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## ICR Overview

Routers can function as broadband network gateways, which aggregate many subscribers and services simultaneously in order to support intelligent IP services such as voice over IP (VoIP) and video on demand (VoD). If the router fails because of chassis (hardware) failure, subscriber downtime can result.

Interchassis redundancy (ICR) enables you to minimize subscriber downtime when the router or access interface on the edge router fails by re-creating subscriber sessions that were originally terminated on the failed router. It also enables you to track the failure of uplink interfaces. In this way, ICR enables you to completely recover from router failure. By using extended Virtual Router Redundancy Protocol (VRRP) features, ICR enables you to track the failure of uplink interfaces, elect the master VRRP instance, and detect failure of a VRRP instance.

Figure 7 illustrates a suitable network for ICR deployment.

Figure 7: Sample Network for ICR Deployment

Consider subscriber login requests that are received at the digital subscriber line access multiplexer (DSLAM). The request is then forwarded to the aggregation network which forwards the requests to the routers that are part of the edge network. In a conventional network, when the router at the edge network fails, it results in subscriber downtime. By configuring ICR, you can reduce subscriber downtime because the login requests are received by both the master (active) and backup routers. After authentication from RADIUS, the master router accepts the login requests and forwards the same to the uplink interface that is part of the core of the network while the backup router rejects the login requests. If the master router fails, login requests are forwarded to the backup router that acts as the master router.

ICR enables load balancing by enabling you to create partitions. An ICR partition is a collection of logical subscribers within a single ICR interface. You can manage each ICR partition using a unique VRRP instance.

You can also create ICR clusters. An ICR cluster consists of a group of chassis participating in ICR. You can use different E Series routers to configure a heterogeneous ICR cluster. For example, you can use an E120 or E320 router with an ES2 4G LM as a backup for subscribers on an ERX1440 router, or use an ERX1440 router with a GE-HDE LM as a backup for subscribers on an E120 or E320 router. However, you must keep in mind the hardware scaling limitations when you configure an ICR cluster containing both E320 routers and ERX routers.

| Note: While deploying ICR, service providers must modify the aggregation network to enable subscriber traffic to reach all corresponding interfaces that are configured as part of the redundancy group.

#### Related Topics

- ICR Scaling Considerations
- Guidelines for Deploying an ICR Partition in Your Network
- Configuring an ICR Partition

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