Icr Scaling Considerations; 1:1 Subscriber Redundancy In A 4-Node Icr Cluster; Figure 8: Sample 1:1 Subscriber Redundancy In A 4-Node Icr Cluster - Juniper SERVICE AVAILABILITY - CONFIGURATION GUIDE V 11.1.X Configuration Manual

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 8 on page 131. 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 8 on page 131 illustrates an example of a typical ICR configuration.
Figure 8: Sample 1:1 Subscriber Redundancy in a 4 Node ICR Cluster
Before failover
75%
36,000 subscribers
12,000 spare capacity
75%
36,000 subscribers
12,000 spare capacity
Single chassis failure - spare capacity reduced to zero
75%
36,000 subscribers
12,000 spare capacity
75%
36,000 subscribers
12,000 spare capacity
Chapter 6: Managing Interchassis Redundancy
100% 100%
48,000 subscribers 48,000 subscribers
No spare capacity No spare capacity
100%
Chassis failure
48,000 subscribers
No spare capacity
ICR Scaling Considerations
131