Chapter Eight 1

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Business Data Communications

• Chapter Eight
• Servers in the Enterprise

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Primary Learning Objectives

• Differentiate between clients and servers
• Describe five server physical components
• Identify major server types
• Understand the concept of well-known ports
• Explain server clustering
• Define system area network

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Clients and Servers

• Networks commonly make use of both clients and
  servers
• Clients request networked resources from servers
• Servers manage and distribute networked resources
  to clients
• Clients and servers both have operating systems
  that differentiate them from each other
• Modern client operating systems are network-aware
• Server operating systems are specialized

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Clients and Servers
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Client and Server Software
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Server Physical Components

• A server has a variety of physical components
• Five physical components particularly important
  to a servers performance are
• Physical case
• Memory
• Processor
• Drive interface
• Network Interface Card

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Physical Case

• A client desktops physical case is usually kept
  to a minimal size as it occupies and shares space
  in a users work environment
• The case occupies a footprint
• Servers are typically secured and locked away,
  with infrequent physical access by staff
• Therefore, a servers footprint can be larger
  than a clients
• The servers physical case is often more rugged
• The servers physical case is referred to as its
  chassis

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Physical Case

• A larger server physical chassis
• Allows technicians more room for working within
  the chassis
• Facilitates upgrading the server
• Provides more bays for expansion
• Offers more space for additional components
• Allows for a larger and more robust power supply
• A server may require a redundant power supply, as
  well as its own internal power surge protector

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Physical Case
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Memory

• Memory is also called RAM, for random access
  memory
• RAM sticks plug into slots housed on a server
  computers motherboard
• Servers generally support much higher capacities
  of RAM than do clients
• A servers RAM slots are often able to support
  higher capacity RAM sticks than a clients

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Memory
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Processor

• A servers processor is also called a CPU, for
  central processing unit
• The CPU is the workhorse of the server and is
  critical for processing of instructions and data
• Server motherboards often support multiple CPUs
• If a server has multiple CPUs, its server
  operating system (SOS) must be able to support
  the number configured
• If multiple CPUs are used, the SOS must be
  capable of managing the CPUs that reference each
  others cache

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Processor
An INTEL server motherboard, model S845WD1-E
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Drive Interface

• Servers usually support more drives than does a
  typical client device
• Drives include
• Floppy
• Tape
• CD
• Hard drive
• Hard drives, in particular, are a key server
  component
• Drives require an interface to the servers CPU

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Drive Interface

• Two common drive interfaces are
• IDE Integrated Drive Electronics
• Is used mostly by clients
• Requires a controller
• SCSI Small Computer System Interface
• Is used mostly by servers
• Requires a controller
• The SCSI controller is often an adapter card that
  plugs into a motherboards expansion slot
• The SCSI adapter card uses a parallel bus to
  communicate with devices connected to the
  parallel bus
• The SCSI adapter can support up to 15 internal
  and/or external devices

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Drive Interface
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Network Interface Card NIC

• Critical server NIC considerations include
• Throughput capacity
• Half- or full-duplex communications
• Direct memory access (DMA)
• Bus mastering
• Buffers
• On-board processor

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Major Types of Servers

• If a resource needs to be shared or managed, a
  server can likely be configured to do it
• Many types of servers are possible, including
• File and application
• Database
• Web, e-mail, and FTP
• Domain Name System (DNS)
• Dynamic Host Configuration Protocol (DHCP)

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File and Application Servers

• Having duplicate files and applications on
  multiple devices raises numerous questions,
  including
• Who has the most current version of the file or
  application?
• How can multiple copies be adequately secured?
• How many copies have been distributed?
• Who maintains these multiple copies?
• File and application servers allow for
  centralized management, control, and distribution
• Users are typically authenticated before being
  given access to networked file and application
  resources

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File and Application Servers

• Must be fast and reliable
• Require sufficient storage to accommodate user
  needs
• Are often implemented in software
• File servers transmit the entire file from the
  server to the client
• For small files this may be suitable
• For large files this may result in a server
  bottleneck
• Application servers control applications, using
  two components
• The client front-end
• The server back-end

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File and Application Servers

• Licensing is an additional legal and ethical
  consideration when sharing files and applications
  across the network
• Three forms of licensing are
• Individual
• Metered
• Site
• For a file or application to be distributed
  across a network, it must be network-compatible
• Not all applications, nor other resources, can be
  shared

