Information Technology Reference
In-Depth Information
VLAN
x
(IP Subnet
x
)
VLAN
y
(IP Subnet
y
)
WLC1
Anchor
WLC2
Foreign
Ethernet in IP Tunnel
Mobility Message Exchange
CAPWAP
Tunnel
CAPWAP
Tunnel
AP1
AP2
Pre-Roam
Data Path
Post-Roam
Data Path
• Client uses same IP address
• Original WLC is Anchor
• New WLC is Foreign
• EoIP tunnel used
• Client database copied
• Re-authentication
• New security session
Wireless Client
Roams from AP1 to AP2
Figure 5-12
Layer 3 Intercontroller Roaming
When you assign WLCs to mobility groups, the WLCs dynamically exchange mobility
messages and data is tunneled via EtherIP between the Anchor and Foreign AP. WLCs
should be placed in mobility groups when intercontroller roaming is possible and for con-
troller redundancy.
Mobility groups support up to 24 controllers. The upper limit of APs supported in a mo-
bility group is determined by the number of APs that the controllers support, which varies
by controller type. A mobility list is a group of controllers configured on a single con-
troller that specifies members in different mobility groups. Controllers can communicate
across mobility groups, and clients can roam between APs in different mobility groups if
the controllers are included in each other's mobility lists. Each WLC is configured with a
list of the members in the mobility group. Mobility lists can support up to 72 controllers
with Release 5.1 or later, up to 48 controllers with Release 5.0.
The WLCs exchange messages using UDP port 16666 for unencrypted messages or UDP
port 16667 for encrypted messages. APs learn the IP addresses of other members of the
mobility group after the CAPWAP join process.
As an example of the scalability, if 24 Cisco 2100 WLCs (25 APs supported per 2100
WLC) are used, 24 * 25 = 144 APs are supported. As another example recall that Cisco
4404-100 series WLCs support 100 APs. If 20 4404-100 WLCs are used, 20 * 100 = 2000
APs are supported.
As a best practice, Cisco recommends minimizing intercontroller roaming in the network.
controllers. Cisco also states that Layer 2 roaming is more efficient than Layer 3 roaming
