WESM zl Management and Configuration Guide WT.01.28 and greater

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Introduction
Layer 2 and Layer 3 Roaming Between RPs and Modules
correctly place WLAN A traffic on different VLANs. If both used the same VLAN
ID, the modules would treat roaming between their RPs as Layer 2 roaming and the
roaming would not be seamless.
To implement Layer 3 roaming, Wireless Edge Services zl Modules perform these
functions:
■ Establish a Layer 3 mobility domain—A domain can include up to 12 mod-
ules, or peers, each of which can support up to 4096 stations. Every station has
a home module (HM) and a current module (CM). The HM is on the same VLAN
as the station, and the station is currently associated to the CM; the two modules
might be the same device.
■ When necessary, tunnel traffic back to a station’s HM—Every module in the
Layer 3 roaming domain establishes a tunnel to every other module. A module
tunnels traffic only when necessary, which is when a station that has an HM on
a different VLAN roams to the module. If a station that has an HM on the same
VLAN roams to the module, the module simply becomes the station’s new HM.
This provisions eliminates unnecessary and inefficient tunneling.
Wireless Edge Services zl Modules’ Layer 3 roaming capabilities provide seamless
roaming (sessions maintained) between RPs on different modules regardless of the
security options on the WLAN. However, fast roaming at Layer 3 is not supported
except when modules implement a redundancy group and Web-Auth. For more
information about roaming, see Chapter 9: “Fast Layer 2 Roaming and Layer 3
Mobility.”