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Configuring a Logical Interface to Be Tracked

VRRP can track whether a logical interface is up, down, or not present, and can also dynamically change the priority of the VRRP group based on the state of the tracked logical interface, triggering a new master router election. VRRP can also track the operational speed of a logical interface and dynamically update the priority of the VRRP group when the speed crosses a configured threshold.

When interface tracking is enabled, you cannot configure a priority of 255 (a priority of 255 designates the master router). For each VRRP group, you can track up to 10 logical interfaces.

To configure a logical interface to be tracked, include the following statements:

track {interface interface-name {bandwidth-threshold bits-per-second priority-cost priority;priority-cost priority;}priority-hold-time seconds;}

You can include these statements at the following hierarchy levels:

  • [edit interfaces interface-name unit logical-unit-number family inet address address vrrp-group group-id]
  • [edit interfaces interface-name unit logical-unit-number family inet6 address address vrrp-inet6-group group-id]
  • [edit logical-systems logical-system-name interfaces interface-name unit logical-unit-number family inet address address vrrp-group group-id]
  • [edit logical-systems logical-system-name interfaces interface-name unit logical-unit-number family inet6 address address vrrp-inet6-group group-id]

The interface specified is the interface to be tracked for the VRRP group. The priority hold time is the minimum length of time that must elapse between dynamic priority changes. A tracking event, such as an interface state change (up or down) or a change in bandwidth, triggers one of the following responses:

  • The first tracking event initiates the priority hold timer, and also initializes the pending priority based on the current priority and the priority cost. However, the current priority remains unchanged.
  • A tracking event or a manual configuration change that occurs while the priority hold timer is on triggers a pending priority update. However, the current priority remains unchanged.

This ensures that Junos OS does not initiate mastership elections every time a tracked interface flaps.

When the priority hold time expires, the current priority inherits the value from the pending priority, and the pending priority ceases.

Note: If you have configured asymmetric-hold-time, VRRP does not wait for the priority hold time to expire before initiating mastership elections if a tracked interface fails (state changes from up to down), or if the available bandwidth for a tracked interface decreases. For more information about asymmetric-hold-time, see Configuring Asymmetric Hold Time for VRRP Routers.

The bandwidth threshold specifies a threshold for the tracked interface. When the bandwidth of the tracked interface drops below the configured bandwidth threshold value, the VRRP group uses the bandwidth threshold priority cost. You can track up to five bandwidth threshold statements for each tracked interface.

The priority cost is the value to be subtracted from the configured VRRP priority when the tracked logical interface goes down, forcing a new master router election. The value can be from 1 through 254. The sum of the costs for all tracked logical interfaces or routes must be less than or equal to the configured priority of the VRRP group.

If you are tracking more than one interface, the router applies the sum of the priority costs for the tracked interfaces (at most, only one priority cost for each tracked interface) to the VRRP group priority. However, the interface priority cost and bandwidth threshold priority cost values for each VRRP group are not cumulative. The router uses only one priority cost to a tracked interface as indicated in Table 1:

Table 1: Interface State and Priority Cost Usage

Tracked Interface State

Priority Cost Usage

Down

priority-cost priority

Not down; media speed below one or more bandwidth thresholds

Priority-cost of the lowest applicable bandwidth threshold

You must configure an interface priority cost only if you have configured no bandwidth thresholds. If you have not configured an interface priority cost value, and the interface is down, the interface uses the bandwidth threshold priority cost value of the lowest bandwidth threshold.

Published: 2013-01-15