1. Lecture#8 Network Devices
Asma AlOsaimi

2. Topics
NICs
HUBS & REPEATERS
SWITCHES & BRIDGES
ROUTERS
DOMAINS

3. NIC
Network interface cards (NICs) are printed circuit boards that are installed in workstations.
They provide the physical connection between the network cable and the workstation. In addition, they possess the circuitry necessary to gain access to the network.
In the past, computers did not come with a pre-installed NIC
However, most modern computers are shipped with NIC already installed and ready to be connected to a network.
Each NIC has a distinctive 6-byte hardware address that identifies the workstation within a segment, such as Ethernet A2-9A-4E-10.
Each NIC has at least one connection port where the network cable is attached. Only one port may be used at any one time.
Although the NIC operates at the physical layer of the OSI model, it is also considered a data link layer device. Part of the NIC’s function is to format information between the workstation and the network, and also, to control the transmission of data onto the wire.

5. Network Devices
Network Devices The four primary devices used in LANs are as follows:
Hubs
Bridges
Switches
Routers
Respective to the OSI model, these devices operate at the following layers:
OSI Layer 1 (physical)—Hubs, repeaters (hubs are considered to be multiport repeaters)
OSI Layer 2 (data link)—Bridges, switches
OSI Layer 3 (network)—Routers
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6. Network+ Guide to Networks, 5th Edition
Repeaters and Hubs
Repeater
Simplest connectivity device regenerating signals
Operates at Physical layer
Has no means to interpret data
Limited scope
One input port, one output port
Receives and repeats single data stream
Suitable for bus topology networks
Extend network inexpensively
Rarely used on modern networks
Limitations; other devices decreasing costs
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7. Repeaters and Hubs (cont’d.)
Repeater with more than one output port
Multiple data ports, uplink port
Repeats signal in broadcast fashion
Operates at Physical layer
Ethernet network hub
Star or star-based hybrid central connection point
Connect workstations, print servers, switches, file servers, other devices
Devices share same bandwidth amount, collision domain
More nodes leads to transmission errors, slow performance
Placement in network varies
Simplest: stand-alone workgroup hub
Different hub to each small workgroup
Placement must adhering to maximum segment and length limitations
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8. Network+ Guide to Networks, 5th Edition
Figure 6-14 A stand-alone hub
Hub (cont’d.)
Hubs vary according to:
Supported media type, data transmission speeds
Passive hubs, Intelligent hubs (managed hubs), Stand-alone hubs (workgroup hubs)
Replaced by switches routers
Limited features
Merely repeat signals
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9. Repeaters and Hubs (cont’d)
Figure 6-13 Hubs in a network design
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10. Network+ Guide to Networks, 5th Edition
Bridges
Connects two network segments
Analyze incoming frames and decide where to send
Based on frame’s MAC address
Operate at Data Link layer
Single input port and single output port
Interpret physical addressing information
Advantages over repeaters and hubs
Protocol independence
Add length beyond maximum segments limits
Improve network performance
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11. Network+ Guide to Networks, 5th Edition
Figure 6-15 A bridge’s use of a filtering database
Disadvantage compared to repeaters and hubs
Longer to transmit data
Filtering database (forwarding table)
Used in decision making
Filter or forward
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12. Network+ Guide to Networks, 5th Edition
Bridges (cont’d.)
New bridge installation
Learn network
Discover destination packet addresses
Record in filtering database
Destination node’s MAC address
Associated port
All network nodes discovered over time
Today bridges nearly extinct
Improved router and switch speed, functionality
Lowered router and switch cost
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13. Network+ Guide to Networks, 5th Edition
Switches
Historically
Switches replaced hubs, eased congestion, provided better security, performance
Disadvantages
Can become overwhelmed despite buffers
Cannot prevent data loss
UDP collisions mount: network traffic halts
Switches replaced workgroup hubs
Decreased cost, easy installation, configuration,
Separate traffic according to port
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14. Network+ Guide to Networks, 5th Edition
Installing a Switch
Follow manufacturer’s guidelines
General steps (assume Cat 5 or better UTP)
Verify switch placement
Turn on switch
Verify lights, self power tests
Configure (if necessary)
Connect NIC to a switch port (repeat for all nodes)
After all nodes connected, turn on nodes
Connect switch to larger network (optional)
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15. Installing a Switch (cont’d.)
Figure 6-17 Connecting a
workstation to a switch
Figure 6-18 A switch on a small network
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16. Network+ Guide to Networks, 5th Edition
Switching Methods
Like hubs, switches are the connectivity points of an Ethernet network.
Devices connect to switches via twisted-pair cabling, one cable for each device.
The difference between hubs and switches is in how the devices deal with the data that they receive.
Whereas a hub forwards the data it receives to all of the ports on the device, a switch forwards it only to the port that connects to the destination device.
It does this by learning the MAC address of the devices attached to it, and then by matching the destination MAC address in the data it receives.
Difference in switches
Incoming frames interpretation
Frame forwarding decisions making
Four switching modes exist
Two basic methods discussed
Cut-Through Mode
Store-and-Forward Mode
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17. Network+ Guide to Networks, 5th Edition
Cut-Through Mode
Switch reads frame’s header
Forwarding decision made before receiving entire packet
Uses frame header: first 14 bytes contains destination MAC address
Cannot verify data integrity using frame check sequence
Can detect runts
Erroneously shortened packets
Runt detected: wait for integrity check
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18. Cut-Through Mode (cont’d.)
Cannot detect corrupt packets
May propagate flawed packets
Advantage
Speed
Disadvantage
Data buffering (switch flooded with traffic)
Best use
Small workgroups needing speed
Low number of devices
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19. Store-and-Forward Mode
Switch reads entire data frame into memory
Checks for accuracy before transmitting information
Advantage over cut-through mode
Transmit data more accurately
Disadvantage over cut-through mode
More time consuming
Best use
Larger LAN environments; mixed environments
Can transfer data between segments running different transmission speeds
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20. Content and Multilayer Switches
Layer 3 switch (routing switch)
Interprets Layer 3 data
Layer 4 switch
Interprets Layer 4 data
Content switch (application switch)
Interprets Layer 4 through Layer 7 data
Advantages
Advanced filtering, statistics keeping, security functions
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21. Content and Multilayer Switches (cont’d.)
Disadvantages
No agreed upon standard
Layer 3 and Layer 4 switch features vary widely
Distinguishing between Layer 3 and Layer 4 switch
Manufacturer dependent
Higher-layer switches
Three times Layer 2 switches
Used in backbone
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22. Network+ Guide to Networks, 5th Edition
Routers
Act as the gateway, connecting LANs to other networks
Multiport connectivity device
Directs data between network nodes
Integrates LANs and WANs
Different transmission speeds, protocols
Operate at Network layer (Layer 3)
Directs data from one segment or network to another
Logical addressing
Protocol dependent
Slower than switches and bridges
Need to interpret Layers 3 and higher information
Interconnect networks that use different technologies (LAN/WAN interfaces)
LAN – usually UTP cabling, can be fiber
Each port on a router connects to different networks – therefore requires a different subnet!
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23. Routers (cont.)
Routers can also connect different Layer 2 technologies, such as Ethernet, Token-ring, and FDDI.
The purpose of a router is to examine incoming packets (Layer 3 data), choose the best path for them through the network, and then switch them to the proper outgoing port.
Routers are the most important traffic-regulating devices on large networks.
Router maintains a routing table.
The routing table contains ip addresses associated with interfaces, out of which the packet will be forward to.

