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Chapter 6 – Connectivity Devices Types of Connectivity Devices • • • • • • Repeater Hubs Bridges Switches Routers Gateways Repeater • Contains one input port and one output port • Suited only to bus topology networks • Allows you to extend the length of the bus network • Serve to amplify an analog or digital signal • Work at the Physical Layer of OSI model • In 10Base2 network, entire bus network cannot exceed 1000 meters, so you can’t use more than 5 repeaters in sequence Hub • Contains multiple ports that connect to a group of clients • Can also use hub to connect servers, printers, as well as other hubs • Hub typically supports the star topology • Hubs may be passive or intelligent – Passive – does nothing but repeat signal – Intelligent – Does internal processing such as permit remote management and data filtering Types of Hubs • • • • Stand alone hub Stackable hubs Modular hubs Intelligent hubs Stand Alone Hub • Used to connect a small group of clients together • Not connected to other hubs in a tree or daisy-chain fashion • Usually contain 24 or less ports • Should the hub fail, the entire network goes down Stackable Hubs • Physically consist of multiple hubs sitting on top of each other • These are designed for the hubs to be linked together • Stackable hubs linked together logically represent one large hub to the network • Some us proprietary high-speed cabling to link the hubs together • For compatibility, it is best to use the same manufacturer for all the stackable hubs in one unit Modular Hubs • More flexible by providing a number of interface optins • Similar to a PC • Contains a system board and slots into which you can insert different adapters which can connect the hub to other hubs, routers, or the backbone • You can attach redundant components to modular hubs • Offer the highest reliability of any of the hubs Intelligent Hubs • Can process data, monitor traffic, provide troubleshooting information • Information generated by hub can be stored in a database • This data can be used to determine problem nodes • Can identify nodes that are generating unnecessary traffic Bridges • Look like repeaters in that bridges have a single input and a single output port • Differ from repeaters in that they can interpret the data • Bridges work a the Data Link Layer (2) • Bridges analyze incoming frames (from one segment) and determine if they should be transmitted out the other segment • The destination MAC address is used to decide whether to retransmit or to discard the packet • Bridge uses a Forwarding Table – See Fig. 6-22 Bridges – Continued • Using Figure 6-22, see how the bridge operates when Client #1 sends info to Client #3 • What happens when Client #1 sends info to Client # 6? Bridges- Continued • A bridge does not know initially what stations are associated with what ports. The Forwarding Table must be built • Once a bridge is installed, it polls the clients on each of its ports to provide their MAC address • Once the bridge receives this information, it is recorded in its Forwarding Table • The filtering of traffic enhances the network performance because the nodes spend less time listening to packets that are not destined for them Switches • These operate at the Data Link Layer (2) • They can interpret MAC address information just like routers • They resemble bridges and may be considered as multiport bridges • Each port on the switch can act like a bridge • If a single device is connected to a port on a switch, then it effectively receives its own dedicated channel without the possibility of a collision • The switch turns the shared channel into several Switches – Continued • Each dedicated channel represents a collision domain • Switches have historically been used to replace hubs • Advantages of switches – Secure because they isolate one device’s traffic from another device’s traffic – Provide separate channel for each device Switches – Continued • Disadvantages of switches – Buffers inside switches can be overwhelmed by heavy traffic and data loss can occur. The devices sending the info do not detect this situation. Higher-level protocols such as TCP will detect the loss of data Two Methods of Switching • Cut-Through Mode • Store and Forward Cut-Through Mode • Switch reads the frame header and decides where to forward the data before it receives the entire packet • In this mode the switch begins transmitting the packet before it receives the Frame Check Sequence at the end of the frame, so it can’t verify frame integrity • It can detect packet fragments or runts • Main advantage is its speed • If switch is flooded with traffic, however, this is not an advantage – data must be stored Store and Forward Mode • The switch reads the entire data frame into memory and checks it for accuracy before transmitting the information • These type switches do not propagate data errors • These can transfer data between segments using different transmission speeds • Example – Network printer is attached to a 100 Mbps port while the workstations that are to use the printer may be connected to the switch through 10Mbps ports VLANs • Switches allow you to create virtual local area networks by logically grouping a number of ports into a broadcast domain • The ports grouped together do not have to reside on the same switch • See Figure 6-24 as a example of a VLAN • To create the VLAN, you must configure the ports correctly Routers • Multiport device that connects dissimilar LANs that use different transmission speeds and a variety of protocols • Operate at the Network Layer (Layer 3) • Slower than switches or bridges because routers use information from Layer 3 such as protocols and logical addresses • Routers are protocol dependent • Keep track of locations of nodes on the network • Determine the best path between two nodes • Protocol being used must be routable (TCP/IP) Routers – Continued • All routers can perform the following: – – – – Connect dissimilar networks Interpret Layer 3 (Network) information Determine the best path from A to B Reroute traffic if a particular path is down • Some additional tasks the router might be able to perform – Prevent broadcast transmissions – Prevent certain type of traffic from getting to a network • Router Manufacturers: Cisco, Nortel • See operation of router, figure 6-26 Routing Protocols • Routers use routing protocols to determine the best path from node A to node B in a network. • These protocols used to collect data about the current network status . From this data the routers build a Routing Table • Four most common routing protocols: – – – – RIP OSPF EIGRP BGP Gateways • Used to connect two completely different networks • Gateways operate at the Application Layer (7) of the OSI model