cisco a+ exam

cisco a+ exam.How GLBP Works In GLBP. routers are divided into two categories: active virtual gateways (AVGs) and active virtual forwarders (AVFs). the AVG is the primary gateway device and is responsible for providing virtual MAC addresses to endpoints when they use ARP requests to resolve the GLBP default gateway address. Broadly speaking, the AVG is responsible for address management in the GLBP group. The AVG is responsible for processing ARP messages requesting resolution of virtual IP addresses. The AVF is the routing device in the GLBP group that is responsible for forwarding traffic. An AVG can also be an AVF. up to four routing devices can be AVFs in the same GLBP. the following is an example in Figure 18.6 to illustrate the basic working of GLBP. In this example, RP.A sends an ARP request for the default gateway MAC address for the primary router (AVG) oPC.A. The AVG responds using a virtual MAC address: here, its own virtual MAC address is provided. Next, PC-B uses the ARP request to provide the default gateway MAC address, and RP-A responds using a virtual MAC address: based on the load balancing algorithm used by GLBP, RP-A provides another virtual MAC address (RP-B's virtual MAC address). Load balancing is discussed in the next subsection. As you can see from this example, RP.A and RP.B forwards traffic for the same VLAN.Figure 18.6 How GLBP works GLBP also supports interface tracking. When interface tracking is enabled, if the tracked interface fails, the AVF will automatically demote and let another AVF take over the processing work associated with that interface. This is similar to the interface tracking feature of HSRP. The Active Virtual Gateway (AVG) can provide the virtual MAC addresses of up to four Active Virtual Forwarders (AVFs) to the endpoints in the subnet/VLANGLBP Load Balancing In GLBP, multiple RPs can be used to forward traffic to achieve load balancing. GLBP supports three load balancing methods. . Round robin method. . Weighted method.Chapter 18 Basic Routing 487 .. Host correlation method.The default load balancing method is the round robin method. In this method, the AVG sequentially provides different AVF default gateway addresses to the clients. If there are two routing devices and six clients. three of the clients will use the AVG,and the other three clients will use the AVFoIn weighted load balancing, the AVG decides which AVF address to provide to the clients based on a weighting factor. This allows you to adjust the GLBP so that the number of hosts using each routing device is proportional to the processing power of the routing device.In host-based load balancing, the same virtual gateway address is provided to the same host each time. However, to provide redundancy, if the routing device corresponding to that address fails, another routing device in the GLBP group will assume its processing.Note The configuration of GLBP is beyond the scope of this book.Be sure to familiarize yourself with when to use static routes and when to use dynamic routing protocols. Understand the syntax of the command iproute and the defaults it uses. Know how to configure a default route. Be able to identify incorrectly configured static routes in the router configuration. Know how to interpret the output of the command showiproute and be able to find the administrative distance and metric values for dynamic routing protocols in it.