254.255.255.netbios-ns: 
NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
02:26:03.752447 IP 169.254.42.56.netbios-ns > 169.254.255.255.netbios-ns: 
NBT UDP PACKET(137): QUERY; REQUEST; BROADCAST
...

It looks like the MS DHCP server traffic can't pass return through the 
access point.  DHCP requests to the MS DHCP server via a physical ethernet 
connection on the same network succeed.

Any thoughts?

Thanks
-JASON

----- Original Message ----- 
From: "Jouni Malinen" <j at w1.fi>
To: "Jason Daly" <jason2 at primarykey.ca>
Sent: Sunday, April 26, 2009 2:12 PM
Subject: Re: Fw: DHCP Fails to Pass Through HostAP AP

> On Mon, Apr 27, 2009 at 04:18:54AM -0400, Jason Daly wrote:
>
>> Sorry to email you directly, but my emails continue to be marked by the 
>> HostAP mailing list as SPAM.  Do you know why?  Also, do you have insight 
>> on my inquiry below?:
>
> I have no idea what is marking the message as spam, but anyway, I do not
> see the message you forwarded, so something is filtering it from me..
> The message itself shows up on the mailing list archive, so I would
> expect that it was delivered and just filtered in my local setup.
>
>> When connecting Windows (XP/Vista) wireless clients to a hostapd AP, DHCP
>> offers do not succeed.  When setting the network interface settings on 
>> the
>> client to use a static configuration connectivity succeeds and client
>> networking through the AP functions well.
>
> Have you verified whether the client is able to receive broadcast frames
> when configured with a static IP address?
>
>> DHCP is working and the bridge functions: I have confirmed this by
>> successfully
>> obtaining a DHCP lease via the notebook's LAN port.
>
> Have you tried using any other client (e.g., a Linux laptop) through
> this AP using DHCP?
>
>> - hostapd 0.6.9
>> - FC10(2.6.29.1-15.fc10.i686)
>> - ath9k
>
> I would expect this combination to work and I have noticed issues in my
> tests. Though, most of the time I do not use bridging, but when I do,
> Windows XP clients has been able to receive an IP address using DHCP.
>
>> Following are the contents of my hostapd.conf file:
>
>> wpa=3
>> wpa_key_mgmt=WPA-PSK
>> wpa_pairwise=TKIP CCMP
>
> I would suggest running a test with simpler configuration, e.g.:
>
> wpa=1
> wpa_pairwise=TKIP
>
> and then another one with:
>
> wpa=2
> wpa_pairwise=CCMP
>
> In theory, this should not change anything as far as DHCP going through
> the bridge is concerned, but at least it verifies whether the issue
> shows up with CCMP as the group cipher or not.
>
>> Is there a setting in hostapd that must be added to allow DHCP to pass
>> through
>> the bridge.  UDP works fine through the bridge, as the client can see the
>> Windows domain and can broadcast for clients on the domain (when 
>> connected
>> via
>> a static IP or via a physical LAN cable).
>
> DHCP should work fine without any additional configuration. The only
> thing that I can think of as a reason would be some kind of problems in
> delivering broadcast frames to the clients. I'm assuming that the DHCP
> server is sending out the responses using broadcast frames in this case.
>
> -- 
> Jouni Malinen                                            PGP id EFC895FA
> 