Network Devices

Repeaters

• A repeater regenerates a signal and passes it on.

• It can also regenerate and retime network signals at the bit level to allow them to travel a longer distance on the media

HUBS

• Hubs are multiport repeaters– The difference between the two devices is

the number of ports – While a repeater has just two ports, a hub

generally has from four to twenty-four ports– Sometimes hubs are called concentrators

•Devices attached to a hub receive all traffic traveling through the hub. •The more devices there are attached to the hub, the more likely there will be collisions. •A collision occurs when two or more workstations send data over the network wire at the same time. •All data is corrupted when that occurs. •Every device connected to the same network segment is said to be a member of a collision domain.

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Hubs And Collision Domains Collision domain – The area of the network where a

host can receive a garbled message resulting from a collision

More collision domains = better performance

How many collision domains exist in the graphic shown?

BridgesBridges

• The bridge makes decisions about whether or not to pass signals on to the next segment of a network

• When a bridge receives a frame on the network, the destination MAC address is looked up in the bridge table to determine whether to filter, flood, or copy the frame onto another segment

•There are times when it is necessary to break up a large LAN into smaller, more easily managed segments. •This decreases the amount of traffic on a single LAN and can extend the geographical area past what a single LAN can support. •The devices that are used to connect network segments together include bridges, switches, routers, and gateways. •Switches and bridges operate at the Data Link layer of the OSI model. •The function of the bridge or switch is to make intelligent decisions about whether or not to pass signals on to the next segment of a network.•They makes these decisions based upon the layer 2 physical address (MAC). •A switch therefore has two main functions:

•switch data frames •build and maintain tables

If placed strategically, a bridge can greatly improve network performance.

•If the destination device is on the same segment as the frame, the bridge blocks the frame from going on to other segments. This process is known as filtering.

•If the destination device is on a different segment, the bridge forwards the frame to the appropriate segment. •If the destination address is unknown to the bridge, the bridge forwards the frame to all segments except the one on which it was received. This process is known as flooding.

Switches

• A switch is sometimes described as a multiport bridge

• A bridge may have just two ports linking two network segments

• All switching equipment performs two basic operations.– Switching data frames

– Building and maintaining switching tables

• Switching alleviates congestion and reduces traffic by increasing the number of collision domains.

• Switches micro segment a network

Switches

A bridge or switch determines whether the frame should be forwarded to the other network segment based on the destination MAC address.

A switch has many ports with many network segments connected to them. A switch chooses the port to which the destination device or workstation is connected.

Ethernet switches are becoming popular connectivity solutions replacing hubs...•reduces network congestion •maximizes bandwidth •reduces collision domain size

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A SWITCH

SMARTER THAN A HUB dedicated bandwidth out each port

no need to share with other ports (unlike a hub)

Can forward messages to a specific host by looking in its MAC table

If destination MAC is not in its MAC table, floods the network out all ports looking for a response

Only the host with the correct MAC address will respond

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More Stuff on Switches

How does the MAC table get built? keeps track of frames being sent between hosts

records the information when there is a response

Collision Domains each port on a switch is its own collision domain

8 port switch = 8 collision domains

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Router Routers – directs traffic based on the destination IP

address

Routers build routing tables; switches build MAC tables

Routers decode packets, switches decode frames

Look only the network portion of the IP address finds the best path to take to get to the destination

Routers do not forward broadcasts!!!

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Default Gateway Used when a host wants to send data to a host on a

different network.

Must be set on the workstation connected to the routing device – the router interface connected to the PC

NIC

• The function of a NIC is to connect a host device to the network medium

• The NIC is also referred to as a network adapter • NICs are considered Layer 2 devices because each NIC carries

a unique code called a MAC address