why "underflow" happens?

[hong zhang]

--- On Wed, 10/12/11, Jouni Malinen <j at w1.fi> wrote:

> From: Jouni Malinen <j at w1.fi>
> Subject: Re: why "underflow" happens?
> To: hostap at lists.shmoo.com
> Date: Wednesday, October 12, 2011, 3:44 PM
> On Sun, Oct 09, 2011 at 09:25:28PM
> -0700, hong zhang wrote:
> > When wpa-psk TKIP key rotation happens during
> connection, "underflow" is complained and then disconnected.
> What does it means?
> 
> > 10-08 08:27:51.153 D/wpa_supplicant( 1791): WPA: RX
> message 1 of Group Key Handshake from 58:8d:09:b1:14:00
> (ver=1)
> > 
> > 10-08 08:27:51.153 D/wpa_supplicant( 1791): WPA:
> EAPOL-Key Key Data underflow (ie=29 len=72 pos=0)
> 
> This indicates that the received EAPOL-Key frame was
> considered to be
> invalid. The following debug entry from wpa_hexdump_key
> would have been
> quite useful in figuring out what exactly was in the
> message (it looks
> like you are running wpa_supplicant on a system that does
> not show that
> in the default debug info, so some additional effort would
> be needed to
> get that information, I'd guess).
> 
> What AP were you using when this happened? The OUI in the
> MAC address
> seems to indicate that it would be a Cisco device. I have
> not seen this
> type of interop issue with any Cisco AP that I've tested
> with.
> 
> -- 
> Jouni Malinen? ? ? ? ? ?

We use AP1250, but set WPA2 instead WPA like
IE: WPA Version 2
                        Group Cipher : TKIP
                        Pairwise Ciphers (1) : TKIP
                        Authentication Suites (1) : PSK

The AP is allowed to set that way. Is it illegal?