Dual-aggregation switch configuration

Dual-switch aggregation can be configured using MCLAG or LACP to provide redundancy, load balancing, and high availability between two switches.

Step 1: Prepare the Switches

• Ensure both switches are powered on and reachable via management interfaces.
• Verify firmware versions are compatible for MCLAG or LACP support.
• For FortiSwitch, confirm that the FortiGate controller is managing the switches if using FortiLink MCLAG .

Step 2: Configure Inter-Switch Links (ICL)

• Connect at least two physical links between the two switches for redundancy.
• On FortiSwitch, enable auto-isl-port-group to group ports from each switch into a single MCLAG when the inter-switch link is formed .
• Ensure mclag-stp-aware and STP are enabled on all ICL trunks to prevent loops (enabled by default), .
• For Cisco or standard LACP, create a port-channel interface and add the inter-switch links to it, enabling LACP in active or passive mode on both ends .

Step 3: Configure MCLAG Peer Group (FortiSwitch)

• On each switch, configure the MCLAG peer group:
  • Use CLI commands: config switch auto-isl-port-group to assign ports to the peer switch .
  • Verify the MCLAG ICL status using: diagnose switch-controller switch-info mclag icl .
• Ensure all FortiLinks are up before connecting downstream devices.

Step 4: Create Aggregated Interfaces

• For FortiSwitch:
  • Create a two-port (or more) LAG towards servers or access switches.
  • Each LAG should include one port from each MCLAG peer switch .
• For Cisco or standard LACP:
  • Navigate to Network -> Interfaces (or CLI).
  • Create a new interface of type 802.3ad aggregate.
  • Add the member physical interfaces.
  • Configure IP, VLANs, and administrative access as needed .

Step 5: Enable IGMP Snooping (Optional)

• On FortiSwitch, enable mclag-igmpsnooping-aware at the global level if multicast traffic is present .
• Disable mcast-snooping-flood-traffic and igmp-snooping-flood-reports on ISL and FortiLink trunks, but enable them on ICL trunks .
• Enable IGMP proxy if required.

Step 6: Verify Configuration

• Check the status of aggregated interfaces and MCLAG peers.
• Ensure traffic flows correctly and failover works if one link or switch fails.
• Use commands like show interface port-channel (Cisco) or diagnose switch-controller switch-info (FortiSwitch) to confirm operational status .

Step 7: Connect Downstream Devices

• Connect servers or access switches to the aggregated interfaces.
• Use dual-homing to both switches for redundancy.
• Confirm that load balancing and failover operate as expected. By following these steps, you can configure a dual-switch aggregation topology that provides high availability, redundancy, and improved bandwidth utilization across your network .