Basics of CAPWAP Tunneling

Basics of CAPWAP Tunneling

CAPWAP, or Control and Provisioning of Wireless Access Points, is a wireless networking protocol that allows communication between wireless access points (APs) and wireless LAN controllers (WLCs). CAPWAP is intended to help manage and control many APs via a central controller.

Fig 1.1- CAPWAP Tunnel

CAPWAP Message Types

CAPWAP defines two types of messages: data messages and control messages

  • Data messages are used to encapsulate and forward frames between wireless clients. They use UDP port 5247 for the data channel.
  • Control messages are used to transmit management information between the wireless LAN controller and the access point. For the control channel, they use UDP port 5246.Control messages can be divided into several types, including discovery, join, configuration, image data, reset, and keep-alive.

CAPWAP Modes of Operation

  • Split MAC mode: In this mode, all layer 2 wireless data and management packets are encapsulated using the CAPWAP protocol and exchanged between the WLC and AP. This mode allows for centralized control and management of the wireless network, but it also demands greater bandwidth and processing power from the WLC.
  • Local MAC mode: In this mode, the APs tunnel or bridge data frames locally, while only management frames are forwarded to the WLC using the CAPWAP protocol. This option decreases the workload on the WLC and network, but it necessitates more intelligence and setup on the APs.

In summary, Split MAC Mode encapsulates all layer 2 management and data frames between the WLC and the AP. Local MAC Mode tunnels data frames locally.

 Formation of CAPWAP Tunnel process

Phase 1 : Discovery Phase:

The AP initially performs a discovery process to locate available WLCs on the network. This can be done through various methods, such as broadcast, DHCP option, DNS resolution, or static configuration.

Phase 2: Join Process:

Once the AP discovers a WLC, it initiates a join process to establish a CAPWAP tunnel. This involves sending a join request to the WLC.

Phase 3 : CAPWAP Data Plane Establishment:

The join request is received by the WLC, and if the WLC accepts the request, it responds with a CAPWAP join response.

The AP and WLC then negotiate and establish a CAPWAP data plane, which is the tunnel for transporting user data between the AP and the WLC.

Phase 4 : Control Plane Establishment:

Once the data plane is established, the control plane connection is set up. This is the channel for exchanging control and management information between the AP and WLC.

Phase 5 : CAPWAP Tunnel Establishment:

The combination of the CAPWAP data plane and control plane forms the CAPWAP tunnel. This tunnel is used for various purposes, including configuration, monitoring, and control of the AP by the WLC.

Phase 6 : Tunnel Maintenance:

The CAPWAP tunnel is maintained throughout the AP's operation. This includes periodic keep-alive messages and the ability to re-establish the tunnel in case of a failure or disruption.

Phase 7 : Data Transfer:

Once the CAPWAP tunnel is established and maintained, the AP can start sending user data to the WLC over the data plane of the CAPWAP tunnel. The WLC is responsible for managing and controlling the connected APs and coordinating their actions.

In simple terms, the CAPWAP tunnel is constructed by discovering, joining, negotiating, and establishing data plane and control plane connections between the wireless access point and the wireless LAN controller. This tunnel is critical for the centralized management and control of wireless networks.

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