SYSTEM ADMINISTRATION
Chapter 1
Logical and Physical Network
Topologies
Understanding Networks
• Networking is the process of connecting two or more
devices together in order to share resources.
• Resources can be hardware or software.
– Hardware: printers, CD-ROMS, modems
– Software: files, folders, applications
• Reduced costs
• Increased productivity
• Increased usefulness and efficiency of computers
Understanding Network
Structure
• Defined by:
– Size of area that it covers
– Type of security being used
• Two basic types of networks
– Local Area Network (LAN)
– Wide Area Network (WAN)
Local Area Network (LAN)
• Limited to one or more buildings in close proximity
• Does not use a public carrier
• Categorized as:
– Peer-to-peer
– Client-server
Peer-to-Peer Network
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Limited in size, no more than 10 nodes
All computers are equal members
No centralized security
Uses share-level security
– Assigns passwords to shares
• Easy and inexpensive to implement
Client-Server Network
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One or more servers centrally control security
Servers run a network operating system (NOS)
Administrators assign user names and passwords
Uses user level security
– Access to shared resources is granted to a user
or group
• May be any size
Wide Area Network (WAN)
• Unlimited in size and scope
• WANs are used to connect LANs
• WANs use telecommunications lines and one or
more routers
• Data transfer speeds on WAN are slower than LAN
• Largest WAN today is the Internet
Topologies
• Logical topology
– Determines media access methods
• Collision Sense Multiple Access with Collision
Detection
• Token Passing
• Physical topology
– Location and arrangement of nodes
– How they are interconnected
– Includes network hardware
– Most common: star, bus, ring, and wireless
Star Topology
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Most common topology in use today
Each node is connected directly to a MAU
Commonly uses twisted pair cable
Advantages of a star topology:
– Easy to install.
– The failure of a single node or cable segment affects
only that node.
– Network faults are easier to troubleshoot and repair.
– Components are common and supported by many
manufacturers.
• Disadvantages of a star topology:
– The MAU constitutes a potential single point of failure.
– The star requires more wiring than other topologies.
Bus Topology
• Linear topology using several pieces of cable in linear
arrangement
• Uses coaxial cable and BNC connectors
• Must be terminated on each end
• Advantages of the bus topology:
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Uses less cable and hardware than other topologies.
Less expensive.
Easier to manage and keep track of wiring.
Simpler to install.
• Disadvantages of the bus topology:
– A single break can bring down a segment or the entire
network.
– Adding additional nodes may affect network performance.
– Can be tough to troubleshoot connection problems.
– Coaxial cable and network adapter cards are more difficult
to find.
Mesh Topology
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Every node has a connection to every other node
Provides a high level of fault tolerance
The Internet uses a hybrid mesh
Advantages of the mesh topology:
– Provides a high level of fault tolerance.
– Network problems are generally easy to isolate.
• Disadvantages of the mesh topology:
– Complexity makes installation and management
difficult.
– Redundancy makes it expensive.
– Reconfiguration of the network or the addition of
another node affects all of the other nodes.
Ring Topology
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A “circle” of cable connects each device to another
Data travels around the circle in one direction
Uses token passing
Advantages of the ring topology:
– Requires less wire than a star network.
– Each workstation can act as a repeater to
regenerate the signal.
• Disadvantages of the ring topology:
– Lack of fault tolerance.
– Most rings are actually wired as a star.
Wireless
• Use either radio frequency (RF) or infrared (IR)
• Ad hoc mode
– When devices connect directly to each other
• Infrastructure or multipoint
– Nodes connect to an access point that is wired to
a network
Troubleshooting Problems with
Shared Resources
• Begin by browsing to the resource with Network
Neighborhood or My Network Places.
– If you can see the resource but it does not allow you
access, check the permissions on the share.
• On the other hand, if you cannot see the shared
resource on the network, try these steps:
– Ensure that the computer that hosts the resource is
turned on. For example, if another user is sharing a
folder of Microsoft Excel spreadsheets and the folder
is physically located on the hard drive of the user’s
computer, you will not be able to see or access the
shared folder.
(continued)
Troubleshooting Problems with
Shared Resources (continued)
– If the computer is on, check the resource to ensure it
is still shared.
– See if you can see other computers on the network.
– Since a connectivity issue may be causing the
problem, you must determine if the problem is at your
computer, the computer with the share, or the entire
network. If you can see other computers on the
network and access their resources, check the
connectivity at the computer hosting the share.
– If you cannot see any other computer on the network,
check your connectivity.