24. Network+ Guide to Networks, 5th Edition
Routers (cont’d.)
Traditional stand-alone LAN routers
Being replaced by Layer 3 routing switches
New niche
Specialized applications
Linking large Internet nodes
Completing digitized telephone calls
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25. Router Characteristics and Functions
Intelligence
Tracks node location
Determine shortest, fastest path between two nodes
Connects dissimilar network types
Large LANs and WANs
Routers indispensible
Router components
Internal processor, operating system, memory, input and output jacks, management control interface
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26. Network+ Guide to Networks, 5th Edition
Figure 6-23 Routers
Modular router
Multiple slots
Holding different interface cards, other devices
Inexpensive routers
Home, small office use
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27. Router Characteristics and Functions (cont’d.)
Router tasks
Connect dissimilar networks
Interpret Layer 3 addressing
Determine best data path
Reroute traffic
Optional functions
Filter broadcast transmissions
Enable custom segregation, security
Support simultaneous connectivity
Provide fault tolerance
Monitor network traffic, diagnose problems
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28. Router Characteristics and Functions (cont’d.)
Directing network data
Static routing
Administrator programs specific paths between nodes
Dynamic routing
Router automatically calculates best path between two nodes
Routing table
Installation
Simple: small office, home LANs
Challenging: sizeable networks
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29. Router Characteristics and Functions (cont’d.)
Figure 6-24 The placement of routers on a LAN
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30. network devices symbols
In the above exhibit, A is a bridge, B is a hub, C is a router and D is a switch.

31. Collision Domains & Broadcast Domain
Collision Domains – A collision domain is defined as a network segment that shares bandwidth with all other devices on the same network segment. Generally speaking, A Collision Domain includes all of the Ethernet segments between a pair of bridges or other layer 2 devices. When two hosts on the same network segment transmit at the same time, the resulting digital signals will fragment or collide, hence the term collision domain.
Broadcast Domain – A broadcast domain is defined as all devices on a network segment that hear broadcasts sent on that segment.

32. All devices plugged into a hub are in the same collision domain and the same broadcast domain.
All devices plugged into a switch are in separate collision domains but the same broadcast domain. Although, you can buy special hardware to break up broadcast domains in a switch, or use a switch capable of creating VLANs. VLANs breakup broadcast domains.
Hubs and Repeaters extend collision and broadcast domains.
Switches, Bridges and Routers break up collision domains.
Routers (and Switches using VLANs) break up broadcast domains.

33. Example#1

34. Example#2

35. Example#3

36. Exercise
5 broadcast domains and 10 collision domains
How many broadcast and collision domains exist in the topology?

37. Network+ Guide to Networks, 5th Edition
Summary
NIC interface cards
Types, installation, testing, IRQ use, Base I/O port use, firmware settings, selection
Repeater and hubs
Bridges
Switches
Installation, switching methods, VLANs and trunking, STP (Spanning Tree Protocol), Content and Multilayer Switches
Router characteristics and functions, protocols
Gateways and other multifunction devices
Network+ Guide to Networks, 5th Edition