Specifications

CHAPTER 9

Wireless LANs in a Campus Network

Lightweight Access Points

Lightweight APs divide the 802.11 processing between the AP and a Cisco Wireless LAN Controller (WLC). This is

sometimes called “split MAC,” because they split the functions of the MAC layer, Layer 2. Their management compo-

nents also include the Wireless Control System (WCS) and a location-tracking appliance. Redundancy consists of multi-

ple WLCs. The AP handles real-time processes, and the WLC handles processes such as:

n Authentication

n Client association/mobility management

n Security management

n QoS policies

n VLAN tagging

n Forwarding of user traffic

The Lightweight Access Point Protocol (LWAPP) supports the split MAC function in traffic between a lightweight AP

and its controller. LWAPP uses AES-encrypted control messages and encapsulates, but does not encrypt, data traffic.

Controllers and APs can also use a new IETF-standard protocol to communicate with each other: the Control and

Provisioning of Wireless Access Points (CAPWAP) protocol. CAPWAP operates very much like LWAPP.

Both LWAPP and CAPWAP operate over UDP. The controller does not have to be in the same broadcast domain and IP

subnet, just IP reachable. Lightweight APs follows this process to discover their controller:

Step 1. The AP requests a DHCP address. The DHCP response includes the management IP address of one or more

WLCs.

Step 2. The AP sends an LWAPP or CAPWAP Discovery Request message to each WLC.

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CCNP SWITCH 642-813 Quick Reference by Denise Donohue