cisco ccna r&s book pdf

cisco ccna r&s book pdf.As described in the previous section, with VLANs, it is easy to isolate broadcast domains. However, this also means that traffic needs to be forwarded between two VLANs with the help of a Layer 3 device, even if both VLANs are created on the same switch. Since the switch is defined as a Layer 2 device, the switch cannot forward traffic between two hosts, even if the source and destination hosts belonging to different VLANs are directly connected to the same switch.An example of inter-VLAN traffic forwarding is shown in Figure 1-31. Host A in VLAN 101 sends traffic to host B in VLAN 102, and both hosts are directly connected to SW1. Since SW1 is a switch that operates at Layer 2, forwarding such traffic requires the intervention of a Layer 3 device (for example, router R1). As seen in Figure 1-31, R1 interconnects to two different ports on the SW1 switch using two different interfaces: interface R1G0/1 connects to the port of SW1 belonging to VLAN 101; interface R1G0/2 connects to the port of SW1 belonging to VLAN 102.Figure 1-31 Inter-VLAN Traffic ForwardingIt is also possible to have R1 connected to one Trunk port of SW1 with only one interface. Following such a connection, R1 is called a single-arm router (Routerona Stick, ROAS), as shown in Figure 1.32.Figure 1-32 Single-Arm Router (ROAS) / JH Both of the previously described connections have forwarding efficiency issues. Let's say that R1 receives a packet from SW1After receiving a packet from SW1, R1 needs to pass it back to SW1, which increases the load on the interconnection link between R1 and SW1. In addition, the encapsulation of the frame plus the processing of the frame by the higher layer protocols can cause performance degradation. To circumvent these problems, Layer 3 functionality has been integrated into traditional Layer 2 switches. A switch with Layer 3 functionality is called a Layer 3 switch, and is sometimes referred to as a multilayer switch. An example of a multilayer switch performing inter-VLAN traffic forwarding is shown in Figure 1.33.Figure 1-33 Multilayer Switch Performing Inter-VLAN Traffic Forwarding1.3.3 Wireless LAN Basics and TechnologiesLike Ethernet (wired access to LAN), wireless LAN (WLAN) is one of the common LAN access technologies. This book will introduce the basics and technologies related to WLANs.36 Chapter 1 Network Protocols and Network Device Basics