Question on HostAP, IAPP link layer update and bridge station cache

Jon-Olov Vatn vatn
Tue Apr 1 06:33:30 PST 2003

28 March 2003 Jouni Malinen wrote:
> On Mon, Mar 24, 2003 at 01:38:25PM +0100, Jon-Olov Vatn wrote:
> ...
> > Now to my question. If one would like to fix this problem, I can see
> > two different approaches, and I wonder what way to go:
> > * "Interaction between hostAP and briding code"
> > * "Inserting link layer update frame in wlan0 input queue"
> I think it would be useful to implement more interaction between Host AP
> and bridging code.

Before I saw your answer I started to work on a solution according to
my second alternative, i.e., upon a successful (re)association the
hostapd would build the IAPP link layer update packet and then to
ask the hostap driver (by ioctl) to treat this packet as if it
came in on the wlan interface (put it in an sk_buff and call netif_rx).

A good way with doing it this way is that the link layer update packet
will then be forwarded on all bridge interfaces except the wlan (e.g. wlan0)
interface where the STA resides. In particular this could be beneficial
if we are putting up WDS links to other APs dynamically.

I made my some changes to the hostap cvs version as of March 24 and in
my small testbed it seems to work. Since this is my first kernel hack
I know that there are probably several ways in which it can be
improved ...
Both the patch and the source of the cvs version of March 24 can be
found at (for at least a week)
for the ones interested. 
To apply the patch first download "hostap-cvs-20030324.tgz"
and "patch-linklayerupdate" to some suitable location then

$> tar zxvf hostap-cvs-20030324.tgz
$> cd hostap-cvs-20030324
$> patch -p1 < ../patch-linklayerupdate

Note, in the patch I have modified the hostapd/hostap.conf file
to use "br0" as IAPP interface. Maybe it is better to use "eth0".
In any case the IAPP interface needs an IP address (see Jouni's
comment below).

> However, before doing this, I would add third option
> to your list:
> * use IAPP to update the previous AP
> Current version of hostapd has quite limited version of this, but it
> should work in the case you described, i.e., having the APs sharing same
> shared physical medium so that they can receive broadcast packets from
> eachother. This requires IP addresses (so that you do not need to
> comment our the initialization). If the APs cannot receive broadcast
> frames from eachother, more complete IAPP implementation would be
> needed.
Thanks. I was using a setup where with a bridge interface (br0) and
two physical interfaces (wlan0 and eth0) associated with br0. eth0
was my "IAPP interface", but only br0 had an IP address. Now I am
using br0 as "IAPP interface" instead.

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