Object Tracking using IP SLA feature tracks the state of an object for reachability using IP SLA. A client process, such as Virtual Router Redundancy Protocol (VRRP) or RIB, registers itself to track objects and receives notifications when a state change occurs.

IP SLA (Service-Level Assurance Protocol) is a Performance Measurement protocol used to analyze IP service levels for IP applications and services. IP SLA employs active traffic-monitoring technology to monitor network traffic continuously.

IP SLA utilizes Internet Control Message Protocol (ICMP) pings to identify link failures and notify registered clients responsible for tracking.

The Object Tracking feature offers complete separation between tracked objects and the actions taken by clients when a tracked object's state changes. Multiple clients, such as VRRP or RIB, can register their interest in the tracking process, monitor the same object, and take different actions when the object changes state. The Tracking feature is present in OAMD (Object-Action Mapping Database).

Each tracked object is identified by a unique number specified in the tracking CLI. Client processes use this number to monitor a specific object.

The tracking process monitors events from the tracked objects, notes any changes in value, and communicates these changes to interested client processes immediately or after a specified delay. The object values are reported as either up or down.

To configure VRRP Object Tracking, the object is set to have a priority-delta value, which is passed to VRRP when a failure occurs. This decrement in the priority of the Virtual Router on the circuit triggers a transition from VR Master to VR Backup.

In this example, two routers, ROUTER-1 (R1) and ROUTER-2 (R2), are configured as Master and backup routers, each with different priorities. The priority-delta value is set to be greater than the difference between both priorities.

R1 is configured with a priority of 150, while R2 is assigned a priority of 100. Since R1 has the higher priority, it initially serves as the Virtual Router Master. The priority-delta value is set to 60, which is greater than the difference between their priorities (150 minus 100).

When the external interface xe41 on R1 fails, the Track state changes to DOWN, and R1's priority decreases to 90 (150 minus 60). However, as R2 still maintains a higher priority (100), it assumes the role of VR Master, ensuring uninterrupted packet routing.

Subsequently, when the track state returns to UP, the VR Backup (R1) regains its original priority of 150, reclaiming the position of VR Master. This transition allows for seamless failover and network continuity.

After shut down the tracked Object (xe41) in R1: