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Chapter 7 Wired and Wireless Local Area Networks - Coggle Diagram
Chapter 7
Wired and Wireless Local Area Networks
1. Why use a LAN?
Information sharing
-Improved decision making
-May reduce data duplication and inconsistency
Resource sharing
-Devices such as printers can be shared by many clients
Software sharing
-Some software can be purchased on a per-seat basis
and resides on server
-Reduces costs, simplifies maintenance and upgrades
Device Management
-Software updates and configuration are easier
2. LAN Componenets
i. Clients
-Devices on the network that request information from servers
ii. Server
-Devices on the network that deliver information or
provide services to clients
iii. Network Interface Cards (NIC)
-Also called network cards and network adapters
-Operate at layers 1 and 2 (Physical & Data link)
-Commonly built into motherboards
-Ethernet NICs contain unique MAC address
iv. Network Cables
-Speed depends on circuit length
v. Hubs and switches
-Link cables from different devices, sometimes more than one type of cabling
-Act as repeaters, reconstructing and strengthening incoming signals
vi. Access Point (APs)
Use radio waves to connect wireless clients to the wired network (instead of connecting using hubs/switches)
-Many APs use power over Ethernet (PoE) for electricity
-No external power is needed
-Power flows over unused twisted pair wires
-Also used by some IP cameras and phones
vii. Software
Network Operating System (NOS)
-Runs on devices and manage networking functions
-E.g., Novel NetWare, Microsoft Windows Server, Linux
-E.g., Cisco IOS or JUNOS on routers
Clients devices typically have network software components included with OS installation
-E.g., TCP/IP included in Windows, OS X, and Linux
-Allows clients to view and access available network resources
Provides
directory services
about LAN resources
Network profiles
specify resources that devices and users can access
4. LAN Design
Current best practice is to use wired LANs for primary network wireless as an overlay network
Select fastest stable technology, cost permitting
-E.g., choose 802.11ac over 802.11n or 1000BASE-T over 100BASE-T
Physical WLAN design
-More challenging than LANs because of interference
-Start with site survey to determine:
Coverage required
Potential sources of interference
Locations of wired hubs/switches and power sources
Number of APs needed
LANs may have very different requirements
-
Load balancers
-
Virtualization
-
Security
-
SAN
3. Wired Ethernet
IEEE 802.3 standards
Used by nearly all LANs today
Originally developed at
Xerox PARC
and standardized by a consortium of
Digital Equipment Corp.
,
Intel and Xerox (DIX)
Layer 2 (Data Link) protocol, but physical layer must meet protocol requirements
Topology
: Basic geographic layout of a network
Types:
-
Logical:
How the network works conceptually
-
Physical:
How the network is physically installed
Hub-based Ethernet
Also called shared or
traditional Etherne
t
Logical
bus topology
means that all devices receive every frame as if they were connected to the same circuit
The
hub
is a
multiport repeater
Hub-based Ethernet uses
physical star
topology
Switch-based Ethernet
Logical
star topology
means that only the destination receives the frame
-Switch reads destination address of the frame and only sends it to the interface (physical port) connected to the circuit
-Uses forwarding tables (also called
MAC or CAM tables
), which are similar to
routing tables
-Breaks up the
collision domain
Physical
star topology
Switch operation
Switches learn which
MAC address
is associated with an interface
(physical port)
by reading the source address on the frame
When a new frame is received, the switch reads the destination MAC address
Looks up destination address in the
forwarding table
-If found, forwards frame to the corresponding interface
-If not found, broadcasts frame to all devices (like a hub)
Switching modes
Store and forward switching
– frames retransmitted after entire frame is received and error check is complete
-Slower, but fewer errors.
Cut-through switching
– frames retransmitted as soon as destination address read
-Low latency, but some capacity wasted.
Fragment-free switching
– frames retransmitted once the header (first 64 bytes) is received and has no errors
-Compromise between store and forward and cut-through.
Media access control
Wired Ethernet uses a contention-based technique called
carrier sense multiple access with collision detection (CSMA/CD)
Carrier Sense (CS):
-A device “listens” to determine if another computer is transmitting
-Only transmit when no other computer is transmitting
Multiple Access (MA):
-Many devices have access to transmit on the network medium
Collision Detection (CD):
-Collisions occur when multiple devices transmit simultaneously
-If a collision is detected, wait a random amount of time and resend
Relies on collision detection rather than avoidance
Commonly called Wi-Fi
A family of standards developed by IEEE formally called 802.11
Uses radio frequencies to transmit signals through the air (instead of cables)
Wi-Fi has many benefits
-Provides network connections where cabling is impossible or undesirable
-Allows device and user mobility
-Potentially more economical than wired networks
802.11 Frame
Includes four address fields
Two addresses have the same meaning as in wired Ethernet, the others are used communicating with APs & other devices
WiFi devices transmit and receive within
frequency ranges
-These frequency ranges are divided into
“channels”
Frequency ranges (in the United States)
-2.4 GHz range
2.412-2.462 Ghz
3 non-overlapping channels
5 GHz range
**5.180-5.320 and 5.75-5.825 Ghz
12 non-overlapping channels**
Larger frequency range →
higher potential bandwidth
Higher frequency →
greater attenuation (i.e., shorter range)
Overlapping channels should be minimized
Security
Security is particularly important for
WLANs
because they are east to discover
Security protocols
-
Wired Equivalent Privacy (WEP)
Insecure and easy to bypass
-
WPA and WPA2 (802.11i)
WPA2 is currently recommended
MAC address filtering
-May prevent casual users from connecting
5. Improving LAN Performance
How can we improve
throughput
, the total data transmitted in a given period of time?
-Identify bottlenecks
The parts of the network restricting data flow
Devices
Servers (check CPU and disk performance)
Clients
Networking devices
-Circuits
-Demand
Devices
-Upgarde server
Software and hardware (CPU, memory, disks)
Redundant array of inexpensive disks (RAID)
Circuits
-Buy faster circuit (e.g., 100BASE-T to 1000BASE-T)
-Add circuit
-Add access points on different channels
-Segment network
Reducing network demand
-Move files to client computers
-Encourage off-peak usage
-Consider blocking or throttling unnecessary network traffic
6. Implications for Cyber Security
Secure access
-Secure switches and wireless APs
-Enforce user login and secure passwords
Policies to enforce and control
Encryption of communication traffic to and from APs
User profile management
Polices
-DRP/BC Plans