Cisco Systems RJ-45-to-AUX manual Groups primarily to facilitate load sharing, 246

∙Active route processor

∙Standby route processor

∙Virtual route processor

All other route processors fall into the “other route processor” category.

Warning	By increasing the number of standby groups on a route processor, you decrease the route
	processor’s performance and increase latency. You’ll increase the number of standby
	groups primarily to facilitate load sharing.

In the Immediate Solutions section, you will learn how to configure the standby priority. If it is not manually assigned, the priority is 100. But what if none of the route processors has been assigned a group priority? If multiple route processors in the group have equal priority, the route processor with the highest IP address for the respective group will be elected as the active route processor. The route processor with the second highest IP address will become the standby route processor. All the other route processors will be placed in a Listen state (see “The HSRP States”).

The standby router will take over once the route processor that is currently active for the group does not receive three hello messages. The actual convergence time is contingent upon the HSRP timers for the group. The HSRP hellotime timer defaults to 3, and the holdtime timer defaults to 10. Interestingly, with HSRP, the standby route processor will take over even if the active router’s LAN interface state is displaying the message interface up line protocol down.

Once the standby route processor becomes active, it will respond to any end station sending packets to the virtual MAC address. When an IP host interface sends an ARP request with the virtual route processor’s address, HSRP will respond with the virtual route processor’s MAC address—not its own. This virtual MAC address is the well−known MAC address of 0000.0c07.ac11, where 11 is the HSRP group identifier.

To find the current IP address of the virtual router, use the show ip arp command and look for the virtual route processor IP and hardware MAC address. You can also use the show standby command.

Route processors using HSRP can provide redundancy for a default gateway as well as load−balance traffic across VLANs and IP subnets (if multiple VLANs are being used, a separate HSRP standby group must be in place for each VLAN). Because route processors can be assigned as members of multiple HSRP standby groups, each standby group can have its own priority and its own active route processor. As shown in Figure 12.2, the active route processor for group 1 assigned to VLAN 1 uses route processor 2. VLAN 2 using standby group 2 will use route processor 2. In the event of a failure, the standby group will begin to use the other route processor. In this situation, load sharing will take place until a failure occurs.

Figure 12.2: VLAN 1 and VLAN 2 utilize load balancing across the multiple route processors.

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