Connectivity and Data Protection
dissimilar vendors’ equipment using incompatible handoff
mechanisms. This event would result in a situation where a mobile
station’s MAC address would be found in two access points’
association tables simultaneously. The 802.11 standard indicates that
when the frames are forwarded to the station by two access points
within range, the station should reply to access point to which it is not
associated using deauthentication or disassociation frames only.¹
In order for roaming to work effectively, set the SSID in all of the
access points in an area to the same value. Because the stations
generally refine their scanning to only access points having the same
SSID as what’s configured in the station, most stations will not pay
attention to access points set to a different SSID. If access points
don’t have the same SSID, a station may first need to completely lose
the signal from the associated access point. The client operating
systems, such as Windows XP, can then offer new wireless networks
(having the different SSID) that the user can choose and associate
with.
Reassociation in a wireless 802.1X/EAP network can be a relatively
slow process in comparison to using Open System or Shared Key
authentication in a scenario in which “fat” or “intelligent” access points
are used. Vendors that support 802.1X/EAP have realized that time-
sensitive connections such as Voice over IP over WLAN (VoWLAN)
may often be momentarily disrupted during a roam due to the lengthy
802.1X authentication process. For this reason, some vendors have
developed proprietary roaming mechanisms (e.g. Cisco’s Fast Secure
Roaming) to aid in speeding the 802.1X authentication process along.
Wireless LAN switches do not generally have this problem because
handoffs between “thin” (limited functionality) access points (which
may often amount to “smart antennas”) are handled internally within
the switch’s firmware.
Data Protection
Confidentiality on a wireless LAN is certainly critical because of the
potential exposure of data frame contents to eavesdroppers. Without
1
IEEE 802.11 - 1999 (R2003) – Section 5.5.c
