Configuring a Logical Interface to Be Tracked for a VRRP Group

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 primary 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 primary 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:

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 primary role 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.

There are two priority-cost statements that show at this hierarchy level. The bandwidth-threshold statement 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. Just under the interface statement there is a priority-cost statement that gives the value to subtract from priority when the interface is down.

The sum of the priority costs for all tracked logical interfaces 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.

Prior to Junos OS Release 15.1, an adjusted priority could not be zero. If the difference between the priority costs and the configured priority of the VRRP group was zero, the adjusted priority would become 1.

The priority value zero (0) indicates that the current primary router has stopped participating in VRRP. Such a priority value is used to trigger one of the backup routers to quickly transition to the primary router without having to wait for the current primary to time out.

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.

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.