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Communication in a cluster setup

The interfaces of Citrix ADC appliances that are added to a cluster, are prefixed with a node ID. This helps identify the cluster node to which the interface belongs. Therefore, the interface identifier c/u, where c is the controller number and u is the unit number, now becomes n/c/u, where n is the node ID. For example, in the following figure, interface 1/2 of node n1 is represented as 0/1/2, interface 1/1 of node n2 is represented as 1/1/1, and interface 1/4 of node n3 is represented as 2/1/4.

Figure 1. Interface naming convention in a cluster

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  • Server communication- The cluster communicates with the server through the physical connections between the cluster node and the server-side connecting device. The logical grouping of these physical connections is called the server data plane.
  • Client communication- The cluster communicates with the client through the physical connections between the cluster node and the client-side connecting device. The logical grouping of these physical connections is called the client data plane.
  • Inter-node communication- The cluster nodes can also communicate with each other. The manner in which they communicate depends on whether the node exists on the same network or across networks.
    • Cluster nodes within the same network communicate with each other by using the cluster backplane. The backplane is a set of interfaces in which one interface of each node is connected to a common switch, which is called the cluster backplane switch. The different types of traffic that goes through backplane, which is used by internode communication are:
      • Node to Node Messaging (NNM)
      • Steered traffic
      • Configuration propagation and synchronization
    • Each node of the cluster uses a special MAC cluster backplane switch address to communicate with other nodes through the backplane. The cluster special MAC is of the form: 0x02 0x00 0x6F <cluster_id> <node_id> <reserved>), where cluster_id is the cluster instance ID, node_id is the node number of the Citrix ADC appliance that are added to a cluster.

The following figures shows the communication interfaces in L2 clusters and L3 clusters.

Figure 2. Cluster communication interfaces - L2 cluster

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Figure 3. Cluster communication interfaces - L3 cluster

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Communication in a cluster setup

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