What is a lightweight access point?
In wireless network architecture, a Lightweight Access Point (LWAP), also known as a LWAP, Thin AP, or Fit AP, signifies a radical departure from the conventional standalone approach. A Wireless LAN Controller (WLC) is intended to have central control over LWAP operations.
Core Characteristics and Definition
An autonomous access point’s architecture is somewhat at odds with that of a lightweight access point.
- Dependency on WLC: In order for LWAPs to function properly, they need to be coupled with an external Wireless LAN Controller (WLC). For management and operation, they are totally dependent on the controller.
- The Term “Lightweight”: The phrase “lightweight” describes how these devices have less local intelligence than an autonomous AP. During the registration procedure, the WLC provides the required firmware and configuration settings. “Dumb APs” is an informal term used to describe LWAPs.
- Hardware: Although APs and LAPs frequently share the same hardware, their operating modes cause them to run separate firmware. In order to boot up, acquire an IP address, and connect with the WLC to download the most recent controller-based firmware, the lightweight AP requires very little firmware.
Split-MAC Architecture
The Media Access Control (MAC) layer functions of LWAPs are split between the centralized WLC and the lightweight AP in a Split-MAC design. In order to overcome the scalability constraints of autonomous AP design, the control and data planes were separated.
| Function | Lightweight AP (LAP) Role | Wireless LAN Controller (WLC) Role |
|---|---|---|
| Real-Time MAC (Data Plane) | Handles the most time-sensitive, real-time Layer 2 functions. Functions include: frame exchange handshake, sending wireless beacons and responding to probe requests, frames acknowledgments and retransmissions, managing frame fragmentation, queueing and prioritization, Layer 2 wireless encryption/decryption, and handling power save mode frames. | Handles management tasks that do not require real-time handling of wireless frames. |
| Control Plane (Management) | Focuses only on real-time MAC functions. Sends real-time signal quality information and monitors the RF channel. | Functions as the central “brain”. It handles centralized configuration (SSID, VLAN, radio settings), client authentication, security management and policies, RF management (channel allocation and power adjustments), managing association and roaming, QoS, and 802.11 to 802.3 frame translation and bridging. |
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Communication and Traffic
The Control and Provisioning of Wireless Access Points (CAPWAP) protocol is used by LWAPs to connect with the WLC. The Lightweight Access Point Protocol (LWAPP) was replaced by CAPWAP.
Between the LAP and the WLC, CAPWAP creates two tunnels:
- Control Tunnel (UDP 5246): Encrypted messages are sent over this tunnel to guarantee secure communication while setting and managing the LAP.
- Data Tunnel (UDP 5247): Client data is transmitted over the Data Tunnel (UDP 5247). Client data is not encrypted by default; however, Datagram Transport Layer Security (DTLS) can be used to enable encryption.
A lightweight AP typically sends client traffic to the WLC via the CAPWAP tunnel, and the controller is then in charge of bridging the traffic into the wired network, in contrast to autonomous APs that bridge client traffic directly to a wired VLAN.
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Advantages and Deployment
Expanding wireless networks is greatly aided by lightweight access points, especially in large-scale settings.
- Centralized Management: Compared to manually configuring parameters (such as SSIDs, VLANs, security mode, and transmit power) on each AP separately, network managers can manage hundreds of access points from a single WLC interface.
- Deployment Ease: LWAPs are intended to be plug-and-play add-ons. Without requiring human setup, a new device connects to the WLC automatically, downloads configurations (such as security settings and protocols), and begins to function.
- Scalability: When coverage or capacity needs to be quickly increased or moved, lightweight network architectures perform best. Although this system initially requires additional hardware (the WLC), as the number of devices in the network increases, the cost of design, implementation, and maintenance decreases.
- Smooth Roaming: Even over Layer 2 and Layer 3 networks, clients can move between LAPs swiftly because to the WLC’s seamless management of client association and roaming.
- Simplified Connectivity: Unlike autonomous APs that need trunk links, a lightweight AP only needs an access link (connected to a single VLAN) because client traffic for all supported VLANs is encapsulated within the CAPWAP tunnel and forwarded to the WLC.
LWAP Operating Modes
Depending on the requirements of the network, lightweight APs can be set up to function in multiple modes:
- Local Mode (Default): All traffic is normally sent back to the WLC through the CAPWAP tunnel (centralized switching), but the AP serves clients.
- FlexConnect Mode: Prevents all traffic from being sent back to the central controller by enabling an AP at a distant location to locally switch traffic between an SSID and a VLAN in the event that the CAPWAP tunnel is unavailable.
- Monitor Mode: In monitor mode, the AP does not transmit or serve clients; instead, it serves as a specialized sensor to look for interference and rogue APs.
- Sniffer Mode: To capture and analyse packets, the AP accepts 802.11 traffic.
- Rogue Detector Mode: Identifying rogue devices is the focus of the Rogue Detector Mode.
- Bridge Mode: Sets up the access point for mesh or point-to-point connections.
- SE-Connect Mode: Dedicated to analysing the spectrum to identify interference sources.
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