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Database Servers

• Provide management access control software that
  makes database records available to users across
  the network
• In most implementations, perform much of the
  processing, with only the result being
  transmitted to the client
• As with application servers, require a client
  front-end process and a server back-end process
• Allow for distributed databases

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Database Server
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Web, E-mail, and FTP Servers

• A Web server runs application layer TCP/IP
  protocols
• A client accessing a Web server utilizes a
  browser
• Web pages hosted on a Web server are expressed
  using HTML HyperText Markup Language
• Two popular Web server programs are
• Apache an open system program
• Internet Information Server (IIS) a Microsoft
  program

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Web, E-mail, and FTP Servers Well-known Ports

• Requests come to a Web server through ports
• These ports are logical designations that
  represent a particular type of requested service
• Port values are also called well-known ports
• The most common port used by a client Web browser
  is well-known port 80
• Well-known ports are primary targets by hackers
• Many application layer server requests have been
  standardized to use particular well-known ports

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Web, E-mail, and FTP Servers A few Well-known
Ports
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Web, E-mail, and FTP Servers

• A client request is initiated through a Uniform
  Resource Locator, or URL
• For most users of a Web server the URL takes the
  form of a World Wide Web (WWW) address
• www.woodbury.edu
• A URL has four parts
• The protocol (HTTP or FTP, for example)
• The servers IP or Domain Name System address
• An optional port number
• The directory or file being requested

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Web, E-mail, and FTP Servers

• Popular e-mail Web server protocols include
• SMTP Simple Mail Transfer Protocol
• POP3 Post Office Protocol version 3
• IMAP Internet Message Access Protocol
• A single physical mail server might be running
  multiple logical mail services
• FTP provides for transfer of files from a server
  to a client, and vice-versa
• Whether Web, e-mail, or FTP, a client component
  and a server component must both be configured

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Domain Name System (DNS) Servers

• DNS servers are critical in a TCP/IP network
• DNS servers resolve logical IP network layer
  addresses to logical application layer domain
  name addresses
• The DNS system is designed around a hierarchy of
  domains
• There are top- and second-level domains
• A domain can have subdomains
• A domain name is resolved when the DNS server
  matches a hosts IP address to a domain name
  address

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Domain Name System (DNS) Servers
Clients must be configured to know who their DNS
server is.
A redundant DNS server can be specified.
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Domain Name System (DNS) Hierarchy
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Dynamic Host Configuration Protocol (DHCP)
Servers

• Clients in a TCP/IP network must be configured to
  know their logical network layer IP address
• This IP address can be manually configured or
  automatically configured using software
• In a small enterprise, manual configuration is
  often practical
• In a large enterprise, with hundreds or thousands
  of clients, manual configuration is not practical
• DHCP servers are used primarily to automate a
  client IP addressing configuration

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Dynamic Host Configuration Protocol (DHCP)
Servers
This Windows client has been configured so that
DHCP has been automatically enabled.
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Proxy Servers

• Are used primarily to provide increased security
• A proxy literally means authorization to act on
  behalf of another
• A proxy server
• Intercepts an internal networked clients request
• Attaches its own IP address to that request
• Hands the request out to the external world, so
  that the external world sees the address of the
  proxy, not the address of the originating client
• Reverses the above process when requested
  resources are returned
• Maintains an address list of which internal
  client is making what request
• Is often used in conjunction with a firewall

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Proxy Servers
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Server Clusters

• Connect multiple physical servers into a single
  logical group
• To clients accessing the server cluster, the
  servers in the cluster appear to be one single
  server
• Servers in the cluster can share their workload,
  resulting in load balancing of network traffic
• Should one of the servers in the cluster fail,
  other servers in the cluster can take over its
  duties
• This is called failover capability
• Servers in a cluster must have a server operating
  system that supports clustering
• Server clusters are highly scalable

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Server Clusters
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System Area Networks

• Are a local network designed for high-speed
  interconnection in cluster environments
• Almost exclusively use a switched fabric
  technology
• A switched fabric refers to the way that physical
  ports within a switch are linked, allowing the
  ports to communicate and transfer data amongst
  themselves
• Fibre Channel, a switching fabric implementation,
  is particularly associated with System Area
  Networks

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In summary

• Servers play a critical role in the enterprise
• Important server components typically include
  case, memory, processors, drive interface, and
  Network Interface Cards
• Common types of servers include file,
  application, database, Web, e-mail, FTP, DNS, and
  DCHP
• Server clustering allows the grouping of multiple
  physical servers into a single logical group
• System Area Networks are one way in which server
  clusters are being implemented