Cisco 3560G 48TS Software Configuration Guide - Page 692

Configuring HSRP Chapter 31 Configuring HSRP Configuring HSRP Group Attributes Although HSRP can run with no other configuration required, you can configure attributes for the HSRP group, including authentication, priority, preemption and preemption delay, timers, or MAC address. Configuring HSRP Priority The standby priority, standby preempt, and standby track interface configuration commands are all used to set characteristics for determining active and standby routers and behavior regarding when a new active router takes over. When configuring priority, follow these guidelines: • Assigning priority helps select the active and standby routers. If preemption is enabled, the router with the highest priority becomes the designated active router. If priorities are equal, the primary IP addresses are compared, and the higher IP address has priority. • The highest number (1 to 255) represents the highest priority (most likely to become the active router). • When setting the priority, preempt, or both, you must specify at least one keyword (priority, preempt, or both). • The priority of the device can change dynamically if an interface is configured with the standby track command and another interface on the router goes down. • The standby track interface configuration command ties the router hot standby priority to the availability of its interfaces and is useful for tracking interfaces that are not configured for HSRP. When a tracked interface fails, the hot standby priority on the device on which tracking has been configured decreases by 10. If an interface is not tracked, its state changes do not affect the hot standby priority of the configured device. For each interface configured for hot standby, you can configure a separate list of interfaces to be tracked. • The standby track interface-priority interface configuration command specifies how much to decrement the hot standby priority when a tracked interface goes down. When the interface comes back up, the priority is incremented by the same amount. • When multiple tracked interfaces are down and interface-priority values have been configured, the configured priority decrements are cumulative. If tracked interfaces that were not configured with priority values fail, the default decrement is 10, and it is noncumulative. • When routing is first enabled for the interface, it does not have a complete routing table. If it is configured to preempt, it becomes the active router, even though it is unable to provide adequate routing services. To solve this problem, configure a delay time to allow the router to update its routing table. 31-6 Catalyst 3560 Switch Software Configuration Guide 78-16156-01