WESM zl Management and Configuration Guide WT.01.28 and greater

1-21
Introduction
ProCurve Wireless Edge Services zl Module
Note The instructions in the rest of this section are based on the assumption that the same
VLAN ID corresponds to the same subnetwork throughout your network. This
assumption is usually, but not always, true. The important consideration for roaming
is that modules assign traffic in the same WLAN to the same subnetwork.
Sometimes, however, your network design makes it impossible for modules to
forward traffic on the same subnetworks. If so, using the same VLAN ID for the
WLAN on every module is no longer valid. Instead configure Layer 3 roaming,
making sure to associate each different subnetwork with a different VLAN ID. See
“Roaming Between RPs on Different Wireless Edge Services zl Modules at Layer
3” on page 1-79.
If the VLAN and subnetwork that you choose for the WLAN is one used in the
traditional wired network, the design is much the same as that for a network with a
single module. If you want to reserve the VLAN for wireless users, however, you
must alter the design slightly. You must be careful not to terminate the VLAN for
wireless users on each module. Instead, extend the VLAN through your infrastruc-
ture. However, do not configure the infrastructure devices to route traffic in and out
of this VLAN but simply to forward the VLAN traffic between the modules.
This design addresses several issues. When a station first associates to an RP, the
module that supports that RP assigns the station a DHCP address with itself as the
default gateway. If the station later roams to a new module, its traffic must be able
to reach the original module. In addition, when all modules use the same Layer 2
subnetwork, they can exchange pre-authentication messages, speeding roaming in
WLANs that require 802.1X authentication.
Figure 1-9 shows a network that includes multiple Wireless Edge Services zl Mod-
ules and separates VLANs for the wireless network from VLANs for the wired
network.