t-4 Host-5 Figure 13-7. GLBP example network Gateways configured with GLBP are called forwarders. Any router that is forwarding packets is called an Active Virtual Forwarder (AVF). One of the routers will be elected as the Active Virtual Gateway (AVG). The AVG has the responsibility for controlling the group and essentially being the brain of the operations. The AVG will control the load-balancing operations, respond to ARP requests, and assign virtual MAC addresses to AVFs. Be careful with terminology here, because the term active means something different with HSRP. The AVG in a GLBP group is determined through priorities. The AVG priority can be preempted SO that a higher-priority member takes control when it comes online. Load balancing can be done based on round-robin, weighted load balancing, or host- dependent methods. We'll use weighted load balancing to allocate a percentage of traffic flow. Host-dependent is a means whereby the same virtual MAC address is al- ways delivered to the same host MAC address. This method allows hosts to always use the same physical gateway unless the gateway goes offline. If no load balancing is specified, GLBP behaves like HSRP, and the AVG acts as the only forwarder. Chapter 13: First Hop Redundancy Saying things like "percentage of traffic flow" and "load balancing" is useful, especially when you're talking to executives, but the phrases are technically inaccurate. GLBP does not load-balance traffic, but rather it load-shares by changing which gateway is advertised when an ARP re- quest is made. Why is this distinction important? Let's say that Host-5 in Figure 13-7 is the corporate email server. If all the other hosts are just workstations, there is a high probability that, regardless of how GLBP distributes its virtual MAC addresses, the email server will consume most of the resources. Here's another way to look at this: though R1 will be the default gateway for 50% of the hosts, if the mail server is assigned to use R3 as its gateway, R3 will likely see 99% of the traff