WLC Port-Channel with Nexus & Catalyst Switches

When deploying Cisco Wireless LAN Controllers (WLCs) in enterprise networks, one of the key design considerations is Link Aggregation (LAG). This feature combines multiple physical links into one logical link, ensuring higher throughput, redundancy, and simplified management. In large networks, WLCs are often connected to Cisco Nexus or Catalyst switches, where port-channels are used.

Fig 1:WLC Port-Channel with Nexus & Catalyst Switches

This guide explains how to configure WLC LAG and integrate it with Nexus or Catalyst switches effectively.

🔹 What is WLC LAG?

• Link Aggregation (LAG) groups all the WLC’s physical ports into a single logical port.
• The WLC doesn’t use LACP (Link Aggregation Control Protocol). Instead, it assumes all ports are bundled.
• All ports on the WLC must connect to the same switch or switch stack.
• The switch side must be configured as a static port-channel (mode on).

Benefits of WLC LAG:
✔️ Increased throughput (bandwidth across all links).
✔️ Simplified configuration (all ports act as one).
✔️ Redundancy — if one port fails, others carry the traffic.

🔹 General Configuration Guidelines

Enable LAG on the WLC

• Go to Controller > General > LAG Mode on Next Reboot.
• Set it to Enabled.
• Save and reboot the controller.

Switch-Side Configuration (Nexus or Catalyst)

• Create a port-channel.
• Set mode to on (static, no LACP).
• Add all physical interfaces connecting to the WLC.
• Configure VLAN trunking as required.

🔹 Example: Cisco Nexus Configuration

interface Ethernet1/1
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 10,20,30
  channel-group 10 mode on

interface Ethernet1/2
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 10,20,30
  channel-group 10 mode on

interface port-channel10
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 10,20,30

🔹 Example: Cisco Catalyst Configuration

interface GigabitEthernet1/0/1
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 10,20,30
  channel-group 1 mode on

interface GigabitEthernet1/0/2
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 10,20,30
  channel-group 1 mode on

interface Port-channel1
  switchport
  switchport mode trunk
  switchport trunk allowed vlan 10,20,30

🔹 Key Notes & Best Practices

• The WLC requires a reboot after enabling LAG.
• All WLC ports must belong to the same port-channel.
• Don’t configure LACP or PAgP — the WLC doesn’t support them.
• If you’re using Nexus vPC, connect both WLC links to the same switch (vPC not supported for WLC LAG).
• Ensure VLANs for management, AP, and WLAN data are properly allowed on the trunk.

🔹 Troubleshooting Tips

• Use show port-channel summary on the switch to verify port-channel status.
• Ensure all interfaces have the same speed, duplex, and trunking configuration.
• On WLC, check Controller > Ports to confirm link status.

✅ In Summary:
Configuring WLC LAG with Nexus or Catalyst switches provides better performance and redundancy while simplifying management. Just remember: WLC uses static port-channels only (mode on), requires a reboot after enabling LAG, and all links must terminate on the same switch or switch stack.