Relevance of GTK key index?

Christian Lamparter chunkeey
Sat Aug 13 13:12:54 PDT 2011

On Friday 12 August 2011 20:03:19 Harshal Chhaya wrote:
> Should the key index used for the GTK (with WPA2-PEAP) matter?
> I am seeing that my clients have problems if the GTK is at index 2 but
> connect just fine if the GTK is at index 1. The connection manager on
> these clients (custom code), restarts the connection process if the
> GTK is at index 2 because it seems that the radio firmware expects the
> GTK at index 1. After a few such tries, the connection succeeds
> because hostapd somehow switches the GTK index to 1 and my connection
> manager is happy.
> I am trying to understand what causes hostapd to use a different index
> and if I can influence it to use index 1 to start with? This will
> avoid all the retries and improve the connection time.
Please, take a look at the spec. It's easy to find the right answers there.

802.11-2007 8.5.6 :
"Because there are two GTKs, the responsibility for updating these keys is
given to the group key state machine (see Figure 8-39). In other words, this
state machine determines which GTK is use at any time."


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