Specifications

CHAPTER 6

First Hop Redundancy

To change the timers on the backup routers, use the following command because they hear the hellos from the master:

Router(config-if)# vrrp 39 timers learn

VRRP cannot track interfaces but can track IP SLA object groups.

GLBP

One issue with both HSRP and VRRP is that only the primary router is in use; the others must wait for the primary to fail

before they are used. These two protocols use groups to get around that limitation. However, Gateway Load Balancing

Protocol (GLBP) enables the simultaneous use of up to four gateways, thus maximizing bandwidth. With GLBP, there is

still one virtual IP address. However, each participating router has a virtual MAC address, and different routers’ virtual

MAC addresses are sent in answer to ARPs for the virtual IP address. GLBP can also use groups up to a maximum of

1024 per physical interface. GLBP is supported only on Cisco 4500 and 6500 series switches.

The load sharing is done in one of three ways:

n Weighted load balancing: Traffic is balanced proportional to a configured weight.

n Host-dependent load balancing: A given host always uses the same router.

n Round-robin load balancing: Each router MAC is used to respond to ARP requests in turn.

GLBP routers elect an Active Virtual Gateway (AVG). It is the only router to respond to ARPs. It uses this capacity to

balance the load among the GLBP routers. The highest priority router is the AVG; the highest configured IP address is

used in case of a tie.

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CCNP SWITCH 642-813 Quick Reference by Denise Donohue

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