📘 CCNA 200-301 v1.1
2.7 Describe physical infrastructure connections of WLAN components (AP, WLC, access/trunk ports, and LAG)
access/trunk ports, and LAG)
A Wireless LAN (WLAN) connects wireless devices (like laptops, phones, tablets) to a wired network using Access Points (APs).
To understand how WLAN physically connects to the network, you need to know the roles of:
- Access Points (APs)
- Wireless LAN Controller (WLC)
- Access Ports and Trunk Ports
- Link Aggregation Group (LAG)
1️⃣ Access Point (AP)
➤ What is an AP?
An Access Point is a network device that provides wireless connectivity to end devices (clients).
It converts wired Ethernet signals into wireless radio signals, allowing wireless devices to join the network.
➤ Physical Connection
- The AP connects physically using an Ethernet cable to a switch port in the wired network.
- This connection provides data and often power (via PoE – Power over Ethernet).
➤ Power Options for APs:
- PoE (Power over Ethernet): The AP gets both data and power from the same Ethernet cable using standards like:
- IEEE 802.3af (PoE)
- IEEE 802.3at (PoE+)
- IEEE 802.3bt (UPOE)
- Or powered by a separate power adapter (less common in enterprise setups).
2️⃣ Wireless LAN Controller (WLC)
➤ What is a WLC?
A Wireless LAN Controller is a central device that manages multiple APs in the network.
It controls configurations, firmware, security policies, and channels for all APs.
➤ How APs Connect to WLC:
There are two main deployment modes:
- Centralized (Lightweight) Mode
- Autonomous (Standalone) Mode
Let’s focus on Lightweight Mode (since this is what Cisco uses in enterprises and is tested in CCNA).
🔹 Lightweight (Controller-Based) AP Connection
- The AP does not manage itself. Instead, it connects to a WLC to get its configuration and forward traffic.
- The AP forms a CAPWAP tunnel (Control And Provisioning of Wireless Access Points) to the WLC.
There are two types of CAPWAP tunnels:
- Control Tunnel: For management and configuration.
- Data Tunnel: For user data traffic.
➤ Physical Path:
Wireless Client → Access Point → Switch → WLC → Wired Network
So, the AP connects physically to the switch, and the WLC connects to the network backbone or core switch.
3️⃣ Access and Trunk Ports
When connecting APs and WLCs to switches, you must decide whether the switch port will be an access port or a trunk port.
Let’s understand both.
🟢 Access Port
- Carries traffic for only one VLAN.
- Used when the device belongs to only one VLAN.
Example in WLAN:
- If an AP only serves users from one VLAN (for example, only employees), the port connecting to it can be an access port assigned to that VLAN.
Configuration Concept:
Switch(config)# interface GigabitEthernet0/1
Switch(config-if)# switchport mode access
Switch(config-if)# switchport access vlan 10
This means:
- The AP will send/receive traffic only on VLAN 10.
🟠 Trunk Port
- Carries traffic for multiple VLANs using tagging (802.1Q tags).
- Commonly used when:
- An AP serves multiple SSIDs (each SSID can be mapped to a different VLAN).
- Or when connecting WLCs that handle multiple VLANs.
Example in WLAN:
- Suppose an AP provides two SSIDs:
- SSID “Staff” → VLAN 10
- SSID “Guest” → VLAN 20
Then the AP’s switch port must be a trunk port to carry both VLANs.
Configuration Concept:
Switch(config)# interface GigabitEthernet0/2
Switch(config-if)# switchport mode trunk
Switch(config-if)# switchport trunk allowed vlan 10,20
4️⃣ LAG (Link Aggregation Group)
➤ What is LAG?
Link Aggregation Group (LAG) combines multiple physical links into one logical link to:
- Increase bandwidth.
- Provide redundancy (if one link fails, traffic continues on others).
It uses the LACP protocol (Link Aggregation Control Protocol, IEEE 802.3ad) to manage these links.
➤ LAG in WLAN Setup:
In a WLC, multiple physical interfaces can be grouped together using LAG to connect to a switch.
- All physical interfaces in the group share the same VLANs and IP addressing.
- LAG improves throughput between the WLC and the switch.
- If one physical cable fails, the others continue to handle the traffic.
Example Setup:
WLC Port1 + WLC Port2 → Switch Port1 + Switch Port2
Combined into one logical LAG link
On Switch (LACP configuration example):
Switch(config)# interface range GigabitEthernet1/0/1 - 2
Switch(config-if-range)# channel-group 1 mode active
🧩 Putting It All Together – Physical Connection Flow
Here’s how the WLAN physical connections work in an enterprise network:
[Wireless Clients]
↓
[Access Point]
↓ (Ethernet cable)
[Access/Trunk Port on Switch]
↓
[Network Infrastructure / Core Switch]
↓
[Wireless LAN Controller (WLC)]
↓
[LAN / Internet]
- The AP connects via a switch port (Access or Trunk).
- The WLC connects to the distribution or core switch.
- LAG may be configured between WLC and switch for better speed and reliability.
- Power is provided to APs via PoE.
- CAPWAP tunnels link APs logically to the WLC.
📋 Exam-Focused Key Points Summary
| Component | Description | Physical Connection | Port Type | Notes |
|---|---|---|---|---|
| Access Point (AP) | Provides wireless access to clients | Ethernet to switch | Access or Trunk | PoE powered, connects to WLC via CAPWAP |
| WLC | Central device controlling multiple APs | Ethernet to core/distribution switch | Trunk or LAG | Manages APs, SSIDs, VLAN mappings |
| Access Port | Carries traffic for one VLAN | One VLAN | Used for single SSID | |
| Trunk Port | Carries traffic for multiple VLANs | Multiple VLANs | Used for multiple SSIDs | |
| LAG | Combines multiple links into one | Multiple cables act as one | Used for redundancy & bandwidth between WLC and switch |
✅ In short (for your students to remember):
“In a Cisco WLAN, Access Points connect to switches (access or trunk ports) and are powered by PoE. The Wireless LAN Controller connects to the network core and controls APs via CAPWAP tunnels. Link Aggregation Groups (LAGs) are used to increase bandwidth and provide redundancy between WLCs and switches.”
