WESM zl Management and Configuration Guide WT.01.28 and greater

9-5
Fast Layer 2 Roaming and Layer 3 Mobility
Overview
user’s credentials to all modules in the group. The other modules cache the credentials
so that they are ready to be sent to the RADIUS server should the user later roam to
one of these modules.
Note that the redundancy group solution does not enable the Web-Auth WLAN to
include any more RPs than the single module solution: a redundancy group, just like
a single module, has a 156 RP limit. The only reason to have multiple Wireless Edge
Services zl Modules support the WLAN would be to add capacity to the system.
Layer 3 Mobility
A station can roam seamlessly between two RPs adopted by the same Wireless Edge
Services zl Module (as long as both RPs support the WLAN). Likewise, a station can
roam seamlessly between two RPs adopted by different modules as long as those RPs
support the same WLAN. However, two modules that do not support the same virtual
LANs (VLANs) complicate the roaming process: the station’s IP address is no longer
valid, so it loses its active sessions.
Wireless Edge Services zl Modules use Layer 3 mobility to solve this problem. You
must enable Layer 3 mobility to support roaming between modules that have these
characteristics:
■ The modules support the same WLAN (or WLANs).
■ Each module places traffic from that WLAN in a different subnetwork. For Layer
3 mobility to function correctly, the different subnetworks must use different
VLAN IDs.
Figure 9-1 illustrates a network that requires Layer 3 mobility. The module on the
left places wireless stations in WLAN A in VLAN 1 while the module on the right
places stations in WLAN A in VLAN 20.