Cisco Cisco 4404 Wireless LAN Controller Références techniques
14
Cisco 440X Series Wireless LAN Controllers Deployment Guide
OL-10043-02
LWAPP Fundamentals
Wireless LAN client data packets are encapsulated in LWAPP between the access point and the wireless
LAN controller. Wireless LAN controllers forward data frames to and from wireless LAN clients after
encapsulating or de-encapsulating the frames.
LAN controller. Wireless LAN controllers forward data frames to and from wireless LAN clients after
encapsulating or de-encapsulating the frames.
When a wireless LAN client sends a packet, it is received by the access point, decrypted if necessary,
encapsulated with an LWAPP header and forwarded to the controller. At the controller, the LWAPP
header is removed and the frame switched from the controller onto a vitrual LAN (VLAN) in the
switching infrastructure. When a client on the wired network sends a packet to a wireless LAN client,
the packet first goes into the wireless LAN controller where it is encapsulated with an LWAPP header
and then forwarded to the appropriate access point. The access point removes the LWAPP header,
encrypts the frame if necessary, and then bridges the frame onto the RF medium.
encapsulated with an LWAPP header and forwarded to the controller. At the controller, the LWAPP
header is removed and the frame switched from the controller onto a vitrual LAN (VLAN) in the
switching infrastructure. When a client on the wired network sends a packet to a wireless LAN client,
the packet first goes into the wireless LAN controller where it is encapsulated with an LWAPP header
and then forwarded to the appropriate access point. The access point removes the LWAPP header,
encrypts the frame if necessary, and then bridges the frame onto the RF medium.
This document focuses on practical deployment scenarios of the Cisco Unified Wireless Network
solution. And it reviews some LWAPP fundamentals to provide the foundation for discussions to follow
in the rest of the document. A detailed discussion of the architecture itself and LWAPP is beyond the
scope of this document.
solution. And it reviews some LWAPP fundamentals to provide the foundation for discussions to follow
in the rest of the document. A detailed discussion of the architecture itself and LWAPP is beyond the
scope of this document.
LWAPP Fundamentals
This section reviews the fundamentals of LWAPP, and provides background information for the
deployment scenarios. The LWAPP protocol is defined by an IETF RFC draft document that is the basis
for the IETF Control and Provisioning of Wireless Access Points (CAPWAP) working group. Today,
LWAPP is the most mature protocol available for wireless network devices.
deployment scenarios. The LWAPP protocol is defined by an IETF RFC draft document that is the basis
for the IETF Control and Provisioning of Wireless Access Points (CAPWAP) working group. Today,
LWAPP is the most mature protocol available for wireless network devices.
LWAPP is a generic protocol with a binding definition for the 802.11 wireless LAN protocol.
LWAPPdefines how access points communicate with wireless LAN controllers. This communication can
be either by means of native, Layer 2 Ethernet frames, or Layer 3 via IP packets. In the Cisco LWAPP
implementation, Layer 3 LWAPP packets are carried in UDP packets.
LWAPPdefines how access points communicate with wireless LAN controllers. This communication can
be either by means of native, Layer 2 Ethernet frames, or Layer 3 via IP packets. In the Cisco LWAPP
implementation, Layer 3 LWAPP packets are carried in UDP packets.
LWAPP messages carry one of two types of payload:
•
LWAPP Data Messages, which are encapsulated and forwarded data frames sent from and to
wireless clients.
wireless clients.
•
LWAPP Control Messages, which are management messages exchanged between the wireless LAN
controller and the access point.
controller and the access point.
The LWAPP protocol header contains a control bit (the C-Bit) which identifies data and control packets.
When Layer 3 LWAPP is used, the LWAPP data and control packets are sent to separate UDP ports.
Because both data and control frames can be fragmented, the payload LWAPP data or control message
can be fragmented.
When Layer 3 LWAPP is used, the LWAPP data and control packets are sent to separate UDP ports.
Because both data and control frames can be fragmented, the payload LWAPP data or control message
can be fragmented.
Phases of LWAPP
The phases of LWAPP operation are as follows:
1.
The access points send an LWAPP Discovery Request message.
2.
Wireless LAN controllers receiving the LWAPP Discovery Request respond with an LWAPP
Discovery Response.
Discovery Response.
3.
From the LWAPP Discovery Responses received, an access point selects a wireless LAN controller
to join.
to join.
4.
The access point then sends an LWAPP Join Request to the selected wireless LAN controller,
expecting an LWAPP Join Response.
expecting an LWAPP Join Response.