Secure Roaming in 802.11 Networks

Chapter 7

with which it has preauthenticated. Both the STA and AP maintain an identifier called the

PMK Identity (PMKID) that permits the two to confirm that they are using the correct PMK

when they begin their four-way exchange.

While the EAPOL authentication exchange between the client and the current access point

closely resembles the EAPOL preauthentication exchange with the neighboring access

points, their Ethernet types differ. As defined by the 802.1X standard, the Ethernet type of

the normal EAPOL frames is 0x888E, whereas the preauthentication frames use the Ethernet

type 0x88C7. It is important that the access point be able to distinguish between ...