Specifications

CHAPTER 9
Wireless LANs in a Campus Network
Step 3. The WLCs respond with an LWAPP or CAPWAP Discovery Response that includes the number of APs
currently associated to it.
Step 4. The AP sends a Join Request to the WLC with the fewest APs associated to it.
Step 5. The WLC responds with a Join Response message; the AP and the controller mutually authenticate each
other and derive encryption keys to be used with future control messages. The WLC then configures the AP
with settings, such as SSIDs, channels, security settings, and 802.11 parameters.
Network Design for Lightweight APs
When using lightweight APs the traffic flow is from the AP, through the network, to the controller, and from there out to
the rest of the network. User traffic is tunneled between the AP and the controller. Make sure that the AP and controller
have Layer 3 connectivity.
The controller placement can be distributed, with a controller in each building or at each site, if no roaming between
buildings is needed. A centralized design, with redundant controllers placed together, such as in a data center, simplifies
management and increases user mobility.
SSIDs and VLANs must be planned, just as with an autonomous AP. But the configuration is done on the controller.
Clients are placed into VLANs based either on the controller they connect to or an authentication process. The manage-
ment VLAN is mapped to the controller. Controllers support both Layer 2 and Layer 3 roaming.
The link between a lightweight AP and the switch is an access port, assigned to a VLAN. The link between the controller
and its connected switch is a trunk link. Controllers with several switch links can create an Etherchannel to the switch to
increase bandwidth. Link aggregation is recommended for the 4400 series and is required on the WiSM and the 3750G
integrated controllers.
Ensure that the AP has a power source, either a PoE switch or a power injector.
[ 108 ]
© 2010 Pearson Education, Inc. All rights reserved. This publication is protected by copyright. Please see page 112 for more details.
CCNP SWITCH 642-813 Quick Reference by Denise Donohue
9781587140112.qxd 11/23/09 11:35 AM Page 108
www.CareerCert.info