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© 2008 Cisco Systems, Inc. All rights reserved. IUWNE v1.0—2-1

Basic Cisco WLAN Installation

Roaming


Mobility Groups, Mobility Domains


Controller > General

A Cisco Wireless LAN Controller (WLC) can only reside in a single mobility group.


Controller > Mobility Management > Mobility Groups

There are two methods to define the mobility group: Add a member using either the New or Edit All option, in which all members are represented in a text format.A controller can know members of other mobility groups.


Roaming Concept

Roaming refers to movement of clients across Cisco APs while transmitting

Roaming can occur across different mobility groups, but must be within a mobility domain

The Cisco WLC can reside in only a single mobility group The following should be consistent for mobility groups:

– Mobility group membership

– Code across all member controllers

– LWAPP mode across all member controllers

– ACLs configured on all member controllers

– WLAN configuration

– Virtual IP address Two types of roaming

– Intrasubnet roaming (Layer 2)

– Intersubnet roaming (Layer 3)


Cisco Wireless Layer 2 Roaming

Single Cisco WLC

Multiple Cisco WLCs in the same subnetwork

Transparent to the client

The session is sustained during connection to the new AP

The client continues using the same DHCP-assigned or static IP address


Client Roaming Within a Subnetwork


Cisco Wireless Layer 3 Roaming

Multiple Cisco WLCs in different subnetworks

Transparent to the client

The session is sustained during connection to the new AP

Tunnel between the anchor Cisco WLC and foreign Cisco WLC along with special handling of the client traffic by both controllers allows the client to continue using the same DHCP or client-assigned IP address while the session remains active

Set up via either a symmetric or asymmetric tunnel


Client Roaming Across Subnetworks


Roaming Example—Preroaming


Roaming Example—Layer 3 Asymmetric


Roaming Example—Layer 3 Asymmetric (Cont.)


Roaming Example—Layer 3 Symmetric


Roaming Example—Layer 3 Symmetric(Cont.)


Symmetric or Asymmetric Tunnelling


Roaming: Tunnels (Symmetric Example)


Cisco Wireless Mobility Anchor


Cisco WirelessMobility Anchor Considerations

A foreign session to the anchor is set up ahead of client IP address determination.– The foreign controller will have no knowledge of Layer 3 client

information.

Web authentication is supported, but authentication will occur on the mobility anchor as opposed to the local controller.

This mobility anchor function is only available on Cisco 4400 Series Wireless LAN Controllers and Cisco WiSM blades.– 2100/WLCM can be foreign controller, but not anchor the guest

tunnel.


WLANs > Mobility Anchors


Controller > Mobility Management > Mobility Anchor Config


Summary

Controllers can be part of the same mobility group, which allows them to exchange information about clients.

Roaming occurs when a stations changes connection point while transmitting.

At Layer 2, credentials are passed from one controller to the other to ensure seamless mobility.

At Layer 3, roaming can be symmetric or asymmetric, to maintain the client IP address or complete connection to the original subnet.

When roaming is asymmetric, the mobility anchor feature allows a partial symmetric configuration based on the WLAN.
