Using cluster link aggregation

Last published : Sep 24, 2026
Cluster link aggregation (CLA) is a group of interfaces of cluster nodes. It is an extension of NetScaler link aggregation. The only difference is that, while link aggregation requires the interfaces to be from the same device, in CLA, the interfaces are from different nodes of the cluster. For more information about link aggregation, see Configuring Link Aggregation.

Points to consider

  • CLA is supported for a cluster of hardware (MPX) appliances.
  • CLA is supported for a cluster of virtual (VPX) appliances that are deployed on ESX, KVM, and SDX hypervisors, with the following restrictions:
    • Dedicated interfaces must be used. It means that the interfaces must not be shared with other virtual machines.
    • If the CLA member interfaces are manually disabled or if the CLA itself is manually disabled, then the interface power down capability is achieved only by the LACP timeout mechanism.
  • When a node becomes inactive:
    • For dynamic CLA, the corresponding CLA interface LACP is turned off but the link remains active.
    • For static CLA, the interfaces are powered off.
  • When a node becomes active:
    • For dynamic CLA, the corresponding cluster LA interfaces' LACP is turned on, link remains active when the node becomes active. If a node becomes passive, then only LACP is turned off.
    • For static CLA, the interfaces are marked as power-on.
  • The number of interfaces that can be bound to CLA is 16 from each node. The maximum number of interfaces in CLA can be (16 * n), where n is the number of nodes in a cluster. The total number of interfaces in CLA depends on the number of interfaces for every port channel on the upstream switch.
  • If a NetScaler appliance uses Intel Fortville interfaces, the switchover of a cluster node to passive mode might cause a few seconds of outage with CLAG. The issue occurs because LACP is enabled for CLAG to function properly, and the outage time depends on NIC LACP timers.
    Note:
    CLA is not supported on VPX appliances that are deployed on XenServer®, AWS, and Hyper-V.
For example, consider a three-node cluster where all three nodes are connected to the upstream switch. A cluster LA channel (CLA/1) is formed by binding interfaces 0/1/2, 1/1/2, and 2/1/2.
Figure 1. Cluster Link Aggregation topology
CLAG topology
A CLA channel has the following attributes:
  • Each channel has a unique MAC agreed upon by cluster nodes.
  • The channel can bind both local and remote nodes' interfaces.
  • A maximum of four CLA channels are supported in a cluster.
  • Backplane interfaces cannot be part of a CLA channel.
  • When an interface is bound to a CLA channel, the channel parameters have precedence over the network interface parameters. A network interface can be bound to one channel only.
  • Management access to a cluster node must not be configured on a cluster LA channel (for example, CLA/1) or its member interfaces. When the node is INACTIVE, the corresponding CLA interface is marked as power-down and looses management access.
Figure 2. Traffic distribution flow using CLA
CLAG flowchart

Backup and restore support of cluster LA on NetScaler MPX

You can backup and restore the cluster setup of LA on NetScaler MPX. The CLA MAC address is independent of the physical interface MAC address of the cluster nodes, and can change after the backup and restore process. The CLA can serve the traffic after a cluster restore process is complete. For more information about backup and restore, see Backup and restore of cluster setup