CONNECTING DEVICES CONNECTING DEVICES In this section, we divide connecting devices into five different categories based on the layer in which they operate in a network. Passive Hubs Active Hubs Bridges Two-Layer Switches Routers Three-Layer Switches Gateways Topics discussed in this section: 15.2
Bridges Designed to create two or more LAN segments, each of which is a separate collision domain Bridges filter traffic by looking at MAC addresses.
A bridge has a table used in filtering decisions. Note A bridge does not change the physical (MAC) addresses in a frame. Bridges A Bridge has filtering capabilities. It can check the MAC address and decide which port should be forwarded or just dropped. 15.13
A learning bridge and the process of learning 1. A send a frame to D The table is blank, frame floods the net, learned A to port 1 for future usage. 2. E send a frame to A Forward the frame only to port 1; learned E to port 3 3. B send a frame to C No entry of C, floods the net and add one more entry, B to port 2 4. The learning continues. 15.15
Switches: Layer 2 A Switch is a Multiport Bridge
Switches Two-layer switch, better performance, multi-port bridge. Allocate a unique port to each station, no collision. Three layer switch, faster and more sophisticated router. Allow faster table lookup and forwarding. 15.1717
LAN Switches Switches Combine the connectivity of a hub with the traffic regulation of a bridge on each port
Routers connecting independent LANs and WANs Router Three layer device, route packets based on IP address. Connect LANs and WANs. Routing tables,which normally dynamic and updated using routing protocols, are used for making decisions about route. 15.19
Connection Media / UTP Implementation EIA/TIA specifies an RJ-45 connector for unshielded twisted-pair (UTP) cable. The letters RJ stand for registered jack, and the number 45 refers to a specific wiring sequence. The RJ-45 connector and jack are the most common
Straight-Through Cables Maintain the pin connection all the way through the cable. Wire connected to pin 1 is the same on both ends. Used to connect such devices as PCs or routers to other devices such as hubs or switches. (One level different.)
Crossover Cable Cross the critical pair to properly align, transmit, and receive signals on devices with like connections. Pin 1 connected to pin 3, pin 2 connected to pin 6. Used to connect similar devices: switch to switch, switch to hub, hub to hub, router to router, PC to PC.
Rollover Cables ( Cisco console cable ) connect a computer terminal to a router's console port. This cable is typically flat and has a light blue color. The console port allows monitoring and configuration of a Cisco hub, switch, or router.
15.26 BACKBONE NETWORKS A backbone network allows several LANs to be connected. In a backbone network, no station is directly connected to the backbone; the stations are part of a LAN, and the backbone connects the LANs. Bus Backbone Star Backbone Connecting Remote LANs Topics discussed in this section:
In a bus backbone, the topology of the backbone is a bus. 15.27
In a star backbone, the topology of the backbone is a star; the backbone is just one switch. 15.28
VIRTUAL LANs We can roughly define a virtual local area network (VLAN) as a local area network configured by software, not by physical wiring. Membership Configuration Communication between Switches IEEE Standard Advantages Topics discussed in this section: 15.29
What are the benefits of a VLAN? A VALN saves company time and money because reconfiguration is done through software. Physical reconfiguration is not necessary. A VLAN provides extra security for a network. Members of a VLAN can send broadcast messages with the assurance that users in other groups will not receive these messages. A VLAN reduces network traffic. A VLAN creates virtual workgroups. Each workgroup member can send broadcast messages to others in the workgroup. This eliminates the need for multicasting and all the overhead messages associated with it. 34