ccna vpn pdf

ccna vpn pdf.Figure 12.1 Example of a VLANThe bottom half of Figure 12.1 shows another example where a switch is connected to four PCo One major difference between a switch and a hub is that all devices connected to the hub belong to the same conflict domain, while each port of the switch is a separate conflict domain. By default, all ports of the switch belong to the same broadcast domain, but in this example, the switch is configured so that PC-E and PC-F are in one broadcast domain (VLAN) and so that PC-G and PC-H are in another broadcast domain.The switch users create VLANs,i.e., split broadcast domains. In a switched network, if all devices are connected together through a switch and no Layer 3 devices are used, the VLANs are not constrained by physical boundaries. For example, VLANs can span multiple switches or be within the boundaries of a single switch, as shown in Figure 12.2. In this example, there are three VLANs o Note that VLANs are not constrained by physical location: PC.A, PC.B, PC.E, and PC-F are connected to different switches but belong to the same VLAN o However, VLANs can also be within the scope of a single switch, as is the case with the VLANs to which PC.C and PC.D belong, which are all connected to Switch A.The switches in the network are responsible for ensuring the integrity of the VLANs. For example, when PC-A generates a broadcast, Switch A and Switch B ensure that only the devices in the current VLAN (PC-B, PC.E, and PC.F) can see the broadcast and not the others; this is true even if the VLAN spans multiple switches as in Figure 12.2.A VLAN is a group of devices within a broadcast domain or subnet that is ideally suited for logically isolating traffic from different groups of users.VLANs limit the range of broadcast traffic and to transmit traffic between VLANs requires routers.VLANs split the broadcast domain, that is, increase the number of broadcast domains and thus reduce the size of the broadcast domain.12.1.1 Subnetting and VLANsLogically speaking, VLANs are also subnets. A subnet (network) is a separate broadcast domain, and by default, broadcasts within one subnet are not forwarded to another subnet; this demarcation function is provided by the router (Layer 3 device). Each subnet must have a unique network number, and routers are required to carry traffic between different subnets. Each broadcast domain created using a switch is a VLAN, so to transfer traffic between VLANs, routing is required.To the user, the physical topology shown in Figure 12.2 is actually similar to Figure 12.3, where the device knows that to send traffic to other VLANs (subnets), it must be forwarded to the default gateway address of the VLAN to which it belongs-the IP address of the router interface.Figure 12.3 Logical Topology Using VLANs One advantage of switches over bridges is that in switched VLAN networks, switches can handle multiple VLANs on a single port if the routing feature used supports VLANs, while routers can route traffic between VLANs on a single port. This special connection is called a trunk and will be discussed in more depth later in the "VLAN Connectivity" section. When using a bridge, each VLAN must be located on a separate router port, which increases the cost of the routing solution. Cisco provides recommendations for the number of devices that can be included in a VLAN, as shown in Table 12.1. Don't forget that these device counts are only Cisco's recommendations, but they are based on years of experience designing and implementing networks. Practical Experience Don't forget that the numbers listed in Table 12.1 are only recommendations: each network and its components are unique. Each network is unique in its own way; I have seen a broadcast domain containing about 1000 devices that worked fine but performed abysmally.12.1.2 Scalability