What is CAPWAP?
A basic, standardized networking protocol called Control and Provisioning of Wireless Access Points (CAPWAP) makes it possible to centrally administer wireless networks.
A centralized Wireless LAN Controller (WLC) uses CAPWAP (RFC 5415), an IETF standard protocol, to manage and control several Wireless Access Points (APs), often referred to as Wireless Termination Points (WTPs). This architecture specifies how APs and controllers communicate for configuration, control, and data tunneling, making deployment, maintenance, and troubleshooting easier in large organizations.
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Key features and functions of CAPWAP include:
Centralized Management and Provisioning
Centralized control and monitoring are made possible by CAPWAP, which also makes big Wireless Local Area Network installations easier and guarantees consistent configuration across several APs.
The WLC pushes configuration data to the AP via CAPWAP for AP Provisioning. This data includes things like:
- SSIDs
- Radio parameters
- Security settings
- QoS policies
- Firmware images (automatic upgrades)
The CAPWAP Workflow (Discovery and Join)
An AP connects to the WLC in a number of steps when it boots up:
- AP Boots and Discovery: The AP obtains an IP address and searches for a WLC using several methods, such as DHCP option 43, DNS resolution (e.g.,
cisco-capwap-controller.localdomain), or limited use of broadcast/multicast.
- DTLS Tunnel Establishment: To create a secure DTLS tunnel, the AP and WLC must first handshake after locating the WLC. Later control communications are protected by this tunnel. Although it incorporates this complete Datagram Transport Layer Security (DTLS) tunnel setup, CAPWAP is based on the earlier Lightweight Access Point Protocol (LWAPP).
- Join and Configuration: A Join Request is sent to the WLC by the AP. After being accepted, the AP gets its operating configuration and downloads any required firmware.
- Operational State: The AP becomes fully operational and begins serving customers when it joins the controller and enters the RUN state.
CAPWAP Tunnels and Channels
CAPWAP establishes a secure logical connection, or tunnel, between the AP and the WLC, which is divided into two distinct channels, typically transported over UDP ports:
| Channel | Purpose | UDP Port | Security/Encryption |
|---|---|---|---|
| Control Channel (Control Message Tunnel) | Used for all management and configuration functions, including the join process, configuration updates, and status monitoring. | 5246 | Secured using DTLS (Datagram Transport Layer Security). Control messages are authenticated and encrypted. |
| Data Channel (Data Tunnel) | Used for encapsulating and forwarding actual client data (end-user traffic) between the AP and the WLC. | 5247 | Encryption is optional. Data packets are transported over the tunnel and are typically not encrypted by default, but if encryption is enabled, they are protected using DTLS. |
Because CAPWAP encapsulates the data within new IP packets, it allows the tunneled data to be switched or routed across the network, meaning the AP and WLC can be separated geographically and logically (Layer 3 Mobility).
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Modes of Operation (Split-MAC Architecture)
The two main operational modes that CAPWAP offers dictate where client data flow is processed:
The whole setup, referred to as the split-MAC architecture, separates Media Access Control (MAC) operations: administrative duties, such as roaming management and authentication, are transferred to the WLC, while real-time functions, such as RF transmit/receive, remain with the AP.
- Centralized Switching / Split MAC Mode (Local Mode):
- The conventional and frequently default mode is this one.
- CAPWAP is used to encapsulate and tunnel all wireless data and management traffic back to the WLC.
- Most MAC layer operations, including data forwarding, are managed by the WLC.
- FlexConnect / Local MAC Mode:
- Because it conserves Wide Area Network (WAN) bandwidth, this mode is frequently used for remote branch offices.
- Control traffic continues to travel to the WLC via the CAPWAP tunnel.
- At the AP, data transmission originates locally. Local client traffic switching and authentication (local bridging) are managed by the AP.
- With this configuration, even in the event that the connection to the WLC is momentarily broken, the AP can still operate and route client traffic.
Importance and Standardization
As an open standard, CAPWAP makes network administration easier, improves security by encrypting control traffic, and permits vendor compatibility. A binding is the protocol’s specification for a certain wireless technology (such as IEEE 802.11); the protocol itself is not dependent on any particular radio technology.
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