# ICR Scaling Considerations

When planning an ICR cluster you must ensure that you have provisioned adequate backup capacity in the event of a worst-case failure scenario such as a multiple hardware or multiple router failure.

| Note: Remember to consider parameters such as link bandwidth, QoS, and line module scaling limitations when you plan the deployment of the ICR cluster.

## 1:1 Subscriber Redundancy in a 4–Node ICR Cluster

Consider a 4–node ICR cluster that consists of four ERX1440 routers, as shown in Figure 10. Each of the four routers is capable of supporting 48,000 PPP/PPPoE subscribers. The degree of redundancy that you can achieve in this cluster is 1:1. For every subscriber, you have a backup destination within the cluster. If one router fails, subscriber load is equally distributed to the other three routers. Thus, no single router serves as a dedicated backup. Instead, each router can be loaded with around 75 percent of its capacity while the remaining 25 percent is available to accommodate subscribers from the failing router. Failure of any one router causes all routers in the cluster to become fully loaded with no spare capacity to accommodate further failures. This is the minimum degree of redundancy in a 4–node ICR cluster.

Figure 10 illustrates an example of a typical ICR configuration.

Figure 10: Sample 1:1 Subscriber Redundancy in a 4–Node ICR Cluster

#### Related Documentation

- Configuring an ICR Partition