WESM zl Management and Configuration Guide WT.01.28 and greater

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Fast Layer 2 Roaming and Layer 3 Mobility
Verifying and Managing Layer 3 Mobility
The Idle status indicates that the local Wireless Edge Services zl Module has not
enabled Layer 3 roaming. Even if the Enable Mobility box is checked, the module
does not enable Layer 3 mobility until you specify a valid local IP address.
A Wireless Edge Services zl Module that remains at the Active-Connecting or
Passive-Connecting status also cannot connect to the peer. Usually, one of two
problems has occurred:
■ The local Wireless Edge Services zl Module and the peer cannot reach each other.
Make sure that each module can ping all other members of the Layer 3 mobility
domain. The local IP addresses must be on VLANs that are tagged on the uplink
VLAN. And either the modules themselves or the modules’ default gateways
must know the necessary routes.
■ The peer has not enabled Layer 3 mobility.
You should also check that this module and the peer enable mobility on the same
WLAN (or WLANs). Even when they do not, the peers can establish a connection;
however, but Layer 3 mobility will not function correctly on the WLAN in question.
Tracking Peer Communications
Layer 3 mobility peers that have established a relationship exchange these messages:
■ Join Events—A Wireless Edge Services zl Module sends a Join Event when a
station first associates with it. This message, which informs all peers that the
station has joined the Layer 3 mobility domain, contains the station’s MAC
address, IP address, and HM VLAN. The HM (the module responsible for
handling the station’s traffic) is typically the module that sends the Join Event
message.
■ Leave Events—A module informs its peers when a station disassociates from
the WLAN completely. (This is different from roaming to a new RP or module.)
■ L2-Roams—A station performs a Layer 2 roam when it reassociates to a new
RP but its HM VLAN remains the same. Wireless Edge Services zl Modules
track only Layer 2 roams that occur between modules. Because the new module
supports the station’s HM VLAN, the new module does not need to tunnel traffic
back to the original HM. Instead, the new module becomes the station’s new
HM, sending out an L2-Roam message to notify peers of the change.
■ L3-Roams—When a Wireless Edge Services zl Module receives a reassociation
request from a station with a different HM VLAN than the module uses, it
determines that a Layer 3 roam is necessary. The new module becomes the
station’s current module (CM), sends an L3-Roam message to the HM, and
begins tunneling the station’s traffic back to the HM.