WESM zl Management and Configuration Guide WT.01.XX and greater

9-7
Fast Layer 2 Roaming and Layer 3 Mobility
Overview
■ The modules store information about all stations associated to any
module in the Layer 3 mobility domain.
The Wireless Edge Services zl Module responsible for handling a station’s
traffic is that station’s home module (HM). All the peers in the Layer 3
roaming domain must track all stations’ HM and HM VLAN. A module can
then recognize when a station that roams to it requires a Layer 3 roam:
the station’s HM VLAN is different from the VLAN supported on that
module.
■ When a Layer 3 roam is necessary, a module tunnels traffic back to the
station’s original module.
Each peer in the Layer 3 mobility domain maintains a Generic Routing
Encapsulation (GRE)-like tunnel to each other peer. (The peers automat-
ically configure the tunnel when you enable Layer 3 mobility.) When a
station roams, the module tunnels all traffic to and from the station,
including Dynamic Host Configuration Protocol (DHCP) and Address
Resolution Protocol (ARP) requests, to the station’s HM.
As you plan Layer 3 roaming, keep in mind that a Layer 3 roaming domain
should be contiguous with the following two domains. (See Figure 9-2.)
■ The Radio Frequency (RF), or Layer 2, roaming domain
Layer 3 roaming takes place in the background on top of RF roaming. That
is, at both Layer 2 and Layer 3, stations always roam within a WLAN.
(Moving to a new WLAN requires the user to select a new wireless
network.) Therefore, all Wireless Edge Services zl Modules in the Layer 3
roaming domain must support the WLAN in question.
In addition, you must not divide a WLAN into multiple Layer 3 roaming
domains.
■ A ProCurve Identity Driven Manager (IDM) location domain
If you use IDM to assign network rights, best practices dictate that devices
in the same Layer 3 roaming domain are also in the same location domain.
Note, however, that you cannot use dynamic VLAN assignments with
Layer 3 mobility.
For seamless Layer 2 roaming for WLANs that use Web-Auth, you must place
all Wireless Edge Services zl Modules in the same redundancy group. So, if
you want to enable Layer 3 mobility as well, you should place modules in the
same redundancy group and Layer 3 mobility domain.