CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

- Cisco lightweight access points handle the following 802.11 real-time requirements:
i) The frame exchange handshake between a client and AP when transferring a frame.
ii) Transmitting beacon frames.
iii) Buffering and transmitting frames for clients in power save operations.
iv) Responding to Probe Request frames originated from clients.
v) Forwarding notifications for the received probe requests to the controller.
vi) Providing real-time signal quality information of every received frame to the controller.
vii) Monitoring each radio channel for noise, interference, and the existence of other WLANs.
viii) Monitoring for the presence or introduction (newly installed) of other access points.
ix) Encryption and decryption except in the case of VPN/IPSec clients.
- All other remaining functionalities that are not time-sensitive are handled by WLAN controllers.
Time sensitivity is not a concern but controller-wide visibility is required. The following are
some of the MAC-layer functions that are provided and handled by Cisco WLAN controllers:
i) 802.11 authentication (security).
ii) 802.11 association, reassociation, and disassociation (mobility).
iii) 802.11 frame translation and bridging.
- LWAPP reduces the amount of processing of access points, and allows the resources on the
access point to focus on wireless access, rather than traffic handling, authentication, encryption,
filtering, and policy enforcement which are handled by WLAN controllers. This approach
improves the effectiveness of centralized WLAN management and security.
- Below lists the operation modes of Cisco WLAN controllers:
Direct Connect Mode The access points directly connected to the Ethernet or PoE interfaces
on a WLAN controller. The WLAN controller connects back to the
existing LAN infrastructure for seamless network integration.
Appliance Mode The access points directly connected to the existing LAN switches.
They communicate with the WLAN controller via LWAPP.
Hybrid Mode The WLAN controller operates in both Direct Connect and Appliance
modes.
- Below lists the ports and interfaces of Cisco WLAN controllers:
Distribution System Port
(built-in)
Service Port
(built-in)
Management Interface
(mandatory)
AP-Manager Interface
(mandatory)
Connects a WLAN controller to a switch port for communication
between the WLAN controller and wired LAN.
Reserved for out-of-band management, similar to the console port
of routers and switches. It is managed via the Service-Port interface
and must be connected to an access mode switch port. Only Cisco
4400 series WLAN controllers have a service port.
The default interface for in-band management. It is also used for
Layer 2 communications between the WLAN controller and
lightweight access points in Layer 2 LWAPP communication mode
(same subnet). It may reside on the same VLAN or subnet as the
AP-manager interface.
A WLAN controller may have one or more AP-manager interfaces
for Layer 3 communications between the WLAN controller and
lightweight access points in Layer 3 LWAPP communication mode
(different subnets). Configuring an AP-manager interface on the
same VLAN or subnet as the management interface results in
optimal access point association, but this is not a requirement.
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Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com