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