~300 bytes length packet encoding problem

Jouni Malinen j at w1.fi
Sat May 12 11:38:52 EDT 2007

On Sun, May 06, 2007 at 08:19:12AM +0200, hostap.20.BertrandB at spamgourmet.com wrote:

> in las ebuild of dhcpcd gentoo pad short packets to 300 bytes this cause
> problem with wpa_supplicant ? hostap driver ?

wpa_supplicant does not touch normal data packets in any way, so this is
not an issue with it. Host AP driver or kernel IEEE 802.11 crypto would
be more likely candidates.

> I got the message : wifi0: TX - encryption failed and dhcpcd failed
> I made tests with different length of packets
> 300 -> ko
> 299 -> ko
> 295 -> ok
> 305 -> ok
> 500 -> ok

I'm unable to reproduce this in my tests.

> the orginal bug at gentoo's 
> http://bugs.gentoo.org/show_bug.cgi?id=175911
> the configuration :
> dhcpcd-3.0.17
> wpa_supplicant-0.5.7
> kernel 2.6.19-gentoo
> card info: "IEEE 802.11b", "Wireless LAN PC Card/11M", "PRISM 2.5",
> "Rev: C"
> driver hostap (from kernel)

I tried with dhcpcd-3.0.16 vs 3.0.16-r1 and verified that the DHCP
packet length changed. 3.0.16-r1 was using 300-byte UDP payload (which
I would assume is the same packet length as you were reporting a problem
with). I was using 2.6.20 kernel from kernel.org, but I would be
surprised in 2.6.19-gentoo version would be significantly different as
far as Host AP driver is concerned.

Are you changing any wireless parameters like fragmentation threshold?
Could you easily test this with a newer kernel version just to make sure
that something was not fixed after 2.6.19? Please also send 'iwconfig'
and 'ifconfig -a' output from the host.

Jouni Malinen                                            PGP id EFC895FA